Iron manufacturing originated about 3500 years ago when iron ore was accidentally heated in the presence of charcoal. The oxygen-laden ore was reduced to a product similar to modern wrought iron.

Today, iron is made from ore in blast furnaces. Oxygen and other elements are removed when the ore is mixed with coke (a material that contains mostly carbon) and limestone and is then blasted by hot air. The gases formed by the burning materials combine with the oxygen in the ore and reduce the ore to iron. This molten iron still contains many impurities, however. Steel is manufactured by first removing these impurities and then adding elements, predominantly carbon, in a controlled manner. Strong steels contain up to 2 percent carbon. The steel is then shaped into bars, plates, sheets, and such structural components as girders (see Iron and Steel Manufacture).

G

Textile Manufacturing

Raw fibers of cotton, wool, or synthetic materials such as nylon and polyester go through a complex series of processes to form fabrics for apparel, home furnishings, and biomedical, recreation, and aerospace products. In most cases, loose tufts of fiber are straightened, and the thick ropelike slivers are thinned for spinning. In the spinning process, the fibers are twisted to add strength. Synthetic fibers are generally made in a continuous string, but sometimes they go through a texturing process to give them a natural appearance. These twisted fibers, known as yarns, are then woven or knitted into fabrics. Weaving is a process that interlaces two sets of yarns, the warp and filling, in a variety of patterns that impart design and different physical characteristics. Knitting is a technique that loops yarns together to form fabric. The fabrics are then dyed, and finishes applied (see Textiles).

H

Lumber Industry

The lumber industry converts trees into construction materials or the precursor material for pulp and paper. Trees are harvested, debarked, then sawed into usable shapes such as boards and slabs. The lumber is graded for use and quality and then dried in large kilns, or ovens. Lumber is manufactured into boards, plywood, composition board, or paneling. Pulp wood for paper is sent directly to the manufacturer without sawing or drying (see Lumber Industry).

I

Automobile Manufacturing

The automobile was the first major manufactured item built by a mass production system using cost-effective assembly line techniques. Today, before an automobile reaches its final assembly point, subsystems, such as the engine, transmission, electrical components, and chassis, are fabricated from raw materials in other specialized facilities. The metallic automobile body parts are stamped and welded together by robots into a unibody, or one-piece, construction. This body is then dipped in a succession of chemical baths that rustproof and provide undercoat and paint treatments. During the final assembly, conveyor systems direct all of the components to stations along the production route. The engine, transmission, fuel tank, radiator, electrical systems, body panels and doors, suspension system, tires, and interior accessories are fastened to the chassis. Rigid quality-control standards at every step ensure that the completed vehicle is safe and built to specifications (see Automobile Industry).

J

Aerospace Industry

The aerospace industry manufactures airplanes, rockets and missiles, among other technologies. The first airplanes were constructed from wood and fabrics; modern airplanes are built from aluminum alloys, titanium, plastics, and advanced textile-reinforced composite materials. As in automobile manufacturing, components such as engines and landing gear are manufactured in separate facilities and then assembled with the wings, rudders, and fuselage to produce the finished airplane. Final assembly is conducted on an assembly line, where the partially manufactured airplane is moved from station to station.

Rockets are built on an individual basis. Rocket casings are created by winding high-strength carbon fibers and epoxy resins onto a cylindrical shape. The epoxy hardens and encapsulates the fibers to produce a strong, lightweight material. Solid rocket fuel is put into the body of the rocket. Thrust nozzles and exit cones are then added along with electronic guidance systems and payloads.

K

Petrochemical Industry

Petrochemicals are manufactured from naturally occurring crude oils and gases. Once removed from the earth, the crude oil is refined into gasoline, heating oil, kerosene, plastics, textile fibers, coatings, adhesives, drugs, pesticides, and fertilizers. Crude oil contains thousands of natural organic chemicals. These are separated by distilling, or boiling off, the compounds at different temperatures. Gases such as methane, ethane, and propane are also released. Methane, when combined with nitrogen and pressurized and heated, yields ammonia, an important ingredient in fertilizers. Simple plastic materials, such as polyethylene and polypropylene, are manufactured by first heating ethane and propane gases and then rapidly cooling them to alter their chemical structure (see Petroleum).

III

FUTURE TECHNOLOGIES

Manufacturing systems today are designed to recycle many of their components. For example, in the automotive industry, excess steel and aluminum can become scrap stock for new metal, rubber tires can be chopped and mixed with asphalt for new roadways, and engine starters can be remanufactured and sold again. Recycling for newer materials, such as composites (combinations of materials designed with superior physical and mechanical properties), has yet to be developed, however.

Emission control will be a critical issue for future manufacturers. Smoke scrubbers must remove dangerous gases and particulates from industrial plant discharges, and manufacturing facilities that dump chemicals into rivers must develop methods of eliminating or reusing these waste products.

The economically advantageous automated factory has become the norm. Most automobile engines are manufactured using robotic tools and handling systems that deliver the engine to various machining sites. Computers with sophisticated inventory tracking programs make it possible for items to be assembled and delivered at the manufacturing facility only as they are needed. In demand-activated manufacturing, when an item is sold a computer schedules the manufacture of an item to replace the unit sent to the customer.

Engineers use computers to help them design new products efficiently. The Boeing 777 jet, for example, was developed in record time by having its entire design and manufacturing systems created on a computer database rather than using traditional blueprints.

Aviation

I

INTRODUCTION

Aviation, term applied to the science and practice of flight in heavier-than-air craft, including airplanes, gliders, helicopters, ornithopters, convertiplanes, and VTOL (vertical takeoff and landing) and STOL (short takeoff and landing) craft (see Airplane; Glider; Helicopter). These are distinguished from lighter-than-air craft, which include balloons (free, usually spherical; and captive, usually elongated), and dirigible airships (see Airship; Balloon).

Operational aviation is grouped broadly into three classes: military aviation, commercial aviation, and general aviation. Military aviation includes all forms of flying by the armed forces—strategic, tactical, and logistical. Commercial aviation embraces primarily the operation of scheduled and charter airlines. General aviation embraces all other forms of flying such as instructional flying, crop dusting by air, flying for sport, private flying, and transportation in business-owned airplanes, usually known as executive aircraft.

II

EARLY HISTORY

Centuries of dreaming, study, speculation, and experimentation preceded the first successful flight. The ancient legends contain numerous references to the possibility of movement through the air. Philosophers believed that it could be accomplished by imitating the wing motions of birds, and by using smoke or other lighter-than- air media. The first form of aircraft made was the kite, about the 5th century bc. In the 13th century, the English monk Roger Bacon conducted studies that led him to the conclusion that air could support a craft in the same manner that water supports boats. At the beginning of the 16th century, Leonardo da Vinci gathered data on the flight of birds and anticipated developments that subsequently became practical. Among his important contributions to the development of aviation were his invention of the airscrew, or propeller, and the parachute. He conceived three different types of heavier-than-air craft: an ornithopter, a machine with mechanical wings designed to flap like those of a bird; a helicopter, designed to rise by the revolving of a rotor on a vertical axis; and a glider, consisting of a wing fixed to a frame on which a person might coast on the air. Leonardo's concepts involved the use of human muscular power, quite inadequate to produce flight with the craft that he pictured. Nevertheless, he was important because he was the first to make scientific proposals.

III

THE 19TH CENTURY

The practical development of aviation took various paths during the 19th century. The British aeronautical engineer and inventor Sir George Cayley was a farsighted theorist who proved his ideas with experiments involving kites and controlled and human-carrying gliders. He designed a combined helicopter and horizontally propelled aircraft and deserves to be called the father of aviation. The British scientist Francis Herbert Wenham used a wind tunnel in his studies and foresaw the use of multiple wings placed one above the other. He was also a founding member of the Royal Aeronautical Society of Great Britain. Makers and fliers of models included the British inventors John Stringfellow and William Samuel Henson, who collaborated in the early 1840s to produce the model of an airliner. Stringfellow's improved 1848 model, powered with a steam engine and launched from a wire, demonstrated lift but failed to climb. The French inventor Alphonse Penaud produced a hand-launched model powered with rubber bands that flew about 35 m (about 115 ft) in 1871. Another French inventor, Victor Tatin, powered his model plane with compressed air. Tethered to a central pole, it was pulled by two traction propellers; rising with its four-wheeled chassis, it made short, low-altitude flights.

The British-born Australian inventor Lawrence Hargrave produced a rigid-winged model, propelled by flapping blades that were operated by a compressed-air motor. It flew 95 m (312 ft) in 1891. The American astronomer Samuel Pierpont Langley produced (1896) steam-powered, tandem-monoplane models with wingspans of 4.6 m (15 ft). They repeatedly flew 915 to 1220 m (3000 to 4000 ft) for about 1.5 min, climbing in large circles. Then, with power exhausted, they descended slowly to alight on the waters of the Potomac River.

Numerous efforts to imitate the flight of birds were also made with experiments involving muscle-powered paddles or flappers, but none proved successful. These included the early attempts of the Austrian Jacob Degen, who carried out various experiments from 1806 to 1813; the Belgian Vincent DeGroof, who crashed to his death in 1874, and the American R. J. Spaulding who actually received a patent for his idea of muscle- powered flight in 1889.

More successful were the attempts of aeronauts who advanced the art through their study of gliding and contributed extensively to the design of wings. They included the Frenchman Jean Marie Le Bris, who tested a glider with movable wings, the American John Joseph Montgomery, and the renowned Otto Lilienthal, of Germany. Lilienthal's experiments with aircraft, including kites and ornithopters, attained greatest success with his glider flights in 1894-96. In 1896, however, he met his death when his glider went out of control and crashed. Percy S. Pilcher, of Scotland, who had attained remarkable success with his gliders, had a fatal fall in 1899. The American engineer Octave Chanute had a limited success with multiplane gliders, in 1896-1902. Chanute's most notable contribution to flight was his compilation of developments, Progress in Flying Machines (1894).

Additional information on aerodynamics and on flight stability was gained by a number of experiments with kites. The American inventor James Means published his results in the Aeronautical Annuals of 1895, 1896, and 1897. Lawrence Hargrave invented the box kite in 1893 and Alexander Graham Bell developed huge human-carrying tetrahedral-celled kites between 1895 and 1910.

Powered experiments with full-scale models were conducted by various investigators between 1890 and 1901. Most important were the attempts of Langley, who tested and flew an unmanned quarter-sized model in 1901 and 1903 before testing a full-scale model of his machine, which he called the aerodrome. This model was the first gasoline-engine-powered heavier-than-air craft to fly. His full-scale machine was completed in 1903 and tested twice, but each launching ended in a mishap. The German aviator Karl Jatho also tested a full-scale powered craft in 1903 but without success.

Advances through the 19th century laid the foundation for the eventual successful flight by the Wright brothers in 1903, but the major developments were the result of the efforts of Chanute, Lilienthal, and Langley after 1885. A sound basis in experimental aerodynamics had been established, although the stability and control required for sustained flight had not been acquired. More important, successful powered flight needed the light gasoline engine to replace the heavy steam engine.

IV

KITTY HAWK AND AFTER

On December 17, 1903, near Kitty Hawk, North Carolina, the brothers Wilbur and Orville Wright made the world's first successful flights in a heavier-than-air craft under power and control. The airplane had been designed, constructed, and flown by them, each brother making two flights that day. The longest, by Wilbur, extended to a distance of 260 m (852 ft) in 59 sec. The next year, continuing the development of their design and improving their skill as pilots, the brothers made 105 flights, the longest lasting more than 5 min. The following year, their best flight was 38.9 km (24.2 mi) in 38 min 3 sec. All these flights were in open country, the longest involving numerous turns, usually returning to near the starting point.

Not until 1906 did anyone else fly in an airplane. In that year short hops were made by a Romanian, Trajan Vuia, living in Paris, and by Jacob Christian Ellehammer, in Denmark. The first officially witnessed flight in Europe was made in France, by Alberto Santos-Dumont, of Brazil. His longest flight, on November 12, 1906, covered a distance of about 220 m (722 ft) in 21.2 sec. The airplane, the 14- bis, was of his own design, made by the Voisin firm in Paris, and powered with a Levavasseur 40-horsepower Antoinette engine. The airplane resembled a large box kite, with a smaller box at the front end of a long, cloth-covered frame. The engine and propeller were at the rear, and the pilot stood in a basket just forward of the main rear wing. Not until near the end of 1907 did anyone in Europe fly for 1 min; Henri Farman did so in an airplane built by Voisin.

In great contrast were the flights of the Wright brothers. Orville, in the U.S., demonstrated a Flyer for the Army Signal Corps at Fort Myer, Virginia, beginning September 3, 1908. On September 9 he completed the world's first flight of more than one hour and, also for the first time, carried a passenger, Lieutenant Frank P. Lahm, for a 6-min 24-sec flight. These demonstrations were interrupted on September 17, when the airplane crashed, injuring Orville and his passenger, Lieutenant Thomas E. Selfridge, who died hours later from a concussion. Selfridge was the first person to be fatally injured in a powered airplane. Wilbur, meanwhile, had gone to France in August 1908, and on December 31 of that year completed a flight of over 2 hours and 20 minutes, demonstrating total control of his Flyer, turning gracefully, and climbing or descending at will. Recovered from his injuries, and with Wilbur's assistance, Orville resumed demonstrations for the Signal Corps in the following July and met their requirements by the end of the month. The airplane was purchased on August 2, becoming the first successful military airplane. It remained in active service for about two years and was then retired to the Smithsonian Institution, Washington, D.C., at which it is displayed today.

Prominent among American designers, makers, and pilots of airplanes was Glenn Hammond Curtiss, of Hammondsport, New York. He first made a solo flight on June 28, 1907, in a dirigible airship built by Thomas Baldwin. It was powered with a Curtiss engine, modified from those used on Curtiss motorcycles. In the following May, Curtiss flew alone in an airplane designed and built by a group known as the Aerial Experiment Association, organized by Alexander Graham Bell. Curtiss was one of the five members. In their third airplane, the June Bug, Curtiss, on July 4, 1908, covered a distance of 1552 m (5090 ft) in 1 min 42.5 sec., winning the first American award, the Scientific American Trophy, given for an airplane flight. At Reims, France, on August 28, 1909, Curtiss won the first international speed event, at about 75.6 km/h (47 mph). On May 29, 1910, he won the New York World prize of $10,000 for the first flight from Albany, New York, to New York City. In August of that year he flew along the shore of Lake Erie, from Cleveland, Ohio, to Sandusky, Ohio, and back. In January 1911 he became the first American to develop and fly a seaplane. The first successful seaplane had been made and flown by Henri Fabre, of France, on March 28, 1910.

The pioneer airplane flight across the English Channel, from Calais, France, to Dover, England, a distance of about 37 km (about 23 mi) in 35.5 min, was made July 25, 1909, by the French engineer Louis Blériot, in a monoplane that he had designed and built.

During the period before World War I the design of both the airplane and the engine showed considerable improvement. Pusher biplanes— two-winged airplanes with the engine and propeller behind the wing—were succeeded by tractor biplanes, with the propeller in front of the wing. Only a few types of monoplanes were used. Huge biplane bombers with two, three, or four engines were introduced by both contending forces in World War I. In Europe, the rotary engine was favored at first, but was succeeded by radial-type engines. In Britain and the U.S., water-cooled engines of the V type predominated.

The first transportation of mail by airplane to be officially approved by the U.S. Post Office Department began on September 23, 1911, at the Nassau Boulevard air meet, Long Island, New York. The pilot was Earle Ovington, who carried the mail bag on his knees, flying about 8 km (5 mi) to Mineola, Long Island, where he tossed the bag overboard, to be picked up and carried to the post office. The service was continued for only a week (see Airmail).

In 1911 the first transcontinental flight across the United States, from New York City to Long Beach, California, was completed by the American aviator Calbraith P. Rodgers. He left Sheepshead Bay, in Brooklyn, New York, on September 17, 1911, using a Wright machine, and landed at his goal on December 10, 1911, 84 days later. His actual flying time was 3 days, 10 hr, and 14 min.

V

WORLD WAR I AND AFTER

During World War I both airplanes and lighter-than-air craft were used by the belligerents. The urgent necessities of war provided the impetus for designers to construct special planes for reconnaissance, attack, pursuit, bombing, and other highly specialized military purposes.

Because of the pressure of war, more pilots were trained and more planes built during the 4 years of conflict than in the 13 years since the first flight.

Many of the surplus military planes released after the war were acquired and operated by wartime-trained aviators, who “barnstormed” from place to place, using such fields as were available. Their operations included practically any flying activity that would provide an income, including carrying passengers, aerial photography, advertising (usually by writing names of products on their airplanes), flight instruction, air racing, and exhibitions of stunt flying.

Notable flights following World War I included a nonstop flight of 1170 km (727 mi) from Chicago to New York City in 1919 by Captain E. F. White of the U.S. Army. In 1920 Major Quintin Brand and Captain Pierre Van Ryneveld, of England, flew from Cairo to Cape Town, South Africa. In the same year, five U.S. Army Air Service planes, each carrying a pilot and a copilot-mechanic, with Captain St. Clair Streett in command, flew from New York City to Nome, Alaska, and returned. In other army exploits, Lieutenant James Harold Doolittle, in 1922, made a one-stop flight from Jacksonville, Florida, to San Diego, California.; Lieutenant Oakley Kelly and Lieutenant John A. Macready made the first nonstop transcontinental flight, May 2-3, 1923, from Roosevelt Field, Long Island, to Rockwell Field, San Diego, California, and the first flight completely around the world was made from April 6 to September 28, 1924. Four Liberty-engined Douglas Cruisers, each with two men, left Seattle, Washington, and two returned. One plane had been lost in Alaska, the other in the North Sea; there were no fatalities.

Transoceanic flying began with the flight of the NC-4, the initials denoting Navy-Curtiss. This huge flying boat flew from Rockaway Beach, Long Island, to Plymouth, England, with intermediate stops including Newfoundland, the Azores, and Lisbon, Portugal; the elapsed time was from May 8 to May 31, 1919. The first nonstop transatlantic flight was made by the British aviators John William Alcock and Arthur Whitten Brown. They flew from St. John's, Newfoundland, to Clifden, Ireland, June 14-15, 1919, in a little over 16 hours. The fliers won the London Daily Mail prize of $50,000.

The first nonstop solo crossing of the Atlantic Ocean was the flight of the American aviator Charles A. Lindbergh from New York City to Paris, a distance of 5810 km (3610 mi) covered in 33.5 hr on May 20-21, 1927. On June 28-29 of the same year Lieutenant Lester J. Maitland and Lieutenant Albert F. Hegenberger (1895-1983) of the U.S. Army made a nonstop flight from California to Hawaii, a distance of 3860 km (2400 mi) in 26 hr. Between August 27 and September 14 two other Americans, William S. Brock and Edward F. Schlee, flew from Newfoundland to Japan, a trip of 19,800 km (12,300 mi).

The first nonstop westward flight by an airplane over the Atlantic was on April 12-13, 1928, by Captain Herman Köhl and Baron Guenther von Hünefeld, Germans, and Captain James Fitzmaurice, an Irishman. They flew from Dublin, Ireland, to Greenly Island, Labrador, a distance of 3564 km (2215 mi). Between May 31 and June 9, 1928, Sir Charles Kingsford Smith and Charles T. P. Ulm, Australian fliers, with Harry W. Lyon and James Warner, Americans, flew the Southern Cross from Oakland, California, to Sydney, Australia, 11,910 km (7400 mi) with stops at Hawaii, the Fiji Islands, and Brisbane, Australia. Three American fliers, Amelia Earhart with pilots Wilmer Stultz and Louis Gordon, crossed the Atlantic from Trepassey Bay, Newfoundland, to Burry Port, Wales, on June 17-18; and from July 3 to 5 Captain Arturo Ferrarin and Major Carlo P. Del Prete, Italian army pilots, made a nonstop flight of 7186 km (4466 mi) across the Atlantic from Rome to Point Genipabu, Brazil.

In 1920 airlines were established for mail and passenger service between Key West, Florida, and Havana, Cuba, and between Seattle, Washington, and Vancouver, British Columbia. In 1921 scheduled transcontinental airmail service between New York City and San Francisco was inaugurated by the U.S. Post Office Department. Congress passed the Kelly Air Mail Act in 1925, authorizing the Post Office Department to contract with air-transport operators for the transportation of U.S. mail. Fourteen domestic airmail lines were established in 1926. Lines were also established and extended between the U.S. and Central and South America and between the United States and Canada.

Between 1930 and 1940, commercial air transportation was greatly expanded, and frequent long-distance and transoceanic flights were undertaken. The transcontinental nonstop flight record was reduced by American aviators flying small planes and, subsequently, transport planes. In 1930 Roscoe Turner flew from New York City to Los Angeles in 18 hr 43 min; Frank Hawks flew from Los Angeles to New York City in 12 hr 25 min. In 1937 Howard Hughes flew from Burbank, California, to Newark, New Jersey, in 7 hr 28 min. In 1939 Ben Kelsey flew from Marsh Field, California, to Mitchell Field, New York, in 7 hr 45 min.

VI

WORLD WAR II

Most of the major countries of the world developed commercial air transportation in varying degrees, with the U.S. gradually gaining ascendancy. On the foundations of the U.S. air-transport industry were built the military-transport commands that played a decisive role in winning World War II.

Largest of all international airlines in operation when World War II began was Pan American Airways, which, with its subsidiaries and affiliated companies, served 47 countries and colonies on 82,000 route miles, linking all continents and spanning most oceans.

The demands of World War II greatly accelerated the further development of aircraft. Important advances were achieved in the development of planes for bombing and combat and for the transportation of parachute troops and of tanks and other heavy equipment. Aircraft became a decisive factor in warfare.

Small aircraft production expanded rapidly. Under the Civilian Pilot Training program of the Civil Aeronautics Administration, private operators expanded their facilities and gave training to thousands of students, who subsequently became the backbone of the army, navy, and marine-air arms. Types of aircraft designed for personal use found extensive military use throughout the world. Large contracts for light planes were awarded by the U.S. Army and Navy in 1941.

During 1941 American military aircraft were in action on all fronts. The number of persons employed in the aviation industry totaled 450,000, compared to about 193,000 employed before World War II. About 3,375,000 passengers, about 1 million more than in 1940, were carried by 18 U.S. airlines. Mail and express loads increased by about 30 percent.

Toward the end of the war, airplane production attained an all-time high, air warfare increased in intensity and extent, and domestic airlines established new passenger- and cargo-carrying records. In the U.S., the number of planes produced in 1944 totaled 97,694, with an average weight of approximately 4770 kg (about 10,500 lb). An outstanding development in the same year was the appearance in air combat of German jet-engined and rocket-propelled fighter planes.

VII

AFTER WORLD WAR II

In 1945, U.S. military-aircraft production was sharply curtailed, but civilian-aircraft orders increased considerably. By the end of the year, U.S. manufacturers held orders for 40,000 planes, in contrast to the former production record for civilian use of 6844 planes in 1941. Again the domestic and international airlines of the U.S. broke all records, with all categories of traffic showing substantial gains over 1944. Both passenger fares and basic freight rates were reduced. International commercial services were resumed in 1945.

The experience gained in the production of military aircraft during the war was utilized in civil-aircraft production following the close of hostilities. Larger, faster aircraft, with such improvements as pressurized cabins, were made available to the airlines. Improved airports, more efficient weather forecasting, additional aids to navigation (see Air Traffic Control), and public demand for air transportation all aided in the postwar boom in airline passenger travel and freight transportation.

Experimentation with new aerodynamic designs, new metals, new power plants, and electronic inventions resulted in the development of high-speed turbojet planes designed for transoceanic flights, supersonic aircraft, experimental rocket planes, STOL craft, and the space shuttle (see Airplane; Jet Propulsion; Space Exploration).

In December 1986 the ultralight experimental aircraft Voyager successfully completed the first nonstop around-the-world flight without refueling. Voyager was designed by Burt Rutan in an unorthodox H shape with outrigger booms and rudders. The aircraft had two engines: one engine in front for takeoffs, landings, and maneuvering; the other in back for in-flight power. Composed mostly of lightweight plastic composite materials, the plane weighed only 4420 kg (9750 lb) at takeoff—with 4500 liters (1200 gallons) of fuel in its 17 fuel tanks—and 840 kg (1858 lb) on landing. Pilots Dick Rutan, Burt's brother, and Jeana Yeager flew 40,254 km (25,012 mi) in 9 days, 3 min, 44 sec at an average speed of 186.3 km/h (115.8 mph), establishing a distance and endurance record. The previous distance record of 20,169 km (12,532 mi) was set in 1962.

In 1967 the Federal Aviation Administration (FAA) replaced the Federal Aviation Agency, which had been created in 1958. The FAA classified the air transportation industry in the U.S. as commercial air carriers, regionals and commuters, helicopters, and all-cargo carriers. Nonscheduled air carriers are in a separate classification. The scheduled airlines maintain a trade association known as the Air Transport Association of America. See Air Transport Industry; Transportation, Department of.

After World War II a marked increase in the use of company-owned airplanes for the transportation of executives took place. In fact, by the early 1980s such craft composed well more than 90 percent of all aircraft active in the U.S. General trends in the U.S. air transport industry, in the 1980s, included airline deregulation (begun in 1978), mergers of airlines, and fluctuating air fares and “price wars.” Three major U.S. airlines ceased operations in 1991: Pan American and Eastern, both which had been flying since 1928, and a relative newcomer, Midway, which was founded in 1979.

Conferences relative to the problems of international flight were held as early as 1889, but it was not until 1947 that an organization was established to handle the problems of large-scale international air travel: the International Civil Aviation Organization (ICAO), an affiliate of the United Nations, with headquarters in Montréal. Working in close cooperation with ICAO is the International Air Transport Association (IATA), which also has its headquarters in Montréal and is comprised of about 100 airlines that seek jointly to solve mutual problems. Another such organization is the Fédération Aéronautique International (FAI).

Aerospace Industry

I

INTRODUCTION

Aerospace Industry, complex of manufacturing firms that produce vehicles for flight—from balloons, gliders, and airplanes to jumbo jets, guided missiles, and the space shuttle. The industry also encompasses producers of everything from seat belts to jet engines and missile guidance systems. The term aerospace is a contraction of the words aeronautics (the science of flight within Earth’s atmosphere) and space flight. It came into use during the 1950s when many companies that had previously specialized in aeronautical products began to manufacture equipment for space flight.

The aerospace industry traces its origins to the Wright brothers’ historic first flights in a heavier-than-air-machine at Kitty Hawk, North Carolina, on December 17, 1903. Until World War I (1914-1918), airplane construction largely remained in the hands of industry pioneers, who built each wood-framed plane by hand. Wartime military needs drove improvement in aircraft design. By the 1930s all-metal planes featuring retractable landing gear and high-performance engines were commonly used to deliver airmail and carry civilian passengers in Europe and the United States. During World War II (1939-1945) the industry made further strides with the introduction of massive production facilities that turned out tens of thousands of airplanes. World War II research and development resulted in radar, electronic controls, jet aircraft with gas-powered turbine engines, and combat rockets.

Postwar tension between the Union of Soviet Socialist Republics (USSR) and the United States drove aerospace technologies to new highs as the two countries raced to establish a presence in space. By the start of the Apollo Program in 1961, development and construction of space flight vehicles and supporting systems occupied a major portion of the American and Soviet aerospace industries. At the close of the 20th century, aerospace firms around the world produced rockets and artificial satellites. Originally developed for national space exploration and military purposes, these spacecraft found peacetime uses in telecommunications, navigation, and meteorology.

II

ECONOMIC IMPORTANCE

More than 40 countries have industries engaged in some form of aerospace production. The largest, the American aerospace industry, employs approximately 900,000 people. American manufacturer The Boeing Company leads the world in production of commercial airplanes and military aircraft. Other major U.S. aerospace manufacturers include the Lockheed Martin Corporation, the world’s largest producer of military aircraft and equipment, and the Raytheon Company, a global leader in air traffic control systems and a major supplier of aircraft, weapons systems, and electronic equipment to the U.S. government.

The European aerospace industry employs about 420,000 people, with workers from the United Kingdom, France, and Germany accounting for more than two-thirds of these employees. Airbus, headquartered in Toulouse, France, is the world’s second largest manufacturer of commercial aircraft. European Aeronautic Defense and Space Company (EADS) owns 80 percent of Airbus, and Britain’s BAE Systems PLC (formerly British Aerospace) owns the other 20 percent.

Canada ranks among the top six aerospace producers in the world. The Canadian industry employs 59,000 people and is a global leader in production of commercial helicopters and business aircraft. Canadian aerospace manufacturer Bombardier ranks third in the production of nonmilitary aircraft and leads the world in the production of business jets and regional jet airliners.

III

PRODUCTS

Products of the aerospace industry fall into four general categories. The largest product category, aircraft, encompasses aircraft produced for military purposes, passenger and cargo transport, and general aviation (business jets, recreational airplanes, traffic helicopters, and all other aircraft). This category also includes aircraft engines. The wide variety of missiles produced for military use makes up another product category. Space vehicles, such as the space shuttle and artificial satellites, and rockets to launch them into space, comprise their own category. The final category is made up of the thousands of different pieces of equipment and equipment systems—both those on board flight vehicles and those on the ground—that make flying a relatively safe and comfortable endeavor.

A

Aircraft and Jet Engines

Sales of aircraft, including their engines and parts, total more than the sales of all other aerospace products combined. The production of military aircraft and accessories has traditionally dominated the field of aircraft production. In the late 20th century, however, the demand for commercial jets increased around the world while global defense spending declined.

A1

Military Aircraft

Aerospace firms produce a broad variety of military aircraft, including fighter jets, bombers, attack aircraft, troop transports, and helicopters. Each type of craft is designed for a specific purpose. Fighter jets engage enemy aircraft, attack targets on or below the Earth’s surface, and perform reconnaissance missions. Bombers specialize in striking at distant surface targets. Attack aircraft carry lighter bombs than bombers and hit surface targets at closer range. Helicopters are used in rescue work, to transport troops and supplies, and less frequently, on attack missions. The Boeing Company, Lockheed Martin Corporation, and Northrop Grumman Corporation are among the largest builders of military aircraft in the world.

A2

Commercial Aircraft

Aerospace products in the commercial aircraft category include jet airplanes used by commercial airlines. Jet airliners generally fall under one of two classifications, depending on the number of aisles in the main passenger cabin. In narrow-body jets, a single aisle divides the cabin into two banks of seats. In wide-body jets, twin aisles separate the cabin into three banks of seats. The first of the wide-body jets, the Boeing 747, entered service in 1970. This massive jetliner is capable of transporting more than 400 passengers. Today, a variety of wide-body jets are produced by Boeing and Airbus. Airbus has launched production of a "superjumbo" jet, the A380, with seating for 555 passengers on two decks. It is scheduled to begin service in 2006.

Narrow-body jets seat fewer passengers. Boeing and Airbus build large narrow-body jets that carry between 100 and 200 passengers. For commuter flights, airlines use smaller jets, called regional jets, some seating as few as six passengers. The majority of these planes are built by Canadian airplane manufacturer Bombardier and Brazilian manufacturer Empresa Brasileira de Aeronautica (Embraer).

A3

Aircraft for General Aviation

Aerospace manufacturers produce more than 30 types of general aviation aircraft, a category that encompasses corporate aircraft, recreational airplanes, planes used to spray agricultural crops, and helicopters for police, ambulance, and patrol service. Corporate aircraft are usually powered by jet engines and carry up to 40 passengers. Major manufacturers in the corporate jet market include the Cessna Aircraft Company, Gulfstream Aerospace Corporation, and Raytheon in the United States, Bombardier in Canada, and Dassault Aviation in France. Recreational pilots commonly fly single-seat or twin-seat planes designed and manufactured by several companies, including Cessna and The New Piper (formerly Piper Aircraft Corporation).

A4

Jet Engines

Other aerospace firms specialize in designing and building the engines that power aircraft. The three most common types of jet engines are the turbojet, the turboprop, and the turbofan (see Jet Propulsion). In turbojet engines, energy produced by burning fuel spins a turbine that compresses the air entering the engine and directs it into a combustion chamber, where it is mixed with fuel vapor and burned. Turboprop engines are driven almost entirely by a propeller mounted in front of the engine. Turbofans combine air passing through the engine, hot engine exhaust, and air from a fan.

Production of large jet engines for airliners is dominated by American jet engine manufacturers General Electric Company and Pratt & Whitney, and Rolls-Royce of Britain. These companies also produce engines for jet fighters, bombers, and transports. Several manufacturers produce smaller gas turbines for corporate jets and helicopters. AlliedSignal Engines, part of Honeywell International in the United States, supplies a wide range of engines for regional airliners, corporate jets, helicopters, and military aircraft.

B

Missiles

Aerospace firms design and build a wide variety of missiles for military use. These range in size from large guided missiles that carry nuclear warheads to small portable rockets carried and launched by foot soldiers. Modern missiles incorporate their own propulsion systems and sophisticated guidance systems.

B1

Surface-Fired Missiles

Surface-fired missiles launch from the ground or the sea. There are two chief types of surface-fired missiles: those fired at targets on Earth’s surface or in its oceans, and those fired at targets in the air. The largest surface-to-surface missiles are intercontinental ballistic missiles (ICBMs), which are capable of carrying nuclear warheads to targets as far as 15,000 km (9,200 mi) away. Soldiers use smaller surface-to-surface missiles against enemy tanks or troops. Still other missiles dive deep into the ocean to search out and destroy enemy submarines. Surface-to-air missiles are used against airborne targets, such as airplanes or other missiles. This category includes the U.S. Army’s Patriot missile system, a large missile and launcher that intercepts and destroys enemy missiles before they strike. The Patriot missile system was developed for the U.S. military by Raytheon and Lockheed Martin. Patriots are also used by Germany, Israel, Japan, and a number of other countries.

B2

Air-Launched Missiles

Air-launched missiles are launched from fighter aircraft. Missiles in this category tend to be short-range. Air-to-air missiles, such as the U.S. Sidewinder missile built by Raytheon and other companies, usually rely on infrared heat-seeking devices to track their targets. These sophisticated missiles follow and destroy enemy aircraft and can change course when their targets do. Air-to-surface missiles commonly incorporate global positioning and inertial guidance systems, or miniature television homing systems.

C

Spacecraft and Launch Vehicles

Aerospace contractors design and build spacecraft for military and commercial purposes, and for use in space exploration. Products in this category include unmanned spacecraft, such as satellites and space probes, and piloted spacecraft. Other aerospace contractors design and build the rockets used to propel spacecraft out of Earth’s atmosphere and into space.

C1

Satellites

Telecommunications companies contract with aerospace manufactures to design and build communications satellites. These Earth-orbiting satellites transmit radio signals from cellular telephones, television broadcasting, and a number of other wireless communications. Military networks of defense-system satellites detect missile and satellite launches in other countries. Surveillance satellites provide a way to monitor activity in other countries, making it possible to detect terrorist actions or other illegal activities. The U.S. military also maintains 24 satellites as part of the global positioning system (GPS), an electronic satellite navigation system. Research satellites gather scientific information. The National Aeronautics and Space Administration (NASA) uses research satellites to observe Earth, other planets and their moons, comets, stars, and galaxies. The Hubble Space Telescope orbits about 610 km (about 380 mi) above Earth’s surface, photographing objects as far as 15 billion light-years away.

The largest manufacturers of satellites include the American companies Hughes Space and Communications Company, Lockheed Martin, and Loral Space & Communications, and the French conglomerate Alcatel. These and other satellite manufacturers develop, build, and sometimes operate satellites for private companies, the military, and governments.

C2

Space Shuttle

The space shuttle is the only piloted spacecraft produced in the United States. It consists of three main components: an orbiter, propulsion systems—two solid rocket boosters and three main engines—and an external fuel tank. Shuttle orbiters are reusable, designed to withstand 100 missions or more each. Many different aerospace contractors contribute to the shuttle’s design, construction, and maintenance. NASA and the United Space Alliance, a partnership between Boeing and Lockheed Martin, oversee shuttle design and construction.

C3

Launch Vehicles

Some aerospace companies design and build launch vehicles—rockets that propel spacecraft out of Earth’s atmosphere and into space. To escape Earth’s atmosphere, launch vehicles must reach velocities of about 30,000 km/h (about 18,500 mph). To achieve this speed and power, aerospace firms build rockets composed of two or more engines, one atop another. The largest manufacturers of launch vehicles include Lockheed Martin, which makes several versions of its Atlas and Titan rockets, and French rocket manufacturer Arianespace, which builds the Ariane launch vehicle. Boeing also manufacturers rockets for use as launch vehicles. Rockets from Boeing’s Delta family, for example, launched all the GPS satellites.

D

Flight Equipment and Navigational Aids

The fourth and final category encompasses the thousands of different pieces of equipment and equipment systems found on flight vehicles and ground-based flight support facilities. Some firms specialize in flight and engine controls for various flight vehicles. The space shuttle orbiter has more than 2,000 different controls and displays in the crew compartment. Other firms design and build instruments for flight navigation and radar systems, landing gear, flight data recorders, and cabin-pressure control systems. Still others manufacture seats, lights, kitchen equipment, and waste management systems. Companies that specialize in missile technology build state-of-the-art guidance systems, such as infrared heat-seeking devices and computer navigational systems.

Aerospace firms also produce ground-based navigational systems that support flight vehicles. These range from the radar, radio, and computers used in air traffic control at airports to the state-of-the-art command and control systems that track and operate spacecraft millions of miles from Earth. Others produce sophisticated remote controls that enable engineers on the ground to change a spacecraft’s course or to operate telescopes or cameras.

IV

RESEARCH AND DEVELOPMENT

The area of research and development constitutes one of the largest expenditures of the aerospace industry. Development of a new flight vehicle might take a decade or more and involve thousands of people. Such an endeavor requires significant advances in equipment and systems—in some cases it calls for entirely new inventions—and several billion dollars. Because the cost of developing new flight vehicles is so high, most large aerospace companies devote their research and development resources to improving existing products. They may redesign aircraft components to make them lighter and more fuel efficient, for example, or redesign wings or body surfaces to make the craft travel faster (see Aerodynamics).

Much of the design process takes place on supercomputers capable of performing billions of operations per second. Computer-aided design enables engineers to test thousands of design parameters, such as the shape or angle of wings. The designer uses a computer to create a model of the flight vehicle’s basic structure, or airframe, and then to simulate flight in various atmospheric conditions (see Computer-Aided Design/Computer-Aided Manufacturing). In addition to the shape and size of the airframe, engineers must also consider thousands of details. For example, they must consider the weight and placement of the engines, how and where fuel will be stored, the type and layout of instruments in the cockpit, and details of the passenger compartment, such as the number of seats and their dimensions. In designing commercial airplanes, engineers must also plan for entertainment systems, food storage and preparation, and the location and number of lavatories.

After preliminary computer designs are in place, engineers build a scale model of the aircraft and subject it to a series of tests in a wind tunnel. Wind tunnels simulate the conditions encountered by the flight vehicle as it moves through the air. Many research facilities have their own wind tunnels. Manufacturers also have access to government-funded wind tunnels, such as NASA’s Ames Research Center tunnel at Moffett Field, California. This massive wind tunnel can accommodate a full-size aircraft with a wingspan of 22 m (72 ft). Observations made during wind tunnel testing confirm or invalidate design assumptions tested on the computer. Engineers use the results of the wind tunnel tests to refine design as necessary.

Once the design has been finalized, engineers build one or more full-size prototypes of the flight vehicle and subject them to a barrage of additional tests. Engineers confirm that the structure can withstand the thundering vibrations and heat produced by the jet engines. They use machines to bend, twist, and push the aircraft to verify that it can withstand the stresses it will likely encounter during flight. Engineers also confirm that flight instruments will withstand the pressure and sub-zero temperatures of high altitudes. The engines, landing gear, navigational systems, and other aircraft equipment undergo equally rigorous testing. Finally, pilots take a prototype for a test flight to verify the results of earlier exercises.

V

MANUFACTURING

The manufacturing process is usually coordinated by a prime contractor that manages a number of subcontractors specializing in particular components of the flight vehicle. Subcontractors build and test their products in their own facilities, then deliver them to the prime contractor’s facility to be integrated into the flight vehicle. The prime contractor oversees the assembly of the flight vehicle, ensures that the project meets schedule and budget requirements, and assumes ultimate responsibility for the safety of the aircraft.

Modern aircraft are often built from parts that come from all over the world. For example, the McDonnell Douglas MD-11 commercial jet, which entered production in the early 1990s, incorporated parts from Italy, Spain, Japan, Brazil, Canada, the United States, and Britain. The exterior panels of the plane’s main body, or fuselage, were produced by the Italian company Aeritalia, which also supplied the plane’s vertical stabilizer and other parts. The Spanish firm CASA made landing-gear doors and the horizontal stabilizer. Japanese companies supplied certain tail parts and movable flaps on the wings called ailerons. Additional ailerons came from Brazil, the nose gear originated in Britain, Canadian firms delivered major wing assemblies, and the engines were built in the United States and Britain. The plane came together at the plant of the prime contractor, McDonnell Douglas, in California.

VI

HISTORY

The earliest aviators made their own wood-framed airplanes by hand. Orville and Wilbur Wright completed their historic 1903 flight in a machine of their own design. While the Wright brothers quietly worked to perfect and patent their flying machine, Brazilian inventor Alberto Santos-Dumont designed and flew a biplane in Paris in 1906. In the following years, fledgling aviation further captured the attention of the public. Wilbur Wright made a triumphal airplane tour of Europe in the summer of 1908. In July 1909 French aviator Louis Blériot flew a plane of his own design across the English channel, completing a highly symbolic journey in the history of flight.

A

The First Airplane Manufacturers

The success of the Wright brothers, Santos-Dumont, and other pioneering aviators created a small demand for flying machines on both sides of the Atlantic Ocean. In Paris, France, the Voisin brothers, who had helped Santos-Dumont build his biplane in 1906, set up the first facility to build airplanes for sale. In the earliest airplane shops, a small number of workers built airplanes from wood and bamboo frameworks covered with fabric. They used modified engines from automobiles and motorcycles or lightweight boat engines to power the planes. They tested new ideas by building the planes to see if they worked.

By 1909 the Voisin brothers had gained a reputation for building reliable airplanes. That year, several competitors arrived with Voisin machines at an aerial exhibition and flying meet held at Rheims, France. Publicity from the exhibition at Rheims brought orders for about 20 more by the end of the year.

B

World War I

In the years leading up to World War I, militaries on both sides of the Atlantic Ocean grew to appreciate the role airplanes could serve in the military. While Wilbur Wright toured Europe to attract the interest of the public, Orville Wright demonstrated their invention before officers of the U.S. Army. Blériot’s successful crossing of the English Channel convinced European militaries of their need for airplanes.

The military saw uses for airplanes in aerial scouting missions and to carry small bombs that were dropped by hand (see Air Warfare). The Nieuport firm, founded in France in 1909, responded to this demand by producing monoplanes for the French army and for military services in Italy, Britain, Russia, and Sweden. Blériot and a number of other manufacturers followed suit, and by the start of World War I in the summer of 1914, Germany, France, Britain, and Russia each had 200 to 300 military planes plus several airships. American manufacturers lagged behind their European counterparts. In 1912 U.S. firms produced just 39 airplanes. In 1915, as the war raged across Europe, the United States Congress formed the National Advisory Committee for Aeronautics (NACA) to fund research and development in the flight industry. Despite this effort, when the United States entered the war in 1917, it had only 16 airplane-building companies, and only 6 of them had built as many as ten airplanes.

The rate of airplane manufacture in Europe and the United States skyrocketed during the war. Britain turned out more than 55,000 airplanes from 1914 to 1918, and Germany produced 40,000 airplanes during the same period. The fledgling American industry also rallied behind the war effort, turning out 14,000 planes in 1918 alone. By the end of the war, the American aerospace industry had grown to 200,000 workers.

C

Innovation Between the Wars

In the years following World War I, the frenzied pace of airplane production slowed, and the aircraft industry turned its attention to improvements to aircraft design. American and British firms, encouraged by NACA in the United States and the Royal Aircraft Establishment in Britain, investigated a broad range of design innovations. Progressive techniques of design, engineering, and construction also came from graduates of newly established professional aeronautical engineering schools, first introduced during the 1920s. These innovation efforts resulted in dramatic changes to aircraft. Wooden airframes gave way to lightweight metal structures, while improvements in engine technology and fuels yielded greater speed and engine reliability.

These and other advances opened up new uses for airplanes. In 1921 the U.S. Post Office began regular transcontinental airmail service between New York City and San Francisco, California. Boeing developed its first commercial aircraft, the Model 40, in 1927 after winning a contract to fly mail for the U.S. Postal Service between Chicago, Illinois, and San Francisco.

In 1933 Boeing introduced the twin-engine Model 247 airplane, an all-metal, low-wing monoplane with retractable landing gear and room for ten passengers. The Model 247 revolutionized commercial aircraft design but was soon displaced by the larger, faster DC-3 designed and built by the Douglas Aircraft Company. The DC-3 carried 21 passengers and could travel across the country in less than 24 hours, though it had to stop many times for fuel. The DC-3 quickly came to dominate commercial aviation in the late 1930s and helped establish the United States as the leading producer of global airline equipment.

D

World War II

In 1939 World War II broke out in Europe. Airplane manufacturers in Britain and France, already overburdened with orders for military aircraft, placed massive orders for planes and equipment with American manufacturers. In response, the American aeronautics industry significantly expanded its production capabilities. By the time the United States entered the war in December 1941, the nation’s aerospace industry was prepared to meet the increased demand for aircraft and produced more than 300,000 aircraft before the war was over.

During the war the geographic centers of U.S. aircraft production, traditionally concentrated on the coasts, became more diversified. Wartime planners moved production inland to improve security against foreign attack and to satisfy the skyrocketing demand for workers. In Wichita, Kansas, formerly center of the light plane industry, manufacturers produced thousands of training aircraft and larger combat planes. New facilities in Atlanta, Georgia, built B-29 bombers, and new plants in the Dallas-Fort Worth region of Texas turned out B-24 Liberator bombers, P-51 Mustang fighters, and AT-6 trainers.

World War II military research also produced technological innovations that forever changed aviation. Rocket scientists in Germany developed missile prototypes that later served as the foundation for space exploration. The most important of these prototypes was the world’s first large-scale rocket, the A-4 (later renamed the V-2).

Wartime efforts also resulted in the use of jet propulsion in military aircraft. In the late 1930s British aeronautical engineer Frank Whittle made the first successful tests of the turbojet engine. The Germans, French, and Italians made subsequent improvements to jet engine design during the war. The British shared their engine technology with the United States, and by the end of World War II in 1945, Germany, Britain, and the United States had built jet-powered fighter planes.

After the war, most airplane manufacturers shifted their efforts back to passenger airplanes. They incorporated technology developed for troop transports during the war, such as pressurized cabins. This innovation enabled pilots to fly at higher altitudes, above turbulent weather, increasing passenger comfort. Lockheed began commercial production of the Constellation, one of the first commercial airplanes with a pressurized cabin. The Constellation joined the Douglas DC-3 and the newer DC-6 in transcontinental and transatlantic service. Together these large, comfortable airliners posed a significant threat to railway travel and ocean liners as the principal modes of long-distance transportation.

E

The Cold War

Following World War II, the United States and the Union of Soviet Socialist Republics (USSR) engaged in a long struggle that came to be known as the Cold War. The defense budgets of both countries escalated during this period as each tried to stay ahead of the other’s military technology. Assisted by NACA research and generous federal funding for aeronautical research and development, American firms such as General Electric and Pratt & Whitney developed powerful jet engines. These new engines powered subsequent generations of military aircraft, such as the North American F-86 Sabre fighter and the Boeing B-47 Stratojet bomber. American manufacturers reaped additional profits during the Cold War by selling helicopters, fighters, and transport aircraft to friendly foreign powers.

In 1957 the USSR put Sputnik, the world’s first artificial satellite, into orbit. In response, the United States revamped its aerospace efforts. In 1958 it restructured NACA and dubbed the new organization the National Aeronautics and Space Administration (NASA). NASA devoted all of its resources to catching up with—and beating—the Soviet space program. The United States also announced its intention to be the first nation to put a human on the moon. This led to the Apollo program, a multibillion-dollar space exploration effort that eventually sent 12 American astronauts to the surface of the moon.

F

Rise of Commercial Air Travel

British aerospace engineers revolutionized the air transport industry when they incorporated the jet engine, previously used only in military aircraft, into a commercial plane. The de Havilland Comet, introduced in 1952, was celebrated as the first commercial airplane powered by jet engines. Unforeseen structural weaknesses in the Comet caused a series of crashes, two of them fatal. The Comet was grounded for investigation for several years, giving American manufacturers the opportunity to catch up to their British counterparts. In the late 1950s Boeing and Douglas introduced the jet-powered 707 and DC-8. Pan American World Airways inaugurated Boeing 707 jet service in October 1958, and air travel changed dramatically almost overnight. Transatlantic jet service enabled travelers to fly from New York City to London, England, in less than eight hours, half the time a propeller airplane took to fly that distance. Boeing’s 707 carried 112 passengers at high speed and quickly completed the displacement of ocean liners and railroads as the principal form of long-distance transportation.

In 1970 Boeing introduced the extremely successful 747, a huge, wide-body airliner. The giant aircraft, nicknamed the “jumbo jet,” could carry more than 400 people and several hundred tons of cargo. Douglas and Lockheed soon turned out their own versions of the jumbo jet, the DC-10 and the L-1011.

G

Globalization and Mergers

The Cold War, the space race, and advances in civil aeronautics made the aerospace industry one of the United States’ largest employers and one of the strongest and most robust industries of any kind in the world. By the late 1960s European aerospace industries were seeking ways to reduce their dependence on American manufacturers.

In an effort to usurp American leadership in the production of civil airliners, Britain and France joined forces to develop the Concorde supersonic transport, the first commercial jet to fly faster than the speed of sound (see Aerodynamics: Supersonics). The Concorde, introduced in 1967, set the stage for other multinational European efforts to build and sell airplanes in competition with the big American aerospace companies. In 1970 French, German, British, and Spanish aerospace companies collaborated to form Airbus Industrie (now Airbus). The Airbus A-300 airplane, introduced four years later, inaugurated a family of air transports that by the early 2000s ranked second only to Boeing in worldwide sales. Additional European programs evolved as multinational groups formed to develop fighters, attack aircraft, and helicopters.

In 1989, the collapse of the USSR and the ensuing demise of the Cold War brought fundamental changes to the global aerospace industrial community. Soviet aerospace agencies reorganized as private entities that often collaborated with Asian, European, and American firms—strategic partnering that put them in better positions to obtain contracts. This strategy touched off a wave of mergers in the American aerospace industry. Martin-Marietta acquired the aerospace division from General Electric Company in 1992, then merged with the aerospace giant Lockheed two years later. In 1997 Boeing acquired longtime rival McDonnell Douglas Corporation and in 2000 acquired Hughes Electronics Corporation’s space and communications division, the world's leading manufacturer of communications satellites. Several European firms announced their intention to combine forces to challenge the newly formed American aerospace giants. In 1999 the French, German, and Spanish partners in the Airbus consortium merged to form the European Aeronautic Defense and Space Company, and by 2001 Airbus was a single centralized company.

Airplane

I

INTRODUCTION

Airplane, engine-driven vehicle that can fly through the air supported by the action of air against its wings. Airplanes are heavier than air, in contrast to vehicles such as balloons and airships, which are lighter than air. Airplanes also differ from other heavier-than-air craft, such as helicopters, because they have rigid wings; control surfaces, movable parts of the wings and tail, which make it possible to guide their flight; and power plants, or special engines that permit level or climbing flight.

Modern airplanes range from ultralight aircraft weighing no more than 46 kg (100 lb) and meant to carry a single pilot, to great jumbo jets, capable of carrying several hundred people, several hundred tons of cargo, and weighing nearly 454 metric tons.

Airplanes are adapted to specialized uses. Today there are land planes (aircraft that take off from and land on the ground), seaplanes (aircraft that take off from and land on water), amphibians (aircraft that can operate on both land and sea), and airplanes that can leave the ground using the jet thrust of their engines or rotors (rotating wings) and then switch to wing-borne flight.

II

HOW AN AIRPLANE FLIES

An airplane flies because its wings create lift, the upward force on the plane, as they interact with the flow of air around them. The wings alter the direction of the flow of air as it passes. The exact shape of the surface of a wing is critical to its ability to generate lift. The speed of the airflow and the angle at which the wing meets the oncoming airstream also contribute to the amount of lift generated.

An airplane’s wings push down on the air flowing past them, and in reaction, the air pushes up on the wings. When an airplane is level or rising, the front edges of its wings ride higher than the rear edges. The angle the wings make with the horizontal is called the angle of attack. As the wings move through the air, this angle causes them to push air flowing under them downward. Air flowing over the top of the wing is also deflected downward as it follows the specially-designed shape of the wing. A steeper angle of attack will cause the wings to push more air downward. The third law of motion formulated by English physicist Isaac Newton states that every action produces an equal and opposite reaction (see Mechanics: The Third Law). In this case, the wings pushing air downward is the action, and the air pushing the wings upward is the reaction. This causes lift, the upward force on the plane.

Lift is also often explained using Bernoulli’s principle, which states that, under certain circumstances, a faster moving fluid (such as air) will have a lower pressure than a slower moving fluid. The air on the top of an airplane wing moves faster and is at a lower pressure than the air underneath the wing, and the lift generated by the wing can be modeled using equations derived from Bernoulli’s principle.

Lift is one of the four primary forces acting upon an airplane. The others are weight, thrust, and drag. Weight is the force that offsets lift, because it acts in the opposite direction. The weight of the airplane must be overcome by the lift produced by the wings. If an airplane weighs 4.5 metric tons, then the lift produced by its wings must be greater than 4.5 metric tons in order for the airplane to leave the ground. Designing a wing that is powerful enough to lift an airplane off the ground, and yet efficient enough to fly at high speeds over extremely long distances, is one of the marvels of modern aircraft technology.

Thrust is the force that propels an airplane forward through the air. It is provided by the airplane’s propulsion system; either a propeller or jet engine or combination of the two.

A fourth force acting on all airplanes is drag. Drag is created because any object moving through a fluid, such as an airplane through air, produces friction as it interacts with that fluid and because it must move the fluid out of its way to do its work. A high-lift wing surface, for example, may create a great deal of lift for an airplane, but because of its large size, it is also creating a significant amount of drag. That is why high-speed fighters and missiles have such thin wings—they need to minimize drag created by lift. Conversely, a crop duster, which flies at relatively slow speeds, may have a big, thick wing because high lift is more important than the amount of drag associated with it. Drag is also minimized by designing sleek, aerodynamic airplanes, with shapes that slip easily through the air.

Managing the balance between these four forces is the challenge of flight. When thrust is greater than drag, an airplane will accelerate. When lift is greater than weight, it will climb. Using various control surfaces and propulsion systems, a pilot can manipulate the balance of the four forces to change the direction or speed. A pilot can reduce thrust in order to slow down or descend. The pilot can lower the landing gear into the airstream and deploy the landing flaps on the wings to increase drag, which has the same effect as reducing thrust. The pilot can add thrust either to speed up or climb. Or, by retracting the landing gear and flaps, and thereby reducing drag, the pilot can accelerate or climb.

III

SUPERSONIC FLIGHT

In addition to balancing lift, weight, thrust, and drag, modern airplanes have to contend with another phenomenon. The sound barrier is not a physical barrier but a speed at which the behavior of the airflow around an airplane changes dramatically. Fighter pilots in World War II (1939-1945) first ran up against this so-called barrier in high-speed dives during air combat. In some cases, pilots lost control of the aircraft as shock waves built up on control surfaces, effectively locking the controls and leaving the crews helpless. After World War II, designers tackled the realm of supersonic flight, primarily for military airplanes, but with commercial applications as well.

Supersonic flight is defined as flight at a speed greater than that of the local speed of sound. At sea level, sound travels through air at approximately 1,220 km/h (760 mph). At the speed of sound, a shock wave consisting of highly compressed air forms at the nose of the plane. This shock wave moves back at a sharp angle as the speed increases.

Supersonic flight was achieved in 1947 for the first time by the Bell X-1 rocket plane, flown by Air Force test pilot Chuck Yeager. Speeds at or near supersonic flight are measured in units called Mach numbers, which represent the ratio of the speed of the airplane to the speed of sound as it moves air. An airplane traveling at less than Mach 1 is traveling below the speed of sound (subsonic); at Mach 1, an airplane is traveling at the speed of sound (transonic); at Mach 2, an airplane is traveling at twice the speed of sound (supersonic flight). Speeds of Mach 1 to 5 are referred to as supersonic; speeds of Mach 5 and above are called hypersonic. Designers in Europe and the United States developed succeeding generations of military aircraft, culminating in the 1960s and 1970s with Mach 3+ speedsters such as the Soviet MiG-25 Foxbat interceptor, the XB-70 Valkyrie bomber, and the SR-71 spy plane.

The shock wave created by an airplane moving at supersonic and hypersonic speeds represents a rather abrupt change in air pressure and is perceived on the ground as a sonic boom, the exact nature of which varies depending upon how far away the aircraft is and the distance of the observer from the flight path. Sonic booms at low altitudes over populated areas are generally considered a significant problem and have prevented most supersonic airplanes from efficiently utilizing overland routes. For example, the Anglo-French Concorde, a commercial supersonic aircraft, is generally limited to over-water routes, or to those over sparsely populated regions of the world. Designers today believe they can help lessen the impact of sonic booms created by supersonic airliners but probably cannot eliminate them.

One of the most difficult practical barriers to supersonic flight is the fact that high-speed flight produces heat through friction. At such high speeds, enormous temperatures are reached at the surface of the craft. In fact, today’s Concorde must fly a flight profile dictated by temperature requirements; if the aircraft moves too fast, then the temperature rises above safe limits for the aluminum structure of the airplane. Titanium and other relatively exotic, and expensive, metals are more heat-resistant, but harder to manufacture and maintain. Airplane designers have concluded that a speed of Mach 2.7 is about the limit for conventional, relatively inexpensive materials and fuels. Above that speed, an airplane would need to be constructed of more temperature-resistant materials, and would most likely have to find a way to cool its fuel.

IV

AIRPLANE STRUCTURE

Airplanes generally share the same basic configuration—each usually has a fuselage, wings, tail, landing gear, and a set of specialized control surfaces mounted on the wings and tail.

A

Fuselage

The fuselage is the main cabin, or body of the airplane. Generally the fuselage has a cockpit section at the front end, where the pilot controls the airplane, and a cabin section. The cabin section may be designed to carry passengers, cargo, or both. In a military fighter plane, the fuselage may house the engines, fuel, electronics, and some weapons. In some of the sleekest of gliders and ultralight airplanes, the fuselage may be nothing more than a minimal structure connecting the wings, tail, cockpit, and engines.

B

Wings

All airplanes, by definition, have wings. Some are nearly all wing with a very small cockpit. Others have minimal wings, or wings that seem to be merely extensions of a blended, aerodynamic fuselage, such as the space shuttle.

Before the 20th century, wings were made of wooden ribs and spars (or beams), covered with fabric that was sewn tightly and varnished to be extremely stiff. A conventional wing has one or more spars that run from one end of the wing to the other. Perpendicular to the spar are a series of ribs, which run from the front, or leading edge, to the rear, or trailing edge, of the wing. These are carefully constructed to shape the wing in a manner that determines its lifting properties. Wood and fabric wings often used spruce for the structure, because of that material’s relatively light weight and high strength, and linen for the cloth covering.

Early airplanes were usually biplanes—craft with two wings, usually one mounted about 1.5 m (about 5 to 6 ft) above the other. Aircraft pioneers found they could build such wings relatively easily and brace them together using wires to connect the upper and lower wing to create a strong structure with substantial lift. In pushing the many cables, wood, and fabric through the air, these designs created a great deal of drag, so aircraft engineers eventually pursued the monoplane, or single-wing airplane. A monoplane’s single wing gives it great advantages in speed, simplicity, and visibility for the pilot.

After World War I (1914-1918), designers began moving toward wings made of steel and aluminum, and, combined with new construction techniques, these materials enabled the development of modern all-metal wings capable not only of developing lift but of housing landing gear, weapons, and fuel.

Over the years, many airplane designers have postulated that the ideal airplane would, in fact, be nothing but wing. Flying wings, as they are called, were first developed in the 1930s and 1940s. American aerospace manufacturer Northrop Grumman Corporation’s flying wing, the B-2 bomber, or stealth bomber, developed in the 1980s, has been a great success as a flying machine, benefiting from modern computer-aided design (CAD), advanced materials, and computerized flight controls. Popular magazines routinely show artists’ concepts of flying-wing airliners, but airline and airport managers have been unable to integrate these unusual shapes into conventional airline and airport facilities.

C

Tail Assembly

Most airplanes, except for flying wings, have a tail assembly attached to the rear of the fuselage, consisting of vertical and horizontal stabilizers, which look like small wings; a rudder; and elevators. The components of the tail assembly are collectively referred to as the empennage.

The stabilizers serve to help keep the airplane stable while in flight. The rudder is at the trailing edge of the vertical stabilizer and is used by the airplane to help control turns. An airplane actually turns by banking, or moving, its wings laterally, but the rudder helps keep the turn coordinated by serving much like a boat’s rudder to move the nose of the airplane left or right. Moving an airplane’s nose left or right is known as a yaw motion. Rudder motion is usually controlled by two pedals on the floor of the cockpit, which are pushed by the pilot.

Elevators are control surfaces at the trailing edge of horizontal stabilizers. The elevators control the up-and-down motion, or pitch, of the airplane’s nose. Moving the elevators up into the airstream will cause the tail to go down and the nose to pitch up. A pilot controls pitch by moving a control column or stick.

D

Landing Gear

All airplanes must have some type of landing gear. Modern aircraft employ brakes, wheels, and tires designed specifically for the demands of flight. Tires must be capable of going from a standstill to nearly 322 km/h (200 mph) at landing, as well as carrying nearly 454 metric tons. Brakes, often incorporating special heat-resistant materials, must be able to handle emergencies, such as a 400-metric-ton airliner aborting a takeoff at the last possible moment. Antiskid braking systems, common on automobiles today, were originally developed for aircraft and are used to gain maximum possible braking power on wet or icy runways.

Larger and more-complex aircraft typically have retractable landing gear—so called because they can be pulled up into the wing or fuselage after takeoff. Having retractable gear greatly reduces the drag generated by the wheel structures that would otherwise hang out in the airstream.

E

Control Components

An airplane is capable of three types of motion that revolve around three separate axes. The plane may fly steadily in one direction and at one altitude—or it may turn, climb, or descend. An airplane may roll, banking its wings either left or right, about the longitudinal axis, which runs the length of the craft. The airplane may yaw its nose either left or right about the vertical axis, which runs straight down through the middle of the airplane. Finally, a plane may pitch its nose up or down, moving about its lateral axis, which may be thought of as a straight line running from wingtip to wingtip.

An airplane relies on the movement of air across its wings for lift, and it makes use of this same airflow to move in any way about the three axes. To do so, the pilot will manipulate controls in the cockpit that direct control surfaces on the wings and tail to move into the airstream. The airplane will yaw, pitch, or roll, depending on which control surfaces or combination of surfaces are moved, or deflected, by the pilot.

In order to bank and begin a turn, a conventional airplane will deflect control surfaces on the trailing edge of the wings known as ailerons. In order to bank left, the left aileron is lifted up into the airstream over the left wing, creating a small amount of drag and decreasing the lift produced by that wing. At the same time, the right aileron is pushed down into the airstream, thereby increasing slightly the lift produced by the right wing. The right wing then comes up, the left wing goes down, and the airplane banks to the left. To bank to the right, the ailerons are moved in exactly the opposite fashion.

In order to yaw, or turn the airplane’s nose left or right, the pilot must press upon rudder pedals on the floor of the cockpit. Push down on the left pedal, and the rudder at the trailing edge of the vertical stabilizer moves to the left. As in a boat, the left rudder moves the nose of the plane to the left. A push on the right pedal causes the airplane to yaw to the right.

In order to pitch the nose up or down, the pilot usually pulls or pushes on a control wheel or stick, thereby moving the elevators at the trailing edge of the horizontal stabilizer. Pulling back on the wheel deflects the elevators upward into the airstream, pushing the tail down and the nose up. Pushing forward on the wheel causes the elevators to drop down, lifting the tail and forcing the nose down.

Airplanes that are more complex also have a set of secondary control surfaces that may include devices such as flaps, slats, trim tabs, spoilers, and speed brakes. Flaps and slats are generally used during takeoff and landing to increase the amount of lift produced by the wing at low speeds. Flaps usually droop down from the trailing edge of the wing, although some jets have leading-edge flaps as well. On some airplanes, they also can be extended back beyond the normal trailing edge of the wing to increase the surface area of the wing as well as change its shape. Leading-edge slats usually extend from the front of the wing at low speeds to change the way the air flows over the wing, thereby increasing lift. Flaps also often serve to increase drag and slow the approach of a landing airplane.

Trim tabs are miniature control surfaces incorporated into larger control surfaces. For example, an aileron tab acts like a miniature aileron within the larger aileron. These kinds of controls are used to adjust more precisely the flight path of an airplane that may be slightly out of balance or alignment. Elevator trim tabs are usually used to help set the pitch attitude (the angle of the airplane in relation to the Earth) of an airplane for a given speed through the air. On some airplanes, the entire horizontal stabilizer moves in small increments to serve the same function as a trim tab.

F

Instruments

Airplane pilots rely on a set of instruments in the cockpit to monitor airplane systems, to control the flight of the aircraft, and to navigate.

Systems instruments will tell a pilot about the condition of the airplane’s engines and electrical, hydraulic, and fuel systems. Piston-engine instruments monitor engine and exhaust-gas temperatures, and oil pressures and temperatures. Jet-engine instruments measure the rotational speeds of the rotating blades in the turbines, as well as gas temperatures and fuel flow.

Flight instruments are those used to tell a pilot the course, speed, altitude, and attitude of the airplane. They may include an airspeed indicator, an artificial horizon, an altimeter, and a compass. These instruments have many variations, depending on the complexity and performance of the airplane. For example, high-speed jet aircraft have airspeed indicators that may indicate speeds both in nautical miles per hour (slightly faster than miles per hour used with ground vehicles) and in Mach number. The artificial horizon indicates whether the airplane is banking, climbing, or diving, in relation to the Earth. An airplane with its nose up may or may not be climbing, depending on its airspeed and momentum.

General-aviation (private aircraft), military, and commercial airplanes also have instruments that aid in navigation. The compass is the simplest of these, but many airplanes now employ satellite navigation systems and computers to navigate from any point on the globe to another without any help from the ground. The Global Positioning System (GPS), developed for the United States military but now used by many civilian pilots, provides an airplane with its position to within a few meters. Many airplanes still employ radio receivers that tune to a ground-based radio-beacon system in order to navigate cross-country. Specially equipped airplanes can use ultraprecise radio beacons and receivers, known as Instrument Landing Systems (ILS) and Microwave Landing Systems (MLS), combined with special cockpit displays, to land during conditions of poor visibility.

V

PROPULSION

Airplanes use either piston or turbine (rotating blades) engines to provide propulsion. In smaller airplanes, a conventional gas-powered piston engine turns a propeller, which either pulls or pushes an airplane through the air. In larger airplanes, a turbine engine either turns a propeller through a gearbox, or uses its jet thrust directly to move an airplane through the air. In either case, the engine must provide enough power to move the weight of the airplane forward through the airstream.

The earliest powered airplanes relied on crude steam or gas engines. These piston engines are examples of internal-combustion engines. Aircraft designers throughout the 20th century pushed their engineering colleagues constantly for engines with more power, lighter weight, and greater reliability. Piston engines, however, are still relatively complicated pieces of machinery, with many precision-machined parts moving through large ranges and in complex motions. Although enormously improved over the past 90 years of flight and still suitable for many smaller general aviation aircraft, they fall short of the higher performance possible with modern jet propulsion and required for commercial and military aviation.

The turbine or jet engine operates on the principle of Newton’s third law of motion, which states that for every action, there is an opposite but equal reaction. A jet sucks air into the front, squeezes the air by pulling it through a series of spinning compressors, mixes it with fuel and ignites the mixture, which then explodes with great force rearward through the exhaust nozzle. The rearward force is balanced with an equal force that pushes the jet engine, and the airplane attached to it, forward. A rocket engine operates on the same principle, except that, in order to operate in the airless vacuum of space, the rocket must carry along its own air, in the form of solid propellant or liquid oxidizer, for combustion.

There are several different types of jet engines. The simplest is the ramjet, which takes advantage of high speed to ram or force the air into the engine, eliminating the need for the spinning compressor section. This elegant simplicity is offset by the need to boost a ramjet to several hundred miles an hour before ram-air compression is sufficient to operate the engine.

The turbojet is based on the jet-propulsion system of the ramjet, but with the addition of a compressor section, a combustion chamber, a turbine to take some power out of the exhaust and spin the compressor, and an exhaust nozzle. In a turbojet, all of the air taken into the compressor at the front of the engine is sent through the core of the engine, burned, and released. Thrust from the engine is derived purely from the acceleration of the released exhaust gases out the rear.

A modern derivative known as the turbofan, or fan-jet, adds a large fan in front of the compressor section. This fan pulls an enormous amount of air into the engine case, only a relatively small fraction of which is sent through the core for combustion. The rest runs along the outside of the core case and inside the engine casing. This fan flow is mixed with the hot jet exhaust at the rear of the engine, where it cools and quiets the exhaust noise. In addition, this high-volume mass of air, accelerated rearward by the fan, produces a great deal of thrust by itself, even though it is never burned, acting much like a propeller.

In fact, some smaller jet engines are used to turn propellers. Known as turboprops, these engines produce most of their thrust through the propeller, which is usually driven by the jet engine through a set of gears. As a power source for a propeller, a turbine engine is extremely efficient, and many smaller airliners in the 19- to 70-passenger-capacity range use turboprops. They are particularly efficient at lower altitudes and medium speeds up to 640 km/h (400 mph).

VI

TYPES OF AIRPLANES

There are a wide variety of types of airplanes. Land planes, carrier-based airplanes, seaplanes, amphibians, vertical takeoff and landing (VTOL), short takeoff and landing (STOL), and space shuttles all take advantage of the same basic technology, but their capabilities and uses make them seem only distantly related.

A

Land Planes

Land planes are designed to operate from a hard surface, typically a paved runway. Some land planes are specially equipped to operate from grass or other unfinished surfaces. A land plane usually has wheels to taxi, take off, and land, although some specialized aircraft operating in the Arctic or Antarctic regions have skis in place of wheels. The wheels are sometimes referred to as the undercarriage, although they are often called, together with the associated brakes, the landing gear. Landing gear may be fixed, as in some general-aviation airplanes, or retractable, usually into the fuselage or wings, as in more-sophisticated airplanes in general and commercial aviation.

B

Carrier-Based Aircraft

Carrier-based airplanes are a specially modified type of land plane designed for takeoff from and landing aboard naval aircraft carriers. Carrier airplanes have a strengthened structure, including their landing gear, to handle the stresses of catapult-assisted takeoff, in which the craft is launched by a steam-driven catapult; and arrested landings, made by using a hook attached to the underside of the aircraft’s tail to catch one of four wires strung across the flight deck of the carrier.

C

Seaplanes

Seaplanes, sometimes called floatplanes or pontoon planes, are often ordinary land planes modified with floats instead of wheels so they can operate from water. A number of seaplanes have been designed from scratch to operate only from water bases. Such seaplanes have fuselages that resemble and perform like ship hulls. Known as flying boats, they may have small floats attached to their outer wing panels to help steady them at low speeds on the water, but the weight of the airplane is borne by the floating hull.

D

Amphibians

Amphibians, like their animal namesakes, operate from both water and land bases. In many cases, an amphibian is a true seaplane, with a boat hull and the addition of specially designed landing gear that can be extended to allow the airplane to taxi right out of the water onto land. Historically, some flying boats were fitted with so-called beaching gear, a system of cradles on wheels positioned under the floating aircraft, which then allowed the aircraft to be rolled onto land.

E

Vertical Takeoff and Landing Airplanes

Vertical Takeoff and Landing (VTOL) airplanes typically use the jet thrust from their engines, pointed down at the Earth, to take off and land straight up and down. After taking off, a VTOL airplane usually transitions to wing-borne flight in order to cover a longer distance or carry a significant load. A helicopter is a type of VTOL aircraft, but there are very few VTOL airplanes. One unique type of VTOL aircraft is the tilt-rotor, which has large, propeller-like rotating wings or rotors driven by jet engines at the wingtips. For takeoff and landing, the engines and rotors are positioned vertically, much like a helicopter. After takeoff, however, the engine/rotor combination tilts forward, and the wing takes on the load of the craft.

The most prominent example of a true VTOL airplane flying today is the AV-8B Harrier II, a military attack plane that uses rotating nozzles attached to its jet engine to direct the engine exhaust in the appropriate direction. Flown in the United States by the Marine Corps, as well as in Spain, Italy, India, and United Kingdom, where it was originally developed, the Harrier can take off vertically from smaller ships, or it can be flown to operating areas near the ground troops it supports in its ground-attack role.

F

Short Takeoff and Landing Airplanes

Short Takeoff and Landing (STOL) airplanes are designed to be able to function on relatively short runways. Their designs usually employ wings and high-lift devices on the wings optimized for best performance during takeoff and landing, as distinguished from an airplane that has a wing optimized for high-speed cruise at high altitude. STOL airplanes are usually cargo airplanes, although some serve in a passenger-carrying capacity as well.

G

Space Shuttle

The space shuttle, flown by the National Aeronautics and Space Administration (NASA), is an aircraft unlike any other because it flies as a fixed-wing airplane within the atmosphere and as a spacecraft outside Earth’s atmosphere. When the space shuttle takes off, it flies like a rocket with wings, relying on the 3,175 metric tons of thrust generated by its solid-fuel rocket boosters and liquid-fueled main engines to power its way up, through, and out of the atmosphere. During landing, the shuttle becomes the world’s most sophisticated glider, landing without propulsion.

VII

CLASSES OF AIRPLANES

Airplanes can be grouped into a handful of major classes, such as commercial, military, and general-aviation airplanes, all of which fall under different government-mandated certification and operating rules.

A

Commercial Airplanes

Commercial aircraft are those used for profit making, usually by carrying cargo or passengers for hire (see Air Transport Industry). They are strictly regulated—in the United States, by the Federal Aviation Administration (FAA); in Canada, by Transport Canada; and in other countries, by other national aviation authorities.

Modern large commercial-airplane manufacturers—such The Boeing Company in the United States and Airbus in Europe—offer a wide variety of aircraft with different capabilities. Today’s jet airliners carry anywhere from 100 passengers to more than 500 over short and long distances.

Since 1976 the British-French Concorde supersonic transport (SST) has carried passengers at twice the speed of sound. The Concorde flies for British Airways and Air France, flag carriers of the two nations that funded its development during the late 1960s and 1970s. The United States had an SST program, but it was ended because of budget and environmental concerns in 1971.

B

Military Airplanes

Military aircraft are usually grouped into four categories: combat, cargo, training, and observation. Combat airplanes are generally either fighters or bombers, although some airplanes have both capabilities. Fighters are designed to engage in air combat with other airplanes, in either defensive or offensive situations. Since the 1950s many fighters have been capable of Mach 2+ flight (a Mach number represents the ratio of the speed of an airplane to the speed of sound as it travels through air). Some fighters have a ground-attack role as well and are designed to carry both air-to-air weapons, such as missiles, and air-to-ground weapons, such as bombs. Fighters include aircraft such as the Panavia Tornado, the Boeing F-15 Eagle, the Lockheed-Martin F-16 Falcon, the MiG-29 Fulcrum, and the Su-27 Flanker.

Bombers are designed to carry large air-to-ground-weapons loads and either penetrate or avoid enemy air defenses in order to deliver those weapons. Some well-known bombers include the Boeing B-52, the Boeing B-1, and the Northrop-Grumman B-2 stealth bomber. Bombers such as the B-52 are designed to fly fast at low altitudes, following the terrain, in order to fly under enemy radar defenses, while others, such as the B-2, may use sophisticated radar-defeating technologies to fly virtually unobserved.

Today’s military cargo airplanes are capable of carrying enormous tanks, armored personnel carriers, artillery pieces, and even smaller aircraft. Cargo planes such as the giant Lockheed C-5B and Boeing C-17 were designed expressly for such roles. Some cargo planes can serve a dual role as aerial gas stations, refueling different types of military airplanes while in flight. Such tankers include the Boeing KC-135 and KC-10.

All military pilots go through rigorous training and education programs using military training airplanes to prepare them to fly the high-performance aircraft of the armed forces. They typically begin the flight training in relatively simple, propeller airplanes and move into basic jets before specializing in a career path involving fighters, bombers, or transports. Some military trainers include the T-34 Mentor, the T-37 and T-38, and the Boeing T-45 Goshawk.

A final category of military airplane is the observation, or reconnaissance, aircraft. With the advent of the Lockheed U-2 spy plane in the 1950s, observation airplanes were developed solely for highly specialized missions. The ultimate spy plane is Lockheed’s SR-71, a two-seat airplane that uses specialized engines and fuel to reach altitudes greater than 25,000 m (80,000 ft) and speeds well over Mach 3.

C

General-Aviation Aircraft

General-aviation aircraft are certified for and intended primarily for noncommercial or private operations.

Pleasure aircraft range from simple single-seat, ultralight airplanes to sleek twin turboprops capable of carrying eight people. Business aircraft transport business executives to appointments. Most business airplanes require more reliable performance and more range and all-weather capability.

Another class of general-aviation airplanes are those used in agriculture. Large farms require efficient ways to spread fertilizer and insecticides over a large area. A very specialized type of airplane, crop dusters are rugged, highly maneuverable, and capable of hauling several hundred pounds of chemicals. They can be seen swooping low over farm fields. Not intended for serious cross-country navigation, crop dusters lack sophisticated navigation aids and complex systems.

VIII

HISTORY

Before the end of the 18th century, few people had applied themselves to the study of flight. One was Leonardo da Vinci, during the 15th century. Leonardo was preoccupied chiefly with bird flight and with flapping-wing machines, called ornithopters. His aeronautical work lay unknown until late in the 19th century, when it could furnish little of technical value to experimenters but was a source of inspiration to aspiring engineers. Apart from Leonardo’s efforts, three devices important to aviation had been invented in Europe in the Middle Ages and had reached a high stage of development by Leonardo’s time—the windmill, an early propeller; the kite, an early airplane wing; and the model helicopter.

A

The First Airplanes

Between 1799 and 1809 English baronet Sir George Cayley created the concept of the modern airplane. Cayley abandoned the ornithopter tradition, in which both lift and thrust are provided by the wings, and designed airplanes with rigid wings to provide lift, and with separate propelling devices to provide thrust. Through his published works, Cayley laid the foundations of aerodynamics. He demonstrated, both with models and with full-size gliders, the use of the inclined plane to provide lift, pitch, and roll stability; flight control by means of a single rudder-elevator unit mounted on a universal joint; streamlining; and other devices and practices. In 1853, in his third full-size machine, Cayley sent his unwilling coachman on the first gliding flight in history.

In 1843 British inventor William Samuel Henson published his patented design for an Aerial Steam Carriage. Henson’s design did more than any other to establish the form of the modern airplane—a fixed-wing monoplane with propellers, fuselage, and wheeled landing gear, and with flight control by means of rear elevator and rudder. Steam-powered models made by Henson in 1847 were promising but unsuccessful.

In 1890 French engineer Clément Ader built a steam-powered airplane and made the first actual flight of a piloted, heavier-than-air craft. However, the flight was not sustained, and the airplane brushed the ground over a distance of 50 m (160 ft). Inventors continued to pursue the dream of sustained flight. Between 1891 and 1896 German aeronautical engineer Otto Lilienthal made thousands of successful flights in hang gliders of his own design. Lilienthal hung in a frame between the wings and controlled his gliders entirely by swinging his torso and legs in the direction he wished to go. While successful as gliders, his designs lacked a control system and a reliable method for powering the craft. He was killed in a gliding accident in 1896.

American inventor Samuel Pierpont Langley had been working for several years on flying machines. Langley began experimenting in 1892 with a steam-powered, unpiloted aircraft, and in 1896 made the first sustained flight of any mechanically propelled heavier-than-air craft. Launched by catapult from a houseboat on the Potomac River near Quantico, Virginia, the unpiloted Aerodrome, as Langley called it, suffered from design faults. The Aerodrome never successfully carried a person, and thus prevented Langley from earning the place in history claimed by the Wright brothers.

B

The First Airplane Flight

American aviators Orville Wright and Wilbur Wright of Dayton, Ohio, are considered the fathers of the first successful piloted heavier-than-air flying machine. Through the disciplines of sound scientific research and engineering, the Wright brothers put together the combination of critical characteristics that other designs of the day lacked—a relatively lightweight (337 kg/750 lb), powerful engine; a reliable transmission and efficient propellers; an effective system for controlling the aircraft; and a wing and structure that were both strong and lightweight.

At Kitty Hawk, North Carolina, on December 17, 1903, Orville Wright made the first successful flight of a piloted, heavier-than-air, self-propelled craft, called the Flyer. That first flight traveled a distance of about 37 m (120 ft). The distance was less than the wingspan of many modern airliners, but it represented the beginning of a new age in technology and human achievement. Their fourth and final flight of the day lasted 59 seconds and covered only 260 m (852 ft). The third Flyer, which the Wrights constructed in 1905, was the world’s first fully practical airplane. It could bank, turn, circle, make figure eights, and remain in the air for as long as the fuel lasted, up to half an hour on occasion.

C

Early Military and Public Interest

The airplane, like many other milestone inventions throughout history, was not immediately recognized for its potential. During the very early 1900s, prior to World War I (1914-1918), the airplane was relegated mostly to the county-fair circuit, where daredevil pilots drew large crowds but few investors. One exception was the United States War Department, which had long been using balloons to observe the battlefield and expressed an interest in heavier-than-air craft as early as 1898. In 1908 the Wrights demonstrated their airplane to the U.S. Army’s Signal Corps at Fort Myer, Virginia. In September of that year, while circling the field at Fort Myer, Orville crashed while carrying an army observer, Lieutenant Thomas Selfridge. Selfridge died from his injuries and became the first fatality from the crash of a powered airplane.

On July 25, 1909, French engineer Louis Blériot crossed the English channel in a Blériot XI, a monoplane of his own design. Blériot’s channel crossing made clear to the world the airplane’s wartime potential, and this potential was further demonstrated in 1910 and 1911, when American pilot Eugene Ely took off from and landed on warships. In 1911 the U.S. Army used a Wright brothers’ biplane to make the first live bomb test from an airplane. That same year, the airplane was used in its first wartime operation when an Italian captain flew over and observed Turkish positions during the Italo-Turkish War of 1911 to 1912. Also in 1911, American inventor and aviator Glenn Curtiss introduced the first practical seaplane. This was a biplane with a large float beneath the center of the lower wing and two smaller floats beneath the tips of the lower wing.

The year 1913 became known as the “glorious year of flying.” Aerobatics, or acrobatic flying, was introduced, and upside-down flying, loops, and other stunts proved the maneuverability of airplanes. Long-distance flights made in 1913 included a 4,000-km (2,500-mi) flight from France to Egypt, with many stops, and the first nonstop flight across the Mediterranean Sea, from France to Tunisia. In Britain, a modified Farnborough B.E. 2 proved itself to be the first naturally stable airplane in the world. The B.E. 2c version of this airplane was so successful that nearly 2,000 were subsequently built.

D

Planes of World War I

During World War I, the development of the airplane accelerated dramatically. European designers such as Louis Blériot and Dutch-American engineer Anthony Herman Fokker exploited basic concepts created by the Wrights and developed ever faster, more capable, and deadlier combat airplanes. Fokker’s biplanes, such as the D-VII and D-VIII flown by German pilots, were considered superior to their Allied competition. In 1915 Fokker mounted a machine gun with a timing gear so that the gun could fire between the rotating propellers. The resulting Fokker Eindecker monoplane fighter was, for a time, the most successful fighter in the skies.

The concentrated research and development made necessary by wartime pressures produced great progress in airplane design and construction. During World War I, outstanding early British fighters included the Sopwith Pup (1916) and the Sopwith Camel (1917), which flew as high as 5,800 m (19,000 ft) and had a top speed of 190 km/h (120 mph). Notable French fighters included the Spad (1916) and the Nieuport 28 (1918). By the end of World War I in 1918, both warring sides had fighters that could fly at altitudes of 7,600 m (25,000 ft) and speeds up to 250 km/h (155 mph).

E

Development of Commercial Aviation

Commercial aviation began in January 1914, just 10 years after the Wrights pioneered the skies. The first regularly scheduled passenger line in the world operated between Saint Petersburg and Tampa, Florida. Commercial aviation developed slowly during the next 30 years, driven by the two world wars and service demands of the U.S. Post Office for airmail.

In the early 1920s the air-cooled engine was perfected, along with its streamlined cowling, or engine casing. Light and powerful, these engines gave strong competition to the older, liquid-cooled engines. In the mid-1920s light airplanes were produced in great numbers, and club and private pleasure flying became popular. The inexpensive DeHavilland Moth biplane, introduced in 1925, put flying within the financial reach of many enthusiasts. The Moth could travel at 145 km/h (90 mph) and was light, strong, and easy to handle.

Instrument flying became practical in 1929, when the American inventor Elmer Sperry perfected the artificial horizon and directional gyro. On September 24, 1929, James Doolittle, an American pilot and army officer, proved the value of Sperry’s instruments by taking off, flying over a predetermined course, and landing, all without visual reference to the Earth.

Introduced in 1933, Boeing’s Model 247 was considered the first truly modern airliner. It was an all-metal, low-wing monoplane, with retractable landing gear, an insulated cabin, and room for ten passengers. An order from United Air Lines for 60 planes of this type tied up Boeing’s production line and led indirectly to the development of perhaps the most successful propeller airliner in history, the Douglas DC-3. Trans World Airlines, not willing to wait for Boeing to finish the order from United, approached airplane manufacturer Donald Douglas in Long Beach, California, for an alternative, which became, in quick succession, the DC-1, the DC-2, and the DC-3.

The DC-3 carried 21 passengers, used powerful, 1,000-horsepower engines, and could travel across the country in less than 24 hours of travel time, although it had to stop many times for fuel. The DC-3 quickly came to dominate commercial aviation in the late 1930s, and some DC-3s are still in service today.

Boeing provided the next major breakthrough with its Model 307 Stratoliner, a pressurized derivative of the famous B-17 bomber, entering service in 1940. With its regulated cabin air pressure, the Stratoliner could carry 33 passengers at altitudes up to 6,100 m (20,000 ft) and at speeds of 322 km/h (200 mph).

F

Aircraft Developments of World War II

It was not until after World War II (1939-1945), when comfortable, pressurized air transports became available in large numbers, that the airline industry really prospered. When the United States entered World War II in 1941, there were fewer than 300 planes in airline service. Airplane production concentrated mainly on fighters and bombers, and reached a rate of nearly 50,000 a year by the end of the war. A large number of sophisticated new transports, used in wartime for troop and cargo carriage, became available to commercial operators after the war ended. Pressurized propeller planes such as the Douglas DC-6 and Lockheed Constellation, early versions of which carried troops and VIPs during the war, now carried paying passengers on transcontinental and transatlantic flights.

Wartime technology efforts also brought to aviation critical new developments, such as the jet engine. Jet transportation in the commercial-aviation arena arrived in 1952 with Britain’s DeHavilland Comet, an 885-km/h (550-mph), four-engine jet. The Comet quickly suffered two fatal crashes due to structural problems and was grounded. This complication gave American manufacturers Boeing and Douglas time to bring the 707 and DC-8 to the market. Pan American World Airways inaugurated Boeing 707 jet service in October of 1958, and air travel changed dramatically almost overnight. Transatlantic jet service enabled travelers to fly from New York City to London, England, in less than eight hours, half the propeller-airplane time. Boeing’s new 707 carried 112 passengers at high speed and quickly brought an end to the propeller era for large commercial airplanes.

After the big, four-engine 707s and DC-8s had established themselves, airlines clamored for smaller, shorter-range jets, and Boeing and Douglas delivered. Douglas produced the DC-9 and Boeing both the 737 and the trijet 727.

G

The Jumbo Jet Era

The next frontier, pioneered in the late 1960s, was the age of the jumbo jet. Boeing, McDonnell Douglas, and Lockheed all produced wide-body airliners, sometimes called jumbo jets. Boeing developed and still builds the 747. McDonnell Douglas built a somewhat smaller, three-engine jet called the DC-10, produced later in an updated version known as the MD-11. Lockheed built the L-1011 Tristar, a trijet that competed with the DC-10. The L-1011 is no longer in production, and Lockheed-Martin does not build commercial airliners anymore.

In the 1980s McDonnell Douglas introduced the twin-engine MD-80 family, and Boeing brought online the narrow-body 757 and wide-body 767 twin jets. Airbus had developed the A300 wide-body twin during the 1970s. During the 1980s and 1990s Airbus expanded its family of aircraft by introducing the slightly smaller A310 twin jet and the narrow-body A320 twin, a unique, so-called fly-by-wire aircraft with sidestick controllers for the pilots rather than conventional control columns and wheels. Airbus also introduced the larger A330 twin and the A340, a four-engine airplane for longer routes, on which passenger loads are somewhat lighter. In 2000 the company launched production of the A380, a superjumbo jet that will seat 555 passengers on two decks, both of which extend the entire length of the fuselage. Scheduled to enter service in 2006, the jet will be the world’s largest passenger airliner.

Boeing introduced the 777, a wide-body jumbo jet that can hold up to 400 passengers, in 1995. In 1997 Boeing acquired longtime rival McDonnell Douglas, and a year the company later announced its intention to halt production of the passenger workhorses MD-11, MD-80, and MD-90. The company ceded the superjumbo jet market to Airbus and instead focused its efforts on developing a midsize passenger airplane, called the Sonic Cruiser, that would travel at 95 percent of the speed of sound or faster, significantly reducing flight times on transcontinental and transoceanic trips.

Engineering

I

INTRODUCTION

Engineering, term applied to the profession in which a knowledge of the mathematical and natural sciences, gained by study, experience, and practice, is applied to the efficient use of the materials and forces of nature. The term engineer properly denotes a person who has received professional training in pure and applied science, but is often loosely used to describe the operator of an engine, as in the terms locomotive engineer, marine engineer, or stationary engineer. In modern terminology these latter occupations are known as crafts or trades. Between the professional engineer and the craftsperson or tradesperson, however, are those individuals known as subprofessionals or paraprofessionals, who apply scientific and engineering skills to technical problems; typical of these are engineering aides, technicians, inspectors, draftsmen, and the like.

Before the middle of the 18th century, large-scale construction work was usually placed in the hands of military engineers. Military engineering involved such work as the preparation of topographical maps, the location, design, and construction of roads and bridges; and the building of forts and docks; see Military Engineering below. In the 18th century, however, the term civil engineering came into use to describe engineering work that was performed by civilians for nonmilitary purposes. With the increasing use of machinery in the 19th century, mechanical engineering was recognized as a separate branch of engineering, and later mining engineering was similarly recognized.

The technical advances of the 19th century greatly broadened the field of engineering and introduced a large number of engineering specialties, and the rapidly changing demands of the socioeconomic environment in the 20th century have widened the scope even further.

II

FIELDS OF ENGINEERING

The main branches of engineering are discussed below in alphabetical order. The engineer who works in any of these fields usually requires a basic knowledge of the other engineering fields, because most engineering problems are complex and interrelated. Thus a chemical engineer designing a plant for the electrolytic refining of metal ores must deal with the design of structures, machinery, and electrical devices, as well as with purely chemical problems.

Besides the principal branches discussed below, engineering includes many more specialties than can be described here, such as acoustical engineering (see Acoustics), architectural engineering (see Architecture: Construction), automotive engineering, ceramic engineering, transportation engineering, and textile engineering.

A

Aeronautical and Aerospace Engineering

Aeronautics deals with the whole field of design, manufacture, maintenance, testing, and use of aircraft for both civilian and military purposes. It involves the knowledge of aerodynamics, structural design, propulsion engines, navigation, communication, and other related areas. See Airplane; Aviation.

Aerospace engineering is closely allied to aeronautics, but is concerned with the flight of vehicles in space, beyond the earth's atmosphere, and includes the study and development of rocket engines, artificial satellites, and spacecraft for the exploration of outer space. See Space Exploration.

B

Chemical Engineering

This branch of engineering is concerned with the design, construction, and management of factories in which the essential processes consist of chemical reactions. Because of the diversity of the materials dealt with, the practice, for more than 50 years, has been to analyze chemical engineering problems in terms of fundamental unit operations or unit processes such as the grinding or pulverizing of solids. It is the task of the chemical engineer to select and specify the design that will best meet the particular requirements of production and the most appropriate equipment for the new applications.

With the advance of technology, the number of unit operations increases, but of continuing importance are distillation, crystallization, dissolution, filtration, and extraction. In each unit operation, engineers are concerned with four fundamentals: (1) the conservation of matter; (2) the conservation of energy; (3) the principles of chemical equilibrium; (4) the principles of chemical reactivity. In addition, chemical engineers must organize the unit operations in their correct sequence, and they must consider the economic cost of the overall process. Because a continuous, or assembly-line, operation is more economical than a batch process, and is frequently amenable to automatic control, chemical engineers were among the first to incorporate automatic controls into their designs.

C

Civil Engineering

Civil engineering is perhaps the broadest of the engineering fields, for it deals with the creation, improvement, and protection of the communal environment, providing facilities for living, industry and transportation, including large buildings, roads, bridges, canals, railroad lines, airports, water-supply systems, dams, irrigation, harbors, docks, aqueducts, tunnels, and other engineered constructions. The civil engineer must have a thorough knowledge of all types of surveying, of the properties and mechanics of construction materials, the mechanics of structures and soils, and of hydraulics and fluid mechanics. Among the important subdivisions of the field are construction engineering, irrigation engineering, transportation engineering, soils and foundation engineering, geodetic engineering, hydraulic engineering, and coastal and ocean engineering.

D

Electrical and Electronics Engineering

The largest and most diverse field of engineering, it is concerned with the development and design, application, and manufacture of systems and devices that use electric power and signals. Among the most important subjects in the field in the late 1980s are electric power and machinery, electronic circuits, control systems, computer design, superconductors, solid-state electronics, medical imaging systems, robotics, lasers, radar, consumer electronics, and fiber optics.

Despite its diversity, electrical engineering can be divided into four main branches: electric power and machinery, electronics, communications and control, and computers.

D1

Electric Power and Machinery

The field of electric power is concerned with the design and operation of systems for generating, transmitting, and distributing electric power. Engineers in this field have brought about several important developments since the late 1970s. One of these is the ability to transmit power at extremely high voltages in both the direct current (DC) and alternating current (AC) modes, reducing power losses proportionately. Another is the real-time control of power generation, transmission, and distribution, using computers to analyze the data fed back from the power system to a central station and thereby optimizing the efficiency of the system while it is in operation.

A significant advance in the engineering of electric machinery has been the introduction of electronic controls that enable AC motors to run at variable speeds by adjusting the frequency of the current fed into them. DC motors have also been made to run more efficiently this way. See also Electric Motors and Generators; Electric Power Systems.

D2

Electronics

Electronic engineering deals with the research, design, integration, and application of circuits and devices used in the transmission and processing of information. Information is now generated, transmitted, received, and stored electronically on a scale unprecedented in history, and there is every indication that the explosive rate of growth in this field will continue unabated.

Electronic engineers design circuits to perform specific tasks, such as amplifying electronic signals, adding binary numbers, and demodulating radio signals to recover the information they carry. Circuits are also used to generate waveforms useful for synchronization and timing, as in television, and for correcting errors in digital information, as in telecommunications. See also Electronics.

Prior to the 1960s, circuits consisted of separate electronic devices—resistors, capacitors, inductors, and vacuum tubes—assembled on a chassis and connected by wires to form a bulky package. Since then, there has been a revolutionary trend toward integrating electronic devices on a single tiny chip of silicon or some other semiconductive material. The complex task of manufacturing these chips uses the most advanced technology, including computers, electron-beam lithography, micro-manipulators, ion-beam implantation, and ultraclean environments. Much of the research in electronics is directed toward creating even smaller chips, faster switching of components, and three-dimensional integrated circuits.

D3

Communications and Control

Engineers in this field are concerned with all aspects of electrical communications, from fundamental questions such as “What is information?” to the highly practical, such as design of telephone systems. In designing communication systems, engineers rely heavily on various branches of advanced mathematics, such as Fourier analysis, linear systems theory, linear algebra, complex variables, differential equations, and probability theory. See also Mathematics; Matrix Theory and Linear Algebra; Probability.

Engineers work on control systems ranging from the everyday, passenger-actuated, as those that run an elevator, to the exotic, as systems for keeping spacecraft on course. Control systems are used extensively in aircraft and ships, in military fire-control systems, in power transmission and distribution, in automated manufacturing, and in robotics.

Engineers have been working to bring about two revolutionary changes in the field of communications and control: Digital systems are replacing analog ones at the same time that fiber optics are superseding copper cables. Digital systems offer far greater immunity to electrical noise. Fiber optics are likewise immune to interference; they also have tremendous carrying capacity, and are extremely light and inexpensive to manufacture.

D4

Computers

Virtually unknown just a few decades ago, computer engineering is now among the most rapidly growing fields. The electronics of computers involve engineers in design and manufacture of memory systems, of central processing units, and of peripheral devices (see Computer). Foremost among the avenues now being pursued are the design of Very Large Scale Integration (VLSI) and new computer architectures. The field of computer science is closely related to computer engineering; however, the task of making computers more “intelligent” (artificial intelligence,), through creation of sophisticated programs or development of higher level machine languages or other means, is generally regarded as being in the realm of computer science.

One current trend in computer engineering is microminiaturization. Using VLSI, engineers continue to work to squeeze greater and greater numbers of circuit elements onto smaller and smaller chips. Another trend is toward increasing the speed of computer operations through use of parallel processors, superconducting materials, and the like.

E

Geological and Mining Engineering

This branch of engineering includes activities related to the discovery and exploration of mineral deposits and the financing, construction, development, operation, recovery, processing, purification, and marketing of crude minerals and mineral products. The mining engineer is trained in historical geology, mineralogy, paleontology, and geophysics, and employs such tools as the seismograph and the magnetometer for the location of ore or petroleum deposits beneath the surface of the earth (see Petroleum; Seismology). The surveying and drawing of geological maps and sections is an important part of the work of the engineering geologist, who is also responsible for determining whether the geological structure of a given location is suitable for the building of such large structures as dams.

F

Industrial or Management Engineering

This field pertains to the efficient use of machinery, labor, and raw materials in industrial production. It is particularly important from the viewpoint of costs and economics of production, safety of human operators, and the most advantageous deployment of automatic machinery.

G

Mechanical Engineering

Engineers in this field design, test, build, and operate machinery of all types; they also work on a variety of manufactured goods and certain kinds of structures. The field is divided into (1) machinery, mechanisms, materials, hydraulics, and pneumatics; and (2) heat as applied to engines, work and energy, heating, ventilating, and air conditioning. The mechanical engineer, therefore, must be trained in mechanics, hydraulics, and thermodynamics and must be fully grounded in such subjects as metallurgy and machine design. Some mechanical engineers specialize in particular types of machines such as pumps or steam turbines. A mechanical engineer designs not only the machines that make products but the products themselves, and must design for both economy and efficiency. A typical example of the complexity of modern mechanical engineering is the design of an automobile, which entails not only the design of the engine that drives the car but also all its attendant accessories such as the steering and braking systems, the lighting system, the gearing by which the engine's power is delivered to the wheels, the controls, and the body, including such details as the door latches and the type of seat upholstery.

H

Military Engineering

This branch is concerned with the application of the engineering sciences to military purposes. It is generally divided into permanent land defense (see Fortification and Siege Warfare) and field engineering. In war, army engineer battalions have been used to construct ports, harbors, depots, and airfields. In the U.S., military engineers also construct some public works, national monuments, and dams (see Army Corps of Engineers).

Military engineering has become an increasingly specialized science, resulting in separate engineering subdisciplines such as ordnance, which applies mechanical engineering to the development of guns and chemical engineering to the development of propellants, and the Signal Corps, which applies electrical engineering to all problems of telegraph, telephone, radio, and other communication.

I

Naval or Marine Engineering

Engineers who have the overall responsibility for designing and supervising construction of ships are called naval architects. The ships they design range in size from ocean-going supertankers as much as 1300 feet long to small tugboats that operate in rivers and bays. Regardless of size, ships must be designed and built so that they are safe, stable, strong, and fast enough to perform the type of work intended for them. To accomplish this, a naval architect must be familiar with the variety of techniques of modern shipbuilding, and must have a thorough grounding in applied sciences, such as fluid mechanics, that bear directly on how ships move through water.

Marine engineering is a specialized branch of mechanical engineering devoted to the design and operation of systems, both mechanical and electrical, needed to propel a ship. In helping the naval architect design ships, the marine engineer must choose a propulsion unit, such as a diesel engine or geared steam turbine, that provides enough power to move the ship at the speed required. In doing so, the engineer must take into consideration how much the engine and fuel bunkers will weigh and how much space they will occupy, as well as the projected costs of fuel and maintenance. See also Ships and Shipbuilding.

J

Nuclear Engineering

This branch of engineering is concerned with the design and construction of nuclear reactors and devices, and the manner in which nuclear fission may find practical applications, such as the production of commercial power from the energy generated by nuclear reactions and the use of nuclear reactors for propulsion and of nuclear radiation to induce chemical and biological changes. In addition to designing nuclear reactors to yield specified amounts of power, nuclear engineers develop the special materials necessary to withstand the high temperatures and concentrated bombardment of nuclear particles that accompany nuclear fission and fusion. Nuclear engineers also develop methods to shield people from the harmful radiation produced by nuclear reactions and to ensure safe storage and disposal of fissionable materials. See Nuclear Energy.

K

Safety Engineering

This field of engineering has as its object the prevention of accidents. In recent years safety engineering has become a specialty adopted by individuals trained in other branches of engineering. Safety engineers develop methods and procedures to safeguard workers in hazardous occupations. They also assist in designing machinery, factories, ships, and roads, suggesting alterations and improvements to reduce the likelihood of accident. In the design of machinery, for example, the safety engineer seeks to cover all moving parts or keep them from accidental contact with the operator, to put cutoff switches within reach of the operator, and to eliminate dangerous projecting parts. In designing roads the safety engineer seeks to avoid such hazards as sharp turns and blind intersections, known to result in traffic accidents. Many large industrial and construction firms, and insurance companies engaged in the field of workers compensation, today maintain safety engineering departments. See Industrial Safety; National Safety Council.

L

Sanitary Engineering

This is a branch of civil engineering, but because of its great importance for a healthy environment, especially in dense urban-population areas, it has acquired the importance of a specialized field. It chiefly deals with problems involving water supply, treatment, and distribution; disposal of community wastes and reclamation of useful components of such wastes; control of pollution of surface waterways, groundwaters, and soils; milk and food sanitation; housing and institutional sanitation; rural and recreational-site sanitation; insect and vermin control; control of atmospheric pollution; industrial hygiene, including control of light, noise, vibration, and toxic materials in work areas; and other fields concerned with the control of environmental factors affecting health. The methods used for supplying communities with pure water and for the disposal of sewage and other wastes are described separately. See Plumbing; Sewage Disposal; Solid Waste Disposal; Water Pollution; Water Supply and Waterworks.

III

MODERN ENGINEERING TRENDS

Scientific methods of engineering are applied in several fields not connected directly to manufacture and construction. Modern engineering is characterized by the broad application of what is known as systems engineering principles. The systems approach is a methodology of decision-making in design, operation, or construction that adopts (1) the formal process included in what is known as the scientific method; (2) an interdisciplinary, or team, approach, using specialists from not only the various engineering disciplines, but from legal, social, aesthetic, and behavioral fields as well; (3) a formal sequence of procedure employing the principles of operations research.

In effect, therefore, transportation engineering in its broadest sense includes not only design of the transportation system and building of its lines and rolling stock, but also determination of the traffic requirements of the route followed. It is also concerned with setting up efficient and safe schedules, and the interaction of the system with the community and the environment. Engineers in industry work not only with machines but also with people, to determine, for example, how machines can be operated most efficiently by the workers. A small change in the location of the controls of a machine or of its position with relation to other machines or equipment, or a change in the muscular movements of the operator, often results in greatly increased production. This type of engineering work is called time-study engineering.

A related field of engineering, human-factors engineering, also known as ergonomics, received wide attention in the late 1970s and the '80s when the safety of nuclear reactors was questioned following serious accidents that were caused by operator errors, design failures, and malfunctioning equipment. Human-factors engineering seeks to establish criteria for the efficient, human-centered design of, among other things, the large, complicated control panels that monitor and govern nuclear reactor operations.

Among various recent trends in the engineering profession, licensing and computerization are the most widespread. Today, many engineers, like doctors and lawyers, are licensed by the state. Approvals by professionally licensed engineers are required for construction of public and commercial structures, especially installations where public and worker safety is a consideration. The trend in modern engineering offices is overwhelmingly toward computerization. Computers are increasingly used for solving complex problems as well as for handling, storing, and generating the enormous volume of data modern engineers must work with.

The National Academy of Engineering, founded in 1964 as a private organization, sponsors engineering programs aimed at meeting national needs, encourages new research, and is concerned with the relationship of engineering to society.

Defense Systems

I

INTRODUCTION

Defense Systems, combination of electronic warning networks and military strategies designed to protect a country from a strategic missile or bomber attack. Defense systems use radar and satellite detection systems to monitor a nation’s airspace, providing data that would allow defense forces to detect and coordinate against such an attack. Several large countries, including the United States, also maintain an arsenal of offensive nuclear weapons as a deterrent to a nuclear attack.

II

STRATEGIC DEFENSE

Modern defense systems originated during World War II (1939-1945) in response to the advent of long-range bomber aircraft. Radar stations in Great Britain were installed to detect approaching German bombers and give British fighter aircraft time to intercept the enemy. Before World War II, most nations focused national defense against assaults from land or sea.

After World War II, the United States enjoyed a brief period of military superiority as the sole possessor of nuclear weapons, but the detonation of the first Soviet atomic bomb in 1949 brought a new military threat. The United States began to focus its defenses on early detection of long-range bombers, to give U.S. fighter aircraft enough time to respond to a large-scale attack.

The ballistic missile threat was the most important development in defense systems. When the first German V-2 ballistic missiles arced over England on September 6, 1944, a new day in warfare dawned. The V-2 traveled at supersonic speeds and was impossible to intercept. After World War II an immediate missile race began between the United States and the Union of Soviet Socialist Republics (USSR). The goal was to build upon German technology and create a long-range intercontinental ballistic missile, or ICBM, that could deliver a nuclear warhead.

A

Deterrence

By 1958, both the United States and the USSR had successfully tested ICBMs and immediately began to improve them. As a result, both nations became extremely vulnerable to attack. The amount of warning that existing national radar systems could give for an incoming bomber attack had been measured in hours, but an ICBM could loft from a launching base in the USSR and impact in the United States within 30 minutes. There were no technical means to stop a missile once launched, so national leaders turned to the idea of deterrence.

Deterrence uses the threat of an offensive attack as a defense—or deterrent—against such an attack. The USSR, with their initial lead in rocket and missile technology, had adopted a so-called first strike strategy. The Soviet leaders recognized that an exchange of nuclear missiles would be so devastating to both countries that the USSR had to launch its missiles first, and in such numbers that a crippled United States would not be able to mount a significant retaliatory strike. The United States publicly said it would never undertake a first strike, deciding instead to develop a second-strike capability of such magnitude that no Soviet first strike would avoid retaliation. This strategy became known as mutually assured destruction, which had the appropriate acronym MAD. The arms buildup between the United States and the USSR, and the tensions surrounding the buildup, became known as the Cold War (because no direct combat took place). Although the world came close to nuclear war on several occasions (see Cuban Missile Crisis), the USSR never dared to launch a first strike, so the United States never had to retaliate.

B

Defense Systems of Other Countries

Although the Cold War ended in the early 1990s, major military powers continue to employ some version of offensive deterrent and defensive warning capability. Shortly after World War II, political and military alliances were created to offer mutual defense. The United States, Britain, France, and several other countries formed the North Atlantic Treaty Organization (NATO), while the USSR and its satellite countries responded with the Warsaw Pact. Practically all countries monitor their own airspace, but for strategic defense the members of these alliances generally looked to either the United States or the USSR for protection.

III

OFFENSIVE DETERRENTS

Several countries such as the United States, Russia, Britain, France and China maintain a force of offensive nuclear weapons to deter against a nuclear attack. The offensive capability of the United States rests on what is known as the Nuclear Triad, comprised of strategic bombers, land-based ICBMs, and submarine-launched ballistic missiles. It was devised so if any one of the three “legs” is destroyed by an attack, the other two can still function. The nuclear powers of the world maintain some or all of these forces.

A

Bombers

The United States had initially (from 1945 through about 1960) depended upon the bomber aircraft of the Strategic Air Command (SAC) to deter an attack from the USSR. In the early years of SAC, these aircraft included the Boeing B-50 and the Consolidated B-36. Later jets such as the Boeing B-47 Stratojet and Boeing B-52 Stratofortress jet bombers were faster and could carry more payload. The United States currently maintains B-52, Rockwell B-1B, and Northrop Grumman B-2 bombers capable of being armed with nuclear weapons as part of its strategic force.

B

ICBMs

The USSR began an intensive ICBM development program after World War II, and the United States responded in kind. While the Soviet bomber fleet never approached that of the United States in size or capability, the Soviet ICBM fleet was truly formidable. The USSR developed greater numbers of ICBMs than the United States, and these had larger warheads, greater range and superior accuracy to U.S. weapons. The USSR also was successful in hardening (or making resistant to a nuclear attack) its silo launch facilities to a far greater degree than the United States was able to do.

C

SLBMs

A similar process followed for the submarine-launched ballistic missile (SLBM), when in the late 1950s the USSR built several submarines able to carry the SS-N-4 Sark missile. In 1960 the United States sent the USS George Washington on patrol, carrying Polaris SLBMs. As technology improved, the SLBM assumed greater importance. A ballistic missile submarine is difficult to detect, can remain on duty for weeks at a time without surfacing, and can fire its missiles from beneath the water’s surface.

D

Coordination and Command

The U.S. Strategic Command monitors defense information from various sources and would coordinate a military response to a nuclear attack. The Strategic Air Command (SAC) was for many years the primary deterrent force. It has been replaced in part by the Air Combat Command. For many years as much as 50 percent of the SAC bomber fleet was on airborne alert, armed with nuclear weapons, and able to attack immediately upon notice.

In the event of an attack, U.S. Strategic Command would collect data and present recommendations to the U.S. president and senior advisers (referred to as the National Command Authority). Only the president can make the decision to use nuclear weapons, even in response to an attack. The plan a president would use to respond to an attack is called the Single Integrated Operational Plan, or SIOP. The SIOP consists of several planned responses to various nuclear scenarios. If the President were to decide to use nuclear weapons, several procedures and code phrases would be used to verify the President’s authority. When the procedures are completed, they would authorize the military to use nuclear weapons. Numerous precautions exist in this process to prevent accidental or unauthorized use of nuclear weapons.

The president and the rest of the National Command Authority would possibly give orders from a modified Boeing 747 called a National Airborne Operations Center (NAOC). By being airborne, command authority is less vulnerable to a ground attack. These airplanes are outfitted with advanced communications equipment so the president can stay in contact with U.S. Strategic Command at all times. U.S. Strategic Command also has a number of airborne command centers that can coordinate military forces in the event that ground centers have been destroyed or damaged.

IV

DEFENSIVE WARNING SYSTEMS

The consequences of a nuclear exchange would be devastating, with casualties estimated to be in the hundreds of millions on both sides and massive damage to the environment. Both the USSR and the United States were aware of the catastrophic scale of a nuclear exchange, and both built elaborate defensive systems to detect an incoming nuclear attack.

A

Radar Networks

From 1949 (when the USSR developed nuclear weapons) to 1959 (when ICBMs became operational), the main strategic threat was bombers. To provide advance warning, several radar posts were built across Canada by joint cooperation between Canada and the United States. The first series of linked radar stations was called the Pinetree Line, established in 1954. Two more lines, the Mid-Canada Line and the Distant Early Warning Line (or DEW Line) were created for more complete radar coverage. The DEW Line, comprising 60 radar sites along the 70th parallel, became operational in 1957.

To warn against ICBMs, the Ballistic Missile Early Warning System (BMEWS) was introduced in 1962. It consists of sophisticated radar sites in Greenland, Alaska, and England. These sites could detect, track and predict impact points of both intercontinental ballistic missiles and smaller intermediate range ballistic missiles (IRBMs) launched from within the USSR. A typical site has four giant scanner search radars, each 50.3 m (165 ft) high and 122 m (400 ft) long; and one tracking radar, a 25.6 m (84 ft) antenna in a 42.6 m (140 ft) diameter housing. The purpose of the BMEWS is to provide sufficient warning time for U.S. bombers to get airborne and ICBM forces to prepare for a counterstrike.

BMEWS is backed up by the Perimeter Acquisition Radar Characterization (PARCS) system. Operating in the U.S. interior, PARCS can detect air traffic over Canada. Four other radar sites monitor the Atlantic and Pacific oceans for possible submarine attacks. These various stations are connected to the North American Aerospace Defense Command (NORAD), to U.S. Strategic Command headquarters, the Pentagon, and to the Canadian Royal Air Force fighter command.

B

NORAD

NORAD was activated in 1957 to provide an integrated command for the air defense of the United States and Canada, and to process the information gathered from various radar sites. The reality of ICBMs required the establishment of a detection and tracking system, and the housing of NORAD in a bombproof site located within the interior of Cheyenne Mountain near Colorado Springs, Colorado. With its increased responsibility, NORAD equipment was expanded to include the Airborne Warning and Control Aircraft (AWACS), Over the Horizon (OTH) radar that warns against low-altitude cruise missiles, and a network of satellites. The DEW Line was replaced with a superior system called the North Warning System; and the Joint Surveillance System (JSS), operated by the U.S. Air Force and the Federal Aviation Administration, provides additional air traffic coverage. NORAD monitors all of these early warning systems, processes the information, and then relates it to U.S. Strategic Command.

C

Soviet Air Defense

The USSR built an even more extensive integrated air defense system, covering the country with radar systems, surface-to-air missile sites and large numbers of interceptors (fast military aircraft designed to destroy attacking airplanes). The USSR built a huge infrastructure of civil and military defense systems, including deep underground blast shelters for the country’s leaders and key industries. Russia continues to maintain this network. The United States has abandoned its rather primitive civil defense efforts of the 1950s, and has not replaced it with any other system.

D

Antiballistic Missile Systems

Active defense systems have been proposed that would use advanced missiles to track and shoot down incoming ICBMs. These are known as antiballistic missile (ABM) systems. The most famous of the antiballistic missile systems was the Strategic Defense Initiative (SDI) proposed by former U.S. president Ronald Reagan in 1983. SDI would have used a combination of laser-equipped satellites and other space-based weapons to destroy ballistic missiles after their launch. Research had begun on SDI, but the program was eventually cancelled due to high cost and the easing of global tensions.

The 1972 Antiballistic Missile (ABM) Treaty signed by the United States and the USSR limits the implementation of antiballistic missile systems. Russia has one system in place around Moscow. The United States had a system in North Dakota, but closed it down due to cost and reliability issues. See also Strategic Arms Limitation Talks.

The Patriot is a missile designed to destroy smaller ballistic missiles. Technology of this type continues to be used as the basis of research to counter ICBMs as well as short-range ballistic missiles, like the Scud missile used by Iraq in the 1991 Persian Gulf War. The United States also indirectly defends against some missiles through the antisubmarine warfare combination of radar, aircraft, missiles, attack submarines and surface ships that track Russian ballistic missile submarines. While none of these weapons have the capability to intercept an enemy missile once launched, they can track and destroy the submarine itself.

V

EXISTING NUCLEAR THREATS

With the end of the Cold War between the former Soviet Union and the United States, the threat of an all-out nuclear attack has diminished. It is unlikely that Russia would undertake a massive first strike against the United States, and both countries have significantly reduced their nuclear forces. Still, the threat of nuclear war and the spread of nuclear weapons remains, evidenced by the nuclear tests of India and Pakistan in 1998. Five other nations admit to having nuclear weapons (their estimated quantity is indicated in parentheses): China (434), France (482), Russia (13,200), the United Kingdom (200) and the United States (15,500). Israel is known to have the capability to deploy nuclear weapons, and still other countries, including Iran, Iraq, Libya, and North Korea, are known to have nuclear weapons programs. See also Arms Control, International, Air Warfare.

Space Exploration

I

INTRODUCTION

Space Exploration, quest to use space travel to discover the nature of the universe beyond Earth. Since ancient times, people have dreamed of leaving their home planet and exploring other worlds. In the later half of the 20th century, that dream became reality. The space age began with the launch of the first artificial satellites in 1957. A human first went into space in 1961. Since then, astronauts and cosmonauts have ventured into space for ever greater lengths of time, even living aboard orbiting space stations for months on end. Two dozen people have circled the Moon or walked on its surface. At the same time, robotic explorers have journeyed where humans could not go, visiting all but one of the solar system’s major worlds. Unpiloted spacecraft have also visited a host of minor bodies such as moons, comets, and asteroids. These explorations have sparked the advance of new technologies, from rockets to communications equipment to computers. Spacecraft studies have yielded a bounty of scientific discoveries about the solar system, the Milky Way Galaxy, and the universe. And they have given humanity a new perspective on Earth and its neighbors in space.

The first challenge of space exploration was developing rockets powerful enough and reliable enough to boost a satellite into orbit. These boosters needed more than brute force, however; they also needed guidance systems to steer them on the proper flight paths to reach their desired orbits. The next challenge was building the satellites themselves. The satellites needed electronic components that were lightweight, yet durable enough to withstand the acceleration and vibration of launch. Creating these components required the world’s aerospace engineering facilities to adopt new standards of reliability in manufacturing and testing. On Earth, engineers also had to build tracking stations to maintain radio communications with these artificial “moons” as they circled the planet.

Beginning in the early 1960s, humans launched probes to explore other planets. The distances traveled by these robotic space travelers required travel times measured in months or years. These spacecraft had to be especially reliable to continue functioning for a decade or more. They also had to withstand such hazards as the radiation belts surrounding Jupiter, particles orbiting in the rings of Saturn, and greater extremes in temperature than are faced by spacecraft in the vicinity of Earth. Despite their great scientific returns, these missions often came with high price tags. Today the world’s space agencies, such as the United States National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA), strive to conduct robotic missions more cheaply and efficiently.

It was inevitable that humans would follow their unpiloted creations into space. Piloted spaceflight introduced a whole new set of difficulties, many of them concerned with keeping people alive in the hostile environment of space. In addition to the vacuum of space, which requires any piloted spacecraft to carry its own atmosphere, there are other deadly hazards: solar and cosmic radiation, micrometeorites (small bits of rock and dust) that might puncture a spacecraft hull or an astronaut’s pressure suit, and extremes of temperature ranging from frigid darkness to broiling sunlight. It was not enough simply to keep people alive in space—astronauts needed to have a means of accomplishing useful work while they were there. It was necessary to develop tools and techniques for space navigation, and for conducting scientific observations and experiments. Astronauts would have to be protected when they ventured outside the safety of their pressurized spacecraft to work in the vacuum. Missions and hardware would have to be carefully designed to help ensure the safety of space crews in any foreseeable emergency, from liftoff to landing.

The challenges of conducting piloted spaceflights were great enough for missions that orbited Earth. They became even more daunting for the Apollo missions, which sent astronauts to the Moon. The achievement of sending astronauts to the lunar surface and back represents a summit of human spaceflight.

After the Apollo program, the emphasis in piloted missions shifted to long-duration spaceflight, as pioneered aboard Soviet and U.S. space stations. The development of reusable spacecraft became another goal, giving rise to the U.S. space shuttle fleet. Today, efforts focus on keeping people healthy during space missions lasting a year or more—the duration needed to reach nearby planets—and in lowering the cost of sending satellites into orbit.

II

HISTORY OF SPACE EXPLORATION

The desire to explore the heavens is probably as old as humankind, but in the strictest sense, the history of space exploration begins very recently, with the launch of the first artificial satellite, Sputnik 1, which the Soviets sent into orbit in 1957. Soviet cosmonaut Yuri Gagarin became the first human in space just a few years later, in 1961. The decades from the 1950s to the 1990s have been full of new “firsts,” new records, and advances in technology.

A

First Forays into Space

Although artificial satellites and piloted spacecraft are achievements of the later 20th century, the technology and principles of space travel stretch back hundreds of years, to the invention of rockets in the 11th century and the formulation of the laws of motion in the 17th century. The power of rockets to lift objects into space is described by a law of motion that was formulated by English scientist Sir Isaac Newton in the 1680s. Newton’s third law of motion states that every action causes an equal and opposite reaction. As predicted by Newton’s law, the rearward rush of gases expelled by the rocket’s engine causes the rocket to be propelled forward. It took nine centuries from the invention of rockets and almost three centuries from the formulation of Newton’s third law for humans to send an object into space. In space, the motions of satellites and interplanetary spacecraft are described by the laws of motion formulated by German astronomer Johannes Kepler, also in the 17th century. For example, one of Kepler’s laws states that the closer a satellite is to Earth, the faster it orbits.

A1

Rockets and Rocket Builders

Rockets made their first recorded appearance as weapons in 12th-century China, but they probably originated in the 11th century. Fueled by gunpowder, they were launched against enemy troops. In the centuries that followed, these solid-fuel rockets became part of the arsenals of Europe. In 1814, during an attack on New Orleans, Louisiana, the British fired rockets—with little effect—at American troops.

In Russia, nearly a century later, a lone schoolteacher named Konstantin Tsiolkovsky envisioned how to use rockets to voyage into space. In a series of detailed treatises, including “The Exploration of Cosmic Space With Reactive Devices” (1903), Tsiolkovsky explained how a multi-stage, liquid-fuel rocket could propel humans to the Moon.

Tsiolkovsky did not have the means to build real liquid-fuel rockets. Robert Goddard, a physics professor in Worcester, Massachusetts, took up that effort. In 1926 he succeeded in building and launching the world’s first liquid-fuel rocket, which soared briefly above a field near his home. Beginning in 1940, after moving to Roswell, New Mexico, Goddard built a series of larger liquid-fuel rockets that flew as high as 90 m (300 ft). Meanwhile, beginning in 1936 at the California Institute of Technology, other experimenters made advances in solid-fuel rockets. During World War II (1939-1945), engineers developed solid-fuel rockets that could be attached to an airplane to provide a boost during takeoff.

The greatest strides in rocketry during the first half of the 20th century occurred in Germany. There, mathematician and physicist Hermann Oberth and architect Walter Hohmann theorized about rocketry and interplanetary travel in the 1920s. During World War II, Nazi Germany undertook the first large-scale rocket development program, headed by a young engineer named Wernher Von Braun. Von Braun’s team created the V-2, a rocket that burned an alcohol-water mixture with liquid oxygen to produce 250,000 newtons (56,000 lb) of thrust. The Germans launched thousands of V-2s carrying explosives against targets in Britain and The Netherlands. While they did not prove to be an effective weapon, V-2s did become the first human-made objects to reach altitudes above 80 km (50 mi)—the height at which outer space is considered to begin—before falling back to Earth. The V-2 inaugurated the era of modern rocketry.

A2

Early Artificial Satellites

During the years following World War II, the United States and the Union of Soviet Socialist Republics (USSR) engaged in efforts to construct intercontinental ballistic missiles (ICBMs) capable of traveling thousands of miles armed with a nuclear warhead. In August 1957 Soviet engineers, led by rocket pioneer Sergei Korolyev, were the first to succeed with the launch of their R-7 rocket, which stood almost 30 m (100 ft) tall and produced 3.8 million newtons (880,000 lb) of thrust at liftoff. Although its primary purpose was for use as a weapon, Korolyev and his team adapted the R-7 into a satellite launcher. On October 4, 1957, they launched the world’s first artificial satellite, called Sputnik (“fellow traveler”). Although it was only a simple 58-cm (23-in) aluminum sphere containing a pair of radio transmitters, Sputnik’s successful orbits around Earth marked a huge step in technology and ushered in the space age. On November 3, 1957, the Soviets launched Sputnik 2, which weighed 508 kg (1,121 lb) and contained the first space traveler—a dog named Laika, which survived for several days aboard Sputnik 2. Due to rising temperatures within the satellite, Laika died from heat exhaustion before her air supply ran out.

News of the first Sputnik intensified efforts to launch a satellite in the United States. The initial U.S. satellite launch attempt on December 6, 1957, failed disastrously when the Vanguard launch rocket exploded moments after liftoff. Success came on January 31, 1958, with the launch of the satellite Explorer 1. Instruments aboard Explorer 1 made the first detection of the Van Allen belts, which are bands of trapped radiation surrounding Earth (see Radiation Belts). This launch also represented a success for Wernher von Braun, who had been brought to the United States with many of his engineers after World War II. Von Braun’s team had created the Jupiter C (an upgraded version of their Redstone missile), which launched Explorer 1.

The satellites that followed Sputnik and Explorer into Earth orbit provided scientists and engineers with a variety of new knowledge. For example, scientists who tracked radio signals from the U.S. satellite Vanguard 1, launched in March 1958, determined that Earth is slightly flattened at the poles. In August 1959 Explorer 6 sent back the first photo of Earth from orbit. Even as these satellites revealed new details about our own planet, efforts were underway to reach our nearest neighbor in space, the Moon.

B

Unpiloted Lunar Missions

Early in 1958 the United States and the USSR were both working hard to be the first to send a satellite to the Moon. Initial attempts by both sides failed. On October 11, 1958, the United States launched Pioneer 1 on a mission to orbit the Moon. It did not reach a high enough speed to reach the Moon, but reached a height above Earth of more than 110,000 km (more than 70,000 mi). In early December 1958 Pioneer 3 also failed to leave high Earth orbit. It did, however, discover a second Van Allen belt of radiation surrounding Earth.

On January 2, 1959, after two earlier failed missions, the USSR launched Luna 1, which was intended to hit the Moon. Although it missed its target, Luna 1 did become the first artificial object to escape Earth orbit. On September 14, 1959, Luna 2 became the first artificial object to strike the Moon, impacting east of the Mare Serentitatis (Sea of Serenity). In October 1959, Luna 3 flew around the Moon and radioed the first pictures of the far side of the Moon, which is not visible from Earth.

In the United States, efforts to reach the Moon did not resume until 1962, with a series of probes called Ranger. The early Rangers were designed to eject an instrument capsule onto the Moon’s surface just before the main spacecraft crashed into the Moon. These missions were plagued by failures—only Ranger 4 struck the Moon, and the spacecraft had already ceased functioning by that time. Rangers 6 through 9 were similar to the early Rangers, but did not have instrument packages. They carried television cameras designed to send back pictures of the Moon before the spacecraft crashed. On July 31, 1964, Ranger 7 succeeded in sending back the first high-resolution images of the Moon before crashing, as planned, into the surface. Rangers 8 and 9 repeated the feat in 1965.

By then, the United States had embarked on the Apollo program to land humans on the Moon (see the Piloted Spaceflight section of this article for a discussion of the Apollo program). With an Apollo landing in mind, the next series of U.S. lunar probes, named Surveyor, was designed to “soft-land” (that is, land without crashing) on the lunar surface and send back pictures and other data to aid Apollo planners. As it turned out, the Soviets made their own soft landing first, with Luna 9, on February 3, 1966. Luna 9 radioed the first pictures of a dusty moonscape from the lunar surface. Surveyor 1 successfully reached the surface on June 2, 1966. Six more Surveyor missions followed; all but two were successful. The Surveyors sent back thousands of pictures of the lunar surface. Two of the probes were equipped with a mechanical claw, remotely operated from Earth, that enabled scientists to investigate the consistency of the lunar soil.

At the same time, the United States launched the Lunar Orbiter probes, which began circling the Moon to map its surface in unprecedented detail. Lunar Orbiter 1 began taking pictures on August 18, 1966. Four more Lunar Orbiters continued the mapping program, which gave scientists thousands of high-resolution photographs covering nearly all of the Moon.

Beginning in 1968 the USSR sent a series of unpiloted Zond probes—actually a lunar version of their piloted Soyuz spacecraft—around the Moon. These flights, initially designed as preparation for planned piloted missions that would orbit the Moon, returned high-quality photographs of the Moon and Earth. Two of the Zonds carried biological payloads with turtles, plants, and other living things.

Although both the United States and the USSR were achieving successes with their unpiloted lunar missions, the Americans were pulling steadily ahead in their piloted program. As their piloted lunar program began to lag, the Soviets made plans for robotic landers that would gather a sample of lunar soil and carry it to Earth. Although this did not occur in time to upstage the Apollo landings as the Soviets had hoped, Luna 16 did carry out a sample return in September 1970, returning to Earth with 100 g (4 oz) of rock and soil from the Moon’s Mare Fecunditatis (Sea of Fertility). In November 1970 Luna 17 landed with a remote-controlled rover called Lunakhod 1. The first wheeled vehicle on the Moon, Lunakhod 1 traveled 10.5 km (6.4 mi) across the Sinus Iridium (Bay of Rainbows) during ten months of operations, sending back pictures and other data. Only three more lunar probes followed. Luna 20 returned samples in February 1972. Lunakhod 2, carried aboard the Luna 21 lander, reached the Moon in January 1973. Then, in August 1976 Luna 24 ended the first era of lunar exploration.

Exploration of the Moon resumed in February 1994 with the U.S. probe called Clementine, which circled the Moon for three months. In addition to surveying the Moon with high-resolution cameras, Clementine gathered the first comprehensive data on lunar topography using a laser altimeter. Clementine’s laser altimeter bounced laser beams off of the Moon’s surface, measuring the time they took to come back to determine the height of features on the Moon.

In January 1998 NASA’s Lunar Prospector probe began circling the Moon in an orbit over the Moon’s north and south poles. Its sensors conducted a survey of the Moon’s composition. In March 1998 the spacecraft found tentative evidence of water in the form of ice mixed with lunar soil at the Moon’s poles. Lunar Prospector also investigated the Moon’s gravitational and magnetic fields. Controllers intentionally crashed the probe into the Moon in July 1999, hoping to see signs of water in the plume of debris raised by the impact. Measurements taken by instruments around Earth, however, did not find evidence of water after the crash, nor did they rule out the existence of water.

C

Scientific Satellites

Years before the launch of the first artificial satellites, scientists anticipated the value of putting telescopes and other scientific instruments in orbit around Earth. Orbiting satellites can view large areas of Earth or can provide views of space unobstructed by Earth’s atmosphere.

C1

Earth-Observing Satellites

One main advantage of putting scientific instruments into space is the ability to look down at Earth. Viewing large areas of the planet allows meteorologists, scientists who research Earth’s weather and climate, to study large-scale weather patterns (see Meteorology). More detailed views aid cartographers, or mapmakers, in mapping regions that would otherwise be inaccessible to people. Researchers who study Earth’s land masses and oceans also benefit from having an orbital vantage point.

Beginning in 1960 with the launch of U.S. Tiros I, weather satellites have sent back television images of parts of the planet. The first satellite that could observe most of Earth, NASA’s Earth Resources Technology Satellite 1 (ERTS 1, later renamed Landsat 1), was launched in 1972. Landsat 1 had a polar orbit, circling Earth by passing over the north and south poles. Because the planet rotated beneath Landsat’s orbit, the satellite could view almost any location on the Earth once every 18 hours. Landsat 1 was equipped with cameras that recorded images not just of visible light but of other wavelengths in the electromagnetic spectrum (see Electromagnetic Radiation). These cameras provided a wealth of useful data. For example, images made in infrared light let researchers discriminate between healthy crops and diseased ones. Six additional Landsats were launched between 1975 and 1999.

The success of the Landsat satellites encouraged other nations to place Earth-monitoring satellites in orbit. France launched a series of satellites called SPOT beginning in 1986, and Japan launched the MOS-IA (Marine Observation System) in 1987. The Indian Remote Sensing satellite, IRS-IA, began operating in 1988. An international team of scientists and engineers launched the Terra satellite in December 1999. The satellite carries five instruments for observing Earth and monitoring the health of the planet. NASA, a member organization of the team, released the first images taken by the satellite in April 2000.

C2

Astronomical Satellites

Astronomical objects such as stars emit radiation, or radiating energy, in the form of visible light and many other types of electromagnetic radiation. Different wavelengths of radiation provide astronomers with different kinds of information about the universe. Infrared radiation, with longer wavelengths than visible light, can reveal the presence of interstellar dust clouds or other objects that are not hot enough to emit visible light. X rays, a high-energy form of radiation with shorter wavelengths than visible light, can indicate extremely high temperatures caused by violent collisions or other events. Earth orbit, above the atmosphere, has proved to be an excellent vantage point for astronomers. This is because Earth’s atmosphere absorbs high-energy radiation, such as ultraviolet rays, X rays, and gamma rays. While such absorption shields the surface of Earth and allows life to exist on the planet, it also hides many celestial objects from ground-based telescopes. In the early 1960s, rockets equipped with scientific instruments (called sounding rockets) provided brief observations of space beyond our atmosphere, but orbiting satellites have offered far more extensive coverage.

Britain launched the first astronomical satellite, Ariel 1, in 1962 to study cosmic rays and ultraviolet and X-ray radiation from the Sun. In 1968 NASA launched the first Orbiting Astronomical Observatory, OAO 1, equipped with an ultraviolet telescope. Uhuru, a U.S. satellite designed for X-ray observations, was launched in 1970. Copernicus, officially designated OAO 3, was launched in 1972 to detect cosmic X-ray and ultraviolet radiation. In 1978 NASA’s Einstein Observatory, officially designated High-Energy Astrophysical Observatory 2 (HEAO 2), reached orbit, becoming the first X-ray telescope that could provide images comparable in detail to those provided by visible-light telescopes. The Infrared Astronomical Satellite (IRAS), launched in 1983, was a cooperative effort by the United States, The Netherlands, and Britain. IRAS provided the first map of the universe in infrared wavelengths and was one of the most successful astronomical satellites. The Cosmic Ray Background Explorer (COBE) was launched in 1989 by NASA and discovered further evidence for the big bang, the theoretical explosion at the beginning of the universe.

The Hubble Space Telescope was launched in orbit from the U.S. space shuttle in 1990, equipped with a 100-in (250-cm) telescope and a variety of high-resolution sensors produced by the United States and European countries. Flaws in Hubble’s mirror were corrected by shuttle astronauts in 1993, enabling Hubble to provide astronomers with spectacularly detailed images of the heavens. NASA launched the Chandra X-Ray Observatory in 1999. Chandra is named after American astrophysicist Subrahmanyan Chandrasekhar and has eight times the resolution of any previous X-ray telescope.

D

Other Satellites

In addition to observing Earth and the heavens from space, satellites have had a variety of other uses. A satellite called Corona was the first U.S. spy satellite effort. The program began in 1958. The first Corona satellite reached orbit in 1960 and provided photographs of Soviet missile bases. In the decades that followed, spy satellites, such as the U.S. Keyhole series, became more sophisticated. Details of these systems remain classified, but it is has been reported that they have attained enough resolution to detect an object the size of a car license plate from an altitude of 160 km (100 mi) or more.

Other U.S. military satellites have included the Defense Support Program (DSP) for the detection of ballistic missile launches and nuclear weapons tests. The Defense Meteorological Support Program (DMSP) satellites have provided weather data. And the Defense Satellite Communications System (DSCS) has provided secure transmission of voice and data. White Cloud is the name of a U.S. Navy surveillance satellite designed to intercept enemy communications.

Satellites are becoming increasingly valuable for navigation. The Global Positioning System (GPS) was originally developed for military use. A constellation of GPS satellites, called Navstar, has been launched since 1978; each Navstar satellite orbits Earth every 12 hours and continuously emits navigation signals. Military pilots and navigators use GPS signals to calculate their precise location, altitude, and velocity, as well as the current time. The GPS signals are remarkably accurate: Time can be figured to within a millionth of a second, velocity within a fraction of a kilometer per hour, and location to within a few meters. In addition to their military uses, slightly lower resolution versions of GPS receivers have been developed for civilian use in aircraft, ships, and land vehicles. Hikers, campers, and explorers carry handheld GPS receivers, and some private passenger automobiles now come equipped with a GPS system.

E

Planetary Studies

Even as the United States and the USSR raced to explore the Moon, both countries were also readying missions to travel farther afield. Earth’s closest neighbors, Venus and Mars, became the first planets to be visited by spacecraft in the mid-1960s. By the close of the 20th century, spacecraft had visited every planet in the solar system, except for the outermost planet—tiny, frigid Pluto.

E1

Mercury

Only one spacecraft has visited the solar system’s innermost planet, Mercury. The U.S. probe Mariner 10 flew past Mercury on March 29, 1974, and sent back close-up pictures of a heavily cratered world resembling Earth’s Moon. Mariner 10’s flyby also helped scientists refine measurements of the planet’s size and density. It revealed that Mercury has a weak magnetic field but lacks an atmosphere. After the first flyby, Mariner 10’s orbit brought it past Mercury for two more encounters, in September 1974 and March 1975, which added to the craft’s harvest of data. In its three flybys, Mariner 10 photographed 57 percent of the planet’s surface.

E2

Venus

The U.S. Mariner 2 probe became the first successful interplanetary spacecraft when it flew past Venus on December 14, 1962. Mariner 2 carried no cameras, but it did send back valuable data regarding conditions beneath Venus’s thick, cloudy atmosphere. From measurements by Mariner 2’s sensors, scientists estimated the surface temperature to be 400°C (800°F—hot enough to melt lead), dispelling any notions that Venus might be very similar to Earth.

In 1973 NASA launched Mariner 10 toward a double encounter with Venus and Mercury. As it flew past Venus on February 5, 1974, Mariner 10’s cameras took the first close-up images of Venus’s clouds, including views in ultraviolet light that recorded distinct patterns in the circulation of Venus’s atmosphere.

The USSR explored Venus with their Venera series of probes. Venera 7 made the first successful planetary landing on December 15, 1970, and radioed 23 minutes of data from the Venusian surface, indicating a temperature of nearly 480°C (900°F) and an atmospheric pressure 90 times that on Earth. More Venera successes followed, and on October 22, 1975, Venera 9 landed and sent back black and white images of a rock-strewn plain—the first pictures of a planetary surface beyond Earth. Venera 10 sent back its own surface pictures three days later.

Beginning in 1978, a series of spacecraft examined Venus from orbit around the planet. These probes were equipped with radar that pierced the dense, cloudy atmosphere that hides Venus’s surface, giving scientists a comprehensive, detailed look at the terrain beneath. The first of this series, the U.S. Pioneer Venus Orbiter (see Pioneer (spacecraft)), arrived in December 1978 and operated for almost 14 years. The spacecraft’s radar data were compiled into images that showed 93 percent of the planet’s large-scale topographic features.

The Soviet Venera 15 and 16 orbiters reached Venus in October 1983, each equipped with radar systems that produced high-resolution images. In eight months of mapping operations, two spacecraft mapped much of Venus’s northern hemisphere, sending back images of mountains, plains, craters, and what appeared to be volcanoes.

After being released from the space shuttle Atlantis, NASA’s radar-equipped Magellan orbiter traveled through space and reached Venus in August 1990. During the next four years Magellan mapped Venus at very high resolution, providing detailed images of volcanoes and lava flows, craters, fractures, mountains, and other features. Magellan showed scientists that the surface of Venus is extremely well preserved and relatively young. It also revealed a history of planetwide volcanic activity that may be continuing today.

E3

Mars

On July 14, 1965, the U.S. Mariner 4 flew past Mars and took pictures of a small portion of its surface, giving scientists their first close-up look at the red planet. To the disappointment of some who expected a more Earthlike world, Mariner’s pictures showed cratered terrain resembling the Moon’s surface. In August 1969 Mariner 6 and 7 sent back more detailed views of craters and the planet’s icy polar caps. On the whole, these pictures seemed to confirm the impression of a moonlike Mars.

NASA’s Mariner 9 went into orbit around Mars in November 1971, providing scientists with the first close-up views of the entire planet. Mariner 9’s pictures revealed giant volcanoes up to five times as high as Mount Everest, a system of canyons that would stretch the length of the continental United States, and—most intriguing of all—winding channels that resemble dry river valleys of Earth. Scientists realized that Mars’s evolution had been more complex and fascinating than they had suspected and that the planet was moonlike in some ways, but surprisingly Earthlike in others.

The USSR’s Mars probes were stymied by technical malfunctions. In November 1971 the Mars 2 spacecraft (see Mars (space program)) went into orbit around the planet and released a landing capsule that crashed without returning any data. Mars 2 became the first artificial object to reach the Martian surface. In December 1971 a lander released by the Mars 3 orbiter reached the surface successfully. However, it sent back only 20 seconds of video signals that included no data. In 1973 two more landing missions also failed. In 1988 the USSR made two unsuccessful attempts to explore the Martian moon Phobos. Contact with the spacecraft Phobos 1 (see Phobos (space program)) was lost due to an error by mission controllers when the spacecraft was on its way to Mars. Phobos 2 reached Martian orbit in January 1989 and sent back images of the planet, but failed before its planned rendezvous with Phobos.

The U.S. Viking probes made the first successful Mars landings in 1976. Two Viking spacecraft, each consisting of an orbiter and lander, left Earth in August and September 1975. Viking 1 went into orbit around Mars in June 1976, and after a lengthy search for a relatively smooth landing site, the Viking 1 lander touched down safely on Mars’s Chryse Planitia (Plain of Gold) on July 20, 1976. The Viking 2 lander reached Mars’s Utopia Planitia (Utopia Plain) on September 3, 1976. Each lander sent back close-up pictures of a dusty surface littered with rocks, under a surprisingly bright sky (due to sunlight reflecting off of airborne dust). The landers also recorded changes in atmospheric conditions at the surface. They searched, without success, for conclusive evidence of microbial life. The landers continued to send back data for several years, while the orbiters took thousands of high-resolution photographs of the planet.

On July 4, 1996, 20 years after Viking 1 arrived, NASA’s Mars Pathfinder spacecraft landed in Mars's Ares Vallis (Mars Valley). Pathfinder used a new landing system featuring pressurized airbags to cushion its impact. The next day, Pathfinder released a 10-kg (22-lb) rover called Sojourner, which became the first wheeled vehicle to operate on another planetary surface. While Pathfinder sent back images, atmospheric measurements, and other data, Sojourner examined rocks and soil with a camera and an Alpha Proton X-ray Spectrometer, which provided data on chemical compositions by measuring how radiation bounced back from rocks and dust. The mission ended when the spacecraft ceased responding to commands from Earth in October 1997.

NASA’s Mars Global Surveyor went into orbit around Mars in September 1997. Designed as a replacement for NASA’s Mars Observer probe, which failed before reaching Mars in 1993, Mars Global Surveyor is equipped with a high-resolution camera and instruments to study the planet’s atmosphere, topography and gravity, surface composition, and magnetic field. Global Surveyor reached orbit around Mars in the fall of 1997, but a problem with an unstable solar panel delayed the start of its mission—mapping the entire planet—for about a year. (In the meantime, Mars Global Surveyor began relaying high-resolution images of select areas in early 1998.) Its mapping operation, slated to last for one Martian year (about two Earth years), began in March 1999. Unlike previous Mars probes, Mars Global Surveyor adjusted its orbit using a technique called aerobraking, which relies on friction with the planet’s upper atmosphere—rather than rocket engines—to slow the spacecraft to bring it into a proper mapping orbit.

Mars Pathfinder and Mars Global Surveyor were part of a series of spacecraft that NASA plans to send to Mars about every 18 months. The next two spacecraft in the series, Mars Climate Orbiter and Mars Polar Lander, began their journeys to Mars in December 1998 and January 1999, respectively. Both probes reached Mars in late 1999, but Mars Climate Orbiter crashed into the planet due to a navigational error, and software defects led to the crash landing of Mars Polar Lander. Japan launched the spacecraft Nozomi (Japanese for “hope”), destined for Mars, on July 4, 1998. Nozomi contains equipment developed by scientists from around the world, including Canadian space scientists. This is the first time Canada has participated in a mission to another planet. Nozomi is scheduled to reach Mars in 2003.

E4

The Outer Planets