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3. Development of rockets. (History of rocketry)

The technology of rocket propulsion appears to have its origins in the period AD 1200–1300 in Asia, where the first “propellant” had been in use for about 1,000 years for other purposes. The early uses were primarily military. Powered by black powder charges, rockets served primarily as bombardment weapons. Performance of these early rockets was poor by modern standards because the only available propellant was black powder, which is not ideal for propulsion. Military use of rockets declined from 1815 to 1936 because of the superior performance of guns.

During the period 1880–1930 the idea of using rockets for space travel grew in public interest. Stimulated by the conceptions of such fiction writers as Jules Verne, the Russian scientist Konstantin E. Tsiolkovsky worked on theoretical problems of propulsion-system design and rocket motion and on the concept of multistage rockets. Robert H. Goddard, an American scientist and inventor also conducted a wide array of rocket experiments from 1908 to 1945. He independently developed ideas similar to those of Tsiolkovsky about spaceflight and propulsion and implemented them, building liquid- and solid-propellant rockets. His developmental work included tests of the world's first liquid-propellant rocket in 1926. A third pioneer, Hermann Oberth of Germany, developed much of the modern theory for rocket and spaceflight independent of Tsiolkovsky and Goddard. He not only provided inspiration for visionaries of spaceflight but played a pivotal role in advancing the practical application of rocket propulsion that led to the development of rockets in Germany during the 1930s.

Due to the work of these early pioneers and a host of rocket experimenters, the potential of rocket propulsion was vaguely perceived prior to World War II, but there were many technical barriers to overcome. Development was accelerated during the late 1930s and particularly during the war years. The most notable achievements in rocket propulsion of this era were the German liquid-propellant V-2 rocket and the Me-163 rocket-powered airplane. The main advances in propulsion that were involved in the wartime technology were the development of pumps, injectors, and cooling systems for liquid-propellant engines and high-energy solid propellants that could be formed into large pieces with reliable burning characteristics.

From 1945 to 1955 propulsion development was still largely determined by military applications. Liquid-propellant engines were refined for use in supersonic research aircraft, intercontinental ballistic missiles (ICBMs), and high-altitude research rockets.

Since 1965, missions have drawn on an ever-expanding technology base, using improved propellants, structural materials, and designs. Present-day missions may involve a combination of several kinds of engines and motors, each chosen according to its function.

4. Kinds of spacecraft

Spacecraft is a general term that includes sounding rockets, unmanned artificial satellites and space probes, space stations, and vehicles for carrying humans to and from space. With the exceptions of the sounding rocket and the space shuttle, spacecraft are considered separately from the rocket-powered vehicle that launches the spacecraft into orbit or boosts it away from Earth's vicinity (see launch vehicle).

A space probe is an unmanned spacecraft that is given a velocity great enough to allow it to escape Earth's gravitational attraction. Space probes may be classed as lunar, planetary, or deep-space. A deep-space probe is a probe sent beyond the Earth-Moon system; if sent to explore other planets, it is also called a planetary probe.

Other classifications of spacecraft are manned or unmanned, active or passive. A passive satellite transmits no radio signals. It may be tracked optically or with radar, and radio communications signals may be “bounced” off its surface. Active satellites send out radio signals to make tracking easier and to transmit data from their instruments to ground stations or other craft.

A space station is an artificial structure placed in orbit and equipped to support human habitation for extended periods.

Spacecraft differ greatly in size, shape, complexity, and purpose. Those that share similarities in design, function, or both are often grouped into program families—e.g., Soyuz, Venera, Salyut, and Gorizont in the U.S.S.R. (later Russia); Explorer, Apollo, Voyager, and Navstar in the United States; SPOT in France; and Meteosat developed by the European Space Agency. Lightness of weight and functional reliability are primary features of spacecraft design. Depending on their mission, spacecraft may spend minutes, days, months, or years in the environment of space. Mission functions must be performed while exposed to high vacuum, extreme variations in temperature, and strong radiation.

A general differentiation of spacecraft is by function—scientific or applications. A scientific satellite or probe carries instruments to obtain data on magnetic fields, space radiation, the Sun or other stars, planets and their moons, and other astronomical objects and phenomena. Applications spacecraft have utilitarian tasks; examples are Earth observation, military reconnaissance, telecommunications, and navigation and global positioning satellites.

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