Text 3. Nasa Sub-Scale Solid-Rocket Motor Tests Material for Space Launch System

A sub-scale solid rocket motor designed to mimic NASA's Space Launch System, or SLS, booster design successfully was tested today by engineers at NASA's Marshall Space Flight Center in Huntsville, Ala. The 20-second firing tested new insulation materials on the 24-inch-diameter, 109-inch-long motor. The motor is a scaled down, low-cost replica of the solid rocket motors that will boost SLS off the launch pad.

Marshall is leading the design and development of the SLS on behalf of the agency. The new heavy-lift launch vehicle will expand human presence beyond low-Earth orbit and enable new missions of exploration across the solar system.

The test will help engineers develop and evaluate analytical models and skills to assess future full-scale SLS solid rocket motor tests. The next full-scale test, Qualification Motor-1 (QM-1), is targeted for spring 2013. Two five-segment solid rocket motors, the world's largest at 154-foot-long and 12-foot diameter, will be used in the first two 70-metric-ton capability flights of SLS.

Previous ground tests of the motors included carbon insulation to protect the rocket's nozzle from the harsh environment and 5000-degree temperatures to which it is exposed. QM-1 will include a new insulation material, provided by a new vendor, to line the motor's nozzle.

"Test firing small motors at Marshall provides a quick, affordable and effective way to evaluate the new nozzle liner's performance," said Scott Ringel, an engineer at Marshall and the design lead for this test. "We have sophisticated analytic and computer modeling tools that tell us whether the new nozzle insulation will perform well, but nothing gives us better confidence than a hot-fire test."

The test also includes several secondary objectives. The team introduced an intentional defect in the propellant with a tool designed to create a specific flaw size. By measuring the temperature inside the motor at the flaw location, the team hopes to gain a better understanding for the propellant's margin for error. Test data also will help the team better understand acoustics and vibrations resulting from the rocket motor's plume.

In addition, NASA's Engineering and Safety Center will use test data to measure a solid rocket motor's plume and how it reacts to certain materials.

Engineers from Marshall's Engineering Directorate designed the test motor with support from ATK Aerospace Systems of Huntsville, Ala. ATK of Brigham City, Utah, the prime contractor for the SLS booster, is responsible for designing and testing the SLS five-segment solid rocket motor.

Text 4. Photography

The optics of photography involves both lenses and the medium in which the electromagnetic radiation is recorded, whether it be a plate, film, or charge-coupled device. Photographers must consider the reciprocity of the camera and the shot which is summarized by the relation Exposure - Aperture Area – Exposure Time – Scene Luminance.

In other words, the smaller the aperture (giving greater depth of focus), the less light coming in, so the length of time has to be increased (leading to possible blurriness if motion occurs). An example of the use of the law of reciprocity is the Sunny 16 rule which gives a rough estimate for the settings needed to estimate the proper exposure in daylight.^[87]

A camera's aperture is measured by a unit less number called the f-number or f-stop, f/#, often notated as  , and given by

where   is the focal length, and   is the diameter of the entrance pupil. By convention, "f/#" is treated as a single symbol, and specific values of f/# are written by replacing the number sign with the value. The two ways to increase the f-stop are to either decrease the diameter of the entrance pupil or change to a longer focal length (in the case of a zoom lens, this can be done by simply adjusting the lens). Higher f-numbers also have a larger depth of field due to the lens approaching the limit of a pinhole camera which is able to focus all images perfectly, regardless of distance, but requires very long exposure times.

The field of view that the lens will provide changes with the focal length of the lens. There are three basic classifications based on the relationship to the diagonal size of the film or sensor size of the camera to the focal length of the lens:

Normal lens: angle of view of about 50° (called normal because this angle considered roughly equivalent to human vision) and a focal length approximately equal to the diagonal of the film or sensor.

Wide-angle lens: angle of view wider than 60° and focal length shorter than a normal lens.

Long focus lens: angle of view narrow than a normal lens. This is any lens with a focal length longer than the diagonal measure of the film or sensor. The most common type of long focus lens is the telephoto lens, a design that uses a special telephoto group to be physically shorter than its focal length.

Modern zoom lenses may have some or all of these attributes.

The absolute value for the exposure time required depends on how sensitive to light the medium being used is (measured by the film speed, or, for digital media, by the quantum efficiency). Early photography used media that had very low light sensitivity, and so exposure times had to be long even for very bright shots. As technology has improved, so has the sensitivity through film cameras and digital cameras.

Other results from physical and geometrical optics apply to camera optics. For example, the maximum resolution capability of a particular camera set-up is determined by the diffraction limit associated with the pupil size and given, roughly, by the Rayleigh criterion.