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NASA-MCAT TELESCOPE: Glossary Terms

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AUTOCOLLIMATION is the process of collimating an instrument (as a telescope) having objective and cross hairs by directing it toward a plane mirror and adjusting the lens and cross hairs so that the latter coincide with their own reflected image. Autocollimation is an optical setup where a collimated beam (of parallel light rays) leaves an optical system and is reflected back into the same system by a plane mirror.

It is used for measuring small tilting angles of the mirror, see autocollimator, or for testing the quality of the optical system or of a part of it. Large-apertur optics, however, are tested with a null corrector avoiding the production of a large plane mirror.

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CCD is a charge-coupled device for the movement of an electrical charge, usually from within the device to an area where the charge can be manipulated; for example, conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time. CCDs move charge between capacitive bins in the device, with the shift allowing for the transfer of charge between bins.

Often the device is integrated with an image sensor, such as a photoelectric device to produce the charge that is being read, thus making the CCD a major technology for digital imaging. Although CCDs are not the only technology to allow for light detection, CCDs are widely used in professional, medical, and scientific applications where high-quality image data is required.

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GEO is a geosynchronous orbit. It is an orbit around a planet or moon with an orbital period that matches the planet or moon's sidereal rotation period. The term most frequently refers to objects that orbit the Earth. The synchronization of rotation and orbital period means that for an observer at a fixed location on the surface, a satellite in geosynchronous orbit returns to exactly the same place in the sky at exactly the same time each day. In principle, any orbit with a period equal to the Earth's rotational period is technically geosynchronous; however, the term is often used to refer to the special case of a geosynchronous orbit that is circular (or nearly circular) and at zero (or nearly zero) inclination, that is, directly above the equator. This is customarily called a geostationary orbit.

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LEO, a low Earth orbit is generally defined as an orbit within the locus extending from the Earth's surface up to an altitude of 2,000 km. Given the rapid orbital decay of objects below approximately 200 km, the commonly accepted definition for LEO is between 160 - 2,000 km (100 - 1,240 miles) above the Earth's surface. The LEO environment is becoming congested with space debris which has caused a growing concern in recent years, since collisions at orbital velocities can be highly damaging or dangerous and can produce even more space debris in the process. The Joint Space Operations Center, part of United States Strategic Command, currently tracks more than 8,500 objects larger than 10 cm in LEO, however a limited Arecibo Observatory study suggested there could be about one million objects larger than 2 millimeters, which are too small to be seen from the ground.

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SSA is space situational awareness. The imaging and characterization of space objects is a cornerstone of space surveillance and a core technical capability required to support the US national interests in space. With the development of rapid launch capabilities and nano-satellites, space situational awareness (SSA) is increasingly critical to provide the vigilance capabilities that will identify, characterize, deter and defend against hostile acts directed at U.S. space assets. In the future, successful combat operations involving aerospace assets will depend on Air Force leaders quickly processing relevant information and then acting decisively. Critical to this process is full-dimensional SSA.

Improved imaging and characterization techniques will revolutionize SSA, allowing more complete exploitation of information for use by senior decision makers. This information will include precise satellite attitude (allowing accurate determination of where a particular satellite may be pointing as it collects information), satellite status (is the satellite functioning as designed), and details on satellite subsystems (including material composition, structure, vibration, operating conditions and system vulnerabilities).

The objective of this research initiative is to further explore and develop many of the basic sciences that form the basis for SSA and related technologies that will ultimately support Air Force mission areas. The focus of this initiative is basic research associated with the characterization of space objects from ground- and space-based sensors.

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