ARC-SECOND ATTITUDE CONTROL FOR THE NESS ASTEROID/SATELLITE TRACKING MICROSAT

摘要

The mission of the Near Earth Space Surveillance (NESS) microsat is two-fold: to search for and track Earth-approach asteroids, and to conduct satellite tracking research. This will be accomplished using a small optical telescope supported by a microsatellite platform in low Earth orbit. The design for NESS is closely based on that of Dynacon's first microsat, MOST. The MOST attitude control system (ACS) is expected to achieve a 7 arc-second (RMS) pointing accuracy, much better than the 360 arc-seconds (0.12°) pointing accuracy typically achieved by past microsats. Key technologies that Dynacon developed to enable this were a microsat-compatible star tracker and reaction wheels. NESS has an even more stringent ACS requirement: in order to detect small, faint asteroids, the satellite's camera must be pointed with an accuracy of about half a camera pixel (1.5 arc-second) for the duration of exposures as long as 100 seconds. This level of ACS performance, approaching that of much larger satellites, such as the Hubble Space Telescope, will be met by adding Fiber Optic Gyros (FOGs), and by further enhancing star tracker accuracy. This paper describes the overall NESS mission and system design. Particular attention is paid to the asteroid-tracking mission requirement, and the NESS control system, in particular how the star tracker and FOGs interact to allow the ACS to meet the pointing requirement. Dynacon has subjected a candidate FOG to laboratory tests; the results of this testing are presented. The test results have been used as input into simulations to predict the overall pointing performance of the NESS attitude control system. The simulation results are presented, demonstrating the attitude control performance achievable using this design approach.