Preliminary star catalog development for the Earth Observation System AM1 (EOS-AM1) mission

Abstract

Star catalogs are essential for determining the expected performance of stellar-inertial attitude determination systems, such as that planned for the Earth Observation System AM1 (EOS-AM1) mission. That spacecraft will use the CT-601 star trackers to maintain long-term attitude knowledge and gyros to measure short-term motion. To determine the sky seen by the CT-601 star trackers, extensive star catalog generation capability has been developed for EOS-AM1 attitude determination studies. The present study begins with the Goddard Space Flight Center SKYMAP catalog as the source and continues with tracker star separation and spectral response properties. It rejects stars that are not usable because of excessive variability in intensity or excessive position error or for which accurate spectra are not available. This study also assesses properties of the resulting star field, including statistics of position errors, brightness (detector magnitude), variability, and spectral class. The resulting catalog is combined with models of the lunar and solar motion and EOS-AM1 star tracker and orbital geometries to determine gaps in the star field induced by lunar blockage of the star trackers. The history of total star gaps over one year of EOS-AM1 operations is assessed, with periods of both minimum and maximum gaps defined, as well as gap statistics. The geometry of the worst-case gap is illustrated. Additionally, the potential for planetary corruption of star measurements is assessed.