Multi-User System for Earth Sensing Spacecraft Attitude Calibration and Analysis

The Teledyne Multiple User System for Earth Sensing (“MUSES”) was developed for commercial Earth imaging and instrument technology development on the International Space Station (ISS). MUSES simultaneously hosts up to four Earth ensing instruments and provides inertial pointing and tracking to orient instruments toward planned targets on the ground. Up to four instruments are robotically installed on MUSES and periodically interchanged as warranted. MUSES was delivered to the ISS in June 2017, with initial testing successfully completed and subsequently documented in an initial requirements verification report. Assessing the performance of the MUSES attitude estimation system is challenging due to the lack of an independent attitude estimate of the platform attitude. A novel approach is introduced herein where the ISS attitude estimate, derived from ISS Global Positioning System sensors, is employed as an independent measure of MUSES platform attitude. Spectral decomposition methods are used to account for the contributions of ISS deformations to the variance in disparities between the ISS and MUSES attitudes and thus enable a less conservative estimate of the variance in MUSES attitude error. Implementing the spectral decomposition results in a best estimate upper bound on MUSES attitude errors of 34.5 and 27.7 arcsec, respectively, in the along-track and cross-track axes. Both the simulated and real results obtained from the spacecraft are presented.