Multi-user system for earth sensing attitude estimation analysis using spectral decomposition

The Teledyne Multiple User System for Earth Sensing (“MUSES”) was developed for commercial earth imaging and instrument technology development on the International Space Station. MUSES simultaneously hosts up to four Earth sensing 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 International Space Station 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 lack of an independent attitude estimate of the platform attitude. A novel approach is introduced herein where the ISS attitude estimate, derived from ISS GPS 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 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 arc seconds, respectively in along-track and cross-track axes.