GPS Attitude Determination.

This report summarizes the progress for the first quarter of FY'96-97 by the Colorado Center for Astrodynamics Research (CCAR) on the application of GPS based attitude determination techniques to near-Earth spacecraft. Two areas are addressed - application of an open architecture receiver for spaceborne attitude determination and coarse spacecraft attitude determination based on GPS signal to noise ratios. We have started work with the GEC Plessey GPSBuilder 2 receiver and identified modifications required to use the receiver for attitude determination functions. In particular we made arrangements for the addition of a second RF section to be added to the receiver and determined that the receiver tracking loop must be modified from a frequency lock loop to a phase lock loop (PLL) design. In the area of coarse attitude determination based on SNR, we have made improvements to a fuzzy estimation algorithm which provide attitude estimates at the 7 deg RMS level for flight data sets from CRISTA SPAS and GANE. We have also begun work on a maximum likelihood estimation technique using these same observables. Two research papers funded under this grant were presented at the ION GPS-96 meeting in Kansas City.