GPS-BASED ATTITUDE DETERMINATION IN DIFFERENT ATTITUDE MODES: EXPERIMENTING WITH A GPS RECEIVER AND A STAR SENSOR ONBOARD THE SERVIS-1 SATELLITE

摘要

GPS receivers are now widely used onboard satellites forrnnavigation. For high accurate attitude determination, starrnsensors are often included in AOCS (Attitude & OrbitrnControl sub-Systems). Combining data from these twornsensors into a single process can reduce the complexityrnof AOCS design and consequently the cost of LEOrnmissions, especially for telecommunication and earthrnobservation. The GPS receiver, with a modest additionalrnhardware and software extension, could be used forrnmedium accurate attitude determination besidesrnnavigation. NEC Toshiba Space Systems developed anrnintegrated system combining the advantages of the twornsensors, called the Integrated Navigation Unit (INU).rnThe components have been tested for almost two years inrnthe space environment onboard the SERVIS-1 satellite.rnData collected in space is used to develop and test arntightly integrated system. Navigational results will berndescribed and GPS-based attitude solutions are comparedrnwith solutions from the star sensor. Results for differentrnsatellite orientations (earth-pointing, sun-pointing andrnduring maneuvers) will be presented. Moreover, anrnalgorithm for the integration of the two sensors and thernadvantages of this approach will be discussed. Improvedrnresults of the integrated system are presented. As anrnexample using INU data, it will be shown that thernintegrated approach can reduce the effect of the South American Anomaly on the attitude solution from the Starrnsensor. The combined GPS-star based attitude estimationrnis expected to be more robust than the individual attitudernestimations.