Advances in GPS Attitude Determining Technology as Developed for the Strategic Defense Command

Richard D. Jurgens and Charles E. Rodgers

Abstract:	Under a contract from the Strategic Defense Command (SDC), Adroit Systems, Inc. has developed and tested an Attitude Determining System (ADS) based on GPS satellite signal interferometry. The relative phase difference of the GPS carrier is measured between a pair of antennas spaced about 1 meter apart to determine the antenna baseline pointing vector. The system requires only three satellites to operate once the position of the antenna is ascertained. Double differencing is used to eliminate RF bias and drift between antennas. The original SDC ADS used only two antennas and a single baseline. To solve the integer cycle ambiguity problem more efficiently, Adroit has implemented a method to use three antennas to form two baselines. This modified system uses a GPS receiver that has only two antenna ports. Having only two antenna ports avoids the expense of adding a third RF module to the receiver. The three antennas form a short and a long baseline. The short baseline is used to obtain a rough baseline pointing vector. This rough vector is then refined using the long baseline measurements to obtain an accurate baseline vector. The second generation of this ADS was designed and delivered in 1990 to teh US Army's Engineer Topographic Laboratories (ETL) for evaluation along side two other systems submitted by other contractors. Test results are presented for all systems. The Adroit Ads can calculate and update pointing information each second. Accuracy was demonstrated to approximately 10 milliradians in one second, and below 1 milliradian with a 300 second sample time.
Published in:	Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991) September 11 - 13, 1991 Albuquerque, NM
Pages:	991 - 1000
Cite this article:	Jurgens, Richard D., Rodgers, Charles E., "Advances in GPS Attitude Determining Technology as Developed for the Strategic Defense Command," Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991), Albuquerque, NM, September 1991, pp. 991-1000.
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