Near Term GPS Application for Shuttle

Charlene Madden, Samuel Lee and Hung Tran

Abstract:	The following addresses the analysis, design and development of methods, hardware and software to incorporate GPS into the existing shuttle navigation system. Trades were performed that addressed the unique characteristics of integrating a new sensor into the mature shuttle. Some of the considerations are; (1) existing complex GN&C software in a centralized GPC (general purpose computer), (2) accommodation for a full range of flight dynamics from boost and orbital velocities to landing operations, (3) a need for triple redundancy of all systems, (4) stringent safety considerations requiring a phased implementation program and (5) ability to withstand SEW (single event upsets from radiation). Incorporation of GPS into shuttle is motivated by several factors. These include eventual TACAN ground station obsolescence, cost savings for TACAN and MSBLS maintenance, expanded landing site opportunities, enhanced autoland capability and significant on orbit improvements (elimination of C-Band tracking, reducing dispersions for rendezvous missions and requiring no ground state vector updates on orbit). Since shuttle has recently purchased new IMU’s, the near term shuttle GPS would use a stand alone receiver integrated with the existing shuttle GPC’s. It is also desirable to use an off-the-shelf, MIL SPEC receiver with a large production base (for future parts availability). Another consideration includes minimizing software changes to both the receiver and GPC’s. Extensive receiver surveys were conducted and several software/hardware options investigated. Detailed code modifications have been developed for one of the options in order to analyze impacts to the existing shuttle GPC’s. A candidate Collins 3M receiver is being modified for shuttle orbital/landing dynamics and tested at the Rockwell ADL in Downey, California. This will be the first prototype receiver to have the full range of shuttle type flight capability. The DFT effort was proposed, funded and is now in progress. The test will fly a Collins 3M receiver on the orbiter using existing antennas and will provide the receiver with position, velocity, attitude and measurement data from the backup flight system (BFS) GPC. Analysis and simulation results indicate that IMU derived position and velocity aiding to the receiver is required to maintain lock through ascent and the blackout region of entry. The DFT will be the first phase of the evolution of shuttle GPS. A detailed full scale implementation plan has been designed, both hardware and software, to minimize development impacts. Initial simulation results and analysis indicate that shuttle can he modified for GPS in a safe and cost effective manner. This effort has been accomplished under several projects, both research oriented and JSC contract funded. It has been a cooperative venture for the shuttle orbiter avionics and navigation community (JSC and con&actors).
Published in:	Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992) September 16 - 18, 1992 Albuquerque, NM
Pages:	863 - 872
Cite this article:	Madden, Charlene, Lee, Samuel, Tran, Hung, "Near Term GPS Application for Shuttle," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 863-872.
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