Status, Plans and Potential Capabilities of Geostationary GPS Transponders

George W. Zachmann

Abstract:	In November 1990 INWARSAT took the decision to include transponders on its third generation communication satellites that will be capable of broadcasting GPS-like signals on GPS's Ll frequency. These transponders hold the potential to augment and enhance GPS in a number of significant ways. Some of the benefits that could accrue to GPS users with little or no increase in user equipment costs include improved integrity, accuracy, coverage and availability. In particular, the aviation community is concerned that GPS satellites have failure modes which can result in large navigation errors for up to an hour or more. One means of dealing with this is to monitor GPS on the ground and generate a GPS integrity message which is transmitted to users in near real time. Satellite transmissions have the advantage of broad coverage and by transmitting on a frequency already being processed in GPS user sets, can minimize the cost to the user community. The RTCA and others have focused such :Eostationary approach using satellites to transmit the integrity channel on GPS's Ll frequency. This paper describes the INMARSAT-III navigation payloads and a GPS Integrity Channel (GIC) Test Bed being developed for the FM which willf permit testing applications a navigation transponder prior to launching the INWARSAT-111s.
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:	159 - 165
Cite this article:	Zachmann, George W., "Status, Plans and Potential Capabilities of Geostationary GPS Transponders," Proceedings of the 5th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1992), Albuquerque, NM, September 1992, pp. 159-165.
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