GPS on the International Space Station Alpha

Penny Saunders, Gregory Barton

Abstract:	The International Space Station Alpha has committed to the incorporation of GPS for navigation, tracking, atti- tude, and timing. With this commitment comes many challenges. The navigation data from GPS is the primary input to the onboard guidance, navigation, and control system. Selective availability will significantly degrade the achievable velocity accuracy that is key for rendezvous and collision avoidance operations. Relative GPS is planned for tracking of the Space Station during mndez- vous operations with the European Space Agency’s Automated Transfer Vehicle. A large degree of up front coordination is required to ensure common satellite track- ing, common processing techniques, and availability of GPS data. Attitude determination performance is affected by many factors such as multipath, thermal variations, and structural deformations. The Space Station’s envi- ronmental and operational constraints are numerous. The temperature of the antennas is expected to vary from -70 to +120 degrees Fahrenheit with temperature oscillations of 30’F every 90 minutes. The cable run between the antennas and the receiver is expected to be as much as 75 feet. The structure is expected to flex when each new segment is attached to the Space Station. The solar panels are expected to provide a multipath rich, constantly changing environment. All of these challenges have led NASA to pursue a GPS attitude determination experiment currently manifested for flight on STS-77. The flight experiment is designed to provide an absolute measure of attitude performance and a test bed for validation of multi- path, visibility, thermal, and structural models. An iner- tial sensor assembly will provide the attitude reference and is co-located with the GPS antenna array ‘in the payload bay of the Orbiter. This paper describes the Space Station GPS requirements, implementation approach, design chal- lenges and development activities.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	631 - 639
Cite this article:	Saunders, Penny, Barton, Gregory, "GPS on the International Space Station Alpha," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 631-639.
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