Closed Loop Navigation and Guidance for Gravity Probe B Orbit Insertion

P. Axelrad, B. W. Parkinson

Abstract:	The objective of the Gravity Probe n (GP-B) satellite is to test two aspects of Einstein's theory of general relativity which predict that a locally inertial Newtonian coordinate frame in orbit around the Earth will rotate. In a circular, 650 km polar orbit, the two effects, known as the geodetic and frame dragging preces­sions, are predicted to be 6.6 arc sec/yr and 42 milliarc sec/yr respectively. These minute rotations will be measured using orbiting gyroscopes whose Newtonian drift rates are less than w-11 deg/yr (0.5 milliarc/sec/yr). This paper addresses the problem of guiding the GP-B spacecraft from its location after initial orbit insertion to this very precise orbit. Specifically, the satellite orbit is required to be circular to within 0.001 eccentricity, polar to within 0.001 degrees inclina­tion, and aligned with the direction or Rigel to within 0.001 degrees. Navigation data supplied by an onboard GPS receiver is used as feedback to a control algorithm designed to minimize the time to achieve the desired orbit. Translational control is provided by the proportional helium thrusters which are used for drag-free and attitude control during the remainder or the science mission. Simulations or the guidance system are presented which give an indication or performance characteristics for a several types of orbit injection errors. This research is the first reported effort to use GPS as a sensor for a closed loop space guidance system.
Published in:	Proceedings of the International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1988) September 19 - 23, 1988 The Broadmoor Hotel Colorado Spring, CO
Pages:	193 - 202
Cite this article:	Axelrad, P., Parkinson, B. W., "Closed Loop Navigation and Guidance for Gravity Probe B Orbit Insertion," Proceedings of the International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1988), Colorado Spring, CO, September 1988, pp. 193-202.
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