Galileo Orbit Determination from Launch through the First Earth Flyby

V. M. Pollmeier and P. H. Kailemeyn

Abstract:	On :8 October 1989, the Galileo spacecraft was launched from Earth orbit toward its ultimate goal, Jupiter. The limited energy available frcrrn the launch vehicle necessitated a circuitous trajectory. utilizing three gravity assists to increase the spacecraft’s energy. Two of these three gravity assists have occurred. The first of these was a flyby of Venus on 10 February 1990 at an altitude of about 16.000 km; the second, a flyby of Earth on 08 December 1990 at an altitude of 960 km. The third will occur on 08 December 1992. following :he first ever close flyby of a main belt asteroid on 29 October 1991. The Galileo Navigation team has used two primary data types to determine the spacecraft’s trajectory, phasecoherent S-band Doppler ar.d range data. In addition to these two dara types, a third data type was utilized for the Earth approach, during the fall of 1990. This was ADOR. Delta Differential One way Range. This data type allows the determination of the spacecraft’s angular position relative to the known astrometric position of a quasar. This data requires the differencing of simultaneously received radio signals from two widely spaced radio antennas. The use of Doppler and ranging during the Venus approach allowed the prediction of the flyby trajectory at Venus to an accuracy of 25 km. some thirty days in advance. The spacecraft’s trajectory at the Earth flyby differed from that planned by 8 km.
Published in:	Proceedings of the 47th Annual Meeting of The Institute of Navigation (1991) June 10 - 12, 1991 Williamsburg Hilton and National Conference Center Williamsburg, VA
Pages:	9 - 16
Cite this article:	Pollmeier, V. M., Kailemeyn, P. H., "Galileo Orbit Determination from Launch through the First Earth Flyby," Proceedings of the 47th Annual Meeting of The Institute of Navigation (1991), Williamsburg, VA, June 1991, pp. 9-16.
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