A NEW APPROACH TO ON-BOARD ORBIT NAVIGATION

Eugene S. Muller and Peter M. Kachmar

Peer Reviewed

Abstract:	Conventional on-board orbit navigation systems derive state vector estimates from measurements of spacecraft position or velocity relative to the surface of the attracting body, or to an orbiting navigation satellite. The accuracy of these systems is seriously limited by the uncertainties associated with the phenomena sensed. The infrared horizon is poorly defined for regions remote from the equator; the ultraviolet and visible horizon require sun illumination, and landmarks must of course be visible. Uncertainties in the knowledge of the navigation satellite being tracked will degrade navigation accuracy unless ephemeris updates from the ground are received periodically, which of course means the system is not totally self-contained. In addition, a clear line of sight to the navigation satellite is required. These constraints severely limit acceptable orbit inclinations and/or portions of the orbit in which measurements may be taken. The orbit navigation scheme described in this paper is free from any of these constraints. Fundamentally, the scheme operates as follows: a small satellite is ejected from the spacecraft into a near orbit. The satellite is tracked from the spacecraft using a radar or optical tracker (the satellite need only be a suitable target for tracking, e.g., a radar reflecting balloon, a small transmitter or a corner cube for laser reflection), and measurements for relative position, referenced to an inertial platform, are processed by an optimum rendezvous navigation filter. This optimum filter drives the relative state uncertainty to zero by updating the inertial state estimates of the spacecraft and the satellite. In the process, the spacecraft inertial state uncertainties are reduced, thus achieving the desire orbit navigation. That the inertial states of two vehicles in near orbits can be determined by determining their relative motion, follows from the fact that a given relative trajectory in inertial space may be generated by only one unique pair of inertial states. Simulation results are presented which illustrate the feasibility of this scheme. The effect of satellite-spacecraft relative trajectory, sensor accuracies, relative parameters sensed, and inertial platform misalignment on navigation accuracy is examined. Platform misalignment is a critical error source, as it is of course in many conventional orbit navigation systems, but simulations show that estimation of this error is also possible with this navigation filter.
Published in:	NAVIGATION: Journal of the Institute of Navigation, Volume 18, Number 4
Pages:	369 - 385
Cite this article:	Muller, Eugene S., Kachmar, Peter M., "A NEW APPROACH TO ON-BOARD ORBIT NAVIGATION", NAVIGATION: Journal of The Institute of Navigation, Vol. 18, No. 4, Winter 1971-1972, pp. 369-385.
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