Abstract
The higher harmonic terms of Earth’s gravitational potential slowly modify the nominal longitude of geostationary Earth orbit (GEO) satellites, while the third-body presence (Moon and Sun) mainly affects their latitude. For this reason, GEO satellites periodically need to perform station-keeping maneuvers, namely, east–west and north–south maneuvers to compensate for longitudinal and latitudinal variations, respectively. During the operational lifetime of GEO satellites, the thrusters’ response when commanded to perform these maneuvers slowly departs from the original nominal impulsive behavior. This paper addresses the practical problem of how to perform reliable east–west station-keeping maneuvers when thruster response is degraded. The need for contingency intervention from ground-based satellite operators is reduced by breaking apart the scheduled automatic station-keeping maneuvers into smaller maneuvers. Orbital alignment and attitude are tracked on-board during and in between sub-maneuvers, and any off nominal variations are corrected for with subsequent maneuvers. These corrections are particularly important near the end of the lifetime of GEO satellites, where thruster response is farthest from nominal performance.
Highlights
Over time, a geostationary Earth orbit (GEO) satellite will drift both in longitude and latitude because of the presence of various perturbations
This paper provides an answer to the following question: “How can a GEO satellite still performing E–W maneuvers using unreliable and degraded thrusters?”
We present an approach for longitudinal station keeping of a GEO satellite with degraded thrusters and with momentum wheels or gyros for attitude control
Summary
A geostationary Earth orbit (GEO) satellite will drift both in longitude and latitude because of the presence of various perturbations. Station-keeping maneuvers will provide unreliable or unexpected results if the thruster performance changes from its expected nominal behavior. This leads to an imperfect correction and potentially to extreme longitudinal drift of the satellite, causing loss in communications quality. Thruster mounting deviations, installation bias, shock shift, thermal deformation, etc., may all lead to non-nominal and/or asymmetric thrusts In these cases, the east–west (E–W) maneuver strategy to adjust the mean longitude must be re-formulated, and a new model is needed to still provide efficient control. “How can a GEO satellite still performing E–W maneuvers using unreliable and degraded thrusters?” To solve this problem, the following issues must be resolved: 1. E–W station keeping under degraded thrusters, is presented at the end of this paper
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