GSTAR III attitude for inclined geostationary orbit
1993; American Institute of Aeronautics and Astronautics; Volume: 16; Issue: 2 Linguagem: Inglês
10.2514/3.20999
ISSN1533-3884
Autores Tópico(s)Space Satellite Systems and Control
ResumoThe satellite GSTAR III is currently providing a multitude of communication services from its 3.9 deg inclined geosynchronous orbit. Nodal crossings are stationkept at 93°W longitude. North-south maneuvers are not implemented and the inclination is permitted to grow naturally. Daily sublatitude and longitude variations trace a figure-eight trajectory as seen from terrestrial observation points, requiring the ground antennas to track the satellite. Left uncompensated, the satellite radiative power footprint and associated radio-frequency polarization plane undergo 24-h cyclic variations. To minimize the daily radiative power variations, the spacecraft antenna boresight is kept targeted at the specified geographic location by programming the flight computer with appropriate roll and pitch bias increments. At later phases of mission life, when the signal polarization plane rotation is no longer acceptable, the momentum vector will be partially skewed in the direction of equatorial normal. At some stage, periodic thruster-assisted spacecraft yaw maneuvers will be required to reduce the polarization plane rotation. This paper describes the attitude maintenance procedures being used to support communication services from a non-nominal orbit. Nomenclature H = spacecraft momentum axis / = inclination of orbit, deg M = angle from ascending node to the satellite, deg TV = orbit normal vector n = orbital rate, 15 deg/h t = time past ascending node, h Z' = spacecraft pitch axis a. = ratio of change in roll attitude to change in satellite latitude a = pivot offset commanded through the APE b = pivot offset commanded bypassing the APE m = maximum pivot offset over a day, deg / = pivot offset limit; 2 deg for GSTAR III t = total offset in satellite momentum wheel pivot, deg e = roll error due to pivot offset as sensed by the ESA \l/ = satellite yaw angle, deg
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