MODELING RADIATION FORCES ACTING ON TOPEX POSEIDON FOR PRECISION ORBIT DETERMINATION

Geodetic satellites, such as GEOSAT, SPOT, ERS-1, and TOPEX/Poseidon require accurate orbital computations to support the scientific data they collect. The TOPEX/Poseidon mission requirements dictate that the mismodeling of the nonconservative forces of solar radiation, Earth albedo and infrared reradiation, and spacecraft thermal imbalances produce in combination no more than a 6-cm radial rms orbit error over a 10-day period. Therefore, a box-wing satellite form has been investigated to model the satellite as the combination of flat plates arranged in the shape of a box and a connected solar array. The nonconservative forces acting on each of the eight surfaces are computed and adjusted independently, yielding vector accelerations which are summed to compute the total aggregate effect on the satellite center of mass. Acceleration profiles from finite element analysis are compared to those from the boxwing model, and these tests indicate that modeling solar radiation pressure acceleration is relatively straightforward. However, the thermal imbalance modeling is made much more complicated given the satellite's complex attitude control law and its relation to the predicted temperature history for each surface.