MODELING RADIATION FORCES ACTING ON TOPEX POSEIDON FOR PRECISION ORBIT DETERMINATION

Geodetic satellites, such as GEOSAT, SPOT, ERS-1, and TOPEX/Poseidon r equire accurate orbital computations to support the scientific data th ey collect. The TOPEX/Poseidon mission requirements dictate that the m ismodeling of the nonconservative forces of solar radiation, Earth alb edo and infrared reradiation, and spacecraft thermal imbalances produc e 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 fo rces acting on each of the eight surfaces are computed and adjusted in dependently, yielding vector accelerations which are summed to compute the total aggregate effect on the satellite center of mass. Accelerat ion profiles from finite element analysis are compared to those from t he boxwing model, and these tests indicate that modeling solar radiati on pressure acceleration is relatively straightforward. However, the t hermal imbalance modeling is made much more complicated given the sate llite's complex attitude control law and its relation to the predicted temperature history for each surface.