RADIATIVE FORCE MODEL PERFORMANCE FOR TOPEX POSEIDON PRECISION ORBIT DETERMINATION/

The TOPEX/Poseidon spacecraft was launched on August 10, 1992 to study the Earth's oceans. To achieve maximum benefit from the altimetric da ta collected, mission requirements dictate that TOPEX/Poseidon's orbit must be computed at an unprecedented level of accuracy. In order to s atisfy these requirements, a nonconservative force model which account s for the satellites's complex geometry, attitude, and surface propert ies has been developed. This ''box-wing'' representation treats the sp acecraft 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 independently, yielding vector accelerations which are summed to compute the aggregate effect on the satellite center-of-mass. Note that for the drag force, only the comp onent parallel to the velocity vector is considered in this process. P arameters associated with each flat plate were derived from a finite e lement analysis of the spacecraft. Certain parameters can be inferred from tracking data and have been adjusted to obtain a better represent ation of the satellite acceleration history. Changes in the nominal mi ssion profile and the presence of an ''anomalistic'' force have compli cated this tuning process. Model performance, parameter sensitivities, and the ''anomalistic'' force will be discussed.