Radiation force modeling for the Topex/Poseidon spacecraft

The largest nongravitational forces that will be acting on the Topex satellite will be those due to incident and emitted radiation on the spacecraft surfaces. In order to minimize the effects of these forces on orbit determination, a detailed model is being developed so that they may be accurately predicted. This model requires a precise description of the spacecraft shape and orientation, evaluation of the solar and earth radiation impinging on the surfaces, and a determination of the radiation being emitted from the surfaces as they heat and cool throughout the orbit. The TRASYS software system is used to evaluate the solar and earth radiation striking each surface of the spacecrat. This software has been modified to include an earth radiation model which follows the seasonal variations in albedo and IR radiation. The SINDA software system is then used to determine the transient temperatures of the spacecraft surfaces.