PREDICTION OF RADIANT ENERGY FORCES ON 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 predicted accurately. This model requires a precise description of the spacecraft shape and orientation, an 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 (albedo and infrared) striking each surface of the spacecraft. This software has been modified to include an Earth radiation model that follows the seasonal variations in albedo and infrared radiation. The SINDA software system is then used to determine the transient temperatures of the spacecraft surfaces. Orbital thermal histories of significant features are given. These temperatures are used to determine the force exerted on each surface due to thermal emission. The emission forces are combined with the incident radiation forces to determine the total force acting on the satellite.