The anomalous acceleration and radiation force calculation for the TOPEX/POSEIDON spacecraf

This thesis describes the analysis of radiation forces which act upon the TOPEX/POSEIDON spacecraft. The purpose of this research is to explain the anomalous acceleration observed by the precision orbit determination team at NASA's Goddard Space Flight Center (GSFC). These forces include the radiation forces acting on the TOPEX/POSEIDON high gain antenna surface, which is not included in the operational orbit determination radiation force model (GSFC macromodel), and the radiation forces acting on the TOPEX/POSEIDON solar array, which experiences warping due to temperature differences between the front and back surfaces; the GSFC macromodel assumes the solar array to be a flat panel.;A preliminary analysis was performed using TOPEX/POSEIDON attitude and temperature telemetry. The alongtrack accelerations due to radiation forces acting on the high gain antenna were computed at a 30 second interval and used to produce daily average alongtrack accelerations. Comparison with the anomalous acceleration showed that the radiation forces acting on the high gain antenna did not produce accelerations which exhibit the same characteristics. A solar array warping model was also developed and the same analysis performed. In this case, the daily average alongtrack accelerations showed characteristics similar to those of the anomalous acceleration.;This analysis led to the development of a radiation force model (modified macromodel) which includes: (1) warping of the TOPEX/POSEIDON solar array; (2) a solar array deployment deflection as large as 2$spcirc$; (3) a few necessary adjustments to certain surface property parameters; and (4) an adjustment to the coefficient of drag $(Csb{d}).$ Estimates of the empirical constant alongtrack acceleration show that the modified macromodel provides an explanation for the anomalous acceleration by reducing the magnitude of the constant alongtrack acceleration estimates and significantly reducing their dependence upon $betaspprime$ (orientation of the sun relative to the TOPEX/POSEIDON orbit plane) without sacrificing orbit precision, increasing the tracking data residuals, or increasing the 1 cycle per revolution alongtrack acceleration amplitudes, thus providing a macromodel for the TOPEX/POSEIDON spacecraft which relies less upon estimation of empirical parameters to absorb unmodeled forces.