MODELING SPACECRAFT EARTH RADIATION PRESSURE DATA TO IMPROVE SPACECRAFT TRAJECTORY ESTIMATION AND DESIGN

This paper examines a method to model both short and longwave radiation from the Earth and determine the net force vector applied to the spacecraft at any point in time. The Clouds and the Earth’s Radiant Energy System (CERES) project has created a data set gathered by 6 operational Earth orbiting satellites and other instruments globally. Hourly SW and LW data are incorporated into the simulation to more accurately determine the likely perturbations at various days through-out the year. This force can be integrated continuously to examine the effect of ERP on trajectory dispersions. Models for the Earth perturbations of interest, and spacecraft trajectory propagation under the main disturbances are simulated using JPL’s MONTE tool. Results for the expected ERP acceleration are presented for a 1000 km Earth orbit with various spacecraft shapes using some common orientations throughout the year. ERP is commonly mod-eled with as few as 6 coefficients that represent the reflected SW and emitted LW energy that is averaged over the entire year and tends to be longitude independent. By incorporating data sets that vary dynamically in both the spatial and time domains, a more accurate near real-time solu-tion for ERP can be estimated. This is expected to result in more accurate orbital propagation re-sults that would reduce the dispersions and covariance. MONTE is able to incorporate spacecraft shape models that more accurately model the accelera-tions in a particular direction. For this paper spherical, cylindrical, plate, and cubic shapes are ex-amined. The latter three shapes are attitude dependent so a few common orientations are examined to show the variance of acceleration with shape and orientation. Orientations examined include shape axis pointing for nadir, zenith, sun pointing, surface tracking and inertial hold. By varying spacecraft shape and orientation, their effect will show additional dispersions in acceleration and the resulting propagation over time.