Attitude and Orbit Propagation of High Area-to-Mass Ratio (HAMR) Objects Using a Semi-Coupled Approach

Abstract

In this paper, a new approach is presented to propagate the attitude and orbital motion of objects with high area-to-mass ratios in near geostationary orbits using a semi-coupled approach. In the case of HAMR objects, their orbits are highly perturbed by non-conservative forces, such as direct radiation pressure. This leads to the fact that orbit and attitude motions are highly coupled. Solar radiation pressure can lead to a rapid attitude motion, which is non-uniform and leads to a high computational burden in integrating the fully coupled system. In the characterization of objects, often light (optical or radar) curve measurements are used. They measure the intensity (actively illuminated radar or passively illuminated optical) of the radiation that is reflected to the observer. General characterization techniques, such as frequency analysis and inversion, neglect the orbit-attitude coupling. A new semi-coupled method is proposed: orbit and attitude motion are initialized as fully coupled and then decoupled and propagated independently, using the values derived in the initialization step as a priori values. Shannon entropy serves as a double metric, orbit and attitude, and the system is triggered to be re-coupled again for a single epoch, as soon as the a priori attitude and integrated attitude or a priori orbit motion and integrated attitude motion deviate significantly. In a second approach, Kullback-Leibler divergence is used as a trigger. Both the Shannon entropy and the Kullback-Leibler divergence based method are compared to the fully coupled integration solution. Integrating the two systems as semi-coupled saves computational time, and gives a measure for which time intervals the system can be viewed as approximately decoupled system, when characterizing the objects via light curve measurements.