Combined Autonomous Absolute and Relative Orbit Control in Low Earth Orbit

Abstract: The recent advances in the field of autonomous absolute and relative orbit control render this technology mature to be used on a routine basis. The step forward in this research is the study of the possibility of combining autonomous absolute and relative orbit control. This paper analyses the problem of the combined autonomous absolute and relative control of a two spacecraft formation in low Earth orbit. One of the two spacecraft keeps its mean orbital elements within their control window whereas the other spacecraft controls the relative motion. The autonomous formation control is meant to meet the distributed payload requirements and to keep the formation safe from a collision risk. The collision avoidance criterion used is the maintenance of a (anti-)parallel alignment of the relative eccentricity and inclination vectors. The overall strategy is verified, by means of numerical simulations, using the TerraSAR-X/TanDEM-X formation as simulation scenario. The simulation results are evaluated and compared with the actual values acquired during the routine operations of the TSX/TDX formation. A first conclusion can thus be formulated about the advantages and disadvantages in the exploitation of an autonomous on-board orbit control with respect to a ground based system.