Safe trajectory design and pose estimation for target monitoring in GEO

Abstract

This paper lies in the framework of mission scenarios, such as Active Debris Removal and On-Orbit Servicing, which require an active spacecraft (chaser) to orbit in close-proximity with respect to a space target. Specifically, these activities involve relative orbital maneuvers, such as monitoring, rendezvous and docking, in which the target-chaser distance ranges from a few tens of meters (depending on the target size) up to contact (in the case of docking). A critical challenge related to the realization of these maneuvers is the need to minimize the risk of collision, considering that the target is a non-cooperative object which may be characterized by uncontrolled rotational dynamics. This goal can be achieved by designing relative trajectories which satisfy specific constraints in terms of safety and stability, on one side, as well as by exploiting relative navigation technologies and algorithms which provide highly accurate estimates of the target-chaser relative motion parameters thus allowing to relax the control requirements. Both these aspects are addressed by this paper with focus on Geostationary Earth Orbits since they represent a particularly crowded orbital region in which the possibility to remove large debris and to extend the operative life of spacecraft, such as telecommunication ones, may have a significant scientific and economic benefit. Hence, an original method is presented to design safety ellipses for target monitoring around GEO targets, which, simultaneously, can provide optimal relative observation geometry for relative navigation (pose determination) using Electro-Optical sensors. The design approach is formulated in mean orbit parameters and it is based on a relative motion model relevant to two-satellite formations which includes the non-Keplerian perturbations due to secular Earth oblateness, as well as the possibility of considering targets moving along a small-eccentricity orbit. An example of trajectory design is shown considering a GEO target as test case. Given this trajectory, pose determination performance is also evaluated within a numerical simulation environment capable of realistically reproducing target-chaser relative dynamics, the operation of a scanning LIDAR selected on board the chaser as relative navigation sensor, and pose estimation algorithms based on the processing of 3D point clouds.