Orbit Precision Analysis of Small Man-Made Space Objects in LEO Based on Radar Tracking Measurements

Abstract

The German Space Operations Center (GSOC) performs collision avoidance for 11 LEO and 2 GEO satellites. Risk detection and maneuver decisions strongly depend on the computed probability of collision that is driven by the anticipated orbit precision of chaser and target. While the orbits of operational satellite are well known this is usually not the case for space debris. Therefore, an improved collision assessment requires refined orbit determination of the chaser object. This paper describes the achievable orbit precision for a small object based on radar measurements. The Tracking and Imaging Radar (TIRA) of Fraunhofer FHR in Wachtberg, Germany, was used to track the Canadian nanosatellite CanX-2 over a period of five days. CanX-2 is a triple CubeSat of the size 10x10x34 cm carrying a dual frequency GPS receiver. A reference trajectory is established by precise orbit determination (POD) from GPS measurements. Radar tracking measurements and derived orbital information are evaluated by comparison against the reference orbit. Statistics of the orbit determination and orbit prediction precision using different radar measurement data arc lengths is presented leading to a better understanding of the prediction uncertainty of critical close approaches between an active satellite and a small object.