Methods for improving the accuracy of an optical staring system for detecting and locating Earth-orbiting space objects

Kurzfassung

The number of space objects (satellites and space debris) is continuously growing. Especially, traffic in low Earth orbit (LEO) increases due to the emergence of CubeSats, the deployment of mega constellations as well as debris formation. Space traffic management is mandatory to manage the congested parts of space. Only when space objects are closely monitored, their trajectories can be precisely calculated and operators of active and maneuverable satellites can perform collision avoidance maneuvers. The detection and orbit determination of space objects in LEO is presently mostly achieved via radar measurements. However, passive optical staring systems are emerging as an additional and cost-effective method for detecting space objects. A portable, wide-angle and fully autonomous passive optical staring system known as APPARILLO is being developed at the Institute of Technical Physics of the German Aerospace Center (DLR). This thesis focuses on two complementary approaches that both aim at improving the positional accuracy of detected space objects with passive optical sensors. The first approach improves the along-track error of detected space objects by a new calibration method that uses a pixel-dependent delay between the camera's trigger signal and the actual sensor detection. This delay is measured with a laboratory test setup and is used to correct the tracking data of a test campaign. By comparing the corrected positional data to satellites with highly precise orbits, it is found that the along-track error is reduced by 75 %, reaching a value as low as 22 arcseconds. The remaining error is on a similar level as the cross-track error and is now limited by astrometric calibration inaccuracies. The second approach provides an initial analysis on how several passive optical staring systems can be used together for space traffic management. In particular, it is calculated how accurate the altitude of a satellite can be obtained via triangulation due to a simultaneous observation with two APPARILLOs placed at different locations on Earth. Optimal spacing between two systems of 1324 km are expected to yield an altitude accuracy of 157 m, while even closer distances of 180 km maintain a good accuracy of 600 m. The two approaches of this thesis showcase substantial enhancements in detection accuracy. The pixel-dependent delay correction will be implemented to all existing APPARILLO systems as well as new prototypes foreseen in future work.