Ground-based autonomous passive-optical staring sensor for orbital object detection and position measurement

Kurzfassung

Active spacecraft operations heavily rely on a space surveillance network, which continuously scans, measures, and predicts space debris particle trajectories to avoid collision risks. Recent activities in large satellite constellations in Low Earth Orbit (LEO) will accumulate more than ten thousand satellites, doubling the number of active spacecraft. Due to the high density of debris, LEO is of highest interest for space surveillance. Beside RADAR sensors, space debris laser ranging can accurately measure the distance to resident space objects allowing highly precise orbit predictions. Due to their small field-of-view (FOV), laser ranging stations rely on an a-priori orbit information, which is usually obtained by a separate sensor network. A passive-optical sensor with a larger FOV represents a complementary tool to deliver the necessary initial orbit determination. Such a sensor is much more cost effective and easier to operate than RADAR sensors and therefore of high interest for a space situational awareness (SSA) network. The development of a passive-optical sensor is described in this thesis, which operates autonomously to detect unknown orbital objects in LEO. This thesis is structured in three parts. Initially a theoretical model is presented to estimate performance of a passive-optical sensor. It shows the influences of system properties and observing conditions on the detection threshold. Furthermore, deterministic simulations using ESA’s PROOF software are performed, which provide a more detailed analysis of the detection rates and detection efficiencies during different observation conditions and system parameters. In the main part, the system setup is explained including the software development, which plays a major role for the automation of the system. An image processing technique is implemented, which is able to reliably identify objects in LEO even when disturbances are present in the source images, such as high, transparent, or smaller clouds. Astrometric calibration is used to transform the coordinates of measured objects into equatorial coordinates and a standardized data export allows for sharing the data with existing tools or databases. A weatherproofed housing protects the camera and lens. A weather station is used to trigger image acquisition. The passive-optical sensor is deployed for continuous observations and the data is automatically uploaded to a webserver. Data analysis shows the performance figures of the system. Observation campaigns under three different line-of-sight (LOS) directions are performed and the detection rate, efficiency, threshold, and uncertainties are analyzed and compared to simulations. A line-of-sight to the North under 45° elevation is found to deliver the highest detection rates, while the observed Along-Track error is about ten times larger than the Cross-Track error. Finally, the determined parameters of the passive-optical system are used to derive requirements to detect space debris as small as 10 cm in diameter.