Satellite and Debris Characterisation with Adaptive Optics Imaging

Abstract

Space debris poses a significant risk to the safety of the space environment. The field of space situational awareness (SSA) has grown in response to the increasing threat of space debris to develop methods to mitigate this threat. Precise tracking and accurate orbit predictions are needed to identify potential collisions so avoidance measures can be taken. Orbital predictions are influenced by physical characteristics which are typically unknown, and therefore must be approximated. Direct observation from a ground based telescope can measure the characteristics of an object, however the image is degraded due to atmospheric turbulence. The distortion can be overcome by using adaptive optics where the wavefront is measured and a correction is applied by a deformable mirror to return a flat wavefront. While modern developments in adaptive optics have been for astronomy applications the same methods can be used for SSA.

This thesis presents the development and operation of Adaptive Optics Imaging (AOI), an adaptive optics system for satellite and debris characterisation. AOI operates on a 1.8 m telescope located at Mt Stromlo Observatory in Canberra, Australia. AOI is capable of capturing high resolution images of objects in low Earth Orbit (LEO) to identify features and characterise objects. Satellites in geostationary orbit (GEO) can be tracked as they pass by a known reference star for accurate position measurement.

AOI was used to significantly improve images capture of stars with a Strehl ratio of 34% obtained. The effectiveness of the AO correction was shown when capturing images of Cosmos 1656 where several features could be observed during closed loop operation that were not evident in open loop. The quality of the images obtained were further improved by implementing a multi-frame blind deconvolution algorithm which made several features such as the panel array and body more visible. The satellite features were measured to obtain an approximation for the size of the satellite.

A process was developed to identify when stars will pass within 15 arcseconds of a GEO satellite. The GEO satellite position would then be measured relative to the known star position allowing an accurate tracking of a satellite. GEO satellite tracking was demonstrated with a simulation, however no on-sky tracing was successful as the GEO satellites were too dim to detect. Show more