Francis Bennet, Research School of Astronomy and Astrophysics, Australian National University, Celine D’Orgeville, Research School of Astronomy and Astrophysics, Australian National University Canberra, Australia, Ian Price, Research School of Astronomy and Astrophysics, Australian National University Canberra, Australia, Francois Rigaut, Research School of Astronomy and Astrophysics, Australian National University Canberra, Australia, Ian Ritchie, Electro Optic Systems, Mount Stromlo Observatory, Canberra, Australia, Craig Smith, Electro Optic Systems, Mount Stromlo Observatory, Canberra, Australia
Keywords: space environment management, space debris, laser ranging, adaptive optics
Abstract:
Earths space environment is becoming crowded and at risk of a Kessler syndrome, and will require careful management for the future. Modern low noise high speed detectors allow for wavefront sensing and adaptive optics (AO) in extreme circumstances such as imaging small orbiting bodies in Low Earth Orbit (LEO). The Research School of Astronomy and Astrophysics (RSAA) at the Australian National University have been developing AO systems for telescopes between 1 and 2.5m diameter to image and range orbiting satellites and space debris. Strehl ratios in excess of 30% can be achieved for targets in LEO with an AO loop running at 2kHz, allowing the resolution of small features (<30cm) and the capability to determine object shape and spin characteristics. The AO system developed at RSAA consists of a high speed EMCCD Shack-Hartmann wavefront sensor, a deformable mirror (DM), and realtime computer (RTC), and an imaging camera. The system works best as a laser guide star system but will also function as a natural guide star AO system, with the target itself being the guide star. In both circumstances tip-tilt is provided by the target on the imaging camera. The fast tip-tilt modes are not corrected optically, and are instead removed by taking images at a moderate speed (>30Hz) and using a shift and add algorithm. This algorithm can also incorporate lucky imaging to further improve the final image quality.
A similar AO system for space debris ranging is also in development in collaboration with Electro Optic Systems (EOS) and the Space Environment Management Cooperative Research Centre (SERC), at the Mount Stromlo Observatory in Canberra, Australia. The system is designed for an AO corrected upward propagated 1064nm pulsed laser beam, from which time of flight information is used to precisely range the target. A 1.8m telescope is used for both propagation and collection of laser light. A laser guide star, Shack-Hartmann wavefront sensor, and DM are used for high order correction, and tip-tilt correction provided by reflected sunlight from the target. The system is expected to achieve a Strehl ratio of 30% at 1064nm, and enable ranging to targets in excess of 2000 km. The system is currently installed and is undergoing commissioning as a natural guide star AO system, before the system is upgraded for laser guide star AO and debris ranging.
This ranging system is aimed at demonstrating the capabilities of AO corrected laser ranging, and will be used as a platform to further develop space environment management techniques and strategies. SERC will continue this development and focus in particular on the development of a high power (>2kW) laser which can modify the orbit of debris using photon pressure.
The AO systems we are developing aim to show how ground based systems can be used to manage the space environment. AO imaging systems can be used for satellite surveillance, while laser ranging can be used to determine precise orbital data used in the critical conjunction analysis required to maintain a safe space environment.
Date of Conference: September 15-18, 2015
Track: Adaptive Optics & Imaging