A Transmitter and Receiver for Lunar Communications on the ANU Optical Ground Station

Abstract

The Australian National University (ANU) Optical Communications Ground Station (OCGS) is currently under development at Mt. Stromlo Observatory in Canberra, Australia. The OCGS will be compatible with a range of wavelengths, coding schemes, and techniques to cover satellites in Low Earth Orbit to Lunar and deep-space, and provide a platform for quantum communication from satellites. We have conducted a feasibility study and preliminary design review for the development of an instrument to support the CCSDS high photon efficiency (HPE) standard so the OCGS can support future lunar missions featuring optical communication terminals. The development of lunar communication capabilities in Australia offers site diversity and increased visibility, allowing for improved optical link availability during missions. We present the preliminary design for the transmitter and receiver which will integrate on the 70 cm telescope in the OCGS. A lab prototype of the transmitter has been built to demonstrate the generation of a pulse position modulation (PPM) waveform which is compatible with the CCSDS high photon efficiency (HPE) standard. The transmitter is made up of four 15 cm apertures which is mounted by a piggyback to the telescope. Each can operate as an independent channel with fine steering control through a fast steering mirror. The apertures are separated by characteristic atmospheric turbulence length r0 to minimise fading at the spacecraft. The receiver is installed at the Nasmyth port of the 70 cm telescope. The receiver features a fast steering mirror to maximise coupling into a multimode fibre. The signal is split with a photonic lantern and sent to several superconducting nanowire single photon detectors (SNSPD).