Design of a ground terminal for deep-space optical communications

Optical links are expected to provide a high-capacity solution for future deep-space communications [1][2][3]. However, demonstrations so far exploiting this technology in space have been limited to near Earth links or inter-satellite links. In order to apply optical communications for deep-space missions, several technology demonstrations using adapted versions of the future optical communication systems have been proposed, including an experiment on board the European Space Agency (ESA) Asteroid Impact Mission (AIM). This paper summarizes the design of the optical ground terminal of the deep space optical communications system for AIM, The Optical Ground Station with a 1 meter telescope can comply with the down link data rate of 400 kbps from 0.5 Astronomical Units. The optomechanical setup of the ground terminal has been carefully designed to simultaneously optimize both the system throughput and the required isolation between the dim received signal and the high power lasers used for the uplink beacon. Special attention has been paid to the implementation of the beacon scanning, the downlink acquisition and the point ahead functionalities. The use of high power lasers introduces thermal constraints that may degrade the link performance through the generation of local turbulence. In order to mitigate this effect, the analysis performed has evaluated solutions to control the temperature of the optomechanical parts. Besides, the receiver system has been designed based on fiber coupled Superconducting Nanowire Single-Photon Detectors (SNSPD), and has been devised to concurrently provide both the detection and the spatial tracking functions. Finally, a control system architecture is introduced, covering all the functionalities required assembling just off the shelf components.