Unmodified Portable Telescope for Space-to-Ground Optical Links

By providing high bandwidth with low power and size, optical communications have received intense interest in space applications. Inter-satellite links are now in everyday service with the European Data Relay System (EDRS), and several competent optical laser terminals for satellites have been constructed. The space-to-ground segment is challenged by atmospheric disturbances, and local weather necessitates site diversity. Fixed observatory-class or containerised ground stations have been demonstrated with favourable results, however, these are expensive to deploy in numbers. An alternative is to base the ground stations on commercial off-the-shelf (COTS) portable telescopes; easily deployable at low cost. We present the lowest cost ground station yet, below 10,000 euros or dollars, with only COTS components and requiring no modifications. In the Portable Optical Ground Station (POGS) described herein, a compact fine-tracking and fibre-coupling assembly replaces the telescope's eyepiece, and an external camera is added for automatic telescope Earth alignment and satellite acquisition. We demonstrate tracking performance at arcsecond-level accuracy and effective coupling into multi-mode fibres. POGS only requires low-resolution 256 by 256 pixel cameras, enabling expansion into short-wave infrared at low cost. All software and plans required to build the system are released as the free and open-source project pypogs, allowing our results to be immediately deployed.