A portable optical ground station for low-earth orbit satellite communications

Small satellite launch opportunities are rapidly expanding and technical capabilities are improving. Several commercial constellations of small satellites for Earth observation and communications are making their way onto orbit, increasing the need for high bandwidth data downlink. Laser communications (lasercom) has the potential to achieve high data rates with a reduction in power and size compared to radio frequency (RF) communications, while simultaneously avoiding the significant regulatory burden of RF spectrum allocation. The primary challenge for lasercom is aligning a narrow beam between the transmitter and receiver. High-precision pointing must be achieved by both the space terminal and the ground station. While existing lasercom ground stations have primarily utilized professional telescopes at observatory-class facilities, making optical ground stations more affordable and transportable is a key enabler for expanding lasercom to small satellites and new applications, as well as establishing networks to mitigate the effects of weather. We describe the development of the Massachusetts Institute of Technology Portable Telescope for Lasercom (MIT-PorTeL) utilizing an amateur telescope augmented with an externally mounted receiver assembly. The ground station has a 28 cm aperture and utilizes a star tracker for automated calibration. The ground station reduces mass by at least 10x and cost by at least 100 x over existing optical ground stations. We present a ground station architecture that enables deployment in less than one hour and that is capable of tracking satellites in low-Earth orbit. We describe the receiver assembly and fine pointing system that enables arcseconds-level pointing accuracy. Finally, we present results from testing the ground station on the roof of an MIT building tracking a star and tracking the International Space Station.