Laser beacon tracking for free-space optical communication on small-satellite platforms in low-earth orbit

Abstract

Free-space optical (FSO) communication, or laser communication, is capable of providing high-rate communication links, meeting the growing downlink demand of space missions, including those on small-satellite platforms. FSO communication takes advantage of the high-gain nature of narrow laser beams to achieve higher link efficiency than traditional radio-frequency systems. In order for a FSO link to be established and maintained, the spacecraft's attitude determination and control system needs to provide accurate pointing at the optical ground station. However, small satellites, such as CubeSats, have limited ground-tracking capabilities with existing attitude sensors. Miniaturized laser beacon tracking system, on the other hand, has the potential to provide precise ground-based attitude knowledge, enabling laser communication to be accomplished on small-satellite platforms. This thesis details the development of a CubeSat-sized laser beacon camera capable of achieving a sub-milliradian attitude knowledge accuracy with low fade probability during various sky conditions, sufficient to support a high-rate FSO communication link on a CubeSat platform on low-Earth orbit. The high-level Nanosatellite Optical Downlink Experiment (NODE) system architecture, the beacon camera conceptual design as well as prototype development are presented in detail. An end-to-end beacon simulation was constructed to validate the attitude sensing performance of the module under expected atmospheric turbulence and sky brightness conditions. The simulation results show a high-accuracy attitude sensing performance and low fade probability, capable of supporting NODE's laser links.