Body pointing, acquisition and tracking for small satellite laser communication

Free-space optical communications in space offer many benefits over established radio frequency based communication links; in particular, high beam directivity results in efficient power usage. Such a reduced power requirement is particularly appealing to small satellites with strict size, weight and power (SWaP) requirements. In the case of free-space optical communication, precise pointing, acquisition and tracking (PAT) of the incoming beam is necessary to close the communication link. Due to the narrow beam of the laser, the critical task of accomplishing PAT becomes increasingly arduous and often requires complex systems of optical and processing hardware to account for relative movement of the terminals. Recent developments in body pointing mecha- nisms have allowed small satellites to point with greater precision. In this work, we consider an approach to a low-complexity PAT system that utilizes a single quad-cell photodetector as an optical spatial sensor, and exploits the body pointing capabilities of the spacecraft to perform the tracking maneuvers, eschewing the need for additional dedicated optical hardware. We look at the PAT performance of this approach from a systems analysis viewpoint and present preliminary experimental results. In particular, we examine the implementation of the system on NASA's TeraByte InfraRed Delivery (TBIRD) demonstration.