On-orbit beam pointing calibration for nanosatellite laser communications

Abstract

We describe techniques developed to optimize beam pointing control for a CubeSat laser downlink demonstration mission being developed at the MIT Space Telecommunications, Astronomy, and Radiation Laboratory. To fine-point its downlink beam, the mission utilizes an uplink beacon signal at 976 nm captured by an on-board AE5deg field-of-view detector and tracked by a 3.6-mm commercial, off-the-shelf MEMS fast steering mirror. As these miniature actuators lack feedback sensors, the system design is augmented with an optical calibration signal to provide the mirror's pointing feedback. We describe the system and introduce calibration algorithms utilizing the feedback signal to achieve higher fidelity beam pointing control. A demonstration in the laboratory is conducted to obtain a quantitative performance analysis using quasi-flight hardware with simulated spacecraft body pointing disturbances. Experimental results show that beacon tracking errors of only 16 μrad root-mean-square are feasible for both axes, significantly exceeding the mission pointing requirement of 0.65 mrad and indicating the feasibility of narrower beams and higher data throughputs for nextgeneration downlink demonstration missions.

High-Precision Dual-Stage Pointing Mechanism for Miniature Satellite Laser Communication Terminals

“…The mentioned missions perform static observations of far objects, while optical communication systems generally deal with dynamic pointing requirements, especially during ground station tracking. Slew rates on 400 km orbits are typically around 20 mrad/s [15], greatly stressing the ADCS and making pointing more challenging compared to static observations. In addition, space telescopes platforms are specifically tailored to the pointing task, meaning that the optical payload strongly depends on the vehicle bus resources to achieve such high accuracy.…”

“…The MIT Nanosatellite Optical Downlink Experiment (NODE) instead integrates a Fast Steering Mirror (FSM) in a 1.2 U to improve the pointing accuracy achieved with the ADCS [20], [15]. NODE will be the payload of the Cubesat Laser Infrared CrosslinK (CLICK) mission which is under joint development by MIT, University of Florida and NASA Ames Research Center [21].…”

CubeSat laser infrared crosslinK mission status

“…For more detail, see Ref. 6. With the payload conducting fine pointing, the payload downlink laser is detected by the OGS using its own near-infrared (NIR) tracking camera.…”

Electrostatic MEMS micromirror servo control for micro laser communication terminal

“…In the same year, the MIT Space Communication Laboratory in the United States used the A8L2.2 MEMS micromirror produced by Mirrorcle to establish an on-board miniaturization system for satellite laser communication. The closed-loop tracking error can reach 20urad, with a standard deviation of 10.5urad [5,6].…”