Pointing, Acquisition, and Tracking for Small Satellite Laser Communications

Pointing, Acquisition, and Tracking for Small Satellite Laser Communications

The CubeSat Laser Infrared CrosslinK (CLICK) mission is a technology demonstrator for a 2U inter-satellite link laser communications terminal deployed on a 6U CubeSat. The pointing, acquisition, and tracking (PAT) system has a full-cone, half-power pointing requirement of 14.6 arcsec to achieve full-duplex laser communications at 20 Mbps at ranges up to 580 km or more. The corresponding single-axis pointing requirement is ±5.18 arcsec (3σ). The PAT system utilizes the satellite’s attitude control system for coarse relative pointing and a fine pointing system (FPS) within the payload to mitigate residual pointing error and maintain the link under environmental and spacecraft-induced disturbances. The FPS uses a MEMS fast steering mirror (FSM) to maintain alignment of the transmit (Tx) and receive (Rx) laser signals. This paper presents a simulation of the FPS control system, which is being used to identify improvements in pointing margins and prototype the flight-level control system. The initial results give an improvement in fine pointing error due to the FPS control error of 28%: from ±2.27 arcsec (3σ) to ±1.63 arcsec (3σ) and an increase in overall fine pointing margin, including optomechanical error, from 0.06% to 5.4%.