On-Orbit Risk Mitigation for a ½-U Orbital Laser Guidestar Link

Abstract

The AMS Beacon is a ½-U laser guidestar payload, scheduled to launch in April 2022 aboard the Agile MicroSat (AMS) 6-U CubeSat. This payload, carrying $a$ 500 mW, 976 nm laser, will be the first to provide an active lasing low Earth orbit reference for high-angle rate adaptive optics (AO). During the science phase of the mission, it will establish a space-to-ground link with an AO-equipped ground station. Due to budget constraints and size, weight, and power (SWaP) limitations, AMS Beacon was designed without gimbals or fast-steering mirrors, to utilize only open-loop body-pointing and generic CubeSat attitude control software. This paper presents the radiometric link analysis that informed our selection of compatible ground station components and fed into the development of an on-orbit search scan pointing re-characterization procedure to mitigate pointing risks. Within the limits of our attitude determination and control system (ADCS), our search mode can accommodate up to 1.75° of pointing error during a single pass, and has the capability to potentially search larger areas by concatenating data from multiple successive passes. As our expected pointing error is approximately 0.1°, this search mode is a fail-safe in case of larger than expected pointing shifts during launch and deployment. Our scheme utilizes AMS's body-pointing capability, AMS telemetry, and ground-based radiometric readings to recover and re-characterize beam alignment knowledge on-orbit. Because this procedure relies on standard CubeSat pointing capabilities and telemetry, we believe that our procedure could be used for future laser guidestar CubeSat payloads.