Ultra-Fine Pointing for Nanosatellite Telescopes with Actuated Booms

Abstract

The smallsat revolution has impacted the architecture of most modern satellites with the notable exception of fine-pointing space telescopes. Conventional attitude control hardware scales poorly as the spacecraft gets smaller, resulting in significant mass and performance penalties for nanosatellites with strict pointing requirements. This paper presents a novel attitude actuation and planning strategy that utilizes actuated booms with tip masses and magnetorquers for three-axis pointing and momentum desaturation. The speed of the booms is an appropriate match for the slowly varying environmental disturbance torques encountered in low-Earth orbit. As a result, these booms do not create the high-frequency jitter that reaction wheels do, lessening the need for complex second-stage correction hardware in the payload. An optimization-based motion planner is able to reason about the orbital ephemeris to ensure the booms never exceed their actuation limits, and a Linear Quadratic Gaussian controller is able to maintain fine-pointing during times of payload operation.