Acquisition, Tracking and Pointing Control of the Bifocal Relay Mirror Spacecraft

Abstract

This paper presents the results of both numerical and experimental studias on the guidance, dynamics and control of the Bifocal Relay Mirror spacecraft. This proposed spacecraft consists of two large gimbaled telescopes, that arc optically couplad and used to redirect, a laser beam from a ground-based source to a distant point. The attitude control system consists of reaction wheels, star trackers and gyros. The optical control system consists of fast steering mirrors and optical tracker sensors. The very tight pointing and jitter requirements, together with the multi-body nature of the spacecraft, make the control of the system very challenging. Numarical simulations have been performed on a complete analytical model of the system dynamics, in order to compare two different control approaches proposed for the attitude and tracking/pointing. Moreover experiments were carried out on a spacecraft simulator test-bed, modelling the transmitter portion of the Bifocal Relay Mirror spacecraft. The main tasks of the presented experiments were: first, to validate the attitude stabilization control together with the target acquisition-tracking-pointing and laser jitter rejection; second, to prove the effectiveness of the test-bed itself as an important tool to be used in the following researches.