Lisa Pathfinder Mission: Attitude and Orbit Control Based on Micropropulsion Systems

Abstract

The main purpose of the LISA Pathfinder mission is to provide in-orbit validation of the critical technology necessary for LISA. LISA (Laser Interferometer Space Antenna) aims at detecting gravitational waves generated by very massive objects such as black holes. Detecting gravitational waves will tell us more about the way space and time are interconnected. The mission consists of placing two test-masses in a nearly perfect gravitational free-fall, and of controlling and measuring their motion with unprecedented accuracy. This is achieved through state-of-the-art technology comprising inertial sensors, a laser metrology system, a drag-free control system and a precise micro-propulsion system (micro-Newton electric propulsion). The micro-Newton electric propulsion coupled with extremely sensible inertial sensors is required for the spacecraft to fly in a purely gravitational orbit (drag-free spacecraft). In order to be able to perform the scientific measurement it is necessary to have a very stable environment which prevent to have onboard other AOCS actuators such as reactions wheels or chemical propulsion to perform nominal AOCS operations. This constraint constituted a major limitation in the design of the AOCS subsystem. The present article provides a comprehensive overview of the micropropulsion Attitude and Orbit Control System (MPACS) architecture, design and performance. It will focus in particular on the challenges of using micro-Newton electric propulsion system and constraints dictated by their performance requirements. LISA Pathfinder is currently in phase C/D and has already passed the Critical Design Review (CDR) both at subsystems and system level. The spacecraft is planned to be launched in late 2011.