ESA GNC Conference Papers Repository

The Gaia spacecraft, which was successfully launched by Soyuz from Kourou in December 2013, is an ESA astronomy mission to investigate the structure and evolution of the galaxy by measuring the positions of one billion stars to unprecedented accuracy. Gaia has been developed by Airbus Defence & Space – France (former Astrium SAS) (prime), with Airbus Defence & Space UK (former Astrium Ltd.) responsible for the electrical service module, including the AOCS. The challenges for the AOCS design are to provide attitude control within a restricted pointing domain, due to thermal constraints, and to provide a fine pointing mode with relative pointing error (RPE) of a few milli-arcseconds (mas). The fine pointing mode needs to use the scientific payload as an AOCS sensor in order to measure angular rate to the accuracy required. This mission is also the first use of European proportional cold gas technology to provide actuation with micro-Newton resolution. This paper presents an overview of the in-orbit performance of the AOCS during the first few months of the mission including the behaviour of the main operational control modes, deployment of the sun shield, LEOP delta-V manoeuvres, use of the micro-propulsion and exploitation of the science payload by the AOCS.