The Gaia astrometry mission: status after phase B completion
- Paper number
IAC-08.A3.4.3
- Author
Dr. Charles Koeck, EADS-Astrium, France
- Coauthor
Mr. Vincent Poinsignon, EADS Astrium, France
- Coauthor
Mr. Frédéric Faye, EADS Astrium, France
- Coauthor
Mr. Rudolph Schmidt, European Space Agency (ESA), The Netherlands
- Year
2008
- Abstract
ESA’s challenging Gaia mission is the sixth cornerstone of the Agency’s Scientific Programme. Gaia aims at creating an extraordinarily precise 3-D map of the Galaxy, mapping and recording more than one billion stars over a five year period. Beginning 2006, the programme implementation phase was kicked off at Astrium. After two years, the design phase is over, and the programme has entered the phase C/D corresponding to the realisation and the qualification of the spacecraft. The full industrial consortium has been built in less than 18 months, and is now working full speed ahead to meet the launch date of late 2011. Astrometry is vital for understanding the structure and evolution of stars, the formation and composition of our Galaxy and ultimately for tracing the origin of the universe. Gaia will provide positional, radial velocity and photometric measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars throughout our Galaxy and into the Local Group. The survey aims for completeness to magnitude 20, with accuracies of 12-24 micro-arc-seconds at magnitude 15. The Gaia mission will mark an unprecedented step forward in astrometry considering the achieved accuracy and the number of objects observed. The Gaia spacecraft is deployed around the Lagrange point L2 of the Earth-Sun system and acquire continuous stellar measurement using the revolving scan technique successfully demonstrated with Hipparcos. The principle is to link stars with large angular distances in a network where each star is connected to a large number of other stars in every direction. The condition of closure of the network ensures the reduction of the position errors of all stars. This is achieved by the simultaneous observation of two fields of views separated by a very stable basic angle, scanning the sky according to a uniform revolving scanning optimising the sky coverage. The spacecraft is fully designed and optimised to provide the instrument with the most stable thermal and dynamical conditions to perform its science mission. Its attitude is three-axis controlled to provide the instrument lines of sight with the required sky scanning law. The spacecraft design is mainly driven by the utmost thermo-mechanical and pointing stability required to reach the measurement accuracy, the need to protect the scientific payload from environmental disturbances and the constraints stemming from the launch vehicle. This calls for: i) the implementation of an all silicon carbide instrument, ii) the avoidance of all mechanical, thermal or electrical source of dynamical disturbances on board the spacecraft, prohibiting the use of mechanisms during science operations, iii) the deployment of a large sunshield sizing about 100 m2 and iv) the use of an attitude control involving the science instrument in the loop and a new micro-propulsion system as only actuator. The paper will recall the basic design features of the mission, the spacecraft and its payload. Highlight will be given on the numerous technical challenges which have progressed since the project kick-off: the basic angle thermo-elastic stability at the spin period (7 micro-arcsec over 6h), the off-axis main mirror ionic beam polishing (20 nanometer achieved on a demonstrator), the micro-propulsion system (thrust with proportional command from 0 to 500 micro-N, and an actuation resolution better than 1 micro-N), and finally the on-board image processing chain, featuring 7 computers running in parallel at a frequency close to 1 GHz each.
- Abstract document
- Manuscript document
IAC-08.A3.4.3.PDF (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.