The GAIA astrometry mission

Paper number

IAC-06-A3.1.03

Author

Dr. Charles Koeck, EADS Astrium, France

Coauthor

Mr. Vincent Poinsignon, EADS Astrium, France

Coauthor

Mr. Rudolph Schmidt, European Space Agency (ESA)/ESTEC, The Netherlands

Coauthor

Mr. Frédéric Faye, EADS Astrium, France

Year

2006

Abstract

ESA’s challenging GAIA mission has been approved as the sixth cornerstone of the Agency’s Scientific Programme. The GAIA mission 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, EADS Astrium has been selected by ESA to design, develop and build the spacecraft due to be launched in 2011 aboard a Soyuz-Fregat.
Distance measurement has been historically one of the most fundamental challenges in astronomy. Astrometry is studied since beginning of mankind, as assistance to location and navigation. It is now 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-arcseconds at magnitude 15. The GAIA mission will mark an unprecedented step forward in astrometry considering the achieved accuracy and the number of objects observed. 

To this purpose, 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 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 large 35 m ESA Cebreros station is used to collect the 100 Tb of science data generated over the mission. Several years of ground processing are then requires to obtain the final survey with the targeted microsecond level accuracy. 
The spacecraft is fully designed and optimised to provide the instrument with the most stable thermal and dynamical conditions to enable it 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 Gaia 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 implementation of an all silicon carbide instrument and avoidance of all mechanical, thermal or electrical source of dynamical disturbances on board the spacecraft, prohibiting the use of mechanisms, relay switches or even heat pipes during science operations, the deployment of a large sunshield sizing about 100 m2 and the use of an attitude control involving the science instrument in the loop and a new micro propulsion system as only actuator.

The spacecraft development programme includes a 1 year phase B2 devoted to the progressive design detailing, the industrial team build up and the selection of the critical technologies, followed by a 4 years phase C/D concluded with the delivery of the fully qualified spacecraft. A subsequent phase E1 covers the launch campaign, the early in-orbit operations, the transfer to the L2 Lagrange point and the final in-orbit commissioning phase including the fine calibration of the Payload module. The rigorous development and AIV programme is driven both by the ultimate level of performance requiring new technologies and concepts, and by the “no risk” approach applicable to ESA cornerstone missions.

Abstract document

IAC-06-A3.1.03.pdf

Manuscript document

IAC-06-A3.1.03.pdf (🔒 authorized access only).

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