THE GAIA PAYLOAD

摘要

Gaia is a cornerstone mission of the European SpacernAgency, approved with launch by end of 2012, butrnstudied with a programmatic assumption of a launch inrnthe 2010 time frame. Gaia will build an extraordinaryrnprecise 3-D map of about one billion stars throughoutrnour Galaxy with an astrometric accuracy of about 10rnμas (micro-arcseconds) for a star magnitude V = 15.rnThe initial Gaia design was made in 1998 by Matra-rnMarconi Space, today EADS-Astrium (France) underrnESA contract, awarded in open competition. Thernconcept included two separate telescopes each having arnvery large focal plane made of about 250 CCDs. Therntarget accuracy of 10 μas for a star magnitude V = 15rnwas shown to be achievable with available CCDrntechnology and with an instrument enveloperncompatible with Ariane 5 launcher.rnIn 2002, the initial design was deeply revisited byrnEADS-Astrium again under ESA contract in view ofrnreducing the programme cost while preserving thernscience objectives. The reassessed concept still makesrnuse of the same measurement principle but with somernmajor modifications: the size of the instrument hasrnbeen scaled down so as to enable a Soyuz-Fregatrnlaunch, and the two astrometric focal planes werernsuperimposed by using a new optical configuration,rntherefore reducing the total number of CCDs from 500rnto about 200. The paper describes the major evolutionrnof Gaia payload.