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|18 May 2004|
Gaia builds upon the European heritage of precision stellar mapping that was exemplified by ESA’s Hipparcos satellite in the late 1980s. Whereas that mission catalogued a hundred thousand stars to high precision, and more than a million to lesser accuracy, Gaia will map a thousand million stars to unprecedented levels of precision.
Gaia’s name was originally derived as an acronym for Global Astrometric Interferometer for Astrophysics. This reflected the optical technique of interferometry that was originally planned for use on the spacecraft. However, the working method has now changed. Although the acronym is no longer applicable, the name Gaia remains to provide continuity with the project.
The entire mission, including launch, ground operations and payload, will cost about €600 million (2009 values). This excludes the scientific processing of the data, by the pan-European Data Processing and Analysis Consortium (DPAC), which is estimated at 2000 person-years of effort.
Gaia is scheduled for a 2013 launch. It will be lifted into space using a Russian Soyuz-Fregat from Sinnamary, part of Europe’s Spaceport in French Guiana.
After launch, Gaia will take about a month to cruise to the Lagrangian point known as L2. This special location, 1.5 million km further from the Sun than Earth (about four times the distance of the Moon), keeps pace with Earth’s yearly revolution around the Sun and thus maintains the positions of the Sun, Earth and spacecraft on a single line. This gravitational equilibrium point offers a clearer view of the cosmos than an orbit around Earth.
Planned mission lifetime
Gaia is designed to fulfil its mission in five years. The mission will begin after the month-long cruise phase and an additional three months at L2 to commission the spacecraft and payload.
A near-circular solar array/sunshield assembly dominates Gaia’s appearance. Above this is a conical service module containing essential systems such as a propulsion module, communications and power. Above that module is a geodesic dome that houses the payload module. The spacecraft will slowly rotate, sweeping its instruments’ fields of view across space and scanning continuously as it does so.
Astro: There are two identical Astro telescopes on Gaia. Both have rectangular primary mirrors, rather than circular ones, and are 1.45 m by 0.50 m. Two smaller mirrors then bring the light to a focus. Three more mirrors then guide the image from the focus to the focal plane. Each instrument looks at a different section of sky, separated by 106.5º. A suite of about 80 Charge Coupled Device (CCD) detectors will image celestial objects. They will precisely map the stars and chart any movement across the sky.
BP/RP: The Blue and Red Photometers share the Astro telescope. They use prisms to generate low-resolution spectra, which are measured using 14 CCD detectors. These data yield information on the colours of stars, which can be used to determine stellar properties such as temperature, mass, age and elemental composition.
RVS: The Radial-Velocity Spectrometer uses the Astro telescope plus additional optics to generate high-resolution spectra. These spectra will be captured by 12 large CCD detectors and will allow astronomers to measure the movement of the celestial objects along the line of sight.
All instruments are being paid for by ESA and will be the collective responsibility of ESA, its industrial partners and its science teams.
ESA Project Manager: Giuseppe Sarri (acting)
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