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GAIA : Smart engineering for sharp astrometry focus

With extreme precision and extreme stability as design drivers, Gaia is a concentrate of technological firsts.

Gaia’s astounding acuity – the mission aims to pick out celestial objects one million times fainter than the human eye can see – is achieved by more than 100 light-detecting sensors, like minuscule digital cameras, mosaicked together to form the largest ever space-bound focal-plane array (nearly a billion pixels packed onto a surface of 0.38m2).

Channelling the light onto the focal-plane array are two telescopes with primary mirrors set at an angle of 106.5° to each other for a wide-field view. Despite the spacecraft’s modest dimensions (the payload module is 3.5m in diameter), an ingenious method of bouncing the collected light through a series of 10 mirrors of different shapes and sizes means that the telescopes’ effective focal length is extended to 35m. Thus Gaia can ‘see’ objects 400,000 times fainter than those visible to the naked eye.

The data from Gaia’s three instruments (taking astrometric, photometric and spectroscopic measurements) should provide a pinpoint location for each star mapped with an error margin of only six microarcseconds, equivalent a penny on the surface of the moon, as viewed from Earth.

Rock-steady stability is crucial for making observations of such minute detail, and this dictated Airbus Defence and Space’s choice of material – silicon carbide (SiC), a ceramic twice as rigid as steel, ultra lightweight, and remarkably resistant to expansion/contraction under temperature change. SiC is the only material which can guarantee the stability, durability and lightness of the probe, and Gaia will be the largest ceramic space instrument ever flown.

There are virtually no moving components on Gaia, to avoid vibration. (Even the Earth-communicating antenna points electronically, not mechanically.) As this ruled out ‘standard’ chemical thrusters, an entirely new type of nitrogen-based thruster for fine attitude pointing which exerts a force as small as a micronewton was specially developed for the mission. You would need a thousand such tiny thrusters to support a sheet of paper

More infos on : From Hipparcos to Gaïa