Telescopes

Each telescope contained a large primary mirror with a collecting area of about 0.7 m^2. These had a rectangular shape to make the most efficient use of the limited space inside the spacecraft. Although these are small mirrors compared with many ground-based telescopes, Gaia had the supreme advantage of observing from space, where there is no atmospheric disturbance to blur the images.

Gaia was just 3.5 m across (excluding the sunshade, which is about 10 m across). Three curved mirrors and three flat mirrors focus and repeatedly fold the light over a total distance of 35 m before it reaches the detectors.

Each of Gaia’s three science instruments used a set of digital detectors – charged coupled devices (CCDs) – to record the starlight falling onto them. Together Gaia’s CCDs made the largest focal plane ever flown to space, a total of one billion pixels covering an area of 0.38 m^2.

On 27 March 2025, Gaia’s control team at ESA’s European Space Operations Centre carefully switched off the spacecraft’s subsystems and sent it into a ‘retirement orbit’ around the Sun.