Gaia is an ambitious mission to chart a three-dimensional map of our Galaxy, the Milky Way. In the process, it is helping us better understand the composition, formation and evolution of the Galaxy. Gaia is providing unprecedented positional measurements for about one billion stars in our Galaxy and Local Group – about 1 percent of the Galactic stellar population – together with radial velocity measurements for the brightest 150 million objects.

Within our own solar system, Gaia is also helping us identify tens of thousands of asteroids by recording the way light from a distant star appears dims as an asteroid passes in front of it.

The mission

Gaia operates in a Lissajous-type orbit around the L2 point of the Sun-Earth system, which is located 1.5 million km from the Earth in the anti-Sun direction. The orbit period is about 180 days and the size of the orbit is typically 340 000 × 90 000 km. 

This location in space offers a very stable thermal environment, very high observing efficiency (since the Sun, Earth and Moon are behind the instrument's field of view) and a low radiation environment.

However, orbits about the L2 point are dynamically unstable; small departures from equilibrium grow exponentially overtime. Like ESA's Herschel and Planck missions, which also orbited about L2, Gaia will use its propulsion system to perform periodic orbit-maintenance manoeuvres.

The spacecraft carries a single integrated instrument that comprises three major functions: astrometry, photometry and spectrometry. The three functions use two common telescopes and a shared focal plane, with each function having a dedicated area on the large 0.5 m x 1 m charge-coupled device (CCD) Focal Plane Assembly detector array.
The Gaia spacecraft was built with EADS Astrium SAS as prime contractor. The Gaia Mission Operations Centre (MOC) is located at ESOC, Darmstadt, Germany. The Gaia Science Operations Centre (SOC) is located at the European Space Astronomy Centre (ESAC), in Villafranca, Spain.

Data release milestones:

• Data Release 1: 14 September 2016
• Data Release 2: 25 April 2018
• Early Data Release 3: 3 December 2020

Next milestone:

• Data Release 3: 2022

Latest news on Gaia

Launch and Early Orbit

Gaia travelled into orbit on 19 December 2013 on a Soyuz-ST rocket from Kourou, Europe's Spaceport in French Guiana. Lift off took place at 10:12 CET. Gaia completed its nominal mission lifetime of five years in July 2019 and is currently in its extended mission.

The critical Launch and Early Orbit Phase (LEOP) lasted approximately four days. In that phase, Gaia performed the first activations – transmitter switch ON, priming of the chemical thrusters, first attitude control and finding of the Sun position – followed by the sunshield deployment. Engineers on ground at ESOC performed orbit determination (to fix the satellite's trajectory), then prepared and executed the critical 'Day 2' manoeuvre to inject Gaia into its final transfer trajectory toward the L2 Lagrange point.

Ground segment & mission control system

Gaia uses the SCOS-2000 mission control system.

Mission operations are conducted by the Flight Control Team at ESOC, comprising spacecraft operations (mission planning, spacecraft monitoring and control, and all orbit and attitude determination and control) as well as scientific instrument operations (quality control and collection of the science telemetry). The ground segment at ESOC comprises all facilities, hardware, software and documentation required to conduct mission operations.

All mission and flight control facilities, except the ground stations, are located at ESOC, including the interfaces for the provision of science telemetry to the Science Operations Centre at ESA/ESAC.

The science data are distributed to ESAC after being stored in dedicated Science Data Servers at ESOC, via high-speed communication lines.