Airbus Defence and Space

Gaia: on the right track

Airbus Defence and Space’s Xavier Moisson, head of Gaia Operations, and Frédéric Faye, Gaia Satellite System Director, take stock of Gaia just a few weeks after its launch from Kourou.

Once it reached the Lagrange L2 point on 14 January, Gaia began transmitting its first data to the European Space Agency (ESA) European Space Operations Centre (ESOC) in Darmstadt, Germany. There are two types of data: the data about the satellite itself, which allow the space observatory’s state of health to be monitored; and the scientific data which are transferred to ESA’s European Space Astronomy Centre (ESAC) in Spain.

A dozen Airbus Defence and Space engineers are processing the satellite data in collaboration with ESA personnel based at ESOC, while the scientific data analysis is taking place at the Toulouse operations centre. The task the teams are currently tackling is the refining of the image-detection settings by refocusing the main instrument.

“We compare the quality of the images received with the quality we expect, and we can thus calibrate telescope optical quality,” Xavier explains. “We then refine the setting of the M2 mirror – the only one of the three on each of the two telescopes that is adjustable – through tiny movements in the region of a few micrometres. This optimises the instrument’s response whenever it detects a star.”

The team also takes into account the observations made by the scientists of the Initial Data Treatment (IDT) unit, who provide a detailed weekly report on the state of health of the satellite’s payload.

This initial series of adjustments should last through to April. At this point the telescope will be completely correctly focused, images will meet the expected level of quality in terms of spectral range and magnitude ranges, and the base angle between the two telescopes will not change. Depending on how successful this first phase is, the team will then proceed to making the very final adjustments, particularly of the Radial-Velocity Spectrometer, which, as Frédéric says, “needs to be able to operate at the level of fractions of electrons in the image in order to take its measurements.”

One month later, when Gaia’s instruments achieve the absolute level of accuracy expected of them, Airbus Defence and Space will hand Gaia over to the customer, ESA. Of the company’s relationship with ESA, Frédéric says: “It’s really a partnership. Everything has gone perfectly with them since the start of the project 10 years ago.

Today, we and the people at ESOC are focusing on operational matters, and ESA’s know-how is first rate,” he adds. Xavier echoes him: “We have a superb relationship with ESAC’s astronomers and scientists.”

The Gaia mission

Gaia’s mission is to produce a detailed map of the Milky Way and reveal the origin, structure and evolution of our galaxy. Gaia will make an inventory of 1% of all the stars in our galaxy – of which there are in total around one billion. During its five-year lifetime, Gaia will observe each of these stars 70 times, recording its light intensity, colour and position in the sky. Gaia is also expected to discover a large number of unknown celestial objects: new asteroids in the solar system, extra-solar icy bodies, young stars, planets, distant stellar explosions, black holes – to name just a few!

A formidable trio

The light collected by Gaia’s two telescopes is analysed by three instruments:

- The main instrument, which has an astrometry function and determines the position of stars in the sky and the speeds at which they move.

- The photometer, which supplies information on the colours of the celestial objects, enabling stellar properties such as the chemical composition, mass and temperature to be calculated.

- The Radial-Velocity Spectrometer, which measures the speed of the star’s movement.