Gaia’s first readings are being held up by technical troubles (Image: ESA)

Galaxy mappers will just have to hold tight – a trio of technical troubles means that the first release of data from the Gaia space telescope has been pushed back to the middle of 2016, nine months later than originally planned.

Launched by the European Space Agency (ESA) in December 2013, Gaia will use its 1.5-gigapixel camera to catalogue a billion stars in our galaxy, including stars that are thousands of times fainter than we can see with the naked eye. The telescope is currently 1.5 million kilometres away from Earth, in a spot known as Lagrange point 2. This is where the combined gravitational forces of the sun and Earth balance with the centrifugal force of the telescope. The alignment of these forces means that any object in this location is always on Earth’s night side.

Gaia detects anything bright enough to trigger its software as the spacecraft slowly scans the sky. As a result, astronomers expect that it will also discover hundreds of thousands of previously unknown celestial objects, from asteroids, to exoplanets to distant black holes.


Light and ice

Gaia managers started taking test images early this year, but soon noticed three issues. For one, more light than anticipated is bending around the 10-metre sunshield and entering the telescope.

Small amounts of water trapped in the spacecraft before launch are being released now that the telescope is in the vacuum of space, and more ice than calculated is accumulating on the telescope’s mirrors. In addition, the telescope itself is expanding and contracting by a few dozen nanometres more than expected because of thermal variations.

Mission managers say the number of stars detected will remain the same even if these complications remain untreated, but the accuracy in measurements of the fainter stars will suffer.

The team has constructed computer models to explain most of the stray light and used them to design new observing strategies to minimise the problem. The other two issues are being investigated in ESA laboratories.

Irreplaceable eye

“We have a good idea how to deal with the problems, now we just need some more time to work with the data,” says Anthony Brown at the Leiden Observatory in the Netherlands, who is chair of the Gaia Data Processing and Analysis Consortium.

The first scientific readings will be collected towards the end of July, three months later than originally planned. On top of this, the team have added six more months to grapple with the subsequent calibration and analysis.

“Nine months delay out of 20 years planning is nothing for a space mission,” says Ulrich Bastian at the University of Heidelberg in Germany, who is the leader of the Heidelberg Gaia group and of the Europe-wide Gaia core processing group. “Even without the problems corrected, Gaia is still a unique, irreplaceable scientific mission.”

When this article was first published on 4 July 2014, the description of Lagrange point 2 was inaccurate. This has now been corrected.