Update from the Gaia Project Team
A series of exhaustive tests have been conducted over the past few months to characterise some anomalies that have been revealed during the commissioning of Gaia following its successful launch in December 2013, as have been discussed in previous blog posts.
Annotated diagram of the Gaia payload module. Click for more information.
Key among these are an increased background seen in Gaia’s focal plane assembly due to stray light entering the satellite and reduced transmission of the telescope optics. In an effort to understand both problems, much of the diagnostic work has been focussed on contamination due to small amounts of water trapped in the spacecraft before launch that has been “outgassing” now that Gaia is in a vacuum.
The water vapour freezes out as ice on cold surfaces and since Gaia’s payload sits at temperatures between –100 and –150°C in the dark behind the big sunshield, that is where it ends up, including on the telescope mirrors. The ice initially led to a significant decrease in the overall transmission of the optics, but this problem was successfully dealt with by using heaters on Gaia’s mirrors and focal plane to remove the ice, before ...