Gaia Space Telescope team battles 'stray light' problems at start of mission

June 17, 2014 by Elizabeth Howell, Universe Today
Artist’s conception of the Gaia telescope backdropped by a photograph of the Milky Way taken at the European Southern Observatory. Credit: ESA/ATG medialab; background: ESO/S. Brunier

Europe's powerful Milky Way mapper is facing some problems as controllers ready the Gaia telescope for operations. It turns out that there is "stray light" bleeding into the telescope, which will affect how well it can see the stars around it. Also, the telescope optics are also not transmitting as efficiently as the design predicted.

Controllers emphasize the light problem would only affect the faintest visible stars, and that tests are ongoing to minimize the impact on the mission. Still, there will be some effect on how well Gaia can map the stars around it due to this issue.

"While there will likely be some loss relative to Gaia's pre-launch performance predictions, we already know that the scientific return from the mission will still be immense, revolutionizing our understanding of the formation and evolution of our Milky Way galaxy and much else," wrote the Gaia project team in a blog post.

Both of these problems have been known publicly since April, and the team has been working hard in recent months to pinpoint the cause. Of the two of them, it appears the team is having the most success with the optics transmission problems. They have traced the issue to water vapor in the that freezes (no surprise since Gaia operates between -100 degrees Celsius and -150 Celsius, or -148 Fahrenheit and -238 Fahrenheit.)

The team turned on heaters on Gaia (on its mirrors and focal plane) to get rid of the ice before turning the temperature back down so the telescope can do its work. While some ice was anticipated (that's why the heaters were there) there was more than expected. The spacecraft is also expected to equalize its internal pressure over time, sending out gases that again, could freeze and cause interference, so more of these "decontamination" procedures are expected.

Soyuz VS06, with Gaia space observatory, lifted off from Europe’s Spaceport, French Guiana, on 19 December 2013. Credit: ESA–S. Corvaja

The stray light problem is proving to be more stubborn. The light waves from sunlight and brighter sources of light in the sky are likely moving around the sunshield and bleeding into the , which was unexpected (but the team is now trying to model and explain.)

Perhaps it was more ice. The challenge is, there were no heaters placed into the thermal tent area that could be responsible for the issue, so the team at first considered moving the position of Gaia to have sunlight strike that area and melt the ice.

Simulations showed no safety problems with the idea, but "there is currently no plan to do so," the team wrote. That's because some tests on ground equipment in European laboratories didn't show any strong evidence for or against layers of ice interfering with the stray light. So there didn't seem to be much point to doing the procedure.

So instead, the idea is to do "modified observing strategies" to collect the data and then tweaking the software on the spacecraft and on the ground to "best optimize the data we will collect," Gaia managers wrote.

"The is variable across Gaia's focal plane and variable with time, and has a different effect on each of Gaia's science instruments and the corresponding science goals. Thus, it is not easy to characterise its impact in a simple way," they added. They predict, however, that a star at magnitude 20 (the limit of Gaia's powers) would see its positional accuracy mapping reduced by about 50%, while stars that are brighter would have less impact.

GAIA Telescope Array – Credit: ESA

"It is important to realize that for many of Gaia's science goals, it is these relatively brighter stars and their much higher accuracy positions that are critical, and so it is good to see that they are essentially unaffected. Also, the total number of stars detected and measured will remain unchanged," the managers added.

The team is also tracking a smaller issue with a system that is supposed to measure the angle of separation between the two telescopes of Gaia. It's needed to measure how small changes in temperature affect the angle between the telescopes. While the system is just fine, the angle is varying more than expected, and more work will be needed to figure out what to do next.

Gaia Space Telescope team battles ‘stray light’ problems at start of mission
A diagram of the Gaia telescope payload (largest size available). Credit: European Space Agency

But nevertheless, Gaia is just about ready to start a science session that will last about a month. The team expects to have a better handle on what the telescope is capable of, and how to work with these issues, after that time. Gaia operates about 1.5 million km (932,000 miles) away from Earth in a gravitationally stable point in space known as L2, so it's a bit too far for a house call such as what we were used to with the Hubble Space Telescope.

Explore further: Image: Where's Gaia?

More information: … pact-and-strategies/

Related Stories

Image: Where's Gaia?

February 18, 2014

( —Disguised in a crowded field of stars, the tiny white dot highlighted in these two images is none other than ESA's Gaia satellite as seen with the Very Large Telescope Survey Telescope at the European Southern ...

Europe's star-hunter Gaia enters orbit

January 8, 2014

A billion-dollar star-hunting telescope slotted into its operational orbit Wednesday prior to harvesting data for the most detailed map yet of the Milky Way, the European Space Agency (ESA) said.

Gaia launch postponement update

October 24, 2013

Yesterday, the decision was taken to postpone the launch of ESA's Gaia mission after a technical issue was identified in another satellite already in orbit.

Video: Time-lapse Gaia

January 14, 2014

Soyuz VS06, with Gaia space observatory, lifted off from Europe's Spaceport, French Guiana, on 19 December 2013.

Gaia secured inside fairing

December 16, 2013

ESA's billion-star surveyor Gaia, less than a week from launch, is now tucked up inside the fairing that will protect it during the first few minutes of ascent into space.

Recommended for you

Stellar nursery blooms into view

December 13, 2017

The OmegaCAM camera on ESO's VLT Survey Telescope has captured this glittering view of the stellar nursery called Sharpless 29. Many astronomical phenomena can be seen in this giant image, including cosmic dust and gas clouds ...

Bright areas on Ceres suggest geologic activity

December 13, 2017

If you could fly aboard NASA's Dawn spacecraft, the surface of dwarf planet Ceres would generally look quite dark, but with notable exceptions. These exceptions are the hundreds of bright areas that stand out in images Dawn ...

Juno probes the depths of Jupiter's great red spot

December 12, 2017

Data collected by NASA's Juno spacecraft during its first pass over Jupiter's Great Red Spot in July 2017 indicate that this iconic feature penetrates well below the clouds. Other revelations from the mission include that ...

New eruptions detected in two luminous blue variables

December 12, 2017

(—Astronomers report the detection of new eruptions in two luminous blue variables, known as R 40 and R 110, located in the Magellanic Clouds. The finding, presented December 5 in a paper published on the arXiv ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.