Gaia Mission Passes Vital Tests

by Jenny Winder on September 20, 2012

Want to stay on top of all the space news? Follow @universetoday on Twitter

Caption: Fully integrated Gaia payload module with nearly all of the multilayer insulation fabric installed. Credit: Astrium SAS

Earlier this month ESA’s Gaia mission passed vital tests to ensure it can withstand the extreme temperatures of space. This week in the Astrium cleanroom at Intespace in Toulouse, France, had it’s payload module integrated, ready for further testing before it finally launches next year. This is a good opportunity to get to know the nuts and bolts of this exciting mission that will survey a billion stars in the Milky Way and create a 3D map to reveal its composition, formation and evolution.

Gaia will be operating at a distance of 1.5 million km from Earth (at L2 Lagrangian point, which keeps pace with Earth as we orbit the Sun) and at a temperature of -110°C. It will monitor each of its target stars about 70 times over a five-year period, repeatedly measuring the positions, to an accuracy of 24 microarcseconds, of all objects down to magnitude 20 (about 400,000 times fainter than can be seen with the naked eye) This will provide detailed maps of each star’s motion, to reveal their origins and evolution, as well as the physical properties of each star, including luminosity, temperature, gravity and composition.

The service module houses the electronics for the science instruments and the spacecraft resources, such as thermal control, propulsion, communication, and attitude and orbit control. During the 19-day tests earlier this month, Gaia endured the thermal balance and thermal-vacuum cycle tests, held under vacuum conditions and subjected to a range of temperatures. Temperatures inside Gaia during the test period were recorded between -20°C and +70°C.

“The thermal tests went very well; all measurements were close to predictions and the spacecraft proved to be robust with stable behavior,” reports Gaia Project Manager Giuseppe Sarri.

For the next two months the same thermal tests will be carried out on Gaia’s payload module, which contains the scientific instruments. The module is covered in multilayer insulation fabric to protect the spacecraft’s optics and mirrors from the cold of space, called the ‘thermal tent.’

Gaia contains two optical telescopes that can precisely determine the location of stars and analyze their spectra. The largest mirror in each telescope is 1.45 m by 0.5 m. The Focal Plane Assembly features three different zones associated with the science instruments: Astro, the astrometric instrument that detects and pinpoints celestial objects; the Blue and Red Photometers (BP/RP), that determines stellar properties like temperature, mass, age, elemental composition; and the Radial-Velocity Spectrometer (RVS),that measures the velocity of celestial objects along the line of sight.

The focal plane array will also carry the largest digital camera ever built with, the most sensitive set of light detectors ever assembled for a space mission, using 106 CCDs with nearly 1 billion pixels covering an area of 2.8 square metres

After launch, Gaia will always point away from the Sun. L2 offers a stable thermal environment, a clear view of the Universe as the Sun, Earth and Moon are always outside the instruments’ fields of view, and a moderate radiation environment. However Gaia must still be shielded from the heat of the Sun by a giant shade to keep its instruments in permanent shadow. A ‘skirt’ will unfold consisting of a dozen separate panels. These will deploy to form a circular disc about 10 m across. This acts as both a sunshade, to keep the telescopes stable at below –100°C, and its surface will be partially covered with solar panels to generate electricity.

Once testing is completed the payload module will be mated to the service module at the beginning of next year and Gaia will be launched from Europe’s Spaceport in French Guiana at the end of 2013.

Find out more about the mission here

About 

Science writer at Urban Times URBNFUTR & 21st Floor. Broadcaster on Under British Skies for Astronomy.FM Radio. Amateur Astronomer. Skeptic. Rational Thinker. Science Geek. Music Lover. Harpist. Singer. Book Worm. BSL User. WooBasher. Dangly Earring Wearer. OU Junky

SJStar September 20, 2012 at 4:51 PM

Hooray!! At last at great UT story with some real meat!

Gaia will likely change our knowledge of our Galaxy and whose resources will give astronomical data to be analysed for many decades to come, and keeping astronomers busy in finding out about what it all means. Combined with the Hipparcos data, our knowledge of all the galactic stars means we might get a glimpse of the Milky Way’s evolution — including a detailed chemical history of the stars within about 250pc. The ESA has wisely Its combined astrometric, photometric and spectroscopic data will draw out our section of the galaxy in minute detail. (I am still amazed that 120 spectra will be taken of every one billion stars over five years!) They predict we will also now the ages of all these stars (between 12th and 20th magnitude) to accuracies of about 13%.

Also the astrometric accuracy is as extrodinary. Hipparcos gave us about 1 mas (milli-arc second accuracy. Gaia is around 7 micro arcseconds! Hipparcos was down to 12.4v magnitude, Gia is 20th in blue or 22nd in red!

What is exciting too, it the means of exploring faint objects in the solar system, variable stars, visual and eclipsing binaries, halo streams of stars (via an instrument known as Hermes), and even exoplanets.

I believe this mission will in hindsight be declared one of the most important watershed moments in astronomy and astrophysics, and when combined with some similar future mission in the 2040s or 2050s, will forever change our perspective of our little place in the Universe.

With all this effort we can only hope the mission is as successful as the amount of planning that has taken place in the last two decades is plainly extraordinary.

Those interested in reading more about this mission should read J.H.J. de Bruijne’s middle-level paper
Science performance of Gaia, ESA’s space-astrometry mission.” (Downloadable pdf)

I look forward with enthusiasm future articles on the upcoming mission. (It might not give as many pretty picture as the Mars rover Curiosity, but it will give a heck of a lot of interesting data.)

Thanks for this story update!

zetetic elench September 20, 2012 at 5:21 PM

no problems generating sufficient electricity there.

Aqua4U September 20, 2012 at 5:59 PM

Whoa Nelly! A 1,000 megapixel camera, with a 1.5 meter mirror, in space! Yes!

SJStar September 20, 2012 at 6:51 PM

Eh? This has nothing to do with the HST as it doesn’t take pictures of the sky. It is an astrometric satellite!

Aqua4U September 21, 2012 at 12:12 AM

From the article above; “Gaia contains two optical telescopes that can precisely determine the
location of stars and analyze their spectra. The largest mirror in each
telescope is 1.45 m by 0.5 m”

From ESA’s Gaia Mission webpage: “Gaia will significantly improve on Hipparcos for a number of different
reasons. For example, the collecting area of the primary mirrors means
that Gaia will collect more than 30 times the light of its predecessor,
allowing for more sensitive and accurate measurements.”

So indeed this mission WILL image the stars. THIS is how it gathers
data, and is called a ‘sky survey’. You need to do some homework SJ….

Emmanuel Joliet September 22, 2012 at 6:18 AM

Sure, taken images, actually frames like a movie but the result won’t be beautiful optical images, will be a catalogue

Aqua4U September 21, 2012 at 12:15 AM

Key word in my statement is _legacy. Fool.

From the article above; “Gaia contains two optical telescopes that can precisely determine the location of stars and analyze their spectra. The largest mirror in each telescope is 1.45 m by 0.5 m”

From ESA’s Gaia Mission webpage: “Gaia will significantly improve on Hipparcos for a number of different reasons. For example, the collecting area of the primary mirrors means that Gaia will collect more than 30 times the light of its predecessor, allowing for more sensitive and accurate measurements.”

So indeed this mission WILL image the stars. THIS is how it gathers
data, and is called a ‘sky survey’. You need to do some homework SJ….

SJStar September 21, 2012 at 2:09 AM

From your crazy logic here, Hipparcos would have produced lots of images, would it not? Where are they? Please show me a Hipparcos image. I’ve never seen one, and nor have you. Why not?

The reason is that the detectors work like vision by the eye. It doesn’t record a built up image, it only records what it sees through a slit 2×5mm. Each lens within the satellite acts like a eye pupil, whose field of view is about 12×30 arcsec.

SJStar September 21, 2012 at 2:33 AM

Oh. I should have said. You need the large area of the mirrors to get down to 20th-22nd magnitude. My eyes can only see down to 6.5 magnitude. Either way, limitations are only the sensitivity of the light detector and the size of the aperture.

SJStar September 21, 2012 at 2:47 AM

To quote a paper by Amir Vosteen et al. that was given at the International Conference on Space Optics in Greece in October 2010, this is how the ‘eyes’ work on Gaia,

The optical path of the WFS, extending between the slit and the GAIA focal plane, includes a beam splitter, imaging optics and a micro-lens array. The imaging optics images the exit apertures of the GAIA telescopes next to each other on the micro-lens array. The micro-lenses each produce an image of the entrance slit on a dedicated CCD at the GAIA focal plane. Thus each micro-lens corresponds to a sample of the telescope pupil and the position of the star image it produces depends on the wave front tilt at that point of the pupil (Shack Hartmann sensor principle). Each WFS instrument ‘sees’ both telescopes of GAIA, allowing to measure wave front distortion at two different GAIA pointing directions.

and that’s how to do your homework…

Comments on this entry are closed.

Previous post:

Next post: