A total of 106 CCDs make up Gaia’s focal plane. Technicians from Astrium France, the Gaia mission’s prime contractor, are seen bolting and aligning the CCDs onto their support structure, at the company’s facility in Toulouse. The structure (the grey plate underneath the CCDs) weighs about 20 kg and is made of silicon carbide, a material that provides remarkable thermal and mechanical stability. Gaia’s CCDs are provided by e2v Technologies of Chelmsford, UK. Each CCD measures 4.7×6 cm, with a thickness of only a few tens of microns. Precisely fitted together on the support structure, the gap between adjacent CCD packages is about 1 mm. Credits: Astrium |
The
largest digital camera ever built for a space mission has been
painstakingly mosaicked together from 106 separate electronic detectors.
The resulting “billion-pixel array” will serve as the super-sensitive
‘eye’ of ESA’s Galaxy-mapping Gaia mission.
While
the naked human eye can see several thousand stars on a clear night,
Gaia will map a billion stars within our own Milky Way Galaxy and its
neighbours over the course of its five-year mission from 2013, charting
their brightness and spectral characteristics along with their
three-dimensional positions and motions.
In
order to detect distant stars up to a million times fainter than the
eye can see, Gaia will carry 106 charge coupled devices (CCDs), advanced
versions of chips within standard digital cameras.
Developed
for the mission by e2v Technologies of Chelmsford, UK, these
rectangular detectors are a little smaller than a credit card, each one
measuring 4.7×6 cm but thinner than a human hair.
The 0.5×1.0 m mosaic has been assembled at the Toulouse facility of Gaia prime contractor Astrium France.
Technicians spent much of May carefully fitting together each CCD
package on the support structure, leaving only a 1 mm gap between them.
Working in double shifts in strict cleanroom conditions, they added an
average four CCDs per day, finally completing their task on June 1.
“The
mounting and precise alignment of the 106 CCDs is a key step in the
assembly of the flight model focal plane assembly,” said Philippe Garé,
ESA’s Gaia payload manager.
A total of 106 CCDs make up Gaia’s focal plane. Technicians from Astrium France, the Gaia mission’s prime contractor, are seen bolting and aligning the CCDs onto their support structure, at the company’s facility in Toulouse. The structure (the grey plate underneath the CCDs) weighs about 20 kg and is made of silicon carbide, a material that provides remarkable thermal and mechanical stability. Gaia’s CCDs are provided by e2v Technologies of Chelmsford, UK. Each CCD measures 4.7×6 cm, with a thickness of only a few tens of microns. Precisely fitted together on the support structure, the gap between adjacent CCD packages is about 1 mm. Credits: Astrium |
The
completed mosaic is arranged in seven rows of CCDs. The main array
comprises 102 detectors dedicated to star detection. Four others check
the image quality of each telescope and the stability of the
106.5-degree angle between the two telescopes that Gaia uses to obtain
stereo views of stars.
In order to increase the sensitivity of its detectors, the spacecraft will maintain their temperature of –110 degrees C.
Gaia’s
CCD support structure, like much of the rest of the spacecraft, is made
of silicon carbide – a ceramic like material, extraordinarily resistant
to deforming under temperature changes.
First
synthesised as a diamond substitute, SiC has the advantage of low
weight: the entire support structure with its detectors is only 20 kg.
Gaia
will operate at the Earth–Sun L2 Lagrange point, 1,5 million kilometers
behind the earth, when looking from the sun, where Earth’s orbital
motion balances out gravitational forces to form a stable point in
space. As the spinning Gaia’s two telescopes sweep across the sky, the
images of stars in each field of view will move across the focal plane
array, divided into four fields variously dedicated to star mapping,
position and motion, colour and intensity and spectrometry.
Scheduled
for launch in 2013, Gaia’s three-dimensional star map will help to
reveal the composition, formation and evolution of the Milky Way,
sampling 1% of our Galaxy’s stars.
Gaia
should also sample large numbers of other celestial bodies, from minor
bodies in our own Solar System to more distant galaxies and quasars near
the edge of the observable Universe.
