Here on Earth we play around with CCD cameras that boast a million pixels. But, can you imagine what a billion pixels could do? That’s the plan for ESA’s Galaxy-mapping Gaia mission. One hundred six electronic plates are being carefully integrated together to add up to the largest digital camera ever built for space… and its mission is to chart the Milky Way.
Beginning in 2013, Gaia’s five year mission will be to photograph a billion stars within our own galaxy – determining magnitude, spectral characteristics, proper motion and dimensional positioning. This information will be gathered by its charge coupled device (CCD) sensor array. Each of the 106 detectors are smaller than a normal credit card and thinner than a human hair. Put simplistically, each plate holds its own array of light-sensitive cells called photosites. Each photosite is its own pixel – just one tiny cell in the whole body of a photograph that could contain hundreds of thousands of pixels! When incoming light strikes the photosite, the photoelectric effect occurs and creates electrons for as long as exposure occurs. The electrons are then kept “stored” in their individual cells until a computer unloads the array, counts the electrons and reassembles them into the “big picture”.
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And what a picture it will be…
In a period of a month, technicians managed to delicately assemble the CCD plates onto the support structure, leaving only a 1 mm gap between them. “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. Upon completion, there will be seven rows of CCD composites with a main bank of 102 strictly dedicated to star detection. The remaining four will monitor image quality of each telescope and the stability of the 106.5º angle between the two telescopes that Gaia uses to obtain stereo views of stars. And, just like cooling a smaller CCD camera, the temperature needs to be maintained at -110ºC to keep up the sensitivity.
Gaia might be heavy on imaging capabilities, but she’s light on weight. The majority of the spacecraft, including the support structure is crafted from a ceramic-like material called silicon carbide. Resistant to warping in extreme temperature conditions, the whole support structure with its detectors weighs in at only 20 kg. She’ll sail out to Lagrange Point L2 – 1.5 million kilometers behind the Earth – where twin telescopes will capture perhaps 1% of our galaxy’s stellar population. While that may seem like a small amount, the information that Gaia’s three-dimensional star map will provide can reveal much more than we already know about the composition, formation and evolution of the Milky Way.
Original Story Source: ESA News.