Roland Piquepaille's Technology Trends
How new technologies are modifying our way of life

lundi 13 septembre 2004

Gaia is an ambitious project from the European Space Agency to create the most precise map of a billion stars in our Galaxy and millions of other celestial objects invisible from current telescopes. When the spacecraft is launched in 2010, it will carry the most sensitive cameras ever made. Its billion-pixel camera will be in fact composed of 170 separate cameras, tiled together in a mosaic to register every object that passes through the field of view. Each individual camera or 'charge-coupled device' (CCD) will have a resolution of almost nine million pixels. Gaia will take images for five years. The above link will provide you with more details about this billion-pixel camera, but here I chose to focus on a particular aspect of the mission: checking the usually unobversable asteroids between the Sun and the Earth because of light conditions. Read more...

Let's start with some details about Gaia's cameras.

Each CCD is itself a major piece of hi-tech kit that converts light into electrical charge and stores it in tiny traps known as ‘pixels’ until the computer reads out this information. With about nine million pixels, Gaia’s CCDs are each between 5 and 10 times larger than those used in digital cameras currently on sale in our shops.

Please note that it's a slight exaggeration. You can buy multi-million pixels cameras for several years now.

The size of each CCD presents some unique manufacturing challenges. Even in the purest silicon, defects can occur. Typically, with the CCDs that are used in our digital cameras on Earth, perhaps 20 or more are manufactured from the same silicon wafer and one or two rejects are tolerable.
However, the Gaia CCDs are so large that only two will fit onto each silicon wafer. So the chance of a defect occurring in a Gaia CCD is considerable.

The news release from ESA then focuses on how to refine the manufacturing process, so please read it for additional information.

Now it's time to turn to one interesting part of the sky, the 'blind spot' found between the Sun and Earth’s orbit, as you can see below.

Gaia blind spot Gaia spacecraft should be ideally situated to check the asteroid blind spot between the Sun and Earth. On the left is an artist's rendition showing which regions of the sky unobservable from Earth could be observed by Gaia. (Credit: Medialab, for ESA)

The image above comes from "Mapping the Galaxy, and watching our backyard," a news release about Gaia published by ESA in July 2004. Here is a link to a Flash animation showing the coverage of this asteroid blind spot by Gaia over time.

Here are more comments from ESA about this area of the sky.

From Earth, we can only observe this area during the daytime (and even then only on clear days without cloud cover), but it is very hard to pick out small objects such as asteroids, because the Sun’s glare renders them virtually invisible.
These asteroids are sometimes moving near enough to Earth to cause concern, but we may not find out about them until they have moved far enough away from the Sun to be seen by a telescope. One particular large group of asteroids, known as the Atens, spends its time weaving between the Sun and Earth’s orbit.

ESA writers were certainly in a bragging mood when they concluded with this.

With the help of its bird’s eye view from space, and its unprecedented accuracy, Gaia is the ideal candidate for keeping track of the Atens, and similar families of asteroids coming close to our home.

For more information about Gaia, you can check this overview or Gaia's home page for even more details, including image and multimedia galleries.

Sources: Various documents from the European Space Agency about Gaia

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