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MissionWhat will DS1 do on its mission? |
MICAS works by projecting images onto a CCD. A CCD typically has a two-dimensional array of hundreds of thousands of charge-isolated wells, each representing a pixel. Light falling on a well is absorbed by a photoconductive substrate, such as silicon, and releases a quantity of electrons proportional to the intensity of the light. The CCD detects and stores an accumulated electrical charge representing the light level on each well. These charges are subsequently read out for conversion to digital data.
XUV photons (extreme ultraviolet light, which comes from the Sun, among other places) are energetic enough to slightly damage the crystalline structure in the CCD. In 1996 the shutter jammed open for a few hours in the CCD of the SOHO mission (a Solar observatory mission) as a solar active region was crossing the disk; and this left a little "burn" on the field of view near the southeast edge of the Sun. This effect is also seen on the Yohkoh spacecraft, which uses a similar CCD to image soft X-rays (around 1 Angstrom wavelength) from the Sun.
The CCDs on all the instruments are kept very cool (about 200 Kelvin, or -80 degrees Celsius) to make them more sensitive. Because the CCD is cold, stray gas molecules inside the spacecraft tend to stick to it -- so a deposit tends to build up slowly on the CCD. Briefly heating the CCD can drive off this layer of contamination.
What is MICAS?
What is electromagnetic radiation?
More about radio waves and electromagnetic radiation
What's an electron?
