From rxpgnews.com
Super-tough sunshield to fly on the James Webb Space Telescope
By NASA/Goddard Space Flight Center,
Nov 12, 2008 - 4:59:37 AM
GREENBELT, Md. - Imagine sunglasses that can withstand the severe cold and heat of space, a barrage of radiation and high-speed impacts from small space debris. They don't exist, but Northrop Grumman engineers have created a Sunshield for NASA's James Webb Space Telescope that can withstand all of those elements. The space telescope needs a Sunshield to block heat from the sun so its cameras and instruments can operate properly a million miles from the Earth, when it launches in 2013.
Any satellite that flies in the depths of space has to be able to withstand the rigors of space, including the icy cold or the intense heat and radiation of a solar flare. Temperatures in space can range from a super-hot 400 K (260 F) to a frigid 30 K (-406 F). In addition, the Webb telescope's Sunshield will be bombarded with tiny meteorites (sand-like grains) and radiation in space, so it has to be tough. It has to stand up against those things, as well as tension and aging under the extreme space environments. The Sunshield's 'aging' occurs from extreme sunburn, said Mark Clampin, NASA's Webb Telescope Observatory Project Scientist at Goddard Space Flight Center, Greenbelt, Md.
Blocking light and heat from the sun will keep the observatory operating at cryogenic (cold) temperatures, enabling its infrared sensors to see distant galaxies, early stars, and planetary systems. That's important because infrared sensors actually measure the heat given off from far away galaxies and stars. Shaded and protected from the Sun, the Sunshield allows the telescope to cool down to a nice and chilly 40 K (-387 F). Any warmer than that and the heat given off from the telescope would corrupt the data. If you could imagine, this would be like going outdoors applying sunscreen of 'SPF' of 1.2 million on your skin, said Martin Mohan, Program Manager for the Webb Telescope at Northrop Grumman, Redondo Beach, Calif. Previous to this crucial technology, materials with thermal properties that reflect the sun without being heated did not exist.
Jonathan Gardner, NASA's Deputy Senior Project Scientist for the Webb Telescope at Goddard said Infrared is heat radiation. In order to see the faint glow of infrared heat from distant stars and galaxies, the telescope has to be very cold. If the telescope were heated by sunlight or the warm glow of the Earth, the infrared light emitted by the telescope would outshine its targets, and it wouldn't be able to see anything.
It would be a lot like going to a movie theatre where they never turned down the house lights. Your eyes wouldn't see the screen very well because they would be swamped by the photons coming from the theatre surroundings
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