NASA set to cryogenically freeze test critical satellite mirrors

NASA’s James Webb satellite will shoot the stars in 2014

full scale model of Webb
NASA said it will this week move some of the larger - 46 lb -- mirror segments of its future James Webb Space Telescope into a cryogenic test facility that will freeze the mirrors to -414 degrees Fahrenheit. 

Specifically NASA will freeze six of the 18 Webb telescope mirror segments at the  X-ray and Cryogenic Facility, or XRCF, at NASA's Marshall Space Flight Center in Huntsville, Ala., in a test to ensure the critical mirrors can withstand the extreme space environments.  All 18 segments will eventually be tested at the site. 

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Marshall's X-ray & Cryogenic Facility is the world's largest X-ray telescope test facility and a unique, cryogenic, clean room optical test location, NASA stated. The test chamber takes approximately five days to cool a mirror segment to cryogenic temperatures. As this cooling takes place, engineers will measure in extreme detail how the shapes of the mirrors change, simulating how they'll react to space temperatures. 

The Webb Telescope mirror segments are made of from beryllium, which is strong and light and each segment of the total 18 hexagonal-shaped mirror segments onboard is 4.26 feet in diameter. 

According to the NASA Web site, when the primary satellite mirror is assembled in space, it will include three different shapes of mirror segments: 6 are "A" segments, 6 are "B" segments and 6 are "C" segments.  The XRCF will collect data from all three sizes - "A, B and C"-- a first for these in the cryogenic facility. This test will also include the engineering development unit, the first primary mirror segment of the Webb telescope that has met flight specifications at ambient temperatures, NASA stated. 

The Webb Telescope mirror will travel into space folded up and will unfold after launch. The telescope will have a large mirror, 21.3 feet in diameter and a sunshield the size of a tennis court, NASA stated.   The Webb  satellite will reside in an orbit about 1 million miles from the Earth. 

There will be four science instruments on JWST: a near-infrared (IR) camera, a near-IR multi-object spectrograph, a mid-IR instrument, and a tunable filter imager. The satellite's instruments will be designed to work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range. It will be sensitive to light from 0.6 to 27 micrometers in wavelength. 

Like NASA's current WISE satellite the spacecraft must be kept cold to see stars and galaxies infrared light.   NASA said because warm objects give off infrared light, or heat, if Webb's mirror was the same temperature as say the  Hubble Space Telescope's, the faint infrared light from distant galaxies would be lost in the infrared glow of the mirror. Thus, Webb needs to be very cold with its mirrors at around -364 degree F. The mirror as a whole must be able to withstand very cold temperatures as well as hold its shape. 

The Webb telescope is scheduled for launch in 2014. 

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