NASA takes 2,000lb heart of space telescope on extreme test ride

NASA James Webb space telescope continues march toward launch

nasa isim
NASA engineers say they have achieved previously unheard of feat: Create from scratch about 900 components that can survive more than six and a half times the force of gravity,  fit in a seven foot-long carlike body that weighs almost  2,000lbs and survive -411 degrees Fahrenheit temperatures.

The engineering breakthrough is officially known as the  Integrated Science Instrument Module Flight Structure, will serve as the structural heart of the James Webb Space Telescope.  the Integrated Science Instrument Module Flight Structure will serve as the structural heart of the James Webb Space Telescope, NASA stated.  The ISIM structure holds all of the instruments needed to perform science with the telescope in very tight alignment.

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"It is the first large, bonded composite space flight structure to be exposed to such a severe environment," said Jim Pontius, ISIM lead mechanical engineer at NASA's Goddard Space Flight Center in Greenbelt, Md.

The ISIM structure is unique NASS said because NASA Goddard engineers created it without any previous guidelines.  The system combines two currently existing composite materials - what NASA calls T300 and M55J -- to create the unique composite laminate.

The engineers discovered that by combining two composite fiber materials, they could create a carbon fiber/cyanate-ester resin system that would be ideal for fabricating the structure's 3-inch diameter square tubes. This was confirmed through mathematical computer modeling and rigorous testing.

From NASA: "To assemble the ISIM structure, the team found it could bond the pieces together using a combination of nickel-iron alloy fittings, clips, and specially shaped composite plates joined with a novel adhesive process, smoothly distributing launch loads while holding all instruments in precise locations -- a difficult engineering challenge because different materials react differently to changes in temperature. The metal fittings also are unique. They are as heavy as steel and weak as aluminum, but offer very low expansion characteristics, which allowed the team to bond together the entire structure with a special adhesive system."

A  26-day test to specifically test whether ISIM would behave as predicted as it cooled from room temperature to the frigid -- important since the science instruments must maintain a specific location on the structure to receive light gathered by the telescope's 21ft  primary mirror. If the contraction and distortion of the structure due to the cold could not be accurately predicted, then the instruments would no longer be in position to gather data.

NASA said that despite repeated cycles of testing, the ISIM  did not crack. Its thermal contraction and distortion were precisely measured to be 170 microns -- the width of a needle -- when it reached 411 degrees Fahrenheit.  NASA noted that the same tests will be used to test other Webb telescope systems, including the telescope backplane, the structure to which the Webb telescope's 18 primary mirror segments will be bolted when the observatory is assembled.

Earlier this year NASA tested some of the Webb's larger - 46 lb -- mirror segments to -414 degrees Fahrenheit.

The tests are being handled at NASA's Marshall Space Flight Center X-ray & Cryogenic Facility,  the world's largest X-ray telescope test facility.   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 a little over 4ft in diameter, NASA stated.

The Webb Telescope mirror will fly 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.

The Webb telescope is scheduled for launch in 2014.

Follow Michael Cooney on Twitter: nwwlayer8  

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