Friday, April 25, 2014
The James Webb Space Telescope (JWST) is one of the most ambitious satellites ever constructed, from its complex construction, launch and deployment, to its orbit around the Earth-Sun L2 Lagrange Point. This orbit is outside the Earth's orbit of the Sun where the combined gravitational pull of the Sun and Earth provides precisely the centripetal force required to orbit with them.
The L2 Lagrange Point is also far enough away from the Earth to avoid the Earth’s infrared radiation that would interfere with the sensitivity of JWST’s instruments. The telescope will sense light in the infrared, and therefore must be cooled to very low temperatures, necessitating an elaborate shade that will shield the mirror from the sun. The shade is a complex mechanical structure that must be folded like an elaborate origami for launch, and then perfectly unfolded to the size only slightly smaller than a basketball court in deep space.
Exelis is working to make this complicated endeavor come off without a hitch when it launches in 2018. Engineers at Exelis GS, as part of a Northrop Grumman-led team, are integrating components to form the optical telescope element — the portion of the telescope that will collect light and provide sharp images of deep space. And IDL, the scientific programming language created by Exelis VIS, was used to create the test planning tool that runs tests for the instrument modules, according to Scott Antonille at NASA's Goddard Space Flight Center.
The testing tool was built with IDL to test the instrument package — the optics and instruments known as the Integrated Science Instrument Module (ISIM). The tool can test all the combinations of light source inputs at different wavelengths across the various instruments. "These very specific tests can be run through the ground system that exercises the actual instruments to make sure they're not running outside the performance envelope," said Antonille.
The test planning tool, largely written in IDL, tracks the useful life of various instrument components, determines how many filter wheel or focus actuations they'll use, and how long they'll be running the test duration. "This is very important because we have 60-90 days of testing scheduled in a cryovac chamber which is very expensive, so optimization is important," according to Antonille.
Some of the testing of JWST's instrumentation will be run in NASA's thermal-vacuum chamber at Goddard Space Flight Center that will expose the instrumentation to conditions similar to those found in the deep space environment. This will be the last, good opportunity to ensure all the instruments are performing as expected where they can be easily fixed. Once testing of the ISIM is complete, it will be shipped to Johnson Space Flight Center and integrated into the telescope to undergo final testing.
JWST is the successor to the Hubble Space Telescope. When the Hubble telescope was designed, it was expected that it would be able to see the first galaxies forming in the early universe, but that didn't happen. Now researchers behind JWST are hoping to probe the early universe by gathering some of the earliest, most distant light. Antonille says that JWST is a versatile science instrument. "Along with the ability to see near the dawn of the universe and observe galaxies as they formed in the early universe, instrument modes like interferometry will allow observation of exoplanets [planets outside the solar system]," says Antonille.
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