JWST testing dodges threat from government closure
BY STEPHEN CLARK
Posted: 23 October 2013
NASA kept a skeleton crew on the job during the partial U.S. government shutdown to watch over a critical component of the James Webb Space Telescope locked inside a cryogenic chamber to test its resiliency to the harsh conditions of space.
Designed to peer deep into the universe, study ancient galaxies and observe extrasolar planets in more detail than ever before, JWST is the successor to the Hubble Space Telescope and promises to rewrite textbooks following its launch in 2018.
The telescope's Integrated Science Instrument Module, or ISIM, houses the mission's four main infrared instruments. The ISIM began the first of three cryogenic tests in August. The ongoing test was added as an effort to reduce risk.
If the 16-day shutdown continued longer than it did, officials were concerned they would have to stop the test and remove the ISIM, which currently contains two of JWST's four science instruments, from Goddard's cryogenic chamber.
Such a move would push back work on the telescope's instrument package for months, or added the risk of troubles on future tests, so NASA opted to keep a group of engineers at Goddard to babysit the hardware, which remained at cryogenic temperatures.
"We had to stop the test work and put the ISIM into a safe state that could be maintained by a small crew," said Matt Greenhouse, ISIM project scientist at Goddard. "We remained at cryogenic temperature throughout the shutdown as the procedure for warming to ambient temperature requires approximately three weeks due to safety limitations on thermal gradients in the ISIM."
Greenhouse said testing of the ISIM resumed Oct. 17, resulting in about two weeks of delays instead of much longer.
"If the shutdown had gone longer, we eventually would have had to abort the test and accept increased risk in getting through the subsequent [cryogenic] tests," Greenhouse said, adding the JWST project will still be able to achieve the most important goals of the first test.
The ISIM's first cryogenic test is due to be over by the end of the year. Next year, workers will install the telescope's other two instruments, which arrived at Goddard this summer, before two more tests to wring out potential problems with the instruments and their support systems.
In October 2015, engineers will have the instruments ready for assembly with JWST's mirrors, focal plane and backplane. The combined telescope and instrument segment will travel to NASA's Johnson Space Center in Houston for another cryogenic test before shipment to Northrop Grumman Corp. in Southern California for attachment to the spacecraft bus.
NASA says the launch of JWST is scheduled for October 2018 aboard a European-provided Ariane 5 rocket from French Guiana.
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