JWST On Cost, On Schedule after Shutdown
CORRECTION: An earlier version of this story should have said the Mid-Infrared Instrument’s cryogenic compressor will be delivered to NASA a few years from now, not this December. In addition, Teledyne Imaging Sensors is based in Thousand Oaks, Calif., not Huntsville, Ala.
WASHINGTON — The two-week U.S. government shutdown that idled nearly 18,000 NASA civil servants had a minimal effect on the James Webb Space Telescope (JWST), which nevertheless is grappling with a number of technical issues that threaten to eat into the 14 months of reserve funding the project has set aside, NASA officials told a National Research Council panel Nov. 4.
Although it has forced NASA to tweak the flagship astrophysics mission’s testing schedule, “the shutdown did not impact the launch date” of October 2018, Eric Smith, acting director of the JWST program office at NASA headquarters here, told the National Research Council’s Committee on Astronomy and Astrophysics.
Even so, the shutdown has nibbled away part of the funding reserve the JWST program office established after the spacecraft’s cost estimate exceeded $8 billion and its launch was postponed another couple of years to 2018. On top of that, JWST’s instruments continue to be pestered by technical difficulties that could gobble up more schedule and funding reserves even as JWST prepares for the most difficult phase of its development: final assembly and testing of the integrated spacecraft.
Each day that JWST teams spend fixing problems with the instruments delays the day that the observatory’s Optical Telescope Element — which exists at the moment as an unassembled collection of mirrors and structural components at various NASA and contractor facilities — is mated with the Integrated Science Instrument Module and the four instruments it hosts. The combined assembly is to be tested in 2016 in an enormous cryogenic vacuum chamber at the Johnson Space Center in Houston in what is expected to be one of the most time-consuming and difficult trials the telescope will face before its launch. “That’s a big test,” Smith said. “We’ve got to go in with much reserve as we can have.”
JWST, which will observe distant galaxies in the infrared spectrum from a location about 1.5 million kilometers from Earth, is now slated to launch in October 2018 from French Guiana aboard Europe’s Ariane 5 rocket. NASA expects building JWST and operating it during its five-year primary mission to cost $8.8 billion, up from the $5 billion the agency estimated in 2008 when construction began in earnest with a goal of launching in 2014.
Roughly 25 percent of JWST’s annual budget is being held in reserve as a hedge against unforeseen development problems. That translates into about “14 months of funded schedule reserve on JWST,” NASA Astrophysics Director Paul Hertz told the committee.
“In principle, you could launch JWST 14 months early, if nothing goes wrong,” Matt Mountain, director of the Space Telescope Science Institute in Baltimore, told SpaceNews in a phone interview during the government shutdown. The institute will serve as JWST’s science and flight operations center.
The only thing that happened during the recent government shutdown that will eat into JWST’s reserves, Smith said, is the delay of a cryogenic test at the Marshall Space Flight Center in Huntsville, Ala. The telescope’s-built backplane, one of the items on the so-called critical path that paces JWST’s whole schedule, started cryogenic testing there in late September only to be interrupted by the partial government shutdown that began Oct. 1.
After the shutdown began, the cryo chamber had to be brought back up to room temperature, Smith said. When Marshall employees returned to work Oct. 17, the chamber had to be cooled back down. In all, extra warming and cooling of the chamber means “three weeks of [the] critical path [were] used by the shutdown,” Smith said. The two-piece backplane, which will support JWST’s 18 beryllium mirrors, instruments and other elements, is due to be shipped the week of Nov. 11 to JWST prime contractor Northrop Grumman Corp.’s Space Park facility in Redondo Beach, Calif., Smith said.
Meanwhile, at the Goddard Space Flight Center in Greenbelt, Md., the shutdown curtailed cryogenic testing of two of JWST’s four primary science instruments.
All four of those instruments are at Goddard, which is managing construction of the massive observatory. By August, two of those instruments — the Fine Guidance Sensor and the Mid-Infrared Instrument — had been bolted onto the telescope’s main instrument housing and placed in a cryogenic vacuum chamber for environment testing. The other two instruments, the Near Infrared Spectrograph and the Near Infrared Camera, each delivered about a year late to Goddard, were not scheduled to be part of the first round of cryo tests, Smith said.
Unlike at Marshall, the Goddard chamber was allowed to remain chilled down. “There was a skeleton crew that just stayed there and looked at a temperature gauge,” Smith said.
The shutdown prevented NASA from finishing observations of the Fine Guidance Sensor and the Mid-Infrared Instrument that began in August, Smith said. Doing so would have taken another two weeks in the chamber after the shutdown ended, and NASA elected not to go that route.
Instead, JWST’s main instrument housing will be pulled out of the chamber on schedule — “in another 10 days or so,” Smith said Nov. 4 — and the Near Infrared Spectrograph and the Near Infrared Camera will be added in preparation for a second round of cryogenic tests in “late spring of 2014,” Smith said. A third instrument cryogenic test would follow in 2015, after the four instruments and their housing have been subject to vibration and acoustic tests, Smith said.
Moving the next round of cryogenic testing to the spring will not tap JWST’s reserves or force NASA to skip any scheduled hardware tests, Smith said.
Before the instruments at Goddard go into the cryo chamber, all but the Mid-Infrared Instrument will have to be fitted with new infrared detectors, Smith said. These crucial components, made by Teledyne Imaging Sensors of Thousand Oaks, Calif., were discovered to be defective in Defense Department testing for another program, Smith said.
Up for a detector swap on Nov. 18 is the Near Infrared Camera, which was built by Lockheed Martin Advanced Technology Laboratory of Palo Alto, Calif., Smith said. The Near-Infrared Spectrograph, from Astrium GmbH of Ottobrunn, Germany, will have its detectors replaced later, as NASA also has to replace the instrument’s microshutters and did not want to disassemble the instrument twice, Smith said.
NASA also faces a number of technical issues with other JWST components, including its secondary mirror and a cryogenic cooler intended to keep the Mid-Infrared Instrument operating at the correct temperature during the telescope’s five-year mission.
JWST’s hexagonal secondary mirror, Smith said, has an unintentional view of the telescope’s tennis-court-sized sunshield. “It’s not seeing the sky,” Smith said. “It’s seeing the sunshield.”
This, he said, is because the “frill” the telescope uses to block out all light but that reflected from JWST’s primary mirror is the wrong shape. “If
“A previous change we made to the frill was too much, so we’ll readjust it,” Smith said. The workaround should be ready in about a month, Smith said.
Also still an issue for the JWST team is a cryogenic cooler for the Mid-Infrared Instrument, which the U.S. Government Accountability Office flagged as a concern in April, citing leaky cryogenic valves. That issue, Smith said Nov. 4, has since been solved. However, there are now problems with the cooler’s compressor, a part of the JWST spacecraft Northrop Grumman is developing, and which is slated for delivery in “a few years,” Smith said.
Meanwhile, the croygenic valves that were repaired now will not be ready until December. They were expected in October, Smith said.
Finally, testers discovered a problem with a series of pins that will separate JWST from the upper stage of the Ariane 5 that launches it to space. The nonexplosive system, Smith said, is generating too great a shock when it releases the pins. The JWST program office thinks “this will be solved in next couple of months, but [it’s] concerning that [we] this got far along” before discovering the problem, Smith said.
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