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Instrument Delays Seen as No Threat to JWST Cost or Launch Date

James Webb Space Telescope's NIRCam. Credit: University of Arizona photo

WASHINGTON — The late delivery of a pair of critical instruments for the James Webb Space Telescope (JWST) poses no threat to the flagship observatory’s development costs or launch date, a senior NASA official said Nov. 15.

“As long as they show up before next fall, we’re definitely on,” Christopher Scolese, director of the Goddard Space Flight Center in Greenbelt, Md., said Nov. 15 at a Capitol Hill luncheon hosted by the Space Transportation Association.

The instruments — the Near-infrared Spectrograph (NIRSpec) and the Near-infrared Camera (NIRCam) — are notionally slated to arrive at Goddard this spring.

“Their delivery is targeted in the April timeframe,” Geoff Yoder, program director for the James Webb Telescope, said Nov. 14. Yoder spoke here during a meeting of the NASA Advisory Council’s Science Committee. Yoder, who earlier this year was running NASA’s astrophysics division, took over as the telescope’s program director in May from Rick Howard, who has retired from the agency.

Lockheed Martin Advanced Technology in Palo Alto, Calif., is building NIRCam using detectors made by Teledyne Imaging Sensors of Camarillo, Calif.

NIRSpec is being built by Astrium GmbH in Ottobrunn, Germany. It is one of two European sensors in Webb’s instrument payload. The spectrometer had to be reassembled after a crack was discovered in the instrument’s optics bench in 2011. An optics bench is hardware to which more sensitive optical components are affixed. As of Nov. 14, “NIRSpec instrument reassembly is complete,” Yoder said.

Problems with NIRCam, construction of which is being overseen by University of Arizona astronomer and principal science investigator Marcia Rieke, first showed up during cryogenic testing at Lockheed earlier this year.

“Two issues were found in the first cryo test: a light leak in the long wavelength arms and also a scattered light path just outside the normal field of view,” Rieke said in a Nov. 15 email. “The light leak was fixed by applying some opaque epoxy around the edge of the leaking area and the scattered light path has been fixed by inserting some baffle vanes into the region just ahead of the detectors in the optical path. These vanes around the edge of the field of view will block the scattered light.”

Yoder told the NASA Advisory Council’s Science Committee that these fixes, which essentially involve modifying NIRCam’s casing to deflect stray light away from sensitive detectors, “should work.”

As of Nov. 18, NIRCam was in a cryogenic chamber at Lockheed’s Palo Alto facility, where cold testing was scheduled to continue through January, Rieke said.

Excluding the costs of University of Arizona support and Teledyne’s detector subcontract, Lockheed’s NIRCam contract is worth about $300 million, Rieke said.

The James Webb Space Telescope is to be ready for launch by Oct. 31, 2018, Yoder told NASA Advisory Council members. NASA and ESA officials are in contact with launch provider Arianespace to determine whether the launch can be pushed up to the beginning of that month. The telescope is to launch aboard an Ariane 5 rocket.

NASA now estimates the flagship astrophysics observatory will cost $8.8 billion to build and operate in space for its primary five-year mission to observe some of the oldest, most distant objects and events in the universe.

Because NIRCam and NIRSpec will not arrive until the spring, engineers at Goddard will put the telescope’s ATK-built Integrated Science Instrument Module through its next round of cryogenic tests with only two of the four imaging instruments that eventually will be slotted there. Those two instruments, the European-built Mid-Infrared Instrument and the Canadian Space Agency’s Fine Guidance Sensor/Near Infrared Imager and Slitless Spectrograph, arrived at Goddard in May and June, respectively.

Initial tests on the partially integrated science module will begin in “late winter or early spring,” prior to the arrival of NIRCam and NIRSpec, Scolese said Nov. 15.

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