WASHINGTON –
Amid rumors of cost growth and technical setbacks, NASA’s James Webb Space Telescope (JWST) recently passed its preliminary design review, a major milestone meant to catch potential problems before the multibillion dollar project moves to the next phase of development.
The hallways and cocktail parties at the National Space Symposium in Colorado Springs, Colo., April 7-10 were rife with talk of a looming $600 million overrun on JWST and a serious technical setback that raised the possibility that the telescope’s designers had chosen the wrong material for its support structure.
Officials at NASA and JWST prime contractor Northrop Grumman Space Technology of Redondo Beach, Calif., said they were flummoxed by the rumors, especially considering that the program had passed its preliminary design review (PDR) the week before, as scheduled. The JWST, the successor to NASA’s Hubble Space Telescope, is slated to launch in 2013.
“What’s kind of irritating me are these rumors out there … that there’s a massive overrun on JWST. It’s just the absolute opposite,” Ed Weiler, NASA associate administrator for science, said April 14. “We have a mission that planned a PDR two-and-a-half years ago for March 2008 and by some miracle … with almost no reserve, [JWST Project Manager] Phil Sabelhaus had a PDR in March 2008.”
What’s more, Weiler said, JWST passed the first time around, something he said not many programs manage to do.
More reviews lay
ahead for JWST, including an
independent cost estimate expected to be completed by summer. While declining – along with
his astrophysics chief, Jon Morse – to
predict what Webb’s Non-Advocate Review team and independent cost estimators might conclude, Weiler said he does not anticipate any unpleasant surprises. “I can’t speak for the independent cost estimate, but we’ve held cost and schedule since 2005 and Phil’s met every single technological milestone,” he said.
Like many rumors, however, the gloom-and-doom scenarios bandied about in recent weeks contain a kernel of truth. But luckily for NASA, talk of a Webb budget debacle, as one source termed it, appear to be greatly exaggerated.
Last fall, JWST’s designers got a scare while testing samples of the carbon composite joints selected to hold together the telescope’s instrument module and backplane, the large structure to which the main sensor’s large hexagonal mirrors are attached. Subjected to temperatures as cold as 30 degrees Kelvin (minus 243 degrees Celsius), the joints failed under less stressful conditions than the designers had predicted.
While the testing showed that the joints were strong enough for the mission, it raised troubling doubts about the designers’ predictive models.
“We went through this whole analysis making sure we had made the samples right,” Sabelhaus told Space News in an April 11 interview. “And eventually what we got to a month or so ago was that the problem wasn’t with the sample, the problem was actually with the modeling.”
Sabelhaus credited Lester Cohen, a structural engineering expert at the Smithsonian Astrophysical Observatory in Cambridge, Mass., with figuring out the tweaks the model needed to accurately predict how the joints would behave under the temperature and pressure stresses they were subjected to during vacuum testing.
Cohen said in an April 14 interview that he never believed there was anything wrong with the materials used for the joint or how the joint was designed. “We found that in this particular case where we have very high thermal stresses, that the models need to be more refined than they were,” he said.
While Cohen did not suspect a materials or engineering problem, Sabelhaus said he did not rule either one out.
“When this problem emerged, until we really found the solution relative to the modeling, we were doing some due diligence on the time and money it would take to go off and look at alternate backplane materials, but we didn’t spend much time on it,” Sabelhaus said. “I can see where someone would have told you we were thinking about that, because we did.”
Sabelhaus said that even when the models did not correlate with the observed results, the joints were still shown to be 1.5 times as strong as they needed to be.
“We feel we’ve basically solved this problem. We’re going to go test some more joints [and] we’re going to do some more modeling before we actually start gluing flight structures together, but we do feel we’ve nailed this problem.”
Sabelhaus said there were cost and schedule impacts resulting from the joint issue, but they were minor. “Overall, from the viewpoint of somebody looking from the outside in, they are going to see zero impact,” he said.
JWST’s budget situation, meanwhile, is more complicated than the modeling issue, making it that much more subject to misinterpretation.
NASA restructured the program in 2005 and delayed JWST’s launch two years to 2013 after several issues caused its total price tag to swell.
JWST program officials estimated that they would have to spend around $3.5 billion to get the telescope built and through its first year of operations. NASA Administrator Mike Griffin, however, ordered the agency’s science division to obtain an independent cost estimate based on more conservative assumptions, resulting in a figure of $4.1 billion – a $600 million difference. Sabelhaus said that in spite of the new, more conservative estimate, the program continued to work toward the more aggressive cost target of $3.5 billion.
“Budgeting JWST at the [more conservative] level would have added $600 million to our budget, but they did not add that money to our budget at the time,” Sabelhaus said. “The decision was made to wait until the time of our confirmation review, which is where we are now.”
Morse said the additional $600 million was set aside as a reserve not included in the official JWST budget, but that this will change once the program gets past this spring’s gauntlet of reviews.
Weiler said Webb’s total price tag – $4.5 billion including 10 years of operations – won’t change as a result of the JWST program adopting the more conservative budget posture later this year.
“The price tag for JWST is the same price tag it was 2.5 years ago. That’s an extremely important point. There has been no cost growth,” Weiler said. “Phil Sabelhaus has kept the project on cost and on schedule and has met all his milestones with increasingly lower reserves each fiscal year of less than 10 percent. And somehow this is being turned into a bad news story by some people out there … I don’t know where this is coming from.”
JWST is scheduled to launch in June 2013 aboard an Ariane 5 rocket the European Space Agency is supplying as its major contribution to the project.
Comments: bberger@space.com