WASHINGTON — NASA’s next-generation flagship astronomy mission likely will need to undergo testing beyond what was previously planned, resulting in a roughly four-month delay that will get worse if Congress does not cover an unrelated cash shortfall the program faces in 2011, according to an agency official.

Phil Sabelhaus, NASA project manager for the James Webb Space Telescope (JWST), said the additional testing was recommended as part of a review of the observatory’s mission-critical design requirements completed in late April. The tests could push the long-delayed JWST’s launch date to October 2014.

Sabelhaus also said the $5 billion successor to the Hubble Space Telescope needs more money than the nearly $445 million currently requested in 2011 to prevent “further slippage to the launch date.”

In late April, the JWST Standing Review Board recommended the program conduct additional component-level verification tests of the spacecraft’s massive sunshield and extend the testing of the integrated telescope assembly by three to four months. The review team also advised increasing JWST’s 2011 budget to prevent further schedule erosion.

“One of the recommendations is to ask Congress for additional funding in |[2011],” Sabelhaus told Space News May 14. “But all the factors have to be folded in, including whether it is practical to think we could get funding in [2011]. If that’s not the case, you may have to go in and look at further slippage to the launch date.”

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Sabelhaus could not say how much more JWST’s price tag is likely to grow, but said additional funding is needed in 2011 regardless of whether the program implements the JWST Standing Review Board’s testing recommendations.

Led by NASA’s Goddard Space Flight Center in Greenbelt, Md., JWST is an infrared telescope with a 6.5-meter foldable mirror and a deployable sunshield the size of a tennis court. An Ariane 5 rocket provided by the European Space Agency is slated to launch JWST to the second Lagrange point, a gravitationally stable spot 1.5 million kilometers from Earth.

Sabelhaus said the recent Mission Critical Design Review conducted by the independent review board confirmed JWST’s design meets all science and engineering requirements for its mission, though its large size makes testing a challenge.

“Given that you can’t test this thing full up you need to do some additional testing to prove the margins that you’ve got are adequate for a successful mission,” he said. “They like the testing we had [planned], they just think we ought to do more.”

However, development of the telescope, led by prime contractor Northrop Grumman Aerospace Systems of Los Angeles, is turning out to be more complicated and costly than planned.

“We’re running a little hotter these days in trying to get this thing designed and built,” he said. “We spent some money over the last few years working off some issues that were hard problems, and we’ve gotten to the point where we’re probably going to need more than we planned on.”

The 2011 budget request NASA sent to Congress in February includes $444.8 million for JWST, or about $60 million more than the agency previously projected needing. That increase comes on top of the $75 million in American Recovery and Reinvestment Act funds NASA added to JWST in 2009 to avert contractor layoffs.

Jon Morse, director of astrophysics at NASA headquarters here, said NASA is closely tracking cost and schedule performance of the telescope.

“It’s especially important for JWST to perform well, since it represents the nation’s next big advance in space astronomy research and occupies such a large fraction, about 40 percent, of the overall Astrophysics Budget,” he told Space News in a May 13 statement. “Additional unplanned delays and overruns threaten to undermine the underlying motives for pursuing complex, new facilities for exploring the cosmic frontier.”

Morse said that as NASA evaluates the review panel’s findings, JWST is still working toward “a summer 2014 launch readiness date.” However, “the schedule for JWST may be adjusted depending on the outcome of this review,” he said.

Sabelhaus said most of the review board’s recommendations will ultimately be adopted, “but that is a process that will take until the late-July timeframe.”