NASA Moon Rocket Could Shake Apart, Experts Say

Seth Borenstein in Washington
Associated Press

January 22, 2008

NASA is wrestling with a potentially dangerous problem in a spacecraft, this time in a moon rocket that hasn't even been built yet.

Engineers are concerned that the new rocket—meant to replace the space shuttle and send astronauts on their way to the moon—could shake violently during the first few minutes of flight, possibly destroying the entire vehicle (picture of the rocket).

"They know it's a real problem," said Carnegie Mellon University engineering professor Paul Fischbeck, who has consulted on risk issues with NASA in the past.

"This thing is going to shake apart the whole structure, and they've got to solve it."

If not corrected, the shaking would arise from the powerful first stage of the Ares I rocket, which will lift the Orion crew capsule into orbit (picture of crew capsule attached to lunar lander).

NASA officials hope to have a plan for fixing the design as early as March. They do not expect the issue to affect the goal of returning astronauts to the moon by 2020. (See "NASA 'On Track' for 2020 Human Moon Mission" [December 11, 2007].)

"I hope no one was so ill-informed as to believe that we would be able to develop a system to replace the shuttle without facing any challenges in doing so," NASA administrator Michael Griffin said in a statement to the Associated Press.

"NASA has an excellent track record of resolving technical challenges. We're confident we'll solve this one as well."

Professor Jorge Arenas of the Institute of Acoustics in Valdivia, Chile, acknowledged that the problem was serious but said, "NASA has developed one of the safest and risk-controlled space programs in engineering history."

The U.S. space agency has been working on a plan to return to the moon, at a cost of more than a hundred billion U.S. dollars, since 2005. (Video: Moon 101.)

The plan involves two different rockets: Ares I, which would carry the astronauts into space, and an unmanned heavy-lift cargo ship, Ares V (picture of the cargo ship).

The concern isn't the shaking on the first stage, but how it affects everything that sits on top: the Orion crew capsule, the instrument unit, and a booster.

That first stage is composed of five reusable solid rocket boosters derived from the type that NASA uses to launch the shuttle.

The shaking problem, which is common to solid rocket boosters, involves pulses of added acceleration caused by gas vortices in the rocket—similar to the wake that develops behind a fast-moving boat, said Arenas, who has researched vibration and space-launch issues.

Those vortices happen to match the natural vibrating frequencies of the motor's combustion chamber, and that combination causes the shaking.

Senior managers were told of the findings last fall, but NASA did not talk about them publicly until the AP filed a Freedom of Information Act request earlier this month and the watchdog Web site Nasawatch.com submitted detailed engineering-oriented questions.

The response to those questions, given to both Nasawatch and AP, were shared with outside experts, who judged it a serious problem.

NASA engineers characterized the shaking as being in what the agency considers the "red zone" of risk, ranking a five on a one-to-five scale of severity.

"It's highly likely to happen, and if it does, it's a disaster," said Fischbeck, an expert in engineering risks.

The first launch of astronauts aboard Ares I and Orion is set for March 2015.

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