Saturday, January 19, 2008
NASA is wrestling with a potentially dangerous problem in a spacecraft
NASA Moon Rocket May Shake Too Much
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.
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.
NASA officials hope to have a plan for fixing the design as early as March, and they do not expect it to delay the goal of returning astronauts to the moon by 2020.
"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 space agency has been working on a plan to return to the moon, at a cost of more than $100 billion, since 2005. It involves two different rockets: Ares I, which would carry the astronauts into space, and an unmanned heavy-lift cargo ship, Ares V.
The concern isn't the shaking on the first stage, but how it affects everything that sits on top: the Orion crew capsule, instrument unit, and a booster.
That first stage is composed of five segments derived from the solid rocket boosters that NASA uses to launch the shuttle and would be built by ATK Launch Systems of Brigham City, Utah.
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 the 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 1-to-5 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.
Severe vibration problem plagues moon rocket design.
Experts at NASA are wrestling with a propulsion system problem in the design of the new moonship that would create dangerously high vibrations for the spacecraft and its astronauts, the space agency said Friday.
Officials said in a statement that they expect to develop by March several options to address the problem with the Ares I rocket, which is in the early design phase.
NASA is counting on the Ares I rocket and the Orion crew capsule attached to it to replace the aging space shuttle, which is facing retirement in 2010.
At current funding levels, NASA hopes to begin launching astronauts to the international space station aboard the new moonship by March 2015.
The vibration problem was first disclosed on Friday by NASA Watch, an Web site focused on space agency issues.
NASA officials declined requests for interviews on Friday, but spokeswoman Beth Dickey provided a lengthy statement that identified the problem as "thrust oscillation," an issue that was discussed by the moonship's development team in October during a design review.
The statement characterized the problem, which was revealed in computer modeling, as a pulsing of the thrust late in the burn of the rocket's first stage.
"These longitudinal forces may increase the loads experienced by the Ares I during flight, and may exceed allowable loads on various portions of the vehicle and allowable forces on the astronaut crew," the statement said.
Program managers assigned the seriousness of the problem a "four" on a risk scale of five and have called on experts from outside of NASA as well as inside the agency for assistance.
Confident in solution
NASA Administrator Michael Griffin expressed confidence the issue will be resolved.
"This is a development project like Apollo. 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," Griffin said in a separate statement. "NASA has an excellent track record of resolving technical challenges. We're confident we'll solve this one as well."
While NASA's Johnson Space Center manages the overall effort to develop the moonship, the propulsion work has been assigned to the Marshall Space Flight Center in Huntsville, Ala.
The Ares I first stage is a longer version of the shuttle's solid rocket booster. The upper stage is comprised of an upgrade of the Apollo-era rocket engine.
Normal design kinks
Thrust oscillation is a phenomenon found in all solid rocket motors, including the two used to power each launch of the space shuttle.
"It is a well and long understood phenomenon in the launch industry," said George Torres , a spokesman for ATK. "Many other launch vehicles at this stage of development have had to deal with this issue and have dealt with it as a normal part of the development process."
Four years ago, President Bush directed NASA's return to the moon with astronauts by 2020.
As part of the directive, Bush instructed the agency to retire the shuttle as it completes the assembly of the space station.
On Dec. 12, NASA awarded the last of the contracts for the development of the Ares I rocket and Orion capsule, a committment of $13.6 billion.
Posted by SANJIDA AFROJ at 7:39 PM