NASA officials denied yesterday that they are cutting corners or cheapening safety standards in preparing the space shuttle for its first flight in more than two years, but they acknowledged there are in-house disputes over how best to analyze and assess improvements made to the orbiter's heat shielding.
Since the space shuttle Columbia disintegrated on reentry on Feb. 1, 2003, NASA engineers have made significant modifications to the foam insulation covering the orbiter's external fuel tank, and have extensively tested the damage potential of chunks of foam and ice that break free of the tank during launch. A chunk of external tank foam severely damaged the heat shielding on Columbia's left wing.
The shuttle program's deputy manager, N. Wayne Hale Jr., said NASA is not "moving the goal posts" on safety standards to give a more optimistic assessment of the risk of catastrophic foam and ice damage to the orbiter.
"This is a very complex engineering problem [that] doesn't come through in a 30-second sound bite," Hale said. "We're not trying to hide anything. We're trying very hard to understand what the risk is."
Hale was responding to a report in the New York Times, which cited internal NASA documents suggesting that the agency is deliberately minimizing risk by changing the standards by which the impact test results are measured.
On Wednesday, NASA announced it was postponing the launch of the shuttle Discovery by one week, to May 22, in large measure to give engineers extra time to assess and analyze the results of tests of foam and ice impacts on the orbiter.
NASA plans to present its final assessment of the external tank redesign at a "flight readiness review" May 10-11.
"This is sausage-making," John Muratore, manager of shuttle systems engineering and integration, said of the internal documents. "This is pretty standard. We're synthesizing a lot of information, and we're in a debris-risk-assessment process."
Hale said the debris analysis available has been passed along to the NASA-appointed Return to Flight Task Group, in charge of assessing the agency's compliance with safety recommendations made after the Columbia tragedy.
Task Group spokesman Dave Drachlis confirmed that the relevant information "has been made available," and the Task Group will meet to deliberate and deliver its final report as soon as it has NASA's data in hand.
In the past two years, NASA engineers in several locations have conducted millions of computer simulations and thousands of impact tests to determine how badly a chunk of foam or ice can damage the thermal protection tile on the shuttle's underbelly or the hard, reinforced carbon-carbon on the orbiter's nose and the leading edges of its wings.
Analysts have boiled down the potential damage scripts to 177 cases and are studying them. Hale said this week he is "very confident" that engineers could finish work in time for launch, barely a month away.
Muratore said shuttle engineers spent six full days trying to figure out the best way to analyze the data and had heard from at least three groups of experts, each of which proposed radically different ways of assessing risk. Each way was "legitimate," he said.
Muratore suggested that structural engineers produced the documents questioning NASA's standards. "These people are rigorous," he said, and wanted to measure the risk by strict aviation standards.
As the debate has progressed, however, "We asked, 'Let's say what the risk is,' and everybody agreed it was the same," Muratore said. "Everybody pretty much agreed that this is a risky business, and the risk is probably down to the equivalent of the other risks we take when we fly."
Both Muratore and Hale objected strongly to any suggestion that NASA has softened its standards in this analysis. "The numbers haven't changed for a year," Muratore said. "This is the most rigorous activity I have ever been involved with. . . . We have done things to verify and validate that are impressive and world-class."
Hale also "found disheartening" reports that NASA still suffers from a "go-fever" culture that stifles debate and adjusts testing standards.
"It is to my everlasting shame," he said, to have been mentioned in the official report of the Columbia accident. "I never want to go to another astronaut memorial or see my name [in such a report]. There will be no cutting corners on my watch."