CAPE CANAVERAL, Fla. - NASA almost certainly violated its own flight safety margins when it repeatedly launched shuttles knowing that they could be hit by foam debris from the external fuel tank, a retired Air Force space expert told Columbia accident investigators yesterday.
Since the orbiter was destroyed Feb. 1, the possibility that falling foam had damaged Columbia's thermal protection tiles has played a key role in the investigation.
The National Aeronautics and Space Administration long had known that insulation from the tanks had gouged the delicate heat-shielding tiles in previous flights; officials, however, had decided it wasn't a safety hazard.
"There is no way you can say you are operating within `safety' margins if you have foam of unknown size impacting the flight surfaces," said Aloysius G. Casey, a retired general who once ran the Air Force's centers for developing ballistic missiles and spacecraft. He spoke at a public hearing held here by the Columbia Accident Investigation Board.
Although NASA has conducted various tests through the years to assess the damage foam debris might cause, the original design of the shuttle never anticipated that risk, Casey said. It is believed that Columbia's left wing was hit by a 2.6-pound piece of foam.
Casey said it is unclear what changes would be needed to ensure that foam has no chance of falling off the external tank. He suggested that reducing the thickness of the insulation may help keep it bonded to the tank during liftoff.
But Casey also warned the board against trying to make comprehensive safety improvements to the shuttle.
"It is impossible in a system as large and complex as the shuttle to identify with any certainty the next most-probable cause of failure," Casey said. So NASA could very well spend a lot of money, he said, on things that are not likely to cause the next problem.
The shuttle has a 98.2 percent probability of flying a successful mission, given it has had two failures out of 113 flights. While that is better than unmanned rocket launchers, it is not good enough for human space flight, Casey said.
Indeed, noted Steve Wallace, a board member and civil aviation accident expert, such a rate in commercial air travel would translate to 640 crashes a day.
The hearing yesterday included testimony from Kennedy Space Center director Roy Bridges and shuttle processing chief Bill Higgins.
Bridges said that in 1999, he had to issue urgent warnings within NASA that he was losing critical skills at Kennedy because of budgetary cutbacks.
The center had 2,498 employees assigned to the shuttle in 1992. By 1999 that number had fallen to 1,687. It now is 1,773.
Bridges said that he had no direct role in assessing the risks facing Columbia.
But he noted that many of Kennedy's physical facilities are "dilapidated and rundown" and that NASA is facing massive future investments if it wants to continue operating the shuttle for another 10 or 20 years as it has indicated. Just new doors, siding and a roof for the vehicle assembly building, where the shuttle is attached to its solid rocket boosters and its external tank, would cost $100 million.
Higgins described the complex system NASA uses to oversee the private contractor that processes the shuttle for launch. It has reduced the number of required inspections to 8,500 specific items that must be looked over before launch.
Separately yesterday, the independent Aerospace Safety Advisory Panel issued a report that said the shuttle fleet is encountering increasing problems as it ages and NASA needs to reconsider how it certifies the vehicles as safe to launch.
The panel's report was written before the Columbia accident, although it had not been publicly issued. The 106-page report said cracks, leaks and other problems were evidence of "degradation" and the space agency should re-evaluate the certification it has on various systems.
Ralph Vartabedian is a reporter for the Los Angeles Times, a Tribune Publishing newspaper.