In a history that includes technical setbacks and failures, NASA has always bounced back with a solution over the four decades of human spaceflight.
But its finding that large pieces of foam fell off the shuttle Discovery's external fuel tank during Tuesday's launch shows that the space agency has failed to solve the cause of the Columbia accident that killed seven astronauts on their return voyage in February 2003.
In the months after the Columbia disaster, NASA learned that foam debris falling off the external tank damaged the sensitive thermal protection system on the orbiter. Columbia burned up over Texas when superheated gases penetrated its wing. NASA then spent more than two years and $1.4 billion trying to improve safety.
However, the recommendations made by Columbia's accident investigators did not force NASA to confront the problem head-on. The board told the space agency to "initiate" a program to eliminate foam debris and "initiate" a program to strengthen the orbiter's thermal protection system, but it did not make NASA adopt a 100% fix to either system.
It also appears that in 2003, NASA rejected efforts by outside experts who proposed comprehensive fixes to the foam problem, because the proposals required aggressive redesigns or advanced foam technology that might have required significant investments.
The path NASA took instead was to fix, at limited cost, an old launch system that it planned to get rid of by the end of the decade.
Retired Navy Adm. Harold W. Gehman Jr., chairman of the Columbia Accident Investigation Board, acknowledged Thursday that the recommendations to NASA left open a window that would have allowed the same scenario of foam debris falling off and damaging the orbiter's thermal protection system.
"We had precious little faith that they could stop this stuff from coming off," Gehman said in an interview. "And lo and behold, they couldn't."
Nonetheless, Gehman defends the decision, saying any binding requirement to fix the system "wasn't reasonable."
Gehman said neither his accident investigators nor NASA had any definitive explanation for why foam even fell off the tank, let alone a proposal for how to stop it.
"At the time, we got mixed and inconsistent explanations why foam fell off," Gehman said. "When we went into the body of research, it was inconsistent and unpersuasive."
John Logsdon, director of the Space Policy Institute at George Washington University and another member of the Columbia board, acknowledged that he thought the board should have issued a tougher recommendation on fixing the foam.
"Could we have been tougher? Hindsight is wonderful," Logsdon said. "We put together a set of recommendations that provided a context in which the shuttle program could move forward. They had budget and schedule constraints."
Even NASA officials acknowledged that they erred. "We decided it was safe to fly as is. Obviously, we were wrong," Bill Parsons, manager of the shuttle program, said Wednesday.
Instead of fixing the debris problem, the board focused many recommendations on allowing astronauts to survive such a foam strike. It required advanced photography of the launches to determine whether debris damaged the orbiter, a capability to repair wings in space and a rescue plan in case astronauts were marooned in orbit.
While such measures might save the lives of astronauts, they would not save the space program from a debilitating loss of another shuttle or a delay in launches, as it is now facing. NASA officials say they do not know how long it will take to fix the new foam problems or how it could affect the future of the space program. Until those solutions are in hand, the shuttles are not supposed to fly.
Outside experts tried to get NASA's attention in 2003 on advanced research they thought might help the space agency keep the foam stuck to the massive external tank. On Thursday, they said they were largely rebuffed by NASA insiders who said they did not have the resources to consider new technology.
Steve Nutt, senior associate dean for research at USC and head of the engineering department's foam research center, submitted a proposal in 2003 to NASA for a fiber-reinforced foam that his team had developed.
Nutt's lab at USC pioneered a system of mixing chopped glass or aramid fibers into the foam, creating dramatic improvements in strength and the ability to resist cracking.
"They said the technology had merit, but the interest kind of dried up," Nutt said. "They said they didn't have the research-and-development budget to assess this technology."
Nutt said NASA never had the information necessary to decide whether his technology would work on the shuttle. He added, "I don't want to bad-mouth NASA. I feel really sorry for those guys. I would still love to talk to someone at NASA."