The Space Shuttle Returns
How NASA recovered from the Columbia tragedy and tackled the job of getting the shuttle flying again.
- By Linda Shiner
- Air & Space magazine, May 2005
(Page 4 of 7)
And yet, despite all the safeguards, when Discovery is launched this spring, some foam will almost certainly shed from the tank.
Wayne Hale, the deputy space shuttle program manager, explained last December that NASA managers interpreted the CAIB's recommendation as "eliminate all debris that could cause damage." After hundreds of tests, the engineers determined that a piece of foam weighing as little as .023 pound, if it came off the top of the tank, could damage the wing leading edge so severely that safe reentry would be questionable. (The piece that struck Columbia's wing weighed an estimated 1.67 pound.) NASA believes that no debris larger than .008 pound will come off; that leaves a safety margin of only .015 pound. "We were very clear from day one...that if in fact the requirement becomes 'No debris,' we are not going to be able to make it-not with this foam system," Neil Otte said.
When the CAIB required "an aggressive program to eliminate all External Tank Thermal Protection System debris-shedding," was it envisioning zero debris? That's the type of question debated by a group of 26 experts appointed by NASA Administrator Sean O'Keefe in June 2003, as NASA began responding to the CAIB's preliminary recommendations. The Return to Flight Task Group, co-chaired by Apollo astronaut Thomas Stafford and shuttle astronaut Richard Covey, who piloted Discovery in 1988 on the shuttle's first flight after the 1986 Challenger accident, shadowed NASA's employees and contractors at every step of their return to flight, questioning their analyses and decisions and compiling its own report, to be delivered to the administrator about six weeks before the next shuttle is launched. (The task group reports to a different administrator from the one who chartered it; O'Keefe left the agency in February to return to academia.)
The task group's job is to make an independent assessment of NASA's response to the CAIB's 15 return-to-flight recommendations. It is a self-described "umpire calling balls and strikes in a zone defined by the CAIB." Last December, the umpire seemed disposed to approve NASA's solution to external tank debris-shedding. Dan Crippen heads the group's panel evaluating actions taken to improve NASA management. A former director of the Congressional Budget Office, Crippen holds a doctorate in public finance and is the only one of the group's leaders who had never worked in the space program.
"The CAIB clearly understood some limitations," he said at a December press conference. "Their intention was to eliminate all debris. Well, if they thought that was possible, they wouldn't have gone on to say, 'Oh, by the way, you ought to be able to inspect for damage, you ought to be able to repair damage.' Because if you had eliminated all debris, then you wouldn't need that. So they clearly understood in their own discourse that their recommendations were subject to imperfection."
Reading the first four CAIB recommendations, the ones that directly address the physical cause of the Columbia tragedy, you can hear What if ? whispered after each one, as if the committee were trying to lock the shuttle's survivability inside a strong box, then inside a combination safe, then inside a bank vault. In the CAIB plan, foam will not shed from the tank. But what if it does? Then the RCC panels on the orbiter's leading edge will be more impact-resistant than they were. But what if they're not? Then the astronauts will be able to inspect and repair them. But what if they can't?
There's no doubt that the next shuttle flight will be the most carefully watched in history. To the 14 tracking cameras active at the Florida launch site, NASA is adding nine more. There are new cameras on the external tank and solid rocket boosters, and more are planned. Department of Defense telescopes, which could have seen the damage done to Columbia's wing had NASA requested photographs of the craft while it was in orbit, will view every shuttle from now on as a matter of course. (The CAIB censured the STS-107 mission controllers for not availing themselves of these assets after seeing foam fall from the tank.)
If a strike should occur during launch, its impact will be detected by 88 accelerometers and temperature sensors newly installed inside the wing. Even if the sensors register no impact, the astronauts, once in orbit, will deploy a new piece of hardware, the Orbiter Boom Sensor System. Attached to the shuttle's robot arm, the 50-foot boom carries two laser imaging systems and a low-light black-and-white television camera that will scan the shuttle's nose cone and the 44 RCC panels on the wings' leading edges to provide three-dimensional maps of those areas.