HOUSTON — The space shuttle Discovery's astronauts say that it's time to put the past year's fixes to the ultimate test, even though NASA acknowledges that still more fixes need to be made.
During a series of news briefings here on Thursday, shuttle managers declared that they have taken care of the particular foam-shedding problem they spotted just after last July's launch of Discovery — by removing a long piece of insulation on the shuttle's external fuel tank known as the protuberance air load ramp, or PAL ramp. But they conceded that much smaller pieces of debris might still be shed by 34 aerodynamic foam ramps designed to keep ice or frost from building up on the tank's external plumbing.
If a big enough piece were to come off one of the ice/frost ramps, and if it struck just the wrong place on the shuttle, and if it did maximum damage, "the results would be catastrophic," said John Chapman, NASA's project manager for the external tank.
However, Chapman said the arguments for testing the fixes made since last July outweighed the arguments for waiting until redesigned ice/frost ramps were ready for launch.
"The real question was, do you fly what you have; or do you make a change to it that may be less than fully certified rignt now, and go fly that; or do you wait an undetermined amount of time and develop this change, which could be many, many months, and then go fly it," he told reporters at NASA's Johnson Space Center in Houston.
Discovery's mission to the international space station, due for launch sometime between July 1 and 19 from NASA's Kennedy Space Center in Florida, would mark only the second shuttle flight since the shuttle Columbia's breakup during re-entry in February 2003.
Investigators said foam debris flying off the fuel tank dealt the fatal blow to Columbia. It took more than two years to redesign the external fuel tank for last year's test mission, and astronauts and mission managers were dismayed to see more foam fly off from Discovery's PAL ramp last July.
During the months that followed, engineers determined that the PAL ramp, which was originally put on the tank to insulate wiring and fuel lines with an aerodynamically shaped strip of foam, really wasn't needed. So the tank was redesigned again, this time sans PAL ramp.
Cleared for takeoff
After a series of wind tunnel tests, shuttle managers this week cleared the shuttle's fuel tank for next month's scheduled launch. But Chapman said the decision to go with the ice/frost ramps as is was not easy. "It was a very close call," he said.
Mission commander Steve Lindsey, who was a veteran test pilot before coming to NASA, said the crew was involved in the discussions and agreed with the outcome.
"We'd just as soon make one change, flight-test it, and then go to the next change, knowing that we eventually need to improve those ice/frost ramps. ... We think it's time to go flight-test," he said.
Lindsey's crewmates concurred. "I'm 100 percent comfortable with the decision," Discovery pilot Mark Kelly told NBC News.
The crew members all said they understood that spaceflight was a risky business, and they said it was time to conduct a real-world aerodynamic test of the PAL ramp removal — which Lindsey called the biggest change ever made to the space shuttle's exterior.
Lindsey said the debate over the ice/frost ramps demonstrated that NASA managers and engineers were being more open in their discussions of safety issues — something that investigators said the space agency needed to do in the wake of the Columbia tragedy.
Wayne Hale, NASA's shuttle program manager, told reporters that the pieces shed by the ice/frost ramps would be far smaller than the 1.6-pound block of foam that felled Columbia. He said engineers project that the maximum weight of such debris pieces would be two-tenths of a pound. "You're looking at smaller and smaller pieces of foam that, by the way, come off less and less frequently," he said.
However, Hale acknowledged as well that the pieces "could be harmful" and were "a hazard that we need to fix" before the scheduled retirement of the shuttle fleet in 2010. "It's important before the end of the program that we do something about those ice/frost ramps," he said.
He emphasized that the ramps would need to be redesigned and tested in wind tunnels before they were actually flown on a mission, and estimated that a fix could be put in place on the third or fourth tank in the production queue. That implies that a shuttle with redesigned ice/frost ramps could fly sometime next year.
NASA is still aiming to get in two more shuttle missions before the end of this year, although Hale said "it's going to be a real tight squeeze" to get Discovery's sister shuttle, Atlantis, ready for its scheduled launch on Aug. 28.
During this flight, Discovery will be taking 5,100 pounds of cargo up to the space station, and bringing 4,700 pounds of trash and equipment back down to Earth. The shuttle will drop off one of its crew members, German astronaut Thomas Reiter, for a six-month stay on the station — bringing the orbital outpost's crew back to its full three-person complement for the first time since 2003.
Discovery's spacewalkers will install a new cooling system for the space station's radiators — as well as a backup cable reel for the station's robotic rail platform, to replace one that had its wires accidentally cut last December.
The shuttle astronauts also will test a whole new set of inspection and repair methods, including a technique that involves attaching a spacewalker to an inspection boom that is in turn attached to the shuttle's robot arm.
The space station's crew will take high-resolution pictures of the shuttle's underbelly before docking, as they did last time. This time, they'll conduct yet another round of inspections late in the mission, just before and just after undocking, to check for potential damage from space debris.
Discovery's crew members said the current 12-day mission agenda was packed, and a 13th day might be added, depending on how well the shuttle conserves its "consumables" — that is, the fuel for the onboard power system.
"We'll be busy," British-American spacewalker Piers Sellers said.
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