Fuel tank's pre-launch foam repair under scrutiny
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: August 5, 2005;
Updated @ 7:50 p.m. with NASA confirmation of prior foam damage
A "tiger team" of NASA and contractor engineers is reviewing the manufacturing history of the shuttle Discovery's external fuel tank to find clues about what might have caused a chunk of foam insulation to pop off during launch July 26. NASA officials said today that foam in the area that pulled away was slightly damaged during the tank's processing, requiring a standard repair for relatively routine cracks and gouges.
The extent of the void was very small and it may have had nothing to do with the foam loss that marred Discovery's launch. But it has caught the interest of the engineering community because if the launch debris incident can be traced to this or any other one-time flaw that only affected Discovery's tank, NASA might be able to return the grounded shuttle program to flight in relatively short order without having to implement generic, fleet-wide modifications.
Time, however, is short. The next available launch window, which originally opened Sept. 9, has shrunk to just four days, now opening Sept. 22 and closing Sept. 25, primarily because Discovery was delayed getting off on its current mission. Whenever the shuttle Atlantis is cleared for the second post-Columbia mission, Discovery must be ready for launch on a rescue mission if major problems develop in orbit.
While most agency observers believe NASA has little chance of resolving the foam issue in time for Atlantis to blast off in the September window, NASA Administrator Michael Griffin has not given up hope.
"Until we run out of lead time to make the September window, we'll preserve it," Griffin told reporters today. "Because that's what the taxpayers pay us to do. When we no longer can make it, we'll tell you and we'll recycle for (the next launch window in) November."
The question of prior damage to the foam on Discovery's tank came up during a post-launch review following the insulation shedding observed during the shuttle's climb to space. A few seconds after the ship's solid-fuel boosters separated, a 0.9-pound chunk of foam ripped away from an aerodynamic ramp used to smooth the supersonic flow of air over external pressurization lines and electrical cables.
The so-called "protuberance air load" - PAL - ramp is sprayed on and shaped by hand. As such, it is subject to more inconsistencies than machine-sprayed foam. But the PAL ramp was not upgraded in the wake of the Columbia disaster because engineers believed its design was sound and because the last known incident of foam shedding from the ramp was in 1983.
A NASA official familiar with the incident said the same area of the ramp that broke free during launch suffered minor damage at some point during its processing. In such cases, red dye is applied that soaks into damaged foam and marks the extent of the problem. Technicians then sand the foam to remove the damaged material.
"There was a defect, a flaw or a gap ... on the PAL ramp," the NASA official said. "It's fairly small defect. As part of our normal procedures, we did a sand-and-blend (repair). We poured dye in the crack and chased the dye. We sand down until the dye is gone. In this case, it left a little bit of an indentation there, which is acceptable within our regulations. It was in the same region as the piece that came off."
One source described the defect as "crush" damage, but the NASA official said to his knowledge, "we don't have any indication of crushing damage. As far as we know, it was just that void there. It's like a crack for lack of a better term."
"It was fairly shallow and they just sanded it out," he said. "This is part of the fault tree, it's one of the boxes we have to check off. But there are more items we have to look at."
The Discovery astronauts, meanwhile, are gearing up to undock from the international space station early Saturday after an action-packed three-spacewalk mission to resupply and service the $30 billion outpost. Here is a timeline of upcoming activities (in EDT and mission elapsed time):
EDT........DD...HH...MM...EVENT 02:43 AM...10...16...04...Noon 03:08 AM...10...16...29...Sunset 03:24 AM...10...16...45...Discovery undocks from the space station 03:24 AM...10...16...45...Initial orbiter separation (+10 seconds) 03:26 AM...10...16...47...ISS holds current orientation 03:29 AM...10...16...50...Range: 50 feet 03:31 AM...10...16...52...Range: 75 feet 03:44 AM...10...17...05...Sunrise 03:53 AM...10...17...14...Range: 400 feet 03:54 AM...10...17...15...Start flyaround 04:05 AM...10...17...26...-R bar crossing (Discovery directly above ISS) 04:11 AM...10...17...32...Russian ground station LOS 04:12 AM...10...17...33...Noon 04:17 AM...10...17...38...-V bar crossing (shuttle behind station) 04:28 AM...10...17...49...+R bar crossing (shuttle below station) 04:40 AM...10...18...01...Sunset 04:41 AM...10...18...02...Separation burn (1.5 fps) 05:09 AM...10...18...30...Separation burn (3.0 fps)Despite the launch-day foam incident, Griffin said Discovery's mission has been one of the most successful on record.
"People who think this has been a horribly troubled flight, not only for them is the glass not half full, there is no glass," he said earlier today. "This has been a great flight. We clearly, as I've said several times, I want to be honest, I want to be open, we made a mistake on the external tank. We have a special team looking at all that, we're going to try to find it and fix it.
"But almost everything we did with the external tank worked. Discovery is six times cleaner in flight than the average shuttle has been. Discovery is in great shape for landing. ... The flight crew did a magnificent job in removing those gap fillers, and so we strongly feel we will have a clean, very nominal re-entry."
Lead flight director Paul Hill said the Discovery astronauts transferred 23 pounds of nitrogen to the space station, 1,700 pounds of fresh water, 1,400 pounds of equipment stored on the shuttle's lower deck and another 3,000 pounds of supplies and equipment brought up in an Italian-built cargo module.
For the trip back to Earth, Discovery is now loaded with 6,300 pounds of no-longer-needed equipment, trash and other gear, including a broken control moment gyroscope that was replaced during one of the crew's spacewalks. NASA engineers want to get the gyro back to Earth to find out what went wrong and how to prevent similar problems in the future.
If all goes well, commander Eileen Collins and her crew mates will test Discovery's re-entry systems Sunday and pack up for the trip back to Earth. Two landing opportunities are available at the Kennedy Space Center - at 4:46 a.m. and 6:21 a.m. Monday - and two more at Edwards Air Force Base, Calif.
But NASA managers want to get Discovery back on the ground in Florida if at all possible and if the weather or some other problem blocks an on-time landing, entry flight director LeRoy Cain likely would extend the mission one day and bring Discovery back to Florida or California on Tuesday.
The official landing strategy has not yet been announced. But here are all of the possible landing opportunities for Discovery and its crew (all times EDT and subject to change; KSC - Kennedy Space Center; EDW - Edwards Air Force Base, Calif.):
ORBIT...SITE....DEORBIT BURN....LANDING Monday, Aug. 8 201.....KSC.....03:43 AM........04:46 AM 202.....KSC.....05:19 AM........06:21 AM 203.....EDW.....06:49 AM........07:52 AM 204.....EDW.....08:25 AM........09:27 AM Tuesday, Aug. 9 217.....KSC.....04:07 AM........05:09 AM 218.....KSC.....05:43 AM........06:45 AM 219.....EDW.....07:12 AM........08:15 AM 220.....EDW.....08:48 AM........09:50 AM Wednesday, Aug. 10 232.....KSC.....02:54 AM........03:57 AM 233.....KSC.....04:29 AM........05:32 AM 234.....EDW.....05:59 AM........07:02 AM 235.....EDW.....07:35 AM........08:37 AMWith Discovery back on terra firma, the shuttle team's focus will shift to the external tank foam problems that developed during launch. Along with the PAL ramp foam, engineers also are concerned about at least two other areas where foam separated from the tank.
"The idea is to really look at it from an engineering standpoint and see what we've found out here," said Bill Gerstenmeir, space station program manager. "This flight was tremendous, we've got data now we've never had before. Now we can see when foam was liberated and exactly how the foam was liberated during ascent. So now you can take that back to maybe a defect that was present in the tank we didn't think about before, or wasn't there. Now you can see what that mechanism is and how it comes off.
"So we have a tremendous chance to learn from this exercise that we can really take our knowledge base of how we apply foam to tank, how we ensure that it doesn't come off or it comes off at a time when it's not a problem to us. We've got a tremendous engineering chance to learn from this test program, this flight we just flew."
Said Griffin, "The good thing is, almost all of the tank changes (made as a result of Columbia) worked. Some didn't. So what's the difference between the ones that did and the ones that didn't? That's what engineers do. And if we can extract that difference, then we can go and look at the next tank, or tanks. ... Now we have actual test data that we can use to see how well we did and in areas where we didn't do as well, why we didn't do as well. We've never had that before. Never."
Griffin said every external tank has "enormous portions of it that are all the same and every tank has areas where there are hand applications of foam or insulation because the automatic machinery isn't that sophisticated."
"And then every tank undergoes at some point in its career, minor damage," he said. "People touch it, or lean on it or whatever in the wrong way and things have to be patched and fixed. Those are the areas that will get a lot of attention.
"But we will never, as long as we manufacture these tanks or much of anything else, we will never be able to eliminate the fact that there is some custom work for each tank. So what we have to have coming out of these test flights is an understanding of which types of custom work are OK and which types of custom work that we do are not yielding good results. And we need to stop that and do something different."
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