NASA hopeful tests can pave way to May shuttle launch
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: October 14, 2005
NASA managers are hopeful an exhaustive series of upcoming tests will help engineers pin down what caused foam insulation to fall off the shuttle Discovery's external tank during launch last July and, if all goes well, clear the way for another launch next May.
"We have not set an official launch date," shuttle program manager Wayne Hale told reporters today. "I want to make that very clear. The shuttle launch date for the next shuttle flight has been, in the lingo that the Eastern Range uses, 'indeterminate' since the foam incident on STS-114.
"We are, however, working toward technical solutions of our problems. ... We have a number of critical things ahead of us that we have to evaluate before we set an official launch schedule. However, based on the discussions that we had at the program board yesterday, it appears that the May launch window is something that we can begin to work toward now."
The launch window opens May 3 and closes May 23. The next window runs from July 1 through July 20 and the next window after that opens Aug. 28 and closes Sept. 14. The launch windows are based the shuttle's ability to reach the international space station and on a requirement to launch, and have the external tank separate, in daylight for photo documentation.
When Discovery blasted off in July, NASA had hoped to launch the second post-Columbia mission in September. But during the shuttle's climb to space, relatively large pieces of foam insulation fell away from five areas of the tank, including a potentially dangerous chunk from a so-called protuberance air load, or PAL, ramp. The PAL ramp is a long aerodynamic barrier made up of hand-sprayed foam designed to smooth the flow of supersonic air across an external cable tray and two pressurization lines.
In the wake of Discovery's launch on mission STS-114, shuttle flights were put on hold. NASA managers did not announce a new target date for the second post-Columbia flight beyond saying launches would be delayed until at least next March.
Then came Hurricane Katrina, which devastated New Orleans and the Gulf Coast. Lockheed Martin processes shuttle external tanks at its Michoud Assembly Facility near New Orleans and while damage was surprisingly slight, the 2,000-member workforce was seriously impacted.
Hale said today the storm and its aftermath set tank processing back at least three months. Some five hundred workers are back on the job at Michoud, but the full work force is not expected back on station until early December.
Even so, Hale said engineers are optimistic they will nail down the causes of the foam shedding in time to support a May launch.
"We are at the point where we believe we have an understanding of the parameters of those problems well enough in hand so we can get internal working schedules to the rest of our elements," Hale said. "Of course, any schedule we have is going to be critically dependent on the work that goes on at Michoud. And that's why the discussion of the work force and the work force returning to Michoud is critical to our scheduling effort. We believe we understand how that is going to take place over the next few weeks."
Richard Gilbrech led a "tiger team" of engineers charged with assessing the foam issue. He said today the team focused on three areas: the launch environment, that is, the forces acting on the foam during ascent; the materials used in the foam; and the way the foam was applied, removed for subsequent modifications and re-applied.
The launch environment was not a factor, the team concluded; the stresses acting on the tank were essentially the same as on previous flights. The materials used in the foam also were unchanged from previous flights with one major exception: the PAL ramp foam was made up of BX-265, a foam formulation slightly different from earlier tanks to comply with the latest environmental regulations.
"The third thing we looked at was processing, was there anything in the way this tank was processed that might give us a clue as to why we had lost foam," Gilbrech said. "The major finding we found was this tank was reworked to a level none of the other tanks prior had been, and we suspect that handling damage, or collateral damage - which is basically risk to the foam from technicians that have to be there and doing their work - we think is a potential contributor.
"I want to make it clear that we found no negligence on the part of the workers at the ET project. They were doing their work per procedure. It's just that we didn't really have an appreciation for the significance this handling damage could have in terms of foam loss."
The PAL ramp foam debris was the largest chunk to fall off Discovery's tank. Engineers believe it probably was the result of a combination of factors, including voids in the foam, possible cracks caused by thermal stresses in the ramp foam and the underlying foam it was applied to and inadvertent crush damage caused by engineers and technicians at Michoud working near the area during processing.
But Gilbrech said engineers do not believe "crushed foam alone could have been the cause of the foam coming off. We believe it was potentially a combination of (factors)."
Said Bill Gerstenmaier, chief of space operations at NASA headquarters: "I think it's really wrong to try to pick out one potential root cause and say that's the underlying problem or that's the smoking gun. Foam is very complicated. The failure mechanism is likely some combination of things and it's really wrong to try to pick out one and then try to focus all your efforts on that. That will actually set you 8up for more problems in the future."
The foam that doomed Columbia came off another aerodynamic ramp intended to keep ice from forming around the two bipod struts that attach the nose of the shuttle to the tank. The ramps were removed for Discovery's flight and replaced with heater strips. Surprisingly, foam popped away from the now-rampless bipod area during Discovery's launch.
As it turns out, engineers believe air inside the heater wiring channel condensed due to the ultra-low temperatures of the tank. The liquid nitrogen then changed back into a gas during launch and popped off overlying foam. Changes are planned to eliminate that threat in the future.
Another area of foam loss during Discovery's flight was from so-called ice-frost ramps, foam that covers the attachment fittings holding pressurization lines in place. Engineers may resolve that problem by drilling small holes in the foam, allowing pathways for trapped air to escape. This technique already is used elsewhere on the tank.
Foam also fell away from a flange area near the top of the hydrogen section of the tank and from the broad acreage foam covering most of the tank's exterior. Gilbrech said the intertank flange foam may have separated because of previous work in that area, but he did not specify what might be the cause of the acreage foam loss other than to say tests were being designed to resolve the issue.
The tank intended for the next shuttle flight is ET-119, which was recently shipped back to Michoud from the Kennedy Space Center. It currently is undergoing extensive inspections and X-ray analysis. The PAL ramps eventually will be removed, sliced every eighth of an inch to look for voids. They will be replaced using improved techniques with special care taken to ensure no inadvertent damage.
"That tank we have to do a number of things to, at the minimum removing and replacing the PAL ramps, re-working the bipod closeout area where we think the wire may have actually allowed cryogenic ingestion of air to condense in an area," Hale said. "We have a number of things that we've got to do before we're ready to do that work."
But Hale repeated that he is optimistic about making the May window.
"I think we have done enough analytical work to lay out a series of tests that over the next couple of months are going to give us a very clear and convincing understanding of why we lost the foam that we did on the external tank and allow us to design new techniques that will allow us to re-apply foam in areas in such a way that it won't come off even from some of these very complex interconnected causes. So we're addressing all those.
"What has taken us from July until October, if you want to think about it, is to come to that level of understanding of the work that's got to go forward to provide an engineering, rigorous understanding of the causes and solutions to foam coming off. What we're all here to report is a great deal of progress and a sense of optimism that we do have an understanding of the work that lies ahead of us."