By Cheryl Pellerin
Washington File Staff Writer
Washington – Although not yet to set a firm launch date for the next space shuttle flight, NASA managers said October 14 that they have made progress in determining why insulating foam is lost during shuttle launches, and are considering a May 3-23 launch window.
An engineering team has been working since July at NASA's Michoud Assembly Facility in New Orleans to understand and fix the problems that contribute to the loss of insulating foam from the space shuttle external tank.
A large piece of foam flew off Discovery's (STS-114) external fuel tank during the July 26 launch of the shuttle. The foam – 61-84 centimeters long, 25-33 centimeters wide and 6-20 centimeters thick – was seen by high-resolution cameras added to the shuttle after the in-flight explosion of the shuttle Columbia in 2003.
The Columbia accident, which occurred during re-entry into the earth's atmosphere, was caused by foam from the external tank hitting the orbiter during launch.
"We have not set an official launch date," said Space Shuttle Program Manager Wayne Hale during a briefing on the status of the space shuttle program at the Johnson Space Center in Texas.
"We are, however, working toward technical solutions to the problems," Hale added, "and are at the point where we believe we have an understanding of the parameters of those problems well enough in hand" to set internal working schedules.
Richard Gilbrech, lead engineer for the external tank "tiger team," said the team's main job is to find the root causes of foam loss on STS-114, determine if those causes are unique to that flight and external tank, and develop near- and long-term recommendations for improvements.
"Before Columbia," Gilbrech said, "the foam's main purpose was to add insulation – to keep propellants cold and protect the external tank from air frictional heating during ascent. After Columbia, we learned that we needed to treat foam as a structure."
Working with foam as a structure is difficult, Gilbrech said, because it is mostly air. It must be structurally sound, but still withstand stresses on launch and ascent and large temperature differences during a flight.
A major focus of the team's scrutiny is a structure on the external tank called the protuberance air load (PAL) ramp, which lost the largest piece of foam.
The PAL ramp prevents unsteady air flow under tank cable trays and pressurization lines. But, Hale said, such ramps were first used as a safety measure in the early stages of the shuttle program – before the aerodynamics of the structure were well understood.
"If we find out that it's not required or perhaps a much smaller ramp is required," Hale said, "and we can eliminate some of the foam from the outside of the tank, then we have eliminated something that can cause problems."
"The goal," he added, is to continue the investigation "with the intention of potentially eliminating the PAL ramp in the future. It's going to take us a couple of flights and about a year's worth of wind tunnel testing to come to a conclusion as to whether or not we can do that."
Hale said the external tank that will be used on Atlantis for STS-121 is at Michoud undergoing nondestructive evaluation of the areas where foam was lost. Afterward, he added, "the PAL ramp will be dissected and looked at very carefully for what we can learn from that."
The greatest uncertainly about the shuttle work schedule comes from a Michoud workforce of more than 2,000 employees who were affected by hurricanes Katrina and Rita, which devastated the Gulf Coast states of Louisiana, Mississippi and Alabama. (See related article.)
Roughly a quarter of the employees are back at work, with nearly all expected back by December 1.
"Our biggest problem is not damage to the [facility], but infrastructure on workers' homes and on the highways," Hale said. "Michaud has lost the equivalent of three months worth of work based on effects of hurricanes."
Still, the NASA managers are confident about the tentative May launch window.
"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," Hale said, "otherwise we wouldn't even be talking about a tentative kind of schedule at this time."
(The Washington File is a product of the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)