NASA Tackles External Tank Tests, Aims for May '06 Shuttle Launch
An image from an onboard camera during Discovery's launch shows the chunk of foam that has led to a grounding of the fleet. The picture was released July 27.
Credit: NASA

With a firm testing plan in hand and its fuel tank factory back on track, NASA is targeting May 2006 for the launch of its next space shuttle mission.

The May launch target, while not set in stone, will allow engineers time to complete a series of tests to determine why potentially dangerous chunks of foam insulation broke free from the shuttle Discovery's external tank during its July launch, NASA officials said. They believe that a combination of worker-caused damage, old application techniques and other factors appear to have contributed to the debris event.

"We don't say we're setting a launch date, but we're clearly aiming for May," said Bill Gerstenmaier, NASA's associate administrator for space operations, during a Friday press conference. "May looks very doable."

A 20-day launch window opens on May 3 for the space shuttle Discovery, NASA officials said, adding that more discussion is needed before the window becomes a firm flight target.

NASA officials previously aimed at March 2006 to launch the second post-Columbia accident flight - STS-121 aboard the Discovery - but said today that recovery efforts from Hurricanes Katrina and Rita led to a loss of about three months of work.

The storms battered NASA's Michoud Assembly Facility in New Orleans, where external tanks are built and investigators were studying the foam shedding issue, and the surrounding area, though the plant itself did not suffer the worst damage, NASA officials said.

"Our biggest problem, frankly, at Michoud is not the damage to the plant," said Wayne Hale, NASA's space shuttle program manager. "It's the damage to the workers' homes."

More than 500 workers of Michoud's 2,000-person strong workforce have resumed their duties, NASA officials said. The facility's workforce is expected to return to its full strength by Dec. 1.

"Final schedule setting will depend on how soon the workforce can get back online," Hale said of NASA's STS-121 launch plans.

 

Tracking debris shedding

A one-pound piece of foam insulation broke free from protective ramp during Discovery's July 26 launch, but did not strike the orbiter. NASA, however, had worked for 2 ? years to prevent the shedding of large foam debris after Columbia disaster that killed seven astronauts on Feb. 1, 2003.

During Columbia's launch, a 1.67-pound piece of foam fell from its fuel tank and gouged a hole in the protective heat shield along the orbiter's left wing leading edge. The resulting damage allowed hot atmospheric gases to enter the wing during reentry and rip the vehicle apart.

Richard Gilbrech, who is leading NASA's "tiger team" investigating the foam shedding problem, external tank workers may have inadvertently crushed or cut foam along a protuberance air load (PAL) ramp, which shields exterior tank cables and pressurized lines during launch, while instituting post-Columbia accident fixes.

An older spray application technique - instead of a newer, enhanced method - and thermal stresses along the seam of where PAL foam meets acreage foam, may also have contributed to debris shedding on Discovery's tank, Gilbrech said.

"I don't know if we'll ever identify one root cause," Gilbrech said.

Engineers plan to conduct tests to determine how much force is required to crush foam, as well as perform non-destructive tests on the next external tank to fly - ET-119 - which NASA shipped to Michoud last month. Tank workers will also remove ET-119's PAL ramp and slice it into 1/8th-inch pieces to further study the foam's integrity, NASA officials said.

Those tests and others must be completed before the fuel tank is shipped back to NASA's Kennedy Space Center (KSC) for Discovery's STS-121 flight, they added.

"Before we set an official launch date, we've got to get through some of the near term work," Hale said. "I think we're beginning to get our hands well around the problems we have."