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NASA Targets March 2006 for Next Space Shuttle Mission

19 August 2005

Engineering teams investigate loss of foam from external tank

By Cheryl Pellerin
Washington File Staff Writer

Washington -- NASA is targeting March 2006 for the next space shuttle mission (STS-121) while it investigates the loss of insulating foam from the space shuttle Discovery’s external tank during its July 26 launch.

A large piece of the foam flew off Discovery’s external fuel tank during the July 26 launch. The foam – 61 to 84 centimeters long, 25 to 33 centimeters wide and 6 to 20 centimeters thick – was seen by high-resolution cameras added to the shuttle after the loss of Columbia in 2003. (See related article.)

At an August 18 press conference at NASA headquarters in Washington, agency Administrator Mike Griffin and William Gerstenmaier, NASA's new associate administrator for space operations, said two engineering teams have identified major areas of concern and are making progress in dealing with the problems. “We are giving ourselves what we hope is plenty of time to evaluate where we are,” Griffin said.

Over the next two weeks, Gerstenmaier said, NASA engineers and field centers will evaluate the proposed March date and determine whether that will be the official launch date.

Gerstenmaier said the delay – STS-121 was originally scheduled to launch in September – probably will not have a major impact on NASA’s ability to complete construction of the International Space Station.

“We are not trying to get a specific number of flights out of the shuttle system,” Griffin said. “We are working toward an orderly and expeditious ... retirement of the shuttle system over the next five years.”

Griffin said NASA would view shuttle missions as a process, not as individual launches. “We’re going to work each mission through the process, being as careful as we can, as deliberate as we can, with the intent to go fly. When we get to the end of that process, we’ll fly.”

Between now and the shuttle’s retirement in 2010, Griffin said, the shuttle will be used to assemble the space station.

“Absent major problems,” he added, “we believe that we can essentially complete the assembly of the space station with the shuttle fleet in the time that we have remaining and that’s what we’re going to try to do.”

Discovery will be used for STS-121 rather than Atlantis, Gerstenmaier said, putting NASA in a better position for future missions to the space station. Atlantis will fly the following mission, STS-115, carrying space-station truss segments which are too heavy to be carried by Discovery.

By changing the lineup, he added, the program will not have to fly back-to-back missions with Atlantis, as previously scheduled.

STS-121 will be the second test flight to the International Space Station in the shuttle return-to-flight series.

FOAM SHEDDING

The main problem being addressed by two engineering teams at NASA’s Michoud Assembly Facility in New Orleans is the shedding of insulating foam from the shuttle’s external tank during launch.

Foam shedding has been a problem during every shuttle launch and was the cause of the Columbia accident that killed seven astronauts.

The Columbia mission lifted off January 16, 2003, for a 17-day science mission featuring microgravity experiments. On re-entering the atmosphere February 1, the orbiter exploded because of a hole made during launch by falling foam from the external tank that damaged panels on the underside of the left wing.

The orbiter and its seven crewmembers were lost 16 minutes before Columbia was scheduled to touch down at Kennedy Space Center in Florida.

The main problem area on the external tank involves one of the two protuberance air-load (PAL) ramps. PAL ramps are designed to prevent unsteady airflow under the tank’s cable trays and pressurization lines during launch.

The ramps consist of thick, manually sprayed layers of foam, a piece of which came off during the Discovery launch – even after extensive modifications for the return-to-flight effort -- but did not hit the orbiter.

Gerstenmaier said NASA would have to repair the PAL ramp before the next launch, but “how exactly we do that, we don’t know yet.”

Before the engineering team chooses a repair technique, he said, “We’re going to understand every bit of data we can get out of the existing tanks.”

The engineers will examine several existing tanks that are ready to fly, he said. “We want to dissect some of the PAL ramps that are already on vehicles,” he said. To do that, they will move the tanks to Michoud to do nondestructive testing, and combine that data with data collected during the Discovery launch.

Gerstenmaier said the engineers are considering removing the existing PAL ramp and spraying a new PAL ramp in its place, but they still have a lot of work to do before they decide on a repair technique.

“We flew 113 flights without seriously addressing the issue of how much foam was coming off the tank – why, where and what it was doing,” Griffin said.

“In a very important sense, this was the first try that the NASA team ever really made to reduce the foam shedding to a minimal and acceptable level,” he added. “I think they did pretty darn well for the first try, and that’s how I’d like for people to view it.”

At NASA's Dryden Flight Research Center in California, final preparations are under way for Discovery's return to Kennedy Space Center in Florida.

The orbiter will be attached to one of NASA's modified Boeing 747 shuttle carrier aircraft for the cross-country ferry flight, scheduled to depart August 19. Arrival at Kennedy Space Center is expected late morning August 20, unless there are weather delays.

Additional information on the shuttles’ return to flight is available on the NASA Web site. 

(The Washington File is a product of the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)