Risk, Schedule Likely To Shape NASA Fuel Tank Decision

by












  Space News Business

Risk, Schedule Likely To Shape NASA Fuel Tank Decision

By TARIQ MALIK
Space News Staff Writer
posted: 06 September 2007
11:43 am ET





CAPE CANAVERAL, Fla


.–


NASA is weighing




several options




for




possibl




e modif




ications to




the




space shuttle fuel tanks after a debris strike etched a deep gouge in




Space Shuttle Endeavour’s




underbelly during its recent launch




, a top shuttle official said Aug. 20




.



Wayne Hale, NASA’s space shuttle program manager, said a team of engineers are studying up to five methods of tweaking fuel tank brackets to avoid the type of foam debris hit that dinged Endeavour.

“They all involve some reduction in the foam around the top of this little bracket,” Hale told reporters in an Aug. 20




briefing.

A small piece of foam about the size of a baseball fell from a bracket on Endeavour’s fuel tank roughly a minute after the shuttle’s Aug. 8 launch. The shuttle




landed safely Aug. 21




here at




Kennedy Space Center




.

Any fuel tank modification, if required, is not expected to add a major delay for NASA’s planned Oct. 23 launch of the shuttle Discovery to deliver the new Harmony connecting node to the international space station.

“It’s a serious problem for us, and we recognize right away that we need to go resolve it before we fly the next mission,”


LeRoy Cain, NASA’s launch integration manager,


said.

But it could affect a planned December flight




of Atlantis to haul the European Space Agency’s Columbus laboratory to the station, Hale said. That flight has a slim, week-




long window that opens Dec. 6 in which to launch to




the space station, he added.

NASA has a relatively tight schedule of at least 11 more shuttle flights planned to complete space station construction by September 2010, when the agency’s three-orbiter fleet is slated for retirement. Nevertheless, engineers will evaluate shuttle fuel tank safety between flights to identify what type of fix, if any, ultimately will be




required, NASA said.



The




nearly 1-gram foam chunk, which may have contained some ice, unexpectedly ricocheted off a metal tank strut and gouged a deep








9-centimeter by 5-centimeter




long divot in the fragile heat-resistant tiles on Endeavour’s belly.



“We didn’t think this could happen before,” Hale said, adding that previous studies predicted such foam debris would sweep harmlessly past an orbiter. “Clearly, we’re smarter now than we were a couple of weeks ago.”

While the resulting damage was later found to pose no risk to the safe return of the orbiter or its seven-astronaut crew, NASA has found similar foam-shedding events on its last few shuttle flights. The damage from any such foam loss to an orbiter’s heat shield is not believed to be catastrophic, like that which led to the 2003 Space Shuttle Columbia accident, but engineers are analyzing it just to be sure, Hale said.

The increased frequency has prompted speculation that an extra hour that has been added to launch countdowns – to allow inspection




teams to scan shuttle fuel tanks for ice build-up – may actually contribute to ice formation that ultimately cracks or loosens foam debris.



NASA engineers




already are planning to replace the foam-covered brackets on fuel tanks, beginning with a planned April 2008, shuttle flight, but discussion is ongoing on whether an interim fix will be required. The space agency has worked continually




to avoid foam debris during liftoff since a chunk of the insulation tore loose during the 2003 launch of Columbia and led to the orbiter’s destruction during re-entry.



Cain told reporters that the space agency delayed the planned Aug. 21 mating of the next scheduled shuttle fuel tank to its twin solid-rocket boosters pending a final design change decision.

Trimming some unnecessary foam insulation from the brackets or coating them in slick solution or oil are among the possible modifications under discussion, he added.

“It’s just another day at the office,” Hale said. “This is the kind of work that we’re into if we want to fly this vehicle throughout its manifest.”