Spaceflight Now




Shuttle launch hinges on data from external tank tests
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: August 13, 2009


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NASA is pressing ahead with preparations to launch the shuttle Discovery Aug. 24 on a space station resupply mission, but Program Manager John Shannon said today a final decision to proceed will depend on the results of last-minute testing this weekend to verify the integrity of external tank foam insulation.

 
Credit: NASA-KSC
 
During the shuttle Endeavour's launch July 15, an unusual amount of foam insulation fell away from external tank No. 131, most of it from the central "intertank" separating the hydrogen and oxygen sections of the tank. A small amount of foam fell from the base of the left-side bi-pod strut that helps hold the shuttle's nose to the tank and another piece of debris fell from one of the so-called ice-frost ramps on the side of the liquid oxygen section.

The bi-pod foam loss is an understood condition, Shannon said, the result of trapped air in foam round a wire bundle that can expand due to atmospheric friction during launch, popping off overlying foam. The problem is magnified with repeated tank loadings and engineers have inspection techniques in place to identify problems.

Engineers still don't know what caused the intertank foam to separate, but 170 plug-pull tests have been carried out in which small cores of foam were pulled with a known force to test the insulation's adhesion to the underlying metal. In all cases, the foam performed at or above specifications.

Even so, engineers ordered a final round of plug-pull tests this weekend from areas of the tank that pose the most risk from a shuttle impact standpoint. That work should be completed this weekend.

The ice-frost ramps are areas of aerodynamically shaped foam around fittings used to attach pressurization lines to the side of the tank. Endeavour's tank was the second in a row to lose foam from the same IFR and engineers want to make sure there are no problems that could affect the IFRs on Discovery's tank, ET-132.

The IFR in question was X-rayed before Discovery's move to launch pad 39A, but three other ice-frost ramps were not. None of those has any history of foam shedding, but some engineers at the shuttle program flight readiness review Monday and Tuesday recommended a roll back to the Vehicle Assembly Building for additional X-ray inspections to make sure there are no problems.

Shannon said the majority of the team opted to proceed with additional testing before next week's executive level FRR.

"Across the board, the vehicle's in great shape," he said. "We're preparing to go fly on Aug. 24, but we have two areas of open work. The first one is to go look at the next tank in line with the X-ray and make sure we don't have a process problem with the ice-frost ramps. The second is to complete the plug pulls and repairs and verify the data (are) good.

"And with that data collected, the majority of the team thought we were in good shape to proceed for the agency flight readiness review. On the intertank, it was complete consensus. On the LO2 ice-frost ramp, about a quarter of the team thought it was still prudent to roll the vehicle back and collect that data on the other three ice-frost ramps. That's what the debate was yesterday."

A rollback to the VAB would delay launch to around Oct. 17, after upcoming Japanese and Russian space station supply and crew rotation missions.

"I would expect that after we get the X-ray data on the next tank, we'll meet again and review the and make sure we're all at a common understanding and go into the flight readiness review with that discussion," Shannon said.

Overnight, engineers used a terahertz X-ray device to examine the ice-frost ramps on external tank No. 133, the next tank in the shuttle launch sequence, to look for any signs of voids in the foam. Air trapped in such voids can expand due to atmospheric friction during launch, causing overlying foam to pop off.

"If they look OK, that's pretty strong evidence you don't have a processing problem," Shannon said. "But there is still some level of doubt. Nobody said we absolutely have to go have that data, where we pull it back (to the VAB) and get the X-ray data. But about a quarter of the engineering community said just to be sure, you should go do this, we recommend you go do this.

"And that'll be the discussion at the agency FRR. We don't require complete consensus, but what we do require is that we hear everybody's position and that we understand their position. I think I understand it very well. All of it has devolved really down to one question: Is there some uncertainty in the process for putting together those ice-frost ramps such that you would need that data? I think the ET-133 data will help us answer that question."

Looking ahead, Shannon said another round of layoffs is planned for October, reducing the shuttle workforce by about 10 percent. An initial round of 900 layoffs was announced at the end of April.

"Two weeks ago, I attended the last space shuttle main engine firing at Stennis (Space Center)," Shannon said. "We have completed the last weld on the last external tank. In January, we will do the last (solid propellant) casting in Utah at the facility out there that produces the solid rocket boosters. In October, we will lay off approximately 1,200 shuttle employees, which is about 10 percent of my current workforce.

"So we are definitely on the pace to shut the program down at the end of 2010. We have communicated all of that, that's not a surprise to anyone."

Counting Discovery's upcoming mission, only seven more flights are planned before the program comes to an end in late 2010 or early 2011. There has been talk of extending shuttle operations to bridge the gap before the debut of a replacement spacecraft, but a presidential commission reviewing manned space flight options for the Obama administration does not appear to favor that approach.

Asked today what it would take to extend shuttle operations, Shannon said "there would be significant work to requalify venders and restart processes. We have had that in the back of our minds ... and we have plans for how we could do that if it is required.

"But we're getting to the point if we don't have a decision late this year, we're going to end up having a gap between when we would stop flying the flights that are currently on the manifest and any new flights that would be out there," he said. "So it's getting very late in the game for us."

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