Space shuttle wing leading edge issue assessed
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: October 10, 2007;
Updated with meeting results
The shuttle Discovery's crew strapped in for a dress-rehearsal countdown today to clear the way for launch Oct. 23 on a critical space station assembly mission. NASA managers, meanwhile, met for a program-level flight readiness review but were unable to reach a consensus on whether to replace three suspect wing leading edge panels or to launch Discovery as is.
Replacing the panels would require moving Discovery off the launch pad and back to its hangar for repairs, work that likely would delay launch for weeks if not longer. A decision on how to proceed is expected next week, after a headquarters-level flight readiness review Tuesday.
The issue involves a protective silicon-carbide coating on the shuttle's reinforced carbon carbon nose cap and wing leading edge panels. The nose cap and 44 RCC leading edge panels - 22 on each wing - protect the shuttle from the most extreme heating during re-entry when temperatures exceed 3,000 degrees Fahrenheit. A breach in Columbia's left wing leading edge led to the shuttle's destruction in 2003.
Since then, NASA and contractor engineers have paid close attention to the RCC panels and nose cap, devising sophisticated non-destructive tests to assess the health of the critical carbon composite material before each flight. In this case, engineers already knew about three RCC panels - 9 right, 13 right and 12 left - that had small areas of coating degradation.
Going into Discovery's launch campaign, the leading theory for the cause of the degradation was a slow process of oxidation. Using a technique known as thermography, engineers showed that the areas of concern were stable and had not worsened over the two most recent flights. Based on that, along with past experience with the panels and other test data, the orbiter project and wing leading edge subsystem engineers concluded in August that Discovery could safely be launched as is. The groups repeated that recommendation today.
In the meantime, the NASA Engineering Safety Center, an independent review group set up after the 2003 Columbia disaster, concluded ongoing analysis of test data did not support the presumed root cause of the coating degradation and that as a result, engineers cannot predict how the damage might evolve over time or accurately assess the danger it might pose. If the coating is lost, a catastrophic burn through could occur.
The NESC today recommended replacing RCC panels 9 right, 13 right and 12 left, work that, if ordered, would cause a significant launch delay because the panels cannot be changed out at the launch pad.
Shuttle program manager Wayne Hale chaired today's program-level review, but no final decisions were made. Discovery's flight is the first to use a new approval process, splitting up the traditional flight readiness review into separate program- and headquarters-level meetings. A NASA spokesman said the RCC issue, along with a handful of other open items, will be reviewed at next Tuesday's senior-level readiness review.
Discovery's crew, meanwhile, donned pressure suits and strapped in aboard the shuttle today for a dress-rehearsal countdown, a milestone training exercise for the entire launch team. Half a world away at the Baikonur Cosmodrome in Kazakhstan, the space station's next full-time crew was successfully launched as preparations for the next shuttle visit move into high gear.
The primary goal of Discovery's mission is to deliver a new multi-hatch module that will serve as the connecting point for European and Japanese research modules scheduled for launch in December and early next year. The astronauts also plan to move a stowed set of solar arrays to its permanent mounting point on the far left end of the station's main power truss.
NASA is attempting to complete the station and retire the space shuttle by the end of fiscal 2010. The agency began the year with a three-month launch delay caused by hail damage to a shuttle's external fuel tank and another major delay now would raise new questions about the agency's ability to complete the lab complex on schedule.
Briefing reporters last month, Hale said he was optimistic about meeting the schedule even if unexpected problems crop up.
"We have a lot of schedule margin to complete the space station by 2010," he said. "As you know, we had a little bit of unfortunate weather early this spring that cost us about three months on the schedule. People frequently ask me, can e complete the international space station by the time the president and Congress have directed us to retire the space shuttle? And my answer is yes, we have plenty of margin.
"We have been exploring a number of options that would allow us to fly flights more rapidly should we encounter some other unforeseen difficulty, say a weather situation like a hurricane or a hail storm or some technical problem. Right now, we think it will take us most of the time to 2010 to complete space station but we have a number of options to ease that schedule, potentially by using more bays of the VAB (Vehicle Assembly Building), potentially by flying Atlantis more often, a number of different options that we could execute that would allow us to take up any slack or any problems that we might encounter.
"So I'm very optimistic we will be able to complete the international space station well ahead of the goal date to retire the shuttle and indeed to service the Hubble Space Telescope about this time next year."