Engineers examine shuttle inspection imagery
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: December 11, 2006
The Discovery astronauts used the space station's robot arm for a quick, unplanned inspection of the shuttle's left wing outboard leading edge panels based on sensor data indicating a possible micrometeoroid hit earlier today. John Shannon, chairman of NASA's Mission Management Team, said if the data reflected a real impact - and that remains to be seen - it was about 100 times below the threshold expected to cause any real damage.
Television views from the station arm did not show any obvious signs of damage to the reinforced carbon carbon panels in question. The astronauts promptly moved on to using the shuttle's robot arm to pull a new solar array truss segment from Discovery's cargo bay for handoff to the station arm. The spacer segment will be attached to the end of the station's main truss during a spacewalk Tuesday.
Shannon said data from a wing leading edge sensor, a post-Columbia system designed to detect possible impacts during launch or in orbit, recorded a 0.12-G "hit" around 5:30 a.m. Impacts registering 1 G "root mean square" are NASA's threshold for concern and that's 10 times less than the force required to cause serious damage.
By that standard, the force recorded by the sensor on the left wing was some 100 times less than required to cause entry-critical damage. But Shannon said time was available in the crew's schedule to take a quick look and while "I don't think anybody saw anything there," it was the right call to check it out.
Of more interest, perhaps, is a photograph taken by the station astronauts earlier today during Discovery's final approach to the outpost. The picture shows an area of the shuttle's belly around one of the two propellant-line umbilical doors that close after the ship's external tank separates in space.
The imagery shows a reddish, cellophane-like material extending from the door hinge line area and chipped heat-shield tiles just outboard of the door.
As for the former, "what the team thinks this is is some purge barrier material," said Shannon. "It's a cellophane-type material that is put inside the external tank umbilical area and it keeps the (pre-launch) nitrogen purge in that area, it's basically like you're sealing it up, like a baggy, so when you get the N2 purge in there, it doesn't just go out in the atmosphere, it stays where you want it to stay.
"This stuff is ... like orange Saran wrap, orange cellophane. It'll burn off very quickly (during re-entry). The team is looking at it just to make sure the compression seal we get around (the door), that this wouldn't interfere with that at all. I think that's going to prove to be very true and it's not going to be an issue. But, of course, the team is still working it."
As for the chipped tile just outboard of the door, "it looks like we had some recirculating flow back in there (during ascent) and something was hitting those tiles and taking small chips out of them," Shannon said. "Is this an issue? I don't know at this point. The team is working on it. I don't expect it to be a big deal. The thing we're always concerned about is if you had tile damage that goes across a seal. It doesn't look like it goes across a seal in any of these, it looks really shallow."
But to be on the safe side, the imagery assessment team "is going to meet at midnight tonight and determine if that's an area we'd like to look at some more, to go do a focussed inspection, or if they have sufficient data ... to clear that as no issue at all."
As part of NASA's post-Columbia safety improvements, shuttle crews are now launched with repair materials capable of fixing relatively minor heat shield damage. But they would be asked to do that only if engineers believed the shuttle was at risk. The damage in question does not appear nearly that serious.
"Am I concerned about this?" Shannon mused. "Not really, not right now. But I refuse to short-circuit the team. I'm going to let them go off and do their analysis and we'll just take it a step at a time."
Discovery docked with the international space station at 5:12 p.m. after a two-day orbital chase. After the impromptu wing inspection, astronaut Nicholas Patrick used Discovery's robot arm to pull the 4,110-pound P5 truss segment from the shuttle's cargo bay. He then handed the spacer segment off to astronaut Sunita Williams, operating the station's robot arm.
Williams, a Navy helicopter pilot and diver, hitched a ride aboard Discovery to join the station's full time crew as a flight engineer. She replaces German astronaut Thomas Reiter, who was launched to the station in July. He will return to Earth aboard Discovery in Williams' place.
The P5 truss segment will serve as a spacer between two huge sets of solar arrays on the left side of the station's main truss. One set of arrays, P4, was attached to the station in September along with a massive rotary joint known as P3 that will rotate the arrays like giant paddle wheels to track the sun.
The arrays that ultimately will be bolted to P5 are currently mounted atop the station's Unity connecting module. The P6 arrays were launched six years ago to serve as an interim source of power during the initial stages of station assembly.
One of the P6 solar wings will be retracted on this flight and the other on the next shuttle mission in March. If all goes well, P6 will be attached to P5 next fall to complete the left side of the station's main solar array truss.
During a spacewalk Tuesday, astronauts Robert Curbeam and Christer Fuglesang, Sweden's first astronaut, plan to bolt P5 to the P4 segment. Two more spacewalks Thursday and Saturday will be devoted to re-wiring the station to take advantage of the permanent power system.