[meteorite-list] Possible Micrometeoroid Hits Space Shuttle's Left Wing

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 12 Dec 2006 08:21:25 -0800 (PST)
Message-ID: <200612121621.IAA23786_at_zagami.jpl.nasa.gov>

http://www.spaceflightnow.com/shuttle/sts116/061211postmmt/

Engineers examine shuttle inspection imagery
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
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.
Received on Tue 12 Dec 2006 11:21:25 AM PST