HOUSTON - The vital heat shield on
the shuttle Atlantis appears to be in good shape after nearly a week linked
with the Hubble Space Telescope, which circles the Earth in a region known to
be littered with more junk than NASA's usual orbital haunts.
After repairing the 19-year-old
Hubble, Atlantis astronauts fired their shuttle's engines on Tuesday to
lower part of their orbit out of the space telescope's 350-mile (563-km) high
neighborhood as a precaution against debris hits.
They also took a second look at
their shuttle's heat shield to make sure the protective panels lining its wing
edges and nose cap were free of any new damage from space
debris or micrometeorites. The survey is a now-standard late inspection,
but NASA isn't expecting any surprises.
"There wasn't anything specific that
anybody was worried about," said Tony Ceccacci, lead flight director for the
mission, in a news briefing here at NASA's Johnson Space Center.
Analysis under way
Engineers on Earth are expected to
complete their analysis of today's inspection late Wednesday.
Atlantis is due to land Friday to
end an 11-day mission to overhaul the Hubble Space Telescope for the fifth and
final time. The astronauts performed five challenging spacewalks to install two
new instruments, perform vital maintenance and repair two broken instruments
that were never designed to be fixed in space.
The astronauts left Hubble more
powerful than ever when they redeployed the space telescope earlier today.
NASA has said Atlantis faced a
higher than usual risk of damage from space debris -about a 1-in-229 chance -
at Hubble's height. The International Space Station orbits Earth at about 220
miles (354 km), where it and visiting shuttles face a 1-in-300 chance of a
serious debris strike.
Because of their different altitudes
and orbits, Atlantis cannot reach the safe haven of the space station if in the
unlikely event it is damaged beyond repair. In an unprecedented precaution, NASA
has a second shuttle - Endeavour - standing by on a Florida launch pad ready to
fly a rescue
mission in case one is needed.
Healthy shuttle
NASA has kept a close watch on
shuttle heat shield health since the 2003 Columbia tragedy, where a piece of
launch debris damaged that shuttle's heat shield and led to the loss of the vehicle
and its seven-astronaut crew. Now, shuttle crews scan their heat shield twice
every mission to check for damage.
Earlier in the Hubble flight, NASA
gave Atlantis a clean bill of health with respect to launch debris. That's not
to say the shuttle reached this point completely unscathed.
During the shuttle's May 11 launch,
a small piece of debris popped free from Atlantis' attached external tank and
left a series of shallow nicks in four of the black, heat-resistant tiles on
the spacecraft's starboard side edge.
The damage is minimal - just small,
shallow dings in thick tiles just forward of where Atlantis' fuselage meets its
starboard side wing.
LeRoy Cain, NASA's deputy shuttle
program manager, said image analysts found that the damage posed no risk to
Atlantis or its crew.
Wing-mounted sensors also detected a
small impact to a heat shield panel on Atlantis' starboard wing while the
shuttle was in Hubble's high orbit. But the hit was too weak to cause any
damage, Cain added.
At one point, a piece of debris
created during a Chinese anti-satellite test in 2007 flew relatively close by
the shuttle, but not close enough to require astronauts to move out of the way.
Even at the lower orbit, Ceccacci
said Mission Control will not relent on their watch for space debris and the
health of Atlantis.
"The only sigh of relief you're
going to get from me is when the wheels are on the ground," Ceccacci said.
"Until we get them home, you still have that anxiety in your heart."
SPACE.com is providing continuous
coverage of NASA's last mission to the Hubble Space Telescope with senior
editor Tariq Malik at Cape Canaveral and reporter Clara Moskowitz in New York. Click here for mission
updates and SPACE.com's live NASA TV video feed.
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