HOUSTON--The heat shield designed to safeguard
NASA's space shuttle
Discovery and its astronaut crew against the searing temperatures of
atmospheric reentry is in good health, mission managers said late Tuesday.
John
Shannon, NASA's deputy shuttle program manager, told reporters that analysts have
settled concerns over two
remaining areas of interest on Discovery's heat shield.
"The vehicle
is extremely clean, and we got all of our areas cleared off," Shannon said
during a night briefing here at NASA's Johnson Space Center. "The thermal
protection system is ready to come home."
Clearing
Discovery's heat shield removes the need to add additional inspections to the busy
Wednesday work roster for the spacecraft's STS-116 crew. The astronauts and
their International Space
Station (ISS) counterparts already have a packed day ahead of them that
spotlights the first-ever solar array retraction in the orbital laboratory's
six years of human habitation.
"We really
wanted to clear the decks of any orbiter issues," Shannon said, adding that
Discovery's crew will perform a final heat shield inspection after undocking
from the ISS next week.
Shannon
that he was surprised that pre-docking photography of Discovery's belly found
no signs of protruding bits of ceramic cloth--known as gap-fillers--or plastic shims,
which have popped up on in one form or another during the last three shuttle
flights.
Discovery's
STS-116
mission is a planned 12-day spaceflight to deliver
a new segment of the ISS, rewire the station's power grid and perform a one-person
crew change for the outpost's Expedition
14 astronauts.
NASA has paid close attention to shuttle
heat shield health since the 2003
Columbia accident, in which wing damage caused by external tank debris at
launch led to the loss of the orbiter and its seven-astronaut crew during
reentry at the mission's end.
Minor
issues
Shannon said analysts first focused on the
port external tank door on Discovery's belly, where high-resolution
photographs showed minor damage to the orbiter's protective heat-resistant tiles
and orange bits of cellophane-like material jutting from the door seal [image].
"The team
worked very hard overnight on both of those problems," Shannon said.
The
cellophane appears to be barrier material used inside shuttle external tank
umbilical areas, Shannon added. The material has been seen to jut out in the past,
is not obstructing the external tank door's seal from its proper closed
position, and will likely burn off quickly during reentry, Shannon said.
Likewise, some
scuffed tiles that appear as white splotches on the uniformly black surface of
Discovery's underbelly near the orbiter's portside external tank door appear to
be the result of recirculated ice or even the cellophane barrier material rubbing
the coating from heat tiles during launch.
Similar
damage has been in many shuttle flights in the same region, NASA officials
said.
Not satisfied
simply with past flight history that the damage-prone region has not impacted
shuttle flight safety, engineers ran a series of analytical assessments of the
damage as well.
"It came
back that we had no concerns at all for that damaged tile area," Shannon said. "So the team was able to very quickly last night able to conclude that none
of the problems around the port external tank door were going to be an issue
for the safe return of Discovery."
Analysts
also cleared a sensor reading indicating a potential it by a micrometeorite
or orbital debris (MMOD) to one of Discovery's wing leading edges. Images
of the region taken by cameras at the tip of the International Space Station's
robotic arm found no signs of damage late Monday, and a subsequent round of
photography using Discovery's own robotic appendage was on tap for Tuesday
night.
"It's not
clear whether we were struck by MMOD or not," Shannon said, adding that impacts
to other nearby areas could have caused the same reading and that no damage has
been found. "We're interested in getting the vehicle back on the ground and taking
a look at it, but it was very clear that we had sufficient imagery to clear the
vehicle of this concern and not worry about it anymore."
In a debris
related note, STS-116 lead spacewalk officer Tricia Mack said that NASA had confirmed
in spacesuit camera video that European Space Agency astronaut Christer
Fuglesang did lose a 7.8-inch extension for a pistol grip tool during a Tuesday
spacewalk to install the new Port 5
(P5) spacer truss at the ISS [image].
The metal extension weighs just under a pound and was last seen drifting in a "portish"
direction, Mack said, adding that debris experts are working to track it.
Discovery's
crew was alerted of the spacecraft's healthy status earlier Tuesday.
"Sounds
like you guys have obviously done your usual thorough analysis," STS-116
commander Mark Polansky said Tuesday. "We're happy to hear that we'll be able
to go ahead with the nominal timeline tomorrow."
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