HOUSTON -
NASA managers are discussing whether a late heat shield inspection that has made
an already busy flight even more so for six astronauts aboard the shuttle
Discovery is worth the extra time and risk, a lead flight director said
Saturday.
Tony
Ceccacci, lead shuttle flight director for Discovery's STS-121 mission, said
flight planners and heat shield experts closely monitored the current crew over the last two days to determine whether the data gleaned from an additional inspection merits the extra rigors placed on orbiter astronauts.
"What we're
trying to see is how difficult this is to do and whether it's worth the risks
of working the crew harder and such," Ceccacci said during a mission update
here at Johnson Space Center (JSC). "We're using this as a good test to make
sure we can accomplish this and accomplish this safely."
The final
inspections, which return up-close views of the reinforced carbon carbon (RCC)
panels fixed to Discovery's nose and wing edges, are aimed at determining
whether micrometeorites or other orbital debris have damaged the orbiter's heat
shield during its eight days of docked operations at the International Space
Station (ISS). If they turn up clear, Discovery will be given approval to
land Monday, but if analysts find a large enough concern the orbiter's crew could return to the
ISS to seek shelter, NASA said.
At the same
time, engineers continue
to watch the tank pressure in one of the orbiter's auxiliary power units
(APU), which appears to be leaking either gaseous nitrogen or toxic hydrazine
fuel. If the leak is hydrazine - it is not yet certain - and remains unchanged,
it should not impact Discovery's planned Monday landing.
Discovery's
STS-121 crew, commanded by veteran shuttle astronaut Steven Lindsey, undocked
from the space station early Saturday at 6:08 a.m. EDT (1008 GMT). After
pulling away from the station toward a station-keeping post some 40 nautical
miles (74 kilometers) from the ISS, the shuttle astronauts went straight into a
final inspection of Discovery's starboard - or right - wing leading edge and
nose cap using a sensor-equipped, 50-foot (15-meter) boom attached to the end
of the shuttle's robotic arm.
The crew
completed a similar survey of the spacecraft's port wing leading edge Friday,
but delved
about an hour into the sleep preparation to complete the task due to a
delay caused by ISS robotic arm glitches.
Lindsey
opted to push ahead with the task anyway, even when given the option to scrub
it from the schedule altogether.
"We're
looking at the future flights to see what would be required to accommodate it,"
Ceccacci said of the added inspections. "The more you take off the plate to
complete the late inspection, now you're taking that out of the mission
timeline and now you have to find a place put that on a later mission. They may
not all line up, and have like a domino effect."
NASA has 15 planned shuttle missions, spread across its three remaining orbiters, to complete the ISS by 2010. The next flight, STS-115 to launch aboard Atlantis slated for a late-August launch, may also has room in its timeline for late heat shield inspections, Ceccacci said.
Discovery's
STS-121 mission is NASA's second shuttle test flight since the 2003 Columbia accident, which
one orbiter and seven astronauts were lost due to a heat shield breach in the
spacecraft's left wing leading edge caused by a 1.67-pound (0.7-kilogram) chunk
of external tank foam the size of a briefcase.
NASA has
since redesigned shuttle external tanks to minimize the amount of foam
insulation shed during launch.
The largest
area shed in Discovery's STS-121 launch weighed less than one ounce total,
covered a space slightly larger than a legal-size piece of paper and fell off
in stages of six smaller pieces, NASA has said.
But the
agency remains vigilant in on-orbit inspections for shuttle heat shields. Discovery's
current STS-121 astronauts and those of NASA's first post-Columbia effort - STS-114 aboard the same orbiter
- conducted intense, comprehensive scans of the shuttle's wing edges, nose cap,
thermal blankets and belly-mounted tiles for signs of damage on Flight
Day 2 of their missions
Analysis
teams on Earth pored over the resulting data and, in both flights, gave the
crews follow-up targets for focused
inspections.
Those
earlier images - which allowed mission managers for to clear Discovery's
current spaceflight to reentry - will be used as a baseline for analysis of the
new imagery from the STS-121 crew, NASA has said.
"We're
going to evaluate and see if the data we get from it and the crew time required
justifies doing it for future flights," Ceccacci said.
Discovery
is currently slated to return to Earth after a 13-day
spaceflight on July 17. The orbiter is expected to land at 9:14 a.m. EDT
(1314 GMT) at Runway 33 of the Shuttle Landing Facility at NASA's Kennedy Space Center in Cape Canaveral Florida.
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