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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