Image: Blanket test
NASA / ARC  /  AP
This photo, provided by NASA Ames Research Center, shows a torn thermal blanket that was taken off the shuttle Endeavor and tested Thursday in a wind tunnel at NASA's Ames Research Center in Mountain View, Calif. The test helped managers decide to clear the shuttle Discovery for landing.
By Alan Boyle Science editor
msnbc.com

Aug. 4, 2005 — After days of analysis and one repair spacewalk, NASA has decided that the shuttle is "safe to fly for re-entry," a top mission manager said Thursday.

The final issue of concern — a torn thermal blanket just below the cockpit window that might shed bits of debris during the shuttle's descent — was cleared off the table Thursday morning after a series of wind-tunnel tests, said deputy shuttle program manager Wayne Hale, who heads Discovery's mission management team.

The tests indicated that even if pieces of cloth debris blew off and struck the aft section of the orbiter, it would be "of negligible concern" and pose no threat to Discovery's safe landing, he said. Under those circumstances, sending spacewalkers out to snip away the torn section would have violated the "first, do no harm" rule, Hale said.

Hale said there was a lengthy discussion about the blanket during Thursday's meeting of mission managers, with dissenting opinions expressed. The managers even heard from some of the engineers who had registered concerns about the shuttle Columbia during its doomed flight in 2003. "This little blanket turned into a huge effort," he told reporters at NASA's Johnson Space Center in Houston.

In the end, the team agreed to clear the shuttle for the flight home.

"To the best of our knowledge and ability ... we believe the vehicle is safe to fly for re-entry," he said. Later, he confirmed that "we have cleared Discovery to re-enter."

However, Hale said no one could guarantee that Discovery's descent, now scheduled for early Monday, would be trouble-free. "That would be untrue and foolish to even try to make that case," he said.

One fix made already
Discovery's crew has already made one fix to the shuttle. During a spacewalk on Wednesday, astronaut Stephen Robinson easily removed two fabric gap fillers that might have posed the risk of another Columbia-type tragedy as the spacecraft passed through the heat of re-entry.

The concern about the gap fillers, and about the torn blanket, arose because Discovery was subjected to unprecedented inspections that NASA set up as a response to the Columbia tragedy, in which seven astronauts were killed.

Video: Remembering Columbia Discovery's crew of seven first got word that another spacewalk would be unnecessary from Mission Control, hours after they delivered a moving tribute to the Columbia astronauts .

“We have good news,” capsule communicator Julie Payette radioed to Discovery. The mission management team concluded that the torn blanket “is safe for return. There’s no issue,” she said.

Japanese astronaut Soichi Noguchi, one of the crew’s assigned spacewalkers, replied: “That’s, I would say, good news.”

Earlier this week, NASA said an analysis of the inspection data for Discovery's protective tiles and reinforced carbon-carbon panels turned up no other potential threats for the shuttle's descent and landing.

If NASA had decided that Discovery was not safe for re-entry, the crew would have had to take refuge on the international space station, where the shuttle is currently docked, and wait for a rescue shuttle to pick them up later this month. Once Discovery was cleared for the return trip, launch team members working on the shuttle Atlantis at NASA's Kennedy Space Center in Florida were told they no longer had to prepare for the high-risk rescue mission, Hale said.

The all-clear meant Discovery's crew could go ahead with preparations for Saturday's scheduled undocking from the station. During a week of docked operations, the astronauts have transferred tons of supplies from the shuttle to the station, and packed tons of old equipment and trash from the station aboard the shuttle. Spacewalkers also replaced a broken-down guidance gyroscope on the station, installed a stowage platform and tested tools that someday may have to be used to repair the shuttle's tiles or reinforced panels.

Foam questions linger
Meanwhile, back on Earth, NASA continued to investigate problems related to foam insulation on the external fuel tanks used by space shuttles. It was a flying piece of foam that damaged Columbia's wing shortly after liftoff in January 2003, setting the stage for the shuttle's catastrophic breakup 16 days later as it plunged through the atmosphere toward its landing.

During Discovery's ascent to orbit on July 26, the fuel tank lost an unexpectedly large piece of foam from an area known as the protuberance air load ramp, or PAL ramp. Although the piece did not hit the shuttle orbiter, NASA said it would hold up on future shuttle flights until the foam problem is fully resolved.

The New York Times reported Thursday that an internal NASA memo warned in December that there were still problems with the way foam was being applied to the fuel tank, and that “there will continue to be a threat of critical debris generation.” A NASA spokesman told the newspaper that the agency had written a response to the memo, but the response could not be released because of confidentiality rules related to export restrictions.

According to the Times, the memo did not argue against launching Discovery. In fact, the memo reportedly said the tank that Discovery used, ET-121, was "ready to support the resumption of flight operations."

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