Experts have still not decided what to do about a thermal blanket below the cockpit that is also causing concern.

Dangling at the end of a 58 feet (17.7 metre) long robotic arm with a hacksaw and forceps, Robinson became the first astronaut ever to carry out a spacewalk beneath the shuttle during orbit.

He easily pulled out the two small pieces of ceramic-coated fabric, protruding from between heat-shielding tiles under the nose of Discovery, using only his gloved hands.

"I am just putting it in my trash bag," he said after triumphantly holding the first piece up for cameras.

Robinson was accompanied on the six hour and one minute walk outside the shuttle by Japanese astronaut Soichi Noguchi.

"Beautiful, it just looked too easy," a NASA ground control official told the astronauts as they returned to the International Space Station.

It was "a great choreography between robotics and you guys out there," she said.

The operation lifted one of the doubts about Discovery's safety as it prepares to return to Earth on August 8.

Engineers had feared that the protruding gap fillers could upset the stability of the shuttle as it reenters the Earth's atmosphere and cause it to overheat in a similar way to the Columbia on February 1, 2003.

The shuttle travels at about 26,500 kilometers per hour (16,700 miles per hour) into the atmosphere, pushing temperatures on its surface to 1,370 degrees Celsius (2,500 Fahrenheit) during reentry.

The contour of the vessel's belly has to be smooth to make sure it does not overheat.

There are thousands of gap fillers on the bottom of each shuttle, used to cushion heat-shielding tiles and fill very small spaces between them. NASA had determined that removing two of them completely posed no risk to the shuttle.

A crack in Columbia's thermal shield caused by a piece of foam that hit the wing during liftoff was blamed for its destruction, which killed all seven crew on board.

Discovery is the first shuttle mission since the Columbia tragedy.

The repair appeared surprisingly easy after Robinson admitted the day that it would be a "delicate" task. Other crew members had expressed "misgivings" about the operation.

Had the fibres resisted, Robinson would have tried using forceps to pull them out, and if that had not worked he had the makeshift hacksaw ready to cut them off.

While the removal of the gap fillers took only about 40 minutes, Robinson and Noguchi stayed outside the ISS for several hours to work on other planned maintenance jobs.

They mounted a tool platform and installed a materials exposure science experiment on the orbiting space station, and meanwhile retrieved a faulty heat dissipator.

Discovery is now expected to leave the ISS on Saturday and return to Earth on Monday after its mission was extended by one day.

NASA's engineers have expressed confidence that shards of foam that came off the external fuel tank during Discovery's liftoff on July 26 did not damage the shuttle in the way that the Columbia was damaged.

However no immediate decision has been taken over what to do about a thermal blanket below Discovery's cockpit which apparently was hit by liftoff debris and has a fold in it. Experts fear it could tear off during reentry.

Flight director Paul Hill said a new unscheduled spacewalk could be staged to fix the blanket but said it was "unlikely."

He said a decision would be taken on Wednesday or Thursday after engineers have finished studying images of the blanket.

President George W. Bush on Tuesday telephoned the Discovery crew to praise their courage.

"I want to thank you for being risk-takers for the sake of exploration," Bush said in a special telephone linkup.

"Thanks for being such great examples of courage for a lot of our fellow citizens," Bush went on. "As you prepare to come back, a lot of Americans will be praying for a safe return."

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Discovery astronauts preparing to carry out a risky repair to the underside of the shuttle admitted Tuesday they are nervous about the operation.

Astronaut Stephen Robinson will carry out the unprecedented repair Wednesday taking a hacksaw and some forceps to cut two ceramic fibre strands that engineers fear could lead to a repeat of the Columbia disaster in 2003.

President George W. Bush telephoned the crew to praise the "risk-takers" of space exploration but one member said he had "misgivings" about the operation.

Robinson will at first try to pull off the strands by hand and then with forceps but if that does not work cut them off with a hacksaw.

"I am pretty comfortable with using tools very carefully," Robinson said in a press conference from Discovery. "But no doubt about it, this is going to be a very delicate task. But as I say a simple one."

NASA experts are worried that the shuttle could overheat because of instability that the gap fillers, which are about one inch (2.5 centimetres) long, dangling from between thermal tiles on the underside of the shuttle, could cause during the descent to Earth.

Japanese astronaut Soichi Noguchi will accompany Robinson on the spacewalk, the third of the mission, which is the first since Columbia disintegrated during re-entry on February 1, 2003, killing all seven crew on board.

"We are all going to be very busy" during the repair walk, Discovery Commander Eileen Collins told reporters. "I think we're all going to be involved somehow."

Discovery crew went over the repair operation and prepared the makeshift hacksaw for Robinson, who said care had to be taken with every movement to avoid scraping the delicate tiles.

"The hacksaw is really a contingency device," Robinson said, "the idea is just to pull out this thin gap filler either by hand or with a pair of forceps, and we'll use the hacksaw only if necessary."

Andy Thomas, an Australian member of the crew, said the astronauts originally had "misgivings" about going underneath the shuttle. Such a repair has never been attempted in the quarter century history of shuttle flights.

"We were concerned about it - we were concerned about the implications of it and what was motivating it," he told reporters from the shuttle.

President Bush praised the astronauts' courage in a special telephone linkup. "I want to thank you for being risk-takers for the sake of exploration," he said.

"Thanks for being such great examples of courage for a lot of our fellow citizens," Bush went on. "As you prepare to come back, a lot of Americans will be praying for a safe return."

Bush concluded: "Thanks for taking my phone call - now get back to work."

The National Aeronautics and Space Administration has been ultra-sensitive about Discovery's safety because of the cause of the Columbia disaster. A piece of foam came off during its liftoff and damaged a wing, which led to superheated gases getting into the shuttle and causing it to break up. All seven astronauts were killed.

Foam also came off during Discovery's liftoff last week but NASA is confident that apart from the gap fillers, Discovery can come back safely.

NASA said it had ordered the repair operation because of the "uncertainty" about leaving the errant pieces of ceramic-covered fabric which stop the shuttle's delicate thermal tiles from touching during the high speed return into the Earth's atmosphere.

The shuttle travels at about 26,500 kilometers (16,700 mph) into the atmosphere expanding and contracting in the extreme heat and cold.

"Given that large degree of uncertainty, life could be normal during entry or some bad things could happen," deputy shuttle programme director Wayne Hale told a news conference late Monday.

"We examined our options to set our minds at rest and make sure that we didn't stay up late at night worrying about bad things happening," Hale added.

Hale said that if the hacksaw did not work another spacewalk could be organised for Thursday or Friday with a new technique.

The shuttle is scheduled to leave the space station Saturday and return to Earth early on August 8.

earlier related report
Washington (AFP) Aug 02, 2005 Discovery astronauts Tuesday were preparing tools and techniques they will use for an unprecedented repair operation on the shuttle's thermal shield to ensure it can make a safe return to Earth.

NASA on Monday decided to cut off two ceramic fibre strands hanging from the belly of the shuttle to end any "uncertainty" about whether it would be in danger on re-entering the Earth's atmosphere, said Wayne Hale, deputy head of the US shuttle programme.

He said it was an example of NASA's new space shuttle program, adding that only when the Discovery was safe for its return to Earth would the repair operation be deemed successful.

Either Japanese astronaut Soichi Noguchi or American Steve Robinson will carry out the repairs during their third spacewalk of the mission on Wednesday, officials said.

NASA experts are worried that the shuttle could overheat because of instability that the gap fillers, dangling from between thermal tiles on the underside of the shuttle, could cause.

"Given that large degree of uncertainty, life could be normal during entry or some bad things could happen," Hale told a news conference.

"We examined our options to set our minds at rest and make sure that we didn't stay up late at night worrying about bad things happening," Hale added.

NASA engineers have spent the past three days "working very hard" to assess the risk from the gap fillers, which are only about an inch (2.5 centimetres) long.

He said the teams had "put together a very simple plan with good safety precautions and mitigations of any hazards that will allow a crewmember to go out and remove those two gap fillers."

To accomplish the task, one of the astronauts -- NASA has not yet said which -- will be carried underneath the shuttle on the station's robotic arm and attempt to either pull out the danglers or cut them off.

On Tuesday, the Discovery crew was going over the repair operation and assembling a makeshift hacksaw with which to cut off the protruding gap filler should it be necessary, NASA said.

The ceramic fiber fillers are used to keep hot gas from flowing into gaps between the thermal outer protection tiles.

At a press conference early Tuesday, astronaut Robinson said the repair was "extremely simple," although care had to be taken with every movement to avoid scraping the shuttle's delicate tiles inadvertently.

"The hacksaw is really a contingency device," Robinson said, "the idea is just to pull out this thin gap filler either by hand or with a pair of forceps, and we'll use the hacksaw only if necessary."

"The thing I'll be watching most closely is the top of my helmet ... because I'll be leaning in toward the orbiter ... so that's what I'll be most careful with," the US astronaut added.

If the repair doesn't work, Hale said earlier, "we can always go back out on Thursday or Friday with improved techniques and try again."

The shuttle is scheduled to leave the space station Saturday and return to Earth early on Monday, August 8.

NASA engineers believe that the operation is unlikely to damage the surrounding thermal tiles but even so, "that risk has got to be mitigated and controlled. Obviously you don't want to make it worse," Hale said.

He said the shuttle could safely re-enter the atmosphere with the errant gap filler removed, even though for one of the two pieces, "there's a possibility that heating could get into that gap."

"For one flight we are well within our safety margins," he said.

The National Aeronautics and Space Administration has been ultra-sensitive about Discovery's safety because it is on the first mission since Columbia broke up as it re-entered the atmosphere on February 1, 2003.

A piece of foam came off Columbia during its liftoff and damaged a wing, which led to superheated gases getting into the shuttle and causing it to break up. All seven astronauts were killed.

Foam also came off during Discovery's liftoff but NASA is confident that apart from the gap fillers, Discovery can come back safely.

NASA's chief administrator admitted Sunday that the US space agency had "goofed" on key safety checks prior to Discovery's launch July 26.

NASA announced the repairs just after Noguchi and Robinson finished a seven hour and 14 minute mission to replace a faulty gyroscope on the International Space Station where Discovery is now docked.

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Related Links SpaceDaily Search SpaceDaily Subscribe To SpaceDaily Express SHUTTLE NEWS Bush Thanks Discovery 'Risk-Takers' Washington (AFP) Aug 02, 2005 US President George W. Bush on Tuesday thanked the astronauts of the space shuttle Discovery for being "risk-takers" on behalf of space exploration and said he would pray for their safe return.     Add to Delicious

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