Discovery's astronauts are preparing for a high-stakes task that's never before been attempted: sending a spacewalker beneath the craft to repair filler sticking out from ship's thermal tile belly.
NASA says the protruding material could cause dangerous overheating during re-entry and lead to another Columbia-type disaster.
So on Wednesday, astronaut Steve Robinson, anchored by the space shuttle's robotic arm, will yank off or cut out the material sticking out. That repair is considered fairly straightforward, and one the astronauts have trained for but never actually tried in space, CBS News Correspondent Mark Strassman reports.
"I am pretty comfortable with using tools very carefully," Robinson said early Tuesday during a crew press conference from aboard the space station. "But no doubt about it, this is going to be a very delicate task. But as I say, a simple one."
Robinson said the makeshift saw will only be used if other methods to remove the gap fillers —0 one about the thickness of an index card and the other, the size of three index cards bonded together — are unsuccessful.
"There won't be any yanking going on at all," Robinson said. "It will be a gentle pull with my hand. If that doesn't work, I have some forceps. I will give it a slightly more than gentle pull. If that doesn't work, I saw it off with a hacksaw."
Nobody's ever worked under the shuttle before and if you're not really careful you could hit the bottom and do some damage. But CBS News Correspondent Peter King reports Robinson seems to be most concerned about something we all worry about during home improvements – hitting his head.
Deputy shuttle program manager Wayne Hale says if none of the proposed methods work, there will likely be some head scratching for a day. However, he says the agency will find another method and try the repair again Thursday or Friday.
Engineers simply don't know enough about potential problems that could be caused by the protruding gap fillers, some of which protect tiles from hitting one another during launch.
"When we first heard about it, I think a number of us did have misgivings," Astronaut Andrew Thomas said. "We were concerned about it. We were concerned about the implications of it."
But after a careful review of information sent from the ground, Thomas said he believes the repairs are justified given "every indication is that the removal of the material should be pretty straightforward and pretty easy."
Hale said the decision to attempt the repairs was simple and a way "to set our minds at rest."
"The bottom line is there is large uncertainty because nobody has a very good handle on the aerodynamics at those altitudes and at those speeds," Hale said. "Given that large degree of uncertainty, life could be normal during entry or some bad things could happen."
Discovery Commander Eileen Collins told Mission Control early Tuesday that her crew would reschedule its joint meal with the space station's crew and instead focus on procedures for the mission's third spacewalk, expected to take seven hours.
Robinson and his spacewalking partner, Soichi Noguchi, will still install a tool platform onto the space station. But once the installation is complete, the spacewalk will alter from the way it was carefully choreographed before last week's launch.
The last minute changes, however, are conservative and won't be a cliffhanger, Robinson said.
"It's going to be like watching grass grow," he stressed. "Nothing is going to happen fast."
Mission Control told Collins that spacewalk trainers would be in early Tuesday to discuss the repairs with Robinson, who along with Noguchi spent more than 300 hours training in a pool where they were weighted down to simulate the zero gravity environment in space.
Spacewalk instructor Cindy Begley said Robinson is going to have to be careful not to cause any additional damage while under Discovery. He'll have to secure his safety tethers behind him and leave any tools he won't need for the repair behind. He will also have to make sure his helmet doesn't bump into the shuttle's fragile bottom.
Aboard Discovery Tuesday, Thomas prepared Noguchi's and Robinson's spacesuits for Wednesday's early morning outing. He also assisted the spacewalking pair in constructing a makeshift hacksaw.
Astronauts James Kelly and Wendy Lawrence, meanwhile, were aboard the space station reviewing how they would operate the station's arm so Robinson's hands would be close enough to make the repairs, but his feet far enough away not to cause any additional damage
Kelly and Lawrence seemed pleased with the plan.
"We wouldn't change a thing," Kelly radioed Mission Control. "We think it is great. We will be ready to fly tomorrow."
Discovery will remain docked at the station until Saturday. The shuttle is set return to Earth early Monday.