Two Discovery astronauts were set to step outside their airlock this morning to find out whether spacewalkers can repair a shuttle's critical heat shields in outer space.
But the work will be strictly experimental, performed on test samples and coached as needed by the engineers back at the Goddard Space Flight Center who made some of their tools.
There were no plans to attempt repairs on any of the real but apparently minor damage Discovery sustained during its ascent to orbit on Tuesday, NASA officials said.
"There's not going to be a tendency to go out and tackle this on the real orbiter unless we have a real serious situation," said Steve Nesbitt, a NASA spokesman in Houston.
"When you do these things, you have to consider whether you're doing more harm than good," he added. "It's not like putting some caulking on the Winnebago."
Photography during Discovery's ascent, and more pictures and laser scans since then, have revealed nothing that NASA officials believe would put the shuttle or its crew of seven in jeopardy during their scheduled return Aug. 7.
Still, because video showed slabs of insulating foam breaking away from Discovery's external fuel tank, NASA ordered all subsequent flights grounded until engineers understand and fix the problem.
Breakaway foam struck heat-shield panels on the shuttle Columbia's right wing and led to the craft's destruction during re-entry on Feb. 1, 2003. All seven crew members were killed.
The Columbia Accident Investigation Board subsequently concluded that all future shuttle flights should carry tools and materials needed to repair such damage while in orbit. NASA ordered their development and planned repair tests on the first two post-Columbia flights.
`Ready to test'
Some of the work fell to the same team at Goddard that developed tools and techniques for astronauts who serviced the Hubble Space Telescope.
"It's the first time we've ever delivered tools where we hope they're not really needed," said the team's manager, Russ Werneth. "But we're ready to test them. We're looking forward to it."
Werneth's team members planned to be at Goddard's facility in Greenbelt early today. They would be on NASA's communications loop, ready to relay any help and information the astronauts request.
Here's how today's experiments were scheduled to go:
Mission specialists Soichi Noguchi, 40, and Stephen Robinson, 49, will don their space suits and climb out of Discovery's airlock at 5:45 a.m. EDT. It will be the first spacewalk for both.
In the shuttle's payload bay, NASA technicians have loaded a Goddard-built pallet carrying a variety of damaged thermal tiles - the same kind that protect the shuttle's belly. There are also samples of cracked and damaged reinforced-carbon panels, like those on the leading edge of the shuttles' wings.
Noguchi and Robinson will tackle the tile repair experiments first. Their primary tool will be a hand-held device called an "emittance wash applicator," which comes stowed in a Goddard-made bag.
A sort of mechanical dauber, the device releases a sticky liquid through four holes in a rectangular nozzle about the size of a tennis ball. The goo is designed to repair shallow gouges and small areas of superficial damage to the ceramic tiles.
The interior of an intact tile provides insulation against the searing heat of re-entry. Its black surface coating of "reaction-cured" glass allows the tiles to shed the heat rather than absorb it. But any damage reduces the tiles' ability to protect the shuttle and its crew.
The experimental repair goo contains fine-grit silicon carbide granules, carried in a liquid called "room-temperature vulcanizing material." Together, the components are supposed to seep into the damaged tile, bond to it and re-establish its heat-shedding capacity.
NASA planners said they would call the experiment a success if Noguchi could coat one 4-inch-by-4-inch tile. But there are a variety of damaged tiles on the pallet to practice on if the astronauts have time.
The spacewalkers will also experiment with foam brushes designed to spread the repair material to areas the applicator can't reach, as well as space wipes to remove excess material from tools or spacesuits.
After 30 minutes, the two astronauts will switch to intentionally damaged samples of the "reinforced carbon-carbon" panels.
For this work, Noguchi and Robinson will pull a high-tech caulking gun from their Goddard-made bag. It dispenses a "pre-ceramic polymer sealant" with carbon-silicon carbide powder.
Called NOAX (for Non-Oxide Adhesive eXperimental), the space caulk is supposed to fill and protect tiny cracks or coating damage up to 4 inches long.