Nasa's shuttle sticking plaster

By Irene Mona Klotz
at the Johnson Space Center, Houston, Texas

Months of hard work by thousands of Nasa scientists, engineers and contractors sits in a hole gouged into a black shuttle heat tile.

The brick-colored putty is still soft, filling the tile block like cake batter in a pan.

This is hardly cutting-edge science.

Nasa, in fact, dusted off a 25-year-old research project to build its spaceship sticking plaster.

Back in the early days of the shuttle programme, managers were concerned that the shuttle's silica tiles, which protect the ship's aluminum skin from the searing temperatures of atmospheric re-entry, would fall off entirely.

Following the shuttle Columbia's accident, Nasa is now preoccupied with patching heat-shield holes.

Tools of the trade

Michael Fowler, who holds a doctorate in materials sciences, showed us what happens when you blast the putty-filled tile with a 2,300-degree heat torch.

"This is the char layer," he said, pointing to a blackened, three-inch (7.5 centimetre) topping that has burst out of the top of the tile.

It looks like burnt marshmallows.

In depth guide: Columbia's last mission

"The important thing is that it did survive," Mr Fowler told the small group of reporters gathered around his table, one of about two dozen displays set up science fair-style in a massive room dominated by an idle Apollo-era vacuum chamber.

At the next stop, Dana Weigel explained different ways the goop could be pumped into damaged tiles by space-walking astronauts and how to counter the unsettling effects of zero-gravity.

There are brushes, putty knives, squeegees, trowels, plastic sheets, high-tech caulking guns, and backpacks to hold the pre-mixed filler.

Before the next shuttle flies, Nasa wants the capability to repair in orbit a tile hole as big as 10-inches by 30-inches by 4 inches (25 by 75 by 10 cm).

"Once we get to the work site, it's very do-able," said astronaut Scott Parazynski.

Tricky wing repairs

Patching tiles is the easier, but tangential, hurdle toward return to flight.

Columbia's demise was due to a breach in the leading edge wing panel, which is made of an entirely different substance.

Only the last two tables in the room display materials and equipment proposed for this type of in-orbit repair.

There is nothing that would even come close to being able to repair the size of breach that brought down Columbia.

"We don't know yet what size holes we will be able to fill," said Bradley Files, who is heading the effort to develop a repair for the wing panels.

"But if we're ever going to be able to use any of this for flight, it's going to have to work."

Even the tile-repair effort, which is quite mature in comparison, has a ring of surrealism: Although Nasa has struggled with tile damage on every flight since the shuttle's debut in 1981, an in-orbit repair would have been necessary only once, when a tile actually came unstuck, leaving a gap in the shield.

Fortuitously, an antenna shaded the area during re-entry.

"We want to have the availability (for tile repair), but we don't expect to use it," said flight director Paul Hill.