NASA admits repair methods for shuttle are risky

HOUSTON — NASA is developing potentially risky flight procedures that would allow astronauts to make in-flight repairs to a space shuttle with heat shield damage of the type that led to the Columbia disaster in February.

Columbia’s breakup with seven astronauts aboard pointed to a range of safety shortcomings at NASA, including the space agency’s inability to inspect and repair a vehicle in space.

NASA chief Sean O’Keefe has vowed that the three remaining shuttles will be grounded until astronauts can thoroughly inspect their craft while it is in orbit and repair any damage to the heat shielding then. Engineers and astronauts have been working for six months to figure out how to do that.

The result is a new list of flight procedures and spacecraft maneuvers, some of which NASA engineers acknowledge will add risks to the already risky business of space travel. Some NASA staffers even use words such as ”outrageous” to describe the innovations.

Shuttle specialists emphasize that the most difficult procedures would be used only in emergencies, and that crews will practice them frequently before going into space.

”Everything we do in the shuttle program involves risk,” says Col. James Halsell, the astronaut in charge of returning the shuttle program to space. ”Our goal needs to be to return to flight . . . in a much safer posture than we were prior to Columbia.”

NASA’s new procedures would include:

* An orbital repair maneuver. The most brutal heat of the shuttle’s re-entry focuses on the underside of the orbiter. That’s where Columbia was hit by a piece of flying foam from its external fuel tank during its launch. The resulting hole allowed hot gases to melt the interior of the spacecraft’s left wing.

So it is vital for astronauts to be able to patch damage to the underside. But for a spacewalking astronaut, working on that part of a shuttle is difficult; there’s nothing to stand on or to hold onto.

An astronaut could easily reach the shuttle’s belly by standing on the end of the robotic arm on the International Space Station. Nearly every shuttle mission over the next few years will fly to the station.

Attaching a spacewalker to the station’s robot arm is nothing new, but figuring out how to position the shuttle within reach of the station’s arm required ingenuity. Space agency engineers call the plan that was hatched ”radical” and ”goofy,” but they think they can reduce the risks.

In the scenario engineers envision, the shuttle’s own robotic arm would grab a part of the space station. Then the arm, bending at all six of its joints, would flip, twirl and spin the shuttle like a baton until the spacecraft was positioned with its belly pointing toward the station.

A shuttle’s arm has never moved anything larger than 50,000 pounds. The shuttle weighs 250,000. A typical arm operation takes an hour; moving the shuttle into position for repairs in this way would take four to seven hours. The maneuver is so complex, a NASA engineer says, that some of the agency’s computer programs that analyze such operations can’t handle it.

Robotics officer Michael Wright says that when he was first asked to work out such a routine, he was ”speechless” and thought the idea was ”outrageous.”

”At first I didn’t think it was going to work because I couldn’t imagine how it was going to work,” he says. Now he thinks it will.

Still, NASA hopes it never has to try such a maneuver. ”That’s something we’d want to be extremely careful about,” says astronaut Steve Robinson, a crewmember on the first flight after Columbia. ”You’ve got the entire international space program right next to each other — the shuttle right next to the station.”

Halsell says NASA is still studying the maneuver and could reject the idea if the risk turns out to be ”significant.”

* A tile repair plan. Much of the shuttle’s belly is clad in square tiles that keep the atmosphere’s heat during re-entry from melting the spacecraft’s aluminum skin.

Chunks of ice or foam easily gouge these tiles. In the late 1970s, NASA tried to develop a way to fill holes in the tile but gave up because the patching material was difficult to handle.

Now NASA has revived that research. Scientists have determined that holes could be filled with a peach-colored putty that hardens quickly and resists heat even better than the tiles. But the sticky material is as difficult to work with as day-old bubble gum.

The solution, engineers say, is to use a device that looks like the nozzle of a gas pump. An astronaut would wear a backpack full of putty, which would flow through a hose into the nozzle. The astronaut would dribble the putty into holes in the tile, controlling the flow with a trigger.

It wouldn’t be easy. The putty is so tacky that it’s easy for the person with the nozzle to create air pockets and mounds, which would weaken the patch. If a hole were overfilled, the putty could swell into a mound and threaten the shuttle’s aerodynamics. The nozzle also must not hit any intact tiles.

Never before has a spacewalker faced a task that demands such dexterity. The stiff gloves that protect a spacewalker’s hands from the cold and heat of space would be another complication.

”This is a tricky technique at best, and it’s a difficult job,” flight director Paul Hill says. Such an admission is rare from NASA officials, who tend to minimize difficulties.

* A shuttle ”pirouette.” The best views of the shuttle when it’s in space are from the space station. So the station’s crew will inspect every visiting shuttle for cracks and holes once shuttle flights resume. To give the station’s residents a good view, the shuttle will execute a new maneuver that Halsell calls a ”pirouette.” The shuttle will slowly approach the station from below. When the two are 600 feet apart, the shuttle will slowly pitch end over end until it has done a somersault.

The maneuver will be executed by the shuttle commander, who leads the mission. Commanders are now training in flight simulators to do the pirouette.

The maneuver is a bit more difficult than the current approach to the space station, says Eileen Collins, who will command the shuttle Atlantis on the first post-Columbia flight. At first, she was leery of the idea because the crew loses sight of the station for several minutes. But now she thinks it’s ”a very safe maneuver. . . . I think it’s very doable.”

Halsell says an analysis found that the pirouette adds no significant risk because it’s performed so slowly and because of the large distance between the shuttle and the station.