Deseret News (Salt Lake City): Discovery may get emergency repairs

HOUSTON -- NASA might send spacewalkers to make emergency repairs on the belly of Discovery to make certain the shuttle and its seven astronauts will survive a fiery atmospheric re-entry.

Engineers fear two dangling pieces of heat-resistant fabric near the shuttle's nose landing gear door might trigger excessive heating -- and potentially, catastrophic damage -- during Discovery's scheduled return to Earth next week.

An analysis of the protruding "gap-fillers," which are thermal barriers between shuttle heat-shield tiles, is to be completed today.

The study might show no repair work is necessary. But the issue is serious enough that NASA engineers spent Sunday planning what would be an unprecedented repair job on the underside of the shuttle.

"The Columbia accident made us realize that we had been playing Russian roulette with the shuttle crews," NASA deputy shuttle program manager Wayne Hale said.

"We are treating it with a great deal of seriousness. We have got a very large group of people looking at this situation, and we're going to evaluate it very thoroughly."

The fabric pieces jut out 0.6 and 1.2 inches, respectively, from the shuttle's belly -- two to four times longer than protuberances detected in the nose landing gear area after previous flights.

Camera-wielding astronauts on the International Space Station spotted them when Discovery did a dramatic

back flip during the shuttle's final approach to the outpost.

The maneuver gave station astronauts -- and engineers on the ground -- the ability to inspect thousands of tiles on the underside of the orbiter.

The tiles protect shuttles and their crews from intense heat encountered during re-entry -- about 2,300 degrees around the nose landing gear region.

Protruding gap fillers were discovered during post-flight inspections after at least nine previous shuttle missions. They increase turbulence during re-entry. The rate that temperatures rise during re-entry can increase by a factor of four.

In a worst-case scenario, that means temperatures could rise to levels that would cause catastrophic damage to the heat shield

The protruding gap fillers on Discovery could cause temperatures near the nose landing gear door to increase 15 to 25 percent, said Steve Poulos, NASA's orbiter project manager.

The problem also increases atmospheric drag. Shuttle steering jets then must exhaust more propellant to keep on course during S- shaped curves that slow the ship from 17,500 mph in orbit to 225 mph at touchdown.

The worst previous gap filler protrusion near the forward part of the orbiter was one quarter-inch long, said Paul Hill, NASA's lead flight director. The larger size of the pieces sticking out from Discovery has prompted serious concerns.

"Clearly, if they were a quarter of an inch or lower, we wouldn't be having this discussion," Hill said. "But because they exceed that quarter of an inch, they are outside our experience base. So we have to rely on the analysis" to determine a course of action.

There is "strong disagreement" among engineers over the need for a repair job, but several options are being considered, Hill said.

The issue is finding a way to get a spacewalker from the cargo bay to an area beneath the nose of the orbiter, a traverse astronauts train for but have never carried out in orbit.

Discovery mission specialist Stephen Robinson or Soichi Noguchi would be anchored to the end of either the shuttle or station robot arm.

An arm operator then would move the cranelike device and the spacewalker into position near Discovery's nose landing gear door. The gap fillers likely would be pulled out by hand. They also could be trimmed with a hacksaw or stuffed back between tiles.

The job would have certain dangers.

Clearances between the robot arm, the station and Discovery would be tight -- 12 inches in certain places. Consequently, the shuttle's fragile heat shield could be struck and damaged.

Another concern: A new 800-pound inspection boom now is latched to the shuttle's 50-foot robot arm. Engineers are uncertain whether the linked appendages could withstand the forces imparted by an anchored astronaut without breaking.

"It isn't something we have ever done before," Hill said. "The idea of going ahead and wrapping the arm and the boom around the vehicle with relatively low clearances to the leading edge of the wing and tile has our robotics and (spacewalk) communities understandably nervous."

Repair work likely would be done on Wednesday during the last of three planned spacewalks. The second of those will take place in the early hours. Robinson and Noguchi aim to replace a broken station gyroscope during that outing.

Discovery now is scheduled to depart the station Saturday, a day later than originally planned. The ship and its crew are due to land at Kennedy Space Center the morning of Aug. 8.