February 04, 2003, Pg. A01

First Mission Shaped Decisions in Last; Shuttle Managers Relied on Experience, Calculations on Tile Damage

By Shankar Vedantam

Eighty seconds after Columbia blasted off Jan. 16, NASA engineers saw a puff on the underside of the left wing and immediately began investigating whether an errant piece of foam had seriously damaged the shuttle.

Over the next two weeks, engineers pored over film clips of the launch and used modeling techniques to guess at the extent and location of the damage, NASA officials said. One important factor stood out as they weighed whether the problem was serious.

It had happened before.

Columbia's first mission, in April 1981, had almost exactly the same problem. Shortly after launch, about 13 to 15 insulating tiles were thought to be dislodged and engineers had to decide whether that would pose a risk to the spacecraft during the fiery reentry into Earth's atmosphere.

In what was to be Columbia's last mission, engineers reached the same conclusion that they had during the first and others: Although there was a "potential for a large damage area to the tile," according to a NASA flight report released yesterday, the spacecraft was not at serious risk.

As a result, ground controllers apparently did not consider the radical measures that might have saved the astronauts' lives -- aborting the mission soon after liftoff or bringing the shuttle in at a reentry angle that could have allowed the crew to parachute to safety.

After the shuttle disintegrated while returning to Earth on Saturday and the damaged tiles emerged as one of the prime candidates for the cause, NASA engineers began examining their calculations and wondering whether they had made a catastrophic mistake. Investigators have focused on the tiles but have not ruled out other possible causes of the disaster.

While it is easy to conclude the engineers were right about the first mission and wrong about the last, what happened this time may be more complicated: Both decisions involved judgment and chance, and those factors can produce unpredictable outcomes when a 178,000-pound spacecraft hurtles through the upper atmosphere at 12,500 mph .

"This is not the first time that we have had debris generated from the external tank that has struck the underside of the wing," said Ron Dittemore, NASA's space shuttle program manager. The thinking was, "this has happened before, yes, it can impact the tile; yes, it could take some of the coating off; yes, it can even gouge out some of the tile. But it has never represented anything more than that."

Film clips taken during liftoff indicated a puff below the left wing -- the result of what was probably a piece of insulation foam hitting it. Pictures taken during the blinding light of liftoff were imprecise in showing the damage, and engineers were left to guess at what had happened.

The astronauts could not see the damage because it was on the bottom of the shuttle. The crew did not have on-board cameras to survey the tiled bottom of the orbiter. NASA had spurned an independent advisory panel's recommendation in 1997 that it create such a camera for use with every flight.

A Jan. 17 review of the film taken at liftoff was followed by analyses and a meeting of engineers on Jan. 20, Dittemore said in a news briefing yesterday. Teams of engineers discussed different aspects of risk -- the teams varied in size from 30 to as few as one or two when the questions became highly specialized. The engineering analysis concluded as early as Jan. 22 that the risk was not serious, a decision confirmed by final reviews on Jan. 23 and 24.

Briefings of senior NASA officials Jan. 24 and 27 confirmed the engineers' conclusion that the spacecraft was not at serious risk.

Since the damage was under the wing, in an area not visible to the astronauts, the engineers on the ground made assumptions about what happened. They started by estimating the size of the projectile that hit the wing.

From the puff in film clips when the foam disintegrated into dust on impact with the wing, the engineers calculated it was probably 20 inches long, 16 inches wide, 6 inches deep and weighed 2.67 pounds.

The calculations erred on the side of caution, Dittemore said, meaning that the foam probably was smaller and lighter.

Next, the engineers estimated the angle at which the foam hit the wing -- and concluded it was quite sharp, a glancing blow.

From these assumptions, the engineers deduced the impacts of the foam hitting one tile and a larger area. Again, this technique had proved highly reliable in the past and usually overestimated the amount of damage, Dittemore said.

The engineers' worst scenarios were either one destroyed tile near the main landing gear door, or many partly damaged tiles.

"Even though you might have localized structural damage, you would not have damage sufficient to cause a catastrophic event nor impact the flying qualities of the vehicle," Dittemore said.

NASA concluded in an internal report on the 12th day of the flight that "thermal analyses indicate localized structural damage but no burn-through, and no safety of flight issue."

But Michael Wiskerchen, an associate director of the University of California's Space Institute and a consultant to NASA on tile safety after the 1986 Challenger shuttle disaster, said, "I don't know how you could get structural damage . . . if you don't melt all that stuff" covering the structure -- such as the shuttle's aluminum skin and the felt beneath any missing tiles.

Wiskerchen said that while NASA's assessment might have been correct, it must have been based on "guesswork" because tile loss at high speeds and temperatures had never been realistically simulated and no space shuttle had ever suffered the loss of tiles on the leading edge of a wing. He said the loss of only a few tiles there could potentially cause intense localized heating because of wind turbulence, and lead to a disaster.

In earlier shuttle missions, engineers on the ground had arranged to have specialized military telescopes take a closer look at the shuttle before reentry. In 1981, the astronauts were able to see the damage to the tiles -- the missing tiles were located on the upper side of the shuttle, which is exposed to less intense heat during reentry.

Military telescopes were used to examine the bottom of the shuttle, said Thomas Moser, a former NASA engineer responsible for tile safety during that first mission.

No such imaging was conducted on the last mission. "We didn't feel that the results would be conclusive one way or another, and so we elected not to request them," said Bill Readdy, NASA's associate administrator of space flight.

Dittemore said that after the engineers concluded the shuttle would be safe, there was no consideration given to having it reenter the atmosphere tilted away from the damaged side. That might have allowed the crew to eject when the shuttle reached a lower altitude, but would have certainly doomed the spacecraft.

There were also no contingency plans to allow the astronauts to escape to the international space station or send a rescue shuttle.

Dittemore said that NASA had relied on the tiles to withstand damage and bring the crew down safely -- and the engineers' analyses would not have warranted escape measures anyway.

The shuttle's history of damaged tiles also has prompted questions about why NASA had not given the astronauts a repair kit to fix the damage, or invented a better insulation system.

"NASA did what they could with what they have," said Ernie Reyes, former director of quality assurance at the Kennedy Space Center. "I'm not saying they didn't do a good job, but they underestimated the damage. If you can't see it, feel it, measure it, how do you know what you are playing with? You can't do it with numbers."

Moser said that NASA considered the repair kit option after the first mission, but concluded it probably would cause more problems than it cured: Astronauts might not be able to get to the damage, and a misapplied tile could result in an uneven surface that could increase friction during reentry.

As for inventing a new tile insulation system, Moser said that the next generation of shuttles probably will have superior materials. But he warned that there were no easy solutions to the shuttle's problems, and that shuttle fixes had a long history of creating problems of their own.

"We had a motto," he said about the danger of creating problems while making improvements. "Better is the enemy of good."

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