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Shuttle Disaster

Is 'safe as possible' safe enough for shuttle?

With no way to make space flight perfectly safe, NASA seeks an acceptable danger level. Still, sometimes things go wrong.


© St. Petersburg Times
published February 16, 2003

HOUSTON -- As NASA investigators try to determine what caused the space shuttle Columbia to break apart, every theory involves something the agency knew was a calculated risk.

Maybe a piece of space junk or small meteorite damaged the shuttle's protective shell.

Or the fragile tiles that protect the shuttle from the intense heat of re-entry cracked or came loose.

Or the foam insulation that peeled away from the shuttle's fuel tank during liftoff damaged the tiles.

The agency's files are full of reports detailing the dangers of these hazards and many more. With spacecraft of 2.5-million parts, a limited budget and a reliance on experimental technology, the shuttle program constantly balances risks with rewards.

At some point, the countdown must begin.

"They get it as safe as they possibly can, but if they waited for it to be perfect, they would never get into space," said Donald Kutyna, a retired Air Force general who served on the commission that investigated the 1986 Challenger disaster.

Deciding what is an acceptable risk is a struggle, Kutyna said.

An independent commission concluded NASA crossed the line of acceptable risk before the catastrophic launch of the shuttle Challenger in 1986. Now investigators are trying to determine if the same type of mistakes are to blame for the loss of the Columbia and its crew.

NASA consultants, astronauts and advisory board members said in interviews that the NASA of 2003 is at least as safety conscious and less politically driven than NASA of 1986, when the agency was trying to keep an ambitious launch schedule.

But NASA still relies on the "normalization of deviance," said Diane Vaughan, an organizational sociologist who has studied the agency extensively. That means components often fail, so the trick is realizing what will be catastrophic and what won't.

"Having problems as part of the normal operation can really make it hard to realize when a problem is serious or not, and when you need to stand down and fix it," said Vaughan, author of The Challenger Launch Decision: Risky Technology, Culture and Deviance at NASA. "If they don't have enough information to fix it, they keep flying with errors."

Two weeks after the Columbia broke apart over Texas, the cause remains a mystery.

Here's what's known publicly so far: About 80 seconds after liftoff on Jan. 16, a 20-inch-long slab of hard foam insulation came loose from the external fuel tank and struck the shuttle's left wing.

As Columbia re-entered the Earth's atmosphere on Feb. 1, an Air Force photo shows possible damage to the shuttle's left wing.

As it flew over Texas, Mission Control in Houston detected a slight rise in temperature at the shuttle's left wheel well, located under the wing, and at the left wing near the fuselage.

Other readings were normal. Mission Control then lost contact with Columbia and it broke apart, 16 minutes before it was to land at Cape Canaveral.

NASA engineers reviewed a videotape showing the foam hitting the wing during takeoff, but decided it wouldn't have caused significant damage to the tiles.

The foam is an example of a vital shuttle part plagued by problems but never considered to pose a risk to the safety of the crew.

As shuttle program manager Ron Dittemore explained, foam had fallen off many times before and the shuttle always had returned.

Now NASA is examining if that judgment was sound.

The hard, spray-on foam insulates the frigid liquid hydrogen and oxygen fuel inside the external tank, preventing condensation and ice from forming. It also protects the fuel from intense heat during launch.

But for more than a decade, NASA records show, the foam has been troublesome, peeling off during liftoff and crashing into the fragile, heat-resistant tiles that protect the shuttle during re-entry into the Earth's atmosphere. In at least three reports, engineers warned that foam damaged tiles.

In 1990, researchers at Stanford and Carnegie Mellon universities found the wheel wells were among a half-dozen places particularly vulnerable to damage from flying foam.

Losing even one tile in this area could prove catastrophic, the study said.

In a followup report in 1994, the researchers estimated that improving the way the foam was applied would cut by about 70 percent the chance of a shuttle accident due to tile failure.

But fixing the problem took time, because the fuel tanks are built years in advance of each mission, then shipped by barge from New Orleans to Cape Canaveral. Technicians tried stopgap measures instead, shaving the insulation to lessen what could peel away and poking tiny holes in it to let air pockets escape. But the foam kept peeling off.

More recently, NASA tried tweaking the formula. But as late as October, insulation hit the solid rocket boosters, apparently with no damage.

To experts who investigated the Challenger disaster, the sequence sounded eerily familiar. That explosion was traced to a faulty seal in the solid rocket booster called an O-ring, a small piece of equipment that had been a problem for at least a year.

The O-ring shrank in morning chill the day of the launch, allowing hot gas to escape from the rocket booster during liftoff. The gas burned through the external tank and exploded.

"The Space Shuttle's Solid Rocket Booster problem began with the faulty design of its joint and increased as both NASA and contractor management first failed to recognize it as a problem, then failed to fix it and finally treated it as an acceptable flight risk," the presidential commission concluded in its final report.

". . . As tests and then flights confirmed damage to the sealing rings, the reaction by both NASA and (its contractor) was to increase the amount of damage considered 'acceptable.' "

Robert Hotz, a member of the Challenger commission, said NASA's motto has always been to do just enough.

"That's a tendency NASA has," Hotz said. "If they get away with something then it's okay. It's an institutional problem."

When NASA administrator Sean O'Keefe testified before Congress on Wednesday, he repeatedly promised to resume space travel and make it "as safe as possible."

Not safe. As safe as possible.

His comments implied America must accept that some astronauts will not return home safely.

Before Challenger's last flight, NASA changed the status of the shuttle from "experimental" to "operational," meaning manned space flight was routine. The agency put a teacher on board. There was talk of charging for rides.

Before Columbia's accident, NASA again was preparing to put a teacher on board.

NASA's ability to evaluate the risk of space flight has been hamstrung by the relative infrequency of its missions, experts said.

Decisions about the capabilities of commercial and military aircraft, by contrast, can rely on thousands and thousands of flying hours, said Richard Blomberg, a former head of the Aerospace Safety Advisory Panel.

Before Challenger, NASA publicly estimated the risk of catastrophe at one in 1,000. Before Columbia, the operating risk was called one in 500. NASA has been working on a second-generation space plane with the stated goal of cutting the risk to one in 10,000.

The risk of getting cancer is one in eight.

NASA has flown the shuttle 113 times and lost two orbiters.

Many experts say that on a machine so complex, with so many parts, odds have no meaning. Eugene Covert, professor emeritus at the Massachusetts Institute of Technology who was a member of the Challenger commission, said it's impossible to define an acceptable level of risk based solely in terms of statistics.

Instead, it's based on a combination of what astronauts, NASA personnel, lawmakers and the public will put up with, he said. Even astronauts, suspended between probability and reality, put little stock in NASA's risk estimates.

Astronaut Jay Buckey, a payload specialist on the Columbia in 1998, said, "It depends on the assumptions that are made, and who's doing the risk assessment. Some are just best guesses."

Former astronaut Winston Scott of Tallahassee, who flew two shuttle missions, including one on the Columbia, put it this way: "Perfection is what NASA strives for, but in reality you never achieve it. Sometimes things just break."

-- Times staff writers Chuck Murphy and Craig Pittman and researcher Kitty Bennett contributed to this report.

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