NASA to try shuttle launch today despite foam problem

Loss of insulation from external fuel tank threatened to delay mission

July 04, 2006|By MICHAEL CABBAGE | MICHAEL CABBAGE,ORLANDO SENTINEL

CAPE CANAVERAL,Fla. -- This afternoon's planned liftoff of space shuttle Discovery is on after a lengthy debate last night over a small chunk of foam insulation that broke off the ship's fuel tank.

Detailed inspections of the shuttle's tank at the launch pad convinced NASA managers the issue did not pose a safety hazard. As a result, shuttle officials cleared Discovery for flight late yesterday without ordering further inspections today.

"There were no dissenters when we went around the room," said William Gerstenmaier, NASA's head of space operations. "There were really no concerns raised, but lots of discussions from many people during the review."

Today's five-minute launch window opens at 2:37 p.m. Forecasters are predicting a 60 percent chance of favorable weather, with thick clouds and showers being the primary concerns.

The foam incident marks the latest chapter in NASA's continuing problem with the tank shedding potentially hazardous debris.

Yesterday's debate focused on a triangular piece of foam about 3 inches long that an inspection team found on Discovery's mobile launch platform after Sunday's countdown was scrubbed by bad weather. It is believed to be the only time a piece of foam has ever been discovered on the pad before flight.

Comparable in size to a small piece of toast, it fell off a bracket that holds a 17-inch wide pipe to the outside of the shuttle's fuel tank. The pipe carries liquid oxygen propellant from a reservoir in the top of the tank to the shuttle's three main engines.

When the 15-story tank was filled with super-chilled liquid oxygen and hydrogen for launch attempts Saturday and Sunday, the cold made it contract slightly. The tank warmed and expanded again after being drained when launch tries were scrubbed on both days.

The foam-covered bracket is built to flex as the tank shrinks and expands. Engineers suspect that rain and condensation caused ice to form in a joint after the tank was fueled for the second time.

"When the tank was emptied and it started to warm up, it started to expand and we think some of the ice stayed in that joint and crushed a little bit of the foam," said John Shannon, NASA's deputy shuttle program manager.

At .0057 pounds, the piece of foam is about half the mass that NASA has calculated would have a 1-in-100 chance of causing catastrophic damage to Discovery's heat shielding.

In comparison, the 1.67-pound piece of foam that caused the Columbia accident in 2003 was nearly 300 times larger. A piece of foam that broke off another ramp during Discovery's launch last year weighed about 1 pound.

"The obvious question is, well, if this were to happen in flight and this piece of foam were to come off, would that have been in issue?" Shannon said. "The answer is no, absolutely, it would not have been an issue. It was less than half the size that we think can cause damage to the orbiter."

Mission managers had three main worries as they studied the foam issue yesterday.

There was uncertainty about whether the rest of the foam on the bracket also would break free. Questions were raised about whether ice would build up on the bracket where the foam fell off. And some engineers were unsure if the structure under where the foam came off would get too hot during launch.

All those questions were answered last night to the satisfaction of shuttle officials after inspections with borescopes and other instruments were completed.

"They fully have shown that the foam was acceptable and ready to go fly," Gerstenmaier said.

The latest foam incident had perhaps more impact on public perception than on shuttle safety.

Problems with the tank and its foam insulation have haunted NASA for more than three years since debris from the tank caused Columbia to break up while returning to Earth in 2003, killing all seven astronauts aboard. After two years of redesign work, a large piece of a foam ramp broke free during the shuttle's return to flight a year ago.

Pundits joked yesterday that the tank now sheds foam even when the shuttle isn't flying.

The debate follows an earlier decision by NASA to launch Discovery despite "no go" votes from the agency's head of safety and chief engineer. Their concern: Three dozen small foam ramps on the tank that could shed potentially dangerous debris were not redesigned before the coming flight.

"We've laid out the data. We've looked at it calmly," Gerstenmaier said. "We're ready to go fly because we're ready to go fly. We're not ready to go fly because of some launch window or some other conditions."

Michael Cabbage writes for the Orlando Sentinel

Baltimore Sun Articles
|
|
|
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.