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Design fears won't stop shuttle launch

Despite concern about the safety of the shuttle's insulating foam, NASA officials will stick with a July launch date.

By TIMES WIRES
Published April 29, 2006

WASHINGTON - NASA officials said Friday that they have decided to go ahead with a July space shuttle launch even though engineers have been unable to correct a potentially serious defect in the insulating foam that cloaks the external fuel tank.

The officials said tests had failed to produce a design that would stop insulation from breaking away during launch from the tank's "ice frost ramps" - foam-covered metal brackets that hold pressure lines and electrical cables to its side.

"The decision was to fly these ice frost ramps as is, knowing that we can expect to have some small foam loss that could pose a risk," shuttle project manager Wayne Hale said during a televised news conference.

The worst case, he said, would occur if the foam "comes off at the maximum mass, which would be on the order of 3 to 3 1/2 ounces, comes off at the worst time and follows the worst possible trajectory to the most vulnerable part of the orbiter."

"It would not be what we would like to have." Hale said. "It would cause what we would call critical damage."

"There was a strong, concerted opinion from several folks that we should wait until we have a good design on these pieces of foam and then change them before we go flying," Hale said.

"But at the end of the day, it is appropriate to make one change at a time with the biggest problem we have, and then work our way to the next situation."

The decision to fly was the latest event in a three-year quest to overcome the multiple shortcomings of the external tank since the shuttle Columbia broke apart over Texas. That disaster was caused by foam debris from the tank that breached the orbiter's heat shielding during launch.

The three remaining shuttles have flown once since then, only to be grounded again when the tank in July lost an unacceptably large piece of insulation from a foam ridge known as the protuberance air load, or PAL, ramp. It serves as a windbreak to protect cables and fuel lines from turbulence during launch.

After months of tests, engineers decided earlier this year to fly the shuttle without the PAL ramp, and have scheduled Discovery for liftoff during a window that opens July 1. Hale said Friday the target date remained unchanged.

After the PAL decision, engineers turned to the 34 ice frost ramps, which protect pipes that pressurize the fuel tanks as they empty during launch and the "cable tray" that contains the tank's electrical lines. The ramps have a history of losing bits of insulation during launch.

Ken Welzyn, chief engineer for the external tank, said experts were focusing on four brackets that begin a launch chilled by the liquid hydrogen fuel beneath them, then warm up as the hydrogen is expended, causing the metal to expand and perhaps crack, tossing off pieces of foam during the critical moments after liftoff.

Information from the Washington Post and Associated Press was used in this report.

[Last modified April 29, 2006, 01:18:13]