No more major shuttle changes

Discovery to fly without further safety changes to fuel tank, NASA managers say

April 29, 2006|By MICHAEL CABBAGE | MICHAEL CABBAGE,ORLANDO SENTINEL

CAPE CANAVERAL, Fla. -- NASA managers said yesterday that there would be no more major safety changes to the space shuttle's external fuel tank until after the next planned launch in July.

The decision follows a debate among engineers on whether to modify so-called ice-frost ramps on the tank's exterior before Discovery's coming flight. The small ramps are crafted from foam insulation that is sprayed by hand on the tank's exterior to prevent the buildup of ice. Concern remains among some engineers that in a worst-case scenario, pieces of the ramp weighing 2 or 3 ounces could break off during launch and hit the orbiter, causing critical damage. However, shuttle managers decided it was riskier to make changes before other tank modifications are fully tested.

"The decision going forward was to fly, leaving these ice-frost ramps as-is, knowing that we will expect to have some small foam loss that could pose a risk to us occur during the next flight or two while we continue to investigate," said Wayne Hale, NASA's shuttle program manager.

Thirty-four of the ice-frost ramps cover fittings used to attach fuel pressurization lines and a tray of electrical cables to the tank. The ramps came under scrutiny as part of a NASA effort to prevent the tank from shedding debris that could cause a repeat of the 2003 Columbia accident. Modified versions of the ramps lost large pieces of foam during tests in a wind tunnel in Tullahoma, Tenn., and did not perform as well as the current design.

Engineers have removed another, larger ramp that shed a chunk of foam weighing more than a pound during Discovery's return to flight last July. That change will expose the smaller ice-frost ramps to higher winds during liftoff.

With two months remaining before the July 1 opening of Discovery's launch window, wind tunnel tests and analyses have yet to confirm that the modified tank is safe to fly. Concern about launching with more than one major change was a big factor in engineers' decision to postpone a possible redesign of the ice-frost ramps until after Discovery's flight.

Removal of the larger ramp "constitutes the largest aerodynamic change that we have made to the space shuttle launch system since it first flew," Hale said. "At the end of the day, we came back to the fact that it is more appropriate to make one change at a time and take care of the biggest problem that we have, and then work our way to the next situation that we'd like to improve."

Michael Cabbage writes for the Orlando Sentinel.

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