Thursday, June 01, 2006

All systems are go for July flight

Foam debris poses acceptable risk to shuttle, NASA says after review


NASA still aims to launch Discovery on July 1 despite a problem that could cause damage severe enough to trigger a rescue mission, officials said Wednesday.
The chances of that happening are about 1 in 100, or about the same probability that other critical systems might fail in flight, leading to the loss of an orbiter and its astronaut crew.
"It's a risky vehicle to fly, and nobody should mistake that. There are a number of things that can cause bad outcomes on this vehicle," shuttle program manager Wayne Hale said.
But the chance of potentially catastrophic damage from foam debris "is consistent with the entire overall risk we fly with the space shuttle," he added.
Hale's comments came at the conclusion of a two-day review considered key to clearing Discovery for launch of NASA's second flight since the 2003 Columbia accident.
Conducted at Kennedy Space Center, the review involved examining engineering analyses carried out to determine if the shuttle's redesigned external tank might shed pieces of foam insulation large enough to cause serious damage to Discovery.
About 100 NASA managers and engineers took part. Some recommended delaying the flight until additional tank modifications could be made. Hale characterized the debate as "spirited" and said managers ultimately decided that flying without further changes is an acceptable risk.
NASA expects small chunks of foam to come off Discovery's tank during flight, Hale said. He also acknowledged there still are areas of the tank that could shed foam debris big enough to do serious damage.
Chief among them: manually applied foam covers designed to keep ice from building up on 34 metal brackets that secure fuel pressurization lines to the outside of the tank.
Engineers are working on a new design that might reduce foam loss from those ice-frost ramps. But tanks equipped with redesigned ramps probably will not be available until late this year or early in 2007, Hale said.
"We think they are a hazard. I want to make that very clear. They are an area of foam insulation that we very definitely need to deal with," he said.
But managers plan to proceed with the launch to test a major change aimed at preventing the type of foam loss experienced on the agency's first post-Columbia mission last summer.
On that flight, a one-pound piece of foam popped off Discovery's tank and nearly struck the right wing. The debris came from a 38-foot-long wedge of insulation designed to provide a windshield for nearby pipes and cables.
NASA removed the Protuberance Air Load, or PAL, ramp from the tank now attached to Discovery at launch pad 39B. The change represents the most significant alteration to the shuttle's structure since the program's first flight in 1981.
The idea is to test the change in flight before making further modifications to shuttle tanks. "In a flight test, you want to make one major change at a time and see how that performs before you make another major change," Hale said.
A couple of hurdles still must be overcome before a July 1 launch attempt.
Managers on Wednesday will conduct a review to examine engineering analyses of wind tunnel tests carried out to determine whether it will be safe to fly a tank without the PAL ramps.
Some engineers are concerned that aerodynamic forces could rip pressurization lines and cabling off the tank if the windshield is not there. That would lead to a catastrophe. Hale said preliminary analyses indicate it is safe to fly without the 34-pound ramp.
Also on tap: a traditional Flight Readiness Review in mid-June. A firm launch date will be set at the end of that two-day meeting at KSC.
The upcoming launch window for Discovery's flight will extend through July 19. NASA's next opportunity after that: A window that stretches from Aug. 28 through Sept. 13.

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