With Discovery parked safely on the tarmac in California, the fate of the nation's manned space program now rests on the research teams assigned by NASA Administrator Michael D. Griffin to figure out why at least four large pieces of insulating foam broke away from the shuttle's enormous external fuel tank.
The teams, composed of engineers from NASA and Lockheed Martin's Michoud assembly facility in Louisiana, where the tanks are manufactured, were scheduled to give a preliminary report yesterday to Griffin and space station manager William H. Gerstenmaier. NASA has promised a fully "transparent" investigation, and initial findings may be made public as early as tomorrow.
"This is the first step back in our return-to-flight sequence," Griffin said, adding that the loss of foam insulation was "the only thing that went wrong with this mission."
An errant piece of foam caused the demise of Columbia in February 2003, and much of the subsequent 2 1/2 -year flight suspension was aimed at resolving that problem. With the shuttle Atlantis poised for a September liftoff but grounded until NASA is satisfied that foam shedding does not jeopardize crew safety, a speedy resolution is deemed essential if the program is to have any hope of regaining its momentum.
Some NASA sources, speaking on the condition of anonymity because they are not authorized to discuss the latest findings, have said in recent days that there is good evidence the biggest foam failure is related to a repair made on Discovery's external tank during its production -- a promising determination that might allow NASA to conclude that the Atlantis tank is not similarly at risk.
That chunk, estimated to weigh 0.9 pounds, peeled off from the "protuberance air load," or PAL, ramp, which protects exterior hardware from aerodynamic stresses during liftoff.
June Malone, a spokeswoman for NASA's Marshall Space Flight Center in Huntsville, Ala., which manages the external tank, said she could not speak about investigators' findings but confirmed that workers at the Michoud plant at one point performed an abrading procedure "in the general vicinity" of the eventual failure. The aim was to smooth out a divot in the tank's foam, which is extremely heat-resistant but easily gouged.
Such fixes are considered routine and are followed by inspections to ensure that foam adhesion has not been compromised.
At least five teams are now looking at that issue and others, with each focusing on a different part of the external tank. Complicating the analysis, Discovery's tank was coated with a patchwork of two different formulations of foam: an older formulation, which is also found on the Atlantis tank and on a spare tank now at Kennedy Space Center, and a newer formulation, which covers the six tanks in Alabama that have their PAL ramps attached.
Unless explanations and ready fixes for Discovery's problems can be identified, NASA and Congress will face the difficult decision of just how much time and effort should be expended on a significant redesign so late in the aging rocket plane's career.
There is a widespread desire in the space program to speed retirement of the 25-year-old shuttle, which by any measure is deep into its autumnal years. The shuttle's primary remaining task is to bring enough components to the international space station to justify a declaration that the orbiting laboratory is "functional," and to maintain a U.S. presence in space until a new breed of space vehicle is ready for testing around 2010.
The PAL ramp underwent extensive testing in the 2 1/2 years after the Columbia disaster, including wind-tunnel tests late last year at the U.S. Air Force's facility in Tullahoma, Tenn.
Discovery Returns to Earth