It must have felt like déjà vu for NASA’s mission management team when it met yesterday to discuss whether the damage to the reinforced carbon panels on Space Shuttle Discovery’s wing leading edges should be replaced per recommendations of an independent safety group. Replacing the three panels would cause a two-month delay in the shuttle’s scheduled October 23 launch date. After four hours of deliberation and a split decision within the engineering team, NASA has announced that it will stick to its schedule while engineers continue to assess the problem.

In a statement to the press, Wayne Hale, NASA’s shuttle chief, said that there is a preponderance of evidence that says that NASA has an acceptable risk to fly. He also said that understanding the cause of the defects is a very complicated problem, and the thermal shielding is a very complicated system that NASA absolutely needs to make sure works properly.

The space shuttle’s thermal protection system is a combination of reinforced carbon-carbon (RCC) on the wing leading edges, thermal blankets on the fuselage, and thermal protective tiles covering the underside of the vehicle and nose cap. This system protects the spacecraft and its human occupants from the extreme heat of reentry into the earth’s atmosphere. Without the RCC, blankets, and tiles, the structural integrity of the shuttle’s aluminum frame would be compromised. In 2003, the world witnessed a devastating disaster after the RCC on the port (left) wing of the Space Shuttle Columbia was damaged during launch. The damage went undetected, and the shuttle, left with a compromised heat-resistant shield, lost structural integrity and broke apart during reentry.

According to NASA spokesman Allard Beutel, the outer coating on three of Discovery’s wing panels–two on the right wing and one on the left–show degradation, an issue that the NASA Engineering and Safety Center (NESC) has been reviewing for the past several months. The center is an independent safety group that provides assessments of critical, high-risk projects for NASA. The center’s recommendation was for NASA to replace the panels before launching the spacecraft.

NASA was faced with a similar decision two months ago, when it detected damage to thermal tiles located on the underside of Endeavour. It took almost a week for NASA’s mission management team to decide, despite an opposing vote from engineers, not to conduct a dangerous space walk to repair the tiles. The shuttle safely returned home, and NASA quickly added a space walk to Discovery’s mission to test the repair technique it would have used on Endeavour. (See “NASA to Test Space Repairs.”)

Hale says that schedule is not a factor in the decision-making process, and NASA will continue to reevaluate the heat-shield coating concerns as new data comes in.