Troubleshooting Of Discovery Continues

HOUSTON — NASA’s space shuttle Program Requirements Control Board met Dec. 2 without arriving at a root cause for the cracks found in the external tank of the shuttle Discovery. Discovery’s final mission, STS-134, has been on hold since Nov. 5, when a hydrogen leak in the external tank’s Ground Umbilical Carrier Plate forced a scrub of the 11-day assembly mission to the International Space Station. The likelihood of initiating the flight during the next available launch period, Dec. 17 to Dec. 20, was not discussed during the 4-hr. Dec. 2 meeting, according to NASA shuttle program spokesman Kyle Herring. More analysis and testing is underway. “Obviously, the thing we are trying to get to is root cause,” Herring says. “That is the one thing we don’t have. We have a lot of data coming together, but the one thing missing is root cause.” During the early November scrub, a 20-in. crack formed in the foam insulation jacketing the 154-ft.-tall external tank. The separation in the foam occurred at the top of the “intertank,” a ribbed region of the tank that separates internal oxygen and hydrogen propellant containers. As the damaged foam was removed, technicians found four cracks in two neighboring stringers. In all, 108 of the 21-ft.-long stringers surround the tank to lend structural support. The cracks were the first found and repaired at the launch pad. Cracks found on other external tanks at NASA’s Michoud Assembly Facility have been blamed on defective parts or mishandling. Previous repairs took place at Michoud. Discovery’s launch has slipped from no-earlier-than dates of Nov. 30, Dec. 3 and Dec. 17. On Nov. 24, Shuttle Program Manager John Shannon said the investigation would not be schedule driven. The flight could be rescheduled for late December, January or February, if necessary. The scope of the analysis includes the fabrication of the stringers; tank assembly; and transportation to Kennedy Space Center, as well as launch preparations. Discovery’s six astronauts have trained to equip the station with a new storage module and install an exterior spare parts platform. The shuttle’s cargo includes 6,500 lb. of research gear, reserve life support gear and other supplies. Two of the astronauts are trained for a pair of spacewalks to reposition equipment that was used to repair the station’s external cooling system in August.