Discovery Mission Faces Further Delay

HOUSTON – During a NASA Shuttle Program Requirements Control Board meeting on Nov. 24, shuttle program managers decided on another incremental delay in plans for an early December launching of Discovery, giving them more time to assess whether external fuel tank damage found after a Nov. 5 launch scrub has introduced additional risk. The decision dashed plans to make a second round of attempts to begin Discovery’s 11-day assembly mission to the International Space Station between Dec. 3 and Dec. 7. Instead, the space agency will look to a launching no earlier than Dec. 17 at 8:51 p.m., EST, if it can work around Russian plans to launch the Soyuz TMA-20 with U.S., Russian and European crewmembers to the orbiting science laboratory on Dec. 15. The Soyuz crew is scheduled to dock on Dec. 17 just after 3 p.m., EST. However, the space agency will not push to launch Discovery until it understands the underlying cause of four cracks in two adjacent aluminum lithium stringers on the intertank of the 154-ft.-long fuel tank; if a tank flaw escaped detection during the production process; and whether additional undetected damage poses a hazard, said Bill Gerstenmaier, NASA’s Associate Administrator for Space Operations. “We have to understand what our exposure is to that problem recurring somewhere else on this tank,” said NASA Shuttle Program Manager John Shannon, who joined Gerstenmaier for a news briefing. “So we are very carefully, very methodically going through it. We’re passing up some launch opportunities to do that. We want to make sure we fully understand the problem before we commit to go fly.” The next launch period extends to Dec. 20, when shuttle managers would pause to prevent the shuttle’s computer timers from rolling over to the New Year on Jan. 1 at a critical time on orbit. Planners are looking at other opportunities to launch after Dec. 20 as well as in January. On Nov. 18, the control board announced a delay that shifted Discovery’s next launch opportunity from Nov. 30 to Dec. 3, also to permit more time to evaluate the external tank. During Discovery’s fleet-leading 39th and final mission, a crew of six astronauts will equip the space station with a storage compartment as well as an external spare parts platform, and new research gear. One and possibly two missions remain as the shuttle fleet nears retirement. STS 134, aboard Endeavour, is tentatively scheduled to lift off for the station on Feb. 27 with the $2 million Alpha Magnetic Spectrometer. Though snagged in 2011 budget deliberations, Atlantis could lift off on the program’s final flight, STS 135, in mid-2011 with a cargo of station supplies. Since Discovery’s Nov. 5 scrub, Kennedy technicians have replaced the leaky Ground Umbilical Carrier Plate that led to the interruption. A fuel tank fixture, the GUCP vents hydrogen vapors to a launch pad flare stack during the final hours of the countdown. But the damage causing lingering concerns was the stringers cracks found beneath a 20-in. crack in the insulating foam that jackets the 154-ft. tall fuel tank. Technicians replaced 13 in. of the damaged metal on neighboring stringers and installed structural doublers. While similar repairs have been carried out at NASA’s external tank Michoud Assembly Facility, Discovery’s were the first attempted at the launch pad. The cracked foam was replaced, as was a cockpit circuit breaker that was blamed for a voltage irregularity that interrupted a previous launch bid.