Discovery aims for Feb. 24 lift off as workers complete fuel tank repairs. Photo Credit/NASA Photo
NASA announced Tuesday that shuttle managers have identified the root cause of the fuel tank cracks that have stalled shuttle Discovery’s final mission since early November.
Repairs are under way at the Kennedy Space Center.
And the space agency is re-scheduling the last two and possibly a third mission that when flown will end NASA’s 30-year-old space shuttle era.
“We absolutely have a root cause,” NASA Shuttle Program Manager John Shannon told a Houston news briefing. “And we have a fix that we are completely confident will eliminate the impact.”
Discovery is tentatively scheduled to lift off on Feb. 24 at 4:50 p.m. EST, initiating an 11-day mission that will equip the International Space Station with a new equipment storage module and an external platform to secure spare parts.
Endeavour, which was headed for an April 1 lift off, will likely not launch until April 18 at the earliest.
On Thursday, Bill Gerstenmaier, NASA’s associate administrator for space operations, declined to discuss the status of Endeavour commander Mark Kelly. Kelly, a veteran astronaut, is the husband of Arizona Congresswoman Gabrielle Giffords, who was among those critically wounded by a gun man at a Jan. 8 Tucson political rally.
The agency has decided to sort out further testing of Endeavour’s fuel tank before establishing the training requirements for Kelly and his five-member crew. Following the shooting, Kelly flew from Houston to Tucson, where Giffords was hospitalized ater surgery.
Meanwhile, Atlantis will be readied for an encore supply mission to the station. The flight, which has yet to be fully funded by the White House and Congress, is tentatively slated for a June 28 lift off. However, Mike Suffredini, NASA’s Station Program Manager, would like the mission to move to late August to ensure the orbital outpost is well stocked with supplies and spare parts before the shuttle retires.
Shannon attributed the cause of the eight cracks found in five of 108 support stringers on Discovery’s fuel tank to a complex combination of factors. The aluminum lithium material from which the 21-foot-long support beams were fabricated came from a lot that had just 65 percent of the desired fracture strength. The tank is assembled in such a way as to contract when internal containers are filled with nearly a half million gallons of chilled liquid oxygen and hydrogen.
Seventy-eight of Discovery’s 108 stringers came from the same weaker lot of materials.
The shock of the cold propellant flow, the contractions and the material weakness combined to induce the cracks, said Shannon.
Endeavour’s fuel tank was assembled with stringers from an older manufacturing lot. Though the same crack issue is not suspected, Endeavour’s tank will under go further testing and X-ray scans to be sure.
The fuel tank assigned to Atlantis has stringers from the weaker materials lot.
This week, technicians began to install a “radius block” modification to all 108 of Discovery fuel tank stringers. The modification goes over the tip of the stringers to give them more strength in the crack prone regions to withstand the cold temperature contractions and the loads of the climb to orbit.
The fuel tank assigned to Atlantis is likely to receive the same upgrade.
