Workers replace Discovery's leaky fuel tank vent line fixture. Photo Credit/NASA photo
Discovery’s final mission moved to a short end-of-the-year launch period on Thursday to permit more time for shuttle engineers to complete repairs to the orbiter’s external fuel tank and managers to assure themselves they understand what led to the damage.
The launching was re-scheduled from Nov. 30 to no earlier than Dec. 3. If not under way by Dec. 6, the flight faces further delays, possibly until late February.
Problems start with Nov. 5 leak
Discovery’s 11-day assembly flight to the International Space Station, the final mission for NASA’s oldest shuttle orbiter, was scrubbed on Nov. 5 by a significant hydrogen leak. The leak was accompanied by a 20 inch long separation in the foam insulation that jackets the external fuel tank. As the damaged foam was removed, technicians found cracks in a pair of adjacent aluminum support stringers on the tank structure.
The leaky fuel tank fixture that vents hydrogen gas to a launch pad flare stack has been replaced. The new Ground Umbilical Carrier Plate successfully passed a series of leak tests over the past two days.
Meanwhile, workers have removed the structural cracks on the stringers and are fastening metal doublers to the damaged portions of the fuel tank.
Safety a concern
Though the repairs appear to be going well, NASA shuttle program managers said Thursday they want more time to understand what led to the cracks and whether the repairs can withstand the launch stresses.
After further analysis, they plan to re-convene on Nov. 24 to discuss a new “flight rationale.”
If the session produces a successful outcome, the agency’s top spaceflight officials will gather on Nov. 29 to review the analysis and repairs before making a “go/no go” decision that could lead to a Dec. 3 launch attempt. That meeting had been set for Nov. 22.
The December launch period ends on Dec. 6 so that a Soyuz spacecraft with three Russian, U. S. and European astronauts can lift off for the station.
Future mission constraints
A range of already scheduled space station activities and shuttle thermal control system restrictions are guiding the opening of the next launch window toward late February.
Currently, Endeavour is scheduled to lift off Feb. 27 on NASA’s final scheduled shuttle mission, a flight to equip the space station with the Alpha Magnetic Spectrometer, an external astronomical observatory.
However, NASA is assessing changes in December and January activities that might permit additional launch opportunities prior to late February.
Discovery’s six astronauts have trained to equip the station with an equipment storage module and an external platform for spare parts.
The final flight will be the 39th for Discovery.