NASA technicians work with Discovery's leaky fuel tank vent line fixture. Photo Credit/NASA Troy Cryder
NASA is still striving for a second bid to launch the shuttle Discovery on her final mission during a Nov. 30 through Dec. 6 launch window, though technicians and engineers are dealing with several external fuel tank problems.
A substantial leak of hydrogen from a vent line fixture on the 154 foot tall fuel tank on Nov. 5 forced a long delay in plans to begin Discovery’s 11-day mission to the International Space Station.
Since then, engineers have found an additional problem, three cracks in the corregated metal structure near the top of the tank. A search for more cracks was under way over the weekend, while engineers develop a strategy to install “doublers” on at least two of the cracks, a pair of narrow 9-inch long openings in the aluminum structure.
The metal surface cracks were found just below a 20-inch long crack in the insulating foam that covers that tank. The foam crack was noticed while launch teams were dealing with the Nov. 5 hydrogen leak.
Metal crack repairs have been made at the big fuel tank’s production factory but not on the launch pad.
Efforts to launch Discovery and a crew of six astronauts were stalled three times between Nov. 1 and 5. First, there was an irregular voltage on a rocket engine computer, then stormy weather and finally the hydrogen leak.
The leak was likely caused by a misaligned seal within the vent line fixture called a Ground Umbilical Carrier Plate, or GUCP. The misalignment was discovered this past week as the leaky GUCP was disassembled. Over the weekend, technicians and engineers, are selecting new seals and other GUCP subcomponents for a replacement assembly that will be installed early next week.
The voltage irregularities were traced to stray contamination in a circuit breaker panel in Discovery’s crew cabin. The panel is being replaced as well.
At some point soon, NASA managers will decide whether to conduct a launch pad fueling test before re-starting a countdown. During the test, Discovery’s fuel tank would be loaded with chilled hydrogen and oxygen propellants to see if the leak reappears.
The upcoming launch window, Nov. 30 through Dec. 6, begins with the end of a lengthy period of high solar heating on the space station’s orbital plane. During most of November, the temperatures are too high for the shuttle’s thermal control system to manage while the ship is docked to the station.
After Dec. 6, NASA will have to give way to Russian space station activities. The Russians plan to launch a Russian, U.S. and European crew of three to the station aboard a Soyuz rocket on Dec. 15.
Beyond early December, the next shuttle launch period opens in late February.
The flight will be Discovery’s 39th. The shuttle will deliver an equipment storage module, an external spare parts platform and research equipment to the station.
Discovery’s astronauts plan a pair of spacewalks as well.