NASA engineers spent this past week examining several issues which prevented space shuttle Discovery from blasting off on her final mission last week, including a hydrogen leak in the GUCP and cracks to the external tank, and remain optimistic about getting Discovery off the ground during the next launch window despite the work ahead.
Technicians disconnected the GUCP (Ground Umbilical Carrier Plate) Tuesday night and believe they have traced the source of a gaseous hydrogen leak which scrubbed Discovery’s launch November 5th to a misaligned flight seal inside the Ground Umbilical Carrier Assembly.
“Why that happened, how that came about, that is what they are trying to determine,” explained NASA spokesman Allard Beutel. “Technicians are working to approve a plan that would allow them to put a new flight seal in, put the carrier plate assembly back on and basically wrap up the replacement of the GUCP, the fitting and all the connectors by early next week,” said Beutel.
Technicians will spend the weekend taking measurements to ensure the best possible alignment of a newly installed GUCP and teams will meet Monday to evaluate the data. Installation is expected to take place early next week.
“The whole thing with the GUCP is proper alignment,” said Beutel. “When it is properly aligned, it doesn’t leak. So they are going to take extra time to make sure they get really good measurements before they put the quick disconnect and flight seal back in.”
Meanwhile, several cracks have been discovered on Discovery’s external fuel tank, which feeds supercooled liquid hydrogen and liquid oxygen to the shuttle’s three main engines during ascent.
Technicians removed damaged foam insulation from the tank Wednesday morning, and in doing so discovered two 9-inch cracks on the tank’s metal body running along one of the vertical stringers, which are aluminum support strips on the intertank area – the divider between the liquid oxygen and liquid hydrogen tanks. Another 3-inch crack was found Friday morning on an adjacent stringer, and is believed to be a result of the stress and pressure loads shifting after the initial cracks occured.
The cracks were not a surprise to NASA, nor is it a problem NASA is unfamiliar with. However, past repairs have only been conducted at NASA’s Michoud Assembly Facility in New Orleans, where the tanks are manufactured, not at the launch pad in Florida while mated to the shuttle and it’s twin solid rocket boosters. Technicians need to remove the cracked section and replace it with a “doubler”, a twice as thick piece of aluminum, for reinforcement. Foam insulation would then be applied over the repaired area and would require roughly 3-4 days to settle.
“They need to build an enclosure around the repaired area to re-foam it and to maintain the proper environmental conditions,” explained Beutel. “It takes several days for the foam to dry, and that assumes you’re not going to get a storm blowing through here.”
Repair plans at the launch pad are in the works, and engineers will reference existing structural math models this weekend to understand the stresses being put on the stringers during launch in order to ensure the repairs will withstand the tremendous forces acting on them during the 17,500 mph ride to orbit.
NASA remains confident they can get Discovery off the ground November 30th, the start of the next launch window. However, many tests need to be conducted after repairs are made, and a lot of data must be thoroughly analayzed before, and after, those repairs are performed.
If all goes well in the coming week, Discovery’s final launch on mission STS-133 would occur in the middle of the night and be visible up and down most of the east coast United States. If NASA cannot ready Discovery in time for the next launch window, her final flight would likely slip into February 2011, which in turn would push back Endeavour’s final flight on STS-134 to late spring or early summer.