Sensors near a repaired hydrogen vent line attached to the shuttle Endeavour's external tank detected only the slightest traces of free hydrogen during a critical fueling test Wednesday, officials said, clearing the way for another launch attempt July 11.
The 7-inch vent line and the ground umbilical carrier plate used to connect it to a port on the side of the external tank will remain in their current configuration and engineers are confident the system will be leak-free when Endeavour is fueled for launch on a space station assembly mission.
"We're in really good shape," said Mike Moses, the shuttle program launch integration manager at the Kennedy Space Center. "We're going to try on the 11th...We got it lined up just right and it doesn't leak."
The vent line is used to carry excess hydrogen gas away from the shuttle when the tank is filled with super-cold propellant. A valve used to route hydrogen to the vent line is closed a few minutes before launch when the tank is pressurized for flight.
Endeavour was grounded June 13 and 17 when sensors near the umbilical attachment plate detected hydrogen concentrations of more than 60,000 parts per million, or 6 percent. The allowable concentration near the shuttle is 4 percent.
After the second launch scrub, engineers collected detailed measurements and concluded the problem was caused by an alignment issue between the hydrogen vent port on the tank and the vent line interface. To ensure a tight fit, engineers replaced a rigid Teflon seal with a more flexible design, modified the umbilical plate mounting pins, and installed washer-like shims to counteract the alignment issue.… Read more