NASA officials again called off the Endeavour launch, after detecting a hydrogen leak while crews filled the shuttle's external fuel tanks. A similar leak forced officials to delay the first launch attempt Saturday.
On Monday, officials said technicians had stopped the leak by installing new seals on the vent lines for the hydrogen fueling system. Deputy shuttle program manager LeRoy Cain said repair crews will have to work harder to resolve the problem.
"This business that we are in is not for the faint of heart. So there are days we do not get to go fly and that is fundamentally because it is not easy. But we recover from these things and it makes us stronger," he said.
Officials said the leak is a major source of concern because sensors on the launch pad are detecting large quantities of hydrogen, a volatile gas.
Launch director Pete Nickolenko said technicians believe a very small leak is causing the problem.
"The leak is essentially the size of the head of a pin, around a seven-inch [17-centimeter] quick-disconnect [valve]. So even though we are talking high concentrations [of gas] it is really a small area altogether," he said.
The shuttle team was facing a tight launch schedule, because an unmanned lunar mission also is set to lift off this week from Kennedy Space Center in Florida. The Lunar Reconnaissance Orbiter had agreed to delay their launch one day to allow Endeavour a second try.
The next opportunity for the shuttle to launch is July 11, if technicians resolve the leak. The delay may affect other future shuttle missions as well.
The Endeavour mission includes plans for five space walks to install the Japanese science module and perform other tasks at the space station. Astronaut Tim Kopra will travel to the station to replace Koichi Wakata, who will return to Earth aboard the shuttle.