CAPE CANAVERAL, Florida NASA canceled plans to launch space shuttle Endeavour on a construction mission to the International Space Station on Saturday due to a potentially dangerous hydrogen leak.
The leak was found as technicians neared completion of the loading of 500,000 gallons (1.9 million liters) of liquid hydrogen and liquid oxygen into the shuttle's fuel tank for a launch attempt at 7:17 a.m. EDT.
"There's no way we could have continued," said NASA launch director Mike Leinbach. "Hydrogen is a very volatile commodity."
The problem is similar to a hydrogen leak that occurred while shuttle Discovery was being prepared for launch in March. NASA discovered a problem with a line that vents gaseous hydrogen from the fuel tank.
Technicians replaced the faulty equipment and the shuttle was successfully launched four days later.
NASA is tentatively retargeting Endeavour's launch for Wednesday, but that would mean the agency would have to delay launch of its robotic moon probe, the debut mission of a new exploration initiative aimed at returning astronauts to the moon by 2020.
Both the shuttle and the Lunar Reconnaissance Orbiter's Atlas rocket use safety and support services from Cape Canaveral Air Force Station, which needs two days to configure equipment for different launch vehicles. LRO is slated to fly on Wednesday.
"We had pretty much agreed ahead of time that we would not bump them off the range," said Mike Moses, the shuttle manager at Kennedy Space Center. "But nothing is a foregone decision."
NASA had reserved three days for launch attempts of LRO, which also includes a payload designed to crash into a crater on the moon to look for signs of water.
NEXT LAUNCH WINDOW
If LRO misses its launch window next week, the flight would have to be rescheduled for the end of the month, which in turn would impact other spacecraft scheduled to fly on future Atlas rockets.
"There are a lot of factors in play," Moses said.
Endeavour is carrying a Japanese-built porch that will be installed on the station's $2.4 billion Kibo complex, Japan's primary contribution to the $100 billion station program.
The lab includes a robot arm and a small airlock so science experiments can be installed outside the station and retrieved without the need for spacewalks by crew members.
Endeavour also is carrying laboratory racks, experiments, supplies and spare parts that will be stored aboard the outpost in preparation for when the shuttle is no longer flying.
NASA has eight shuttle missions remaining to complete construction of the station. It plans to retire the three-ship fleet at the end of 2010.
The Endeavour crew plans to spend 12 days at the station and conduct five spacewalks to install the porch, replace batteries and tackle a long list of maintenance tasks.
The mission is NASA's first since the station's live-aboard crew was expanded to six members from three last month.
When the shuttle crew arrives, it will bring the total number of people aboard the space station to a record 13.