Gas Leak Prevents Space Shuttle Launch Again

This story was updated at 4:35 a.m. EDT.

CAPE CANAVERAL, Fla. - The space shuttle Endeavour's launch plans were thwarted again early Wednesday when a hydrogen gas leak, the same glitch that stopped the spacecraft from lifting off last week, appeared for a second time.

The potentially dangerous hydrogen gas leak from a vent pipe on Endeavour's external fuel tank forced NASA to stop fueling the shuttle in preparation for its planned launch at 5:40 a.m. EDT (0940 GMT) Wednesday.

"We did our standard troubleshooting techniques," NASA launch director Mike Leinbach said. Unfortunately, "it never cleaned up."

Endeavour will now have to wait until July before again trying to blast off from Launch Pad 39A here at NASA's Kennedy Space Center on an ambitious construction flight to the International Space Station.

"I'm sure you all know that we postponed again," Endeavour commander Mark Polansky wrote via Twitter. "It's a reminder that spaceflight is NOT routine. We will fly home to Houston this morning."

Gas leak returns

NASA officially called off today's launch attempt at 1:55 a.m. EDT (0555 GMT). The agency was already scrambling to make up for hours of lost time due to stormy weather that delayed the fueling of Endeavour's external tank. The shuttle's seven-astronaut crew had not yet boarded the spacecraft when NASA called off the launch attempt.

"The team did an outstanding job over these last four days to get to this point," Leinbach said. "It was just a heck of a lot of work that the guys pulled off. I sure wish we could have rewarded them and the astronauts with a launch."

Mission managers had worked furiously earlier this week to swap out the leaky seal between the hydrogen gas vent pipe on Endeavour's external tank in the hopes that it would fix the glitch, which prevented a June 13 launch attempt. The repairs went smoothly, but the persistent leak appeared again today shortly after ground crews began fueling the shuttle's giant orange external tank.

The leak is about the size of the head of a pen, compared to the 7-inch wide vent pipe, STS-127 shuttle launch director Pete Nickolenko said. "It's really a very small area altogether in which we're trying to chase down a leak," he said

This problem has cropped up before: An almost identical leak halted the launch plans of the space shuttle Discovery's STS-119 mission in March. In that case, the seal swap-out worked, and Discovery was able to launch four days later than planned.

Now mission managers will have to probe more deeply into the root cause of this failure to try to prevent it in the future.

"This business that we're in is not for the faint of heart," NASA deputy shuttle program manager LeRoy Cain said at a post-delay briefing. "There are times when we don?t get to go fly and that?s fundamentally because it's not easy. Like problems we've had in the past, we'll get past this one as well and move forward."

The glitch appeared after an earlier weather hurdle had finally been cleared. Endeavour's towering orange fuel tank was set to begin filling late Tuesday at 8:15 p.m. EDT (0015 GMT), but NASA had to delay almost three hours because of thunderstorms and lightning near the launch pad that pose a risk of igniting the vehicle's highly flammable liquid hydrogen and liquid oxygen propellants.

The weather cleared just in time for the latest possible start, and fueling began shortly after 11:00 p.m. EDT (0200 GMT). NASA teams appeared to be on track to launch as scheduled despite the lost time until the gas leak resurfaced.

Standing down

Endeavour will stand down until July 11 to allow a pair of unmanned lunar probes to launch from the nearby Cape Canaveral Air Force Station. That launch, which had also been scheduled for Wednesday, was pushed back to give Endeavour a second liftoff opportunity. Now the moon mission will likely try to blast off on Thursday or Friday.

While NASA does expect the delay to cause a ripple down through future flights planned for later this year, the delays should not impact plans to retire the shuttle fleet in 2010 after eight more missions, Cain said. Endeavour's mission is NASA's third of up to five shuttle flights planned for this year.

Endeavour is slated for a busy 16-day mission to the International Space Station to deliver an outdoor research platform for the Japanese Kibo laboratory. Commander Mark Polansky will lead a seven-member crew through five challenging spacewalks and complicated robotic work to install the new lab piece, plus a load of spare supplies for the station.

The shuttle will also carry a new long-duration crewmember for the space station, NASA astronaut Tim Kopra, who is due to replace current station resident Koichi Wakata of Japan as an Expedition 20 flight engineer.

SPACE.com is providing continuous coverage of STS-127 with reporter Clara Moskowitz at Cape Canaveral and senior editor Tariq Malik in New York. Click here for mission updates and SPACE.com's live NASA TV video feed.

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