Weather Clouds Endeavour's Third Attempt at ISS Mission

Grounded twice in June by a potentially dangerous launch pad hydrogen leak, the space shuttle Endeavour's third attempt to lift off for the International Space Station is threatened by a far more mundane but equally lethal issue: bad weather.

Liftoff is scheduled for July 11 at 7:39 p.m. EDT, but due to expected showers, thunderstorms and anvil clouds in the area, NASA said July 9 the launch is only a 40 percent go. "That is always the remaining issue that we have," NASA Test Director Steve Payne said in a Thursday briefing. "If there's a hole in the clouds, we'll go for it. If not, then we'll go for it the next day. But we would rather get it done on Saturday."

Payne added that all others systems are go. The seven-person crew spent July 9 reviewing their flight plans, relaxing and checking out their launch-and-entry suits. "All systems are in excellent shape," Payne said. "The STS-127 flight crew, Endeavour and launch team are ready to go."

Resource Library:

Endeavour is scheduled to dock at the ISS July 13 with a cargo bay full of work that includes what Endeavour Commander Mark Polansky calls "really big pieces of equipment" and will require five spacewalks over the course of the 16-mission. The primary mission purpose is to deliver the final permanent components of Japan's Kibo laboratory complex, a literal "front porch" on the ISS for space-exposed science experiments.

After the crew's frustrating June, Polansky said, "I can tell you that this crew and the entire operations team are both eager and ready to get to work. Hopefully the next time we talk to you will be from orbit."

The Endeavour's original launch date was June 13, but it was canceled 5 hours before launch due to a potentially dangerous vent line hydrogen gas leak. NASA tried again on June 17 but called the mission when the hydrogen leak reappeared. The leaks were similar to one that NASA encountered while trying to launch Discovery four months ago.

That flight was delayed four days because of the problem and shortened as well. Atlantis, however, encountered no such trouble during its countdown in May for the Hubble Space Telescope repair mission.

Since the Endeavour crew stood down June 17, NASA engineers have pinpointed the leak to a plate that attaches the vent line to Endeavour's external fuel tank. The plate was slightly misaligned, allowing a small leak to happen during the fueling process. After NASA completed a fueling test July 1, the space agency declared the problem fixed.

"This one I feel really good about, that we've got that problem licked and we're not going to see another GUCP [Ground Umbilical Carrier Plate] leak again on the next launch attempt," Mike Moses, head of the shuttle's mission management team, told reporters.

Once the Endeavour reaches the ISS, things will be as busy inside the shuttle and space station as the spacewalkers, with all three of the available robotic arms being put to use, sometimes all on the same day. The shuttle's Canadarm and the station's Canadarm2 will be put through their regular paces for surveys, unloading cargo and moving equipment and spacewalkers around, and a new Japanese robotic arm will be making its debut to transfer science experiments.