NASA will try to launch the space shuttle Endeavour on July 11, nearly a month late, after plugging a potentially dangerous hydrogen gas leak, top mission managers said Wednesday.

Endeavour successfully passed a leak check during a fueling test at its seaside Florida launch pad today, setting the stage for a planned 7:39 p.m. EDT (2339 GMT) liftoff toward the International Space Station on July 11, said Mike Moses, who leads the shuttle's mission management team.

NASA initially tried to launch Endeavour on June 13, then again on June 17, but the hydrogen gas leak in the shuttle's external fuel tank thwarted both attempts.

Engineers pinpointed the leak in a misaligned ground umbilical carrier plate (GUCP) on the tank. The plate connects to a vent line that siphons excess hydrogen gas safely away from the shuttle during fueling.

"This one I feel really good about, that we've got that problem licked and we're not going to see another GUCP leak again on the next launch attempt," Moses told reporters.

Leak fix a success

Engineers replaced a Teflon seal and realigned the problematic plate using special washers to plug the leak, which did not reappear during today's fueling test at the Kennedy Space Center in Cape Canaveral, Fla.

"Looks like the tank performed well," said Endeavour's commander Mark Polansky via his Twitter page.

Polansky is leading a seven-astronaut crew tasked with delivering the last piece of Japan's massive Kibo laboratory to the International Space Station during a marathon 16-day mission. It is NASA's third shuttle flight of the year, but the first to the station since the outpost doubled its crew size to six people last month.

NASA has strict rules on the amount of hydrogen gas that can be near a space shuttle at launch time because the extremely flammable gas can pose an explosion risk to the shuttle and its astronaut crew.

During fueling, the space shuttle's external tank is loaded with about 526,000 gallons of super-cold liquid hydrogen and liquid oxygen. Some of that hydrogen boils into gas over time and must be safely vented away from the shuttle and be harmlessly burned off elsewhere.

Endeavour's repaired tank passed today's test with flying colors, mission managers said.

"There were absolutely no leak indications whatsoever noted on the two leak detectors," said NASA launch director Pete Nickolenko. "We'll continue to look at the data, and our next step is to move toward launch."

The Endeavour astronauts are slated to go into quarantine this weekend and return to their Florida spaceport on Tuesday, Polansky said. The countdown to Endeavour's July 11 launch will begin next Wednesday night, NASA officials said.

Atlantis window work

While one team of engineers prepares Endeavour for launch, another is tackling a window issue on the shuttle Atlantis.

During the shuttle's May flight to the Hubble Space Telescope, a work light knob jammed up against a flight deck window pane and dashboard panel. Initially the knob was stuck fast, but engineers managed to remove it on Tuesday by pressurizing Atlantis' cabin and applying dry ice on the knob.

Moses said technicians plan to take a mold of the window to see if the knob has caused damage that would require replacing the inner window, a potentially lengthy repair that could sideline Atlantis for up to eight months.

The shuttle is currently slated to launch supplies and parts to the International Space Station on Nov. 12.

"It could take a very long time, it sounds very scary," Moses said of any serious repair. "But then again, I've learned this team is really good at re-sequencing and coming up with some creative ways to do some work in parallel."

Copyright © 2009 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.