Shuttle Launch Delayed to July by Hydrogen Leak

"I'm sure you all know that we postponed again," commander Mark Polansky wrote in a Twitter update. "It's a reminder that spaceflight is NOT routine."

Space shuttle Endeavour sits on the launch pad early Wednesday morning June 17, 2009. Racing against...

Space shuttle Endeavour sits on the launch pad early Wednesday morning June 17, 2009. Racing against the clock, NASA began fueling shuttle Endeavour for a Wednesday launch to the international space station after thunderstorms caused a three-hour delay. Hydrogen gas is leaking again from a vent line on space shuttle Endeavour's external fuel tank causing an additional delay and threatening to postpone the launch until July. (AP Photo)

(AP)

Noted Cain: "This business that we're in is not for the faint of heart."

NASA bumped an unmanned moon shot — its first in a decade — to give Endeavour this second chance of flying before a thermal blackout period kicks in.

That moon mission, featuring two science probes, is now scheduled for a Thursday launch.

After Saturday, unfavorable sun angles prevent Endeavour from taking off before July 11. Cain said it was too soon to know whether NASA would be able to make a July 11 launch.

The baffling leak — which has struck two of the past three shuttle flights — is about the size of the point of a ballpoint pen. Something has changed in the techniques or materials for the parts, and an engineering investigation hopefully will find out once and for all, Cain said.

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The latest leak occurred a little earlier in the fueling and had different characteristics.

Endeavour was set to deliver the third and last segment of Japan's massive space station lab along with hundreds of pounds of food for the six space station occupants. A new space station resident also was supposed to go up and swap places with a Japanese astronaut who's been up there since March.

The space station crew doubled in size late last month.

When Endeavour finally flies, it will be one of the longer international space station visits — nearly two weeks docked at the orbiting outpost — and include five spacewalks.

Once the shuttle pulls up at the space station, there will be 13 people together in space for the first time ever.

Delaying until July is expected to push back the next few shuttle flights.

NASA is up against a 2010 deadline for carrying out its final eight shuttle flights, all of them trips to the space station. The White House wants the three remaining shuttles retired and the space station completed by the end of next year.