Another hydrogen leak will keep the space shuttle Endeavour's crew on the ground for another month while NASA investigates the problem. The space agency scrubbed today's scheduled launch early this morning when a gaseous hydrogen leak was detected at the same location where a similar leak halted the shuttle's original June 13 launch.

"We're going to step back and figure out what the problem is and go fix it," Deputy Space Shuttle Program Manager LeRoy Cain said in a statement. Even if all goes well, NASA expects the shuttle to launch no earlier than July 11.

NASA engineers found the leak at the Ground Umbilical Carrier Plate (GUCP), which is the vent to the launch pad and the flare stack (or elevated chimney) where the vented hydrogen is burned off. (For pictures of what the GUCP looks like, visit The venting system (pdf), located outside the shuttle's external fuel tank, is designed to carry excess hydrogen safely away from the launch pad as the Endeavor blasts off. During launch, the external fuel tank supplies the shuttle's main engines with liquid oxygen and hydrogen propellants.

The engines transform this liquid into gaseous hydrogen, which is returned to the external tank to provide pressure and keep the propellant flowing out of the tank. A valve is then supposed to regulate this flow of gaseous hydrogen from the main engines back to the fuel tank so it delivers propellant to the main engines at the correct pressure.

NASA believes a seal on the external fuel tank that was misaligned when it was coupled to one of the shuttle's engines caused the leak, NASA Shuttle Test Director Stephen Payne, said Monday during a press conference.

Endeavour experienced a similar problem in November, when flight controllers noticed gaseous hydrogen flowing from one of the shuttle's engines at a higher than normal rate. After the shuttle returned from that mission, engineers discovered that the suspect flow control valve was cracked and a small piece was missing. A similar problem delayed Discovery's March launch for four days as ground crews swapped out the suspect seal between the vent pipe and the shuttle, according to

Endeavour's current 16-day mission is expected to include five spacewalks and complete construction of the Japan Aerospace Exploration Agency's Kibo laboratory on the International Space Station (ISS). NASA had the option of launching June 21 but decided against it because the angle of the Sun would put the shuttle in direct sunlight for too long, leading to a shorter mission and requiring the crew to cut one of the space walks, Payne said Monday. The shuttle could overheat if it was docked at the space station during those dates, the BBC reports.

The shuttle's problems likewise pushed back the launch of the moon-probing Lunar Reconnaissance Orbiter (LRO) and Lunar Crater Observation and Sensing Satellite (LCROSS), which was originally supposed to launch today. That launch is expected to take place Friday, the Washington Post reports.

Image of Nov. 14, 2008, Endeavour launch © Ray Bahr via Flickr