An unexpected hydrogen leak aboard NASA shuttle Endeavour forced the agency to delay the shuttle's scheduled Saturday launch until Wednesday at the earliest.

"Our crew is taking things in stride and will be ready to go when called," Canadian astronaut Julie Payette said in a message posted on the Canadian Space Agency web site.  

This particular crew has reportedly worked around 18 months to prepare for this mission, so a four-day delay to get the shuttle fixed isn't a catastrophe, another mission astronaut said yesterday during a press conference.

The shuttle has until June 20 to launch towards the ISS, or Endeavour's launch will have to be pushed back until early July.

Flight engineers found the leak near a vent line that connects the external fuel tank to the shuttle itself.  Onboard sensors detected the liquid hydrogen leak as NASA began fueling the external tank, and the shuttle launch was scrubbed several hours before scheduled liftoff.

There is an interesting scheduling conflict NASA faces now, with the Lunar Reconnaissance Orbiter also scheduled to head into space from Kennedy Space Center on Wednesday.  Endeavour flight managers will discuss launching both the shuttle and orbiter in the next week, but it's unsure if the managers of the orbiter mission are willing to alter flight schedules.

"Obviously, the 17th is a range problem, there's a conflict out there with LRO/LCROSS," according to Kennedy Space Center manager Mike Moses.  "We haven't even begun to work that yet... We'll start those negotiations tomorrow and see where we get, both with the Range and with the NASA payload."

NASA plans to launch Endeavour to finish construction on the International Space Station (ISS), as there is still so much work to be done and very few launch opportunities available.

The Endeavour's leak is similar to a fuel leak suffered by shuttle Discovery in March, which cost NASA to delay its launch for four days.  NASA officials believed they had the problem fixed after Discovery's problems several months ago, and will continue to try and prevent the mistake from happening again.

This most recent delay causes headaches as NASA faces a high level of pressure to finish construction on the ISS before the current shuttle fleet is retired in 2010.  Until the next-generation Constellation U.S. rocket technology is finished, however, NASA will pay Russia to ferry supplies and astronauts into space.