The U.S. space agency NASA says it will make a final decision Monday on when to try again to launch the space shuttle Endeavour, as crews work on a leaky hydrogen gas line.
The leak forced the postponement of Saturday's scheduled launch from the Kennedy Space Center in Florida.
The next opportunity for launch is Wednesday, but a rocket bearing an unmanned moon explorer is set for launch the same day.
Officials say they will try for an early-morning launch of the shuttle on Wednesday, but if that is not possible, they will go ahead and launch the moon explorer instead. The shuttle would then launch Saturday. If the shuttle launches Wednesday, the moon probe will go out Friday or Saturday.
Officials halted Saturday's launch about seven hours in advance of the scheduled liftoff. NASA said a leak in the gas line was detected during fueling. Launch director Mike Leinbach noted that hydrogen is very volatile and can burn, even in small concentrations.
Endeavor's 16-day mission is the last of three flights dedicated to building a Japanese laboratory attached to the International Space Station.
The shuttle will deliver an external platform for the laboratory that will enable long-duration space exposure studies of materials and experiments.
The seven-member shuttle crew is to carry out five spacewalks to attach the platform, which is as big as a bus and the single largest component of the space station.
A similar hydrogen gas leak forced a delay in the launch of the space shuttle Discovery in March. Discovery later successfully launched and completed its mission.
Some information for this report was provided by Reuters.