CAPE CANAVERAL, Florida — NASA encountered frustrating fuel leaks during a make-or-break test of its new moon rocket on Monday, casting doubt on when astronauts could take off for a trip around the moon.

The leaks — reminiscent of the rocket's delayed debut three years ago — sprang just a couple of hours into the daylong fueling operation at Kennedy Space Center.

Launch controllers began loading the 98-meter rocket with super-cold hydrogen and oxygen at midday. More than 2.6 million liters had to flow into the tanks and remain on board for several hours, mimicking the final stages of an actual countdown.

But excessive hydrogen quickly built up near the bottom of the rocket. Hydrogen loading was halted at least twice as the launch team scrambled to work around the problem using techniques developed during the previous Space Launch System countdown in 2022. That first test flight was plagued by hydrogen leaks before finally soaring without a crew.

The four astronauts assigned to the mission — three US astronauts and one Canadian — monitored the critical dress rehearsal from nearly 1,600 kilometers away in Houston, home to Johnson Space Center. They have been in quarantine for the past one and a half weeks, awaiting the outcome of the practice countdown.

Monday's fueling demo will determine when they can blast off on the first lunar voyage by a crew in more than half a century.

At best, NASA could launch Commander Reid Wiseman and his crew to the moon no sooner than Sunday. The rocket must be flying by Feb 11 or the mission will be called off until March. The space agency only has a few days in any given month to launch the rocket, and the extreme cold has already shortened February's launch window by two days.

Running behind because of the bitter cold snap, the countdown clocks began ticking Saturday night, giving launch controllers the chance to go through all the motions and deal with any lingering rocket problems. The clocks were set to stop half a minute before reaching zero, just before engine ignition.

The nearly 10-day mission will send the astronauts past the moon, around the mysterious far side and then straight back to Earth, with the goal of testing the capsule's life support and other vital systems. The crew will not go into lunar orbit or attempt to land.

Agencies via Xinhua