Nasa stopped the countdown at the launchpad in Florida five minutes ahead of a test ‘launch’, following a hydrogen leak from a connection linking the launch tower to the rocket, which can hold three million litres of hydrogen and oxygen.

“The Artemis II wet dress rehearsal countdown was terminated at the T-5:15 minute mark due to a liquid hydrogen leak at the interface of the tail service mast umbilical, which had experienced high concentrations of liquid hydrogen earlier in the countdown as well,” a Nasa statement reads.

During tanking, Nasa engineers spent “several hours” troubleshooting a liquid hydrogen leak in an interface used to route the cryogenic propellant into the rocket’s core stage, which put them behind on the countdown.

“Attempts to resolve the issue involved stopping the flow of liquid hydrogen into the core stage, allowing the interface to warm up for the seals to reseat, and adjusting the flow of the propellant,” Nasa said.

“Teams successfully filled all tanks in both the core stage and interim cryogenic propulsion stage before a team of five was sent to the launch pad to finish Orion closeout operations.”

Problems were also encountered with the hatch to the Orion capsule earlier in the launch sequence. A valve associated with crew module pressurisation, which was replaced, required retorquing, and closeout operations took longer than planned.

It follows similar failed launches of the Artemis I in 2022, when two liquid hydrogen leaks spoiled launches twice in one week.

Artemis II aims to take four astronauts around the moon and back to Earth for the first time in more than 50 years.

NASA now plans a second rehearsal, meaning the earliest the rocket could launch is March.