NASA has aborted an attempt to launch its giant, next-generation rocketship for second time in a week due to fuel leak.

The space agency, in a statement, said pre-flight operations were called off for the day about three hours before its launch.

The uncrewed test flight aimed at launching the capsule out to the moon and back, was to have marked the inaugural voyage of both the SLS and Orion a half-century after the last lunar mission of Apollo, the forerunner of the Artemis program.

The countdown was scrubbed after Kennedy Space Centre technicians made three failed attempts to fix a "large" leak of super-cooled liquid hydrogen propellant being pumped into the rocket's core-stage fuel tanks, agency officials said.

Mission managers proceeded with a second launch attempt once the earlier issues had been resolved to their satisfaction.

After a review of data from the latest difficulties, NASA concluded the new hydrogen leak was too tricky and time-consuming to finish troubleshooting and fix on the launch pad before the current launch period allotted to the mission expires on Tuesday.

NASA's Artemis mission manager Mike Sarafin, said efforts to resolve the latest technical snag would entail "several weeks of work.