Nasa’s new moon rocket has sprung another dangerous fuel leak, forcing launch controllers to call off their second attempt to send a crew capsule into lunar orbit with test dummies.

The first attempt earlier in the week was also marred by escaping hydrogen, but those leaks were elsewhere on the 322ft (98-metre) rocket, the most powerful ever built by Nasa.

Launch director Charlie Blackwell-Thompson and her team tried to plug Saturday’s leak the way they did the last time: stopping and restarting the flow of super-cold liquid hydrogen in hopes of removing the gap around a seal in the supply line.

They attempted this twice, and also flushed helium through the line. But the leak persisted.

Ms Blackwell-Thompson finally halted the countdown after three to four hours of effort.