The US space agency has postpone the launch of its new Artemis I Moon rocket for the second time in a week.
According to reports, till now controllers were unable to stop a hydrogen leak on the new vehicle, almost from the start of Saturday’s countdown procedure.
Nasa now has another opportunity to launch the rocket on Monday or Tuesday.
After that the vehicle will have to return to its assembly building for inspection and maintenance, which will mean further delays.
The Space Launch System is the most powerful rocket ever developed by Nasa, and much of the enormous thrust comes from burning almost three million litres of super-cold liquid hydrogen and oxygen in four big engines on the vehicle’s underside.
But when controllers sent the early morning command to fill the rocket’s hydrogen tank, an alarm went off, indicating there was a leak.
The problem was traced to the connection where the hydrogen was being pumped into the vehicle.
Controllers tried a number of fixes, including allowing the hardware to warm up for short periods, hoping this might reset the seal. But without success.
It’s possible Nasa could try again in the next few days. But if the rocket needs to be rolled back to the engineering building for further work this will introduce several weeks of delay.
Saturday’s attempt to despatch the Space Launch System (SLS) rocket had been scheduled for the start of a two-hour window beginning at 14:17 local time (19:17 BST; 18:17 GMT).
The 100m-tall vehicle’s objective was to hurl a human-rated capsule in the direction of the Moon, something that hasn’t happened since Project Apollo ended in 1972.