The American space agency has called off the launch of its big new Moon rocket – the Space Launch System.
Controllers struggled to get an engine on the 100m-tall vehicle cooled down to its correct operating temperature.
They’d previously worried about what appeared to be a crack high up on the rocket but eventually determined it was merely frost build-up.
The SLS is the biggest rocket ever developed by Nasa. It will be used to send astronauts back to the Moon.
The maiden flight is just a demonstration with no-one aboard, but ever more complex missions are planned for the future that will see people live on the lunar surface for weeks at a time.
Nasa has the option to try again on Friday, if the engine issue can be resolved easily.
But it’s possible the rocket may have to be rolled back to the assembly building at the Kennedy Space Center for more extensive work. This could see the flight slip further into September.
Engine bleed problem couldn’t be rectified
Launch director Charlie Blackwell-Thompson cancelled the planned launch of Artemis I as a result of an engine bleed issue, Nasa says.
The Space Launch System (SLS) rocket is said to be in a “stable configuration”, and engineers will now work on gathering data to see what went wrong.
The rocket was due to be launched a short time ago, at 08:33 Florida time (13:33 BST).
The next available opportunity for a launch is 2 September, Derrol Nail of Nasa says, although he adds this is dependent on the fix for the engine bleed issue.
BBC