The National Aeronautics and Space Administration on Monday postponed the test flight of Artemis 1 spacecraft because of a fuel leak and an engine problem reported during the lift-off. The spacecraft was supposed to orbit the moon.

“This is a very complicated machine, a very complicated system, and all those things have to work, and you don’t want to light the candle until it’s ready to go,” NASA Administrator Bill Nelson said, according to the Associated Press.

The flight was meant to test the Space Launch System rocket and the Orion crew capsule. There were no humans inside the capsule. Instead, NASA had placed test dummies fitted with sensors to measure vibration, cosmic radiation and other variables, the Associated Press reported.

The Artemis mission aims to put astronauts on the moon for the first time since the United States’ Apollo programme ended 50 years ago. If the mission goes well, astronauts will climb aboard for the second flight and fly around the moon and back as soon as 2024. A two-person lunar landing could follow by the end of 2025.