The National Aeronautics and Space Administration on Saturday called off a test flight of its Artemis 1 spacecraft for the second time because of a fuel leak. The agency said that it will not launch the rocket anytime soon.

The first attempt at the launch was called off on August 29 also because of a fuel leak and an engine problem reported during the lift-off.

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.

The flight was meant to test the Space Launch System rocket – the most powerful one that NASA has ever built – and the Orion crew capsule. There were no humans inside the capsule. Instead, mannequins fitted with sensors had been placed there to measure vibration, cosmic radiation and other variables.

The current launch period for the mission is “definitely off the table” keeping in mind the positions of the earth and the moon, Jim Free, associate administrator for Exploration Systems Development said on Saturday, according to AFP.

The next possible time windows for the launch are September 19 to October 4, and October 17 to 31.

NASA Administrator Bill Nelson said that safety was a priority, particularly on a test flight such as this one, according to the Associated Press. He said that there was a need to verify the rocket’s systems “before we put four humans up on the top of it”.