NASA said it needs to replace hydrogen-fueling equipment on its new moon rocket after scrubbing the launch for the second time in a week, a decision that means the spaceship won’t fly until at least late September.

"I look at this as a part of our space program, of which safety is the top of the list,” NASA administrator Bill Nelson said at an afternoon news conference where officials explained that engineers tried multiple times to stop a hydrogen leak. Some hardware will be replaced, and one of the options being considered to do that involves moving the rocket back to the massive Vehicle Assembly Building — which would delay the mission by several weeks.

The mission, called Artemis I, is the initial step in NASA’s ambitious plan to send the first woman and the first person of color to the surface of the moon as early as 2025. The goal is to prove the new Space Launch System can send an uncrewed capsule called Orion into lunar orbit, before NASA feels comfortable putting astronauts on board.