Nasa called off its latest attempt to launch the groundbreaking Artemis 1 moon rocket on Saturday after failing to stem a fuel leak discovered during tanking. It was the second time in five days that technical issues had kept the spacecraft on the launchpad. Mission managers at Kennedy Space Center waited until late in the countdown to scrub the liftoff after the failure of several workarounds to try to plug the leak of liquid hydrogen as it was being pumped into the core stage of the Space Launch System (SLS) rocket. Bill Nelson, head of the US space agency, indicated that the severity of the problem, deep inside one of the rocket engines, made it unlikely launchpad fixes would be possible, and Artemis would probably have to be rolled back to the vehicle assembly building for more substantial repairs. That would mean the next backup launch opportunity of Monday is also unsustainable, and the maiden test flight of humanity’s first crew-capable moon mission in 50 years will be further delayed. Senior Nasa officials said the next attempt would be delayed until at least the end of September. “This is part of the space business,” he said. “We’ll go when it’s ready. We don’t go until then, and especially on a test flight because we’re going to stress this and test it, and test that heat shield and make sure it’s right before we put four humans up on the top. “Although the [next launch] window opens in early October, I suspect it’ll be more like the middle.” Nelson said that mission managers would meet later on Saturday to make a final decision. Nasa’s Artemis launch director Charlie Blackwell-Thompson agreed with a recommendation of the fuel systems team and called off the launch at 11.17am local time (4.17pm BT), with 2 hours and 30 minutes left in the countdown. The fuel leak, which became apparent during early morning tanking of 2.76m litres (730,000 gallons) of liquid hydrogen and oxygen, is separate from the engine cooling issue that forced the postponement of the first launch attempt last Monday. Officials said they had identified that problem as a faulty sensor rather than an issue with the cooling system or engine itself. But the latest setback will be a disappointment for the agency keen to showcase the progress it has made in returning humans to the lunar surface for the first time since the Apollo 17 mission of 1972. This 38-day mission, to 40,000 miles beyond the moon and back, is uncrewed, but must be successful before astronauts can board a second test flight planned for 2024, then a moon landing on Artemis III currently scheduled for no earlier than late 2025. Upwards of a quarter-million spectators had packed the beaches and causeways of Florida’s space coast on the Labor Day holiday weekend, eager to witness a moment of history. Mission managers indicated the liquid hydrogen leak was inside one of the four RS-25 engines on SLS, which will become the most powerful rocket ever to leave Earth when it finally launches. The engines are recycled from the long-retired space shuttle programme, and combine to provide 15% more thrust than the Saturn V rockets of the Apollo era.