Nasa is delaying a decision on the timing of its next launch attempt for Artemis 1, the US space agency’s first human-rated moon rocket in 50 years, after calling off Monday’s scheduled liftoff late in the countdown because of an issue related to “engine bleed”. Engineers at Nasa’s launch complex in Cape Canaveral, Florida, discovered the problem with one of the four core-stage engines of the Space Launch System (SLS) rocket during overnight loading of 2.76m litres (730,000 gallons) of liquid hydrogen and oxygen fuel needed to send the spacecraft off on its 1.3m-mile, 42-day journey to the far side of the moon and back. They were unable to find a fix in time to meet a two-hour launch window that opened at 8.33am (1.33pm BST) on Monday, and afterwards were troubleshooting the issue to assess readiness for the next available opportunity, on Friday 2 September. “Friday is definitely in play. We just need a little bit of time to look at the data, but the team is setting up for a 96-hour recycle,” Mike Sarafin, Nasa’s Artemis mission manager, told a lunchtime press conference. “We’re going to play all nine innings. We’re not giving up yet.” Sarafin said no decision could be made until mission managers conducted a readiness review beginning on Tuesday afternoon, noting that he did not believe the problem was with the engine itself, but in the bleed system that “conditions” it with cryogenic propellant and adjusts the temperature for launch. “The team … also saw an issue with a vent valve at the inner tank, so the combination of not being able to get the engine three chilled down and then the vent valve issue caused us to pause today, and we felt like we needed a little more time,” he said. Sarafin added that poor weather conditions at launchpad 39B at Kennedy Space Center throughout Monday’s window would also have precluded the launch taking place. The uncrewed Artemis flight is a crucial test mission designed to gauge the capabilities of the SLS rocket and six-person Orion crew capsule ahead of humanity’s planned return to the moon for the first time in half a century. If Artemis 1 ultimately succeeds, astronauts will be onboard an interim test flight along the same route 40,000 miles beyond the moon and back, a trek scheduled for 2024. The first moon landing since Apollo 17 in December 1972 would follow a year or so later, with Nasa declaring it will carry the first woman to walk on the lunar surface. Upwards of a quarter of a million people flocked to Florida’s space coast on Monday to watch a moment in history now postponed to later this week, or even later in September or October, if engineers cannot quickly diagnose and address the cause of the engine bleed issue. Problems with the rocket, which is made by Boeing, first arose during a “hot fire” test in January last year, when the engines shut down one minute into a scheduled eight-minute run. The project at that stage was already almost three years behind schedule and $3bn (£2.55bn) over budget. Critics say the ultimate cost to the US taxpayer of the Artemis programme, projected to reach $93bn (£79bn) by 2025, and which has longer-term goals of placing the first humans on Mars in 15 to 20 years’ time, cannot be justified. But the Nasa administrator, Bill Nelson, a former space shuttle astronaut, said there was greater purpose in placing new human footprints in lunar soil now from those of the 12 men of the Apollo programme who did so over six missions in a past generation. “We need to be on the moon for much longer periods of time than just landing like we used to, stayed a couple of days and left,” Nelson told NBC’s Meet the Press on Sunday. “This time we’re going back, we’re going to live there, we’re going to learn there. We’re going to develop new technologies, all of this so we can go to Mars with humans. “All of this is to develop where we may be living on other worlds. They may be floating worlds, they may be the surface of Mars. But this is just part of our push outward, our quest to explore, to find out what’s out there in this universe.” Nasa’s shuttle program, which was retired in 2011, limited crewed missions to lower Earth orbit, and subsequently private US space companies, including Elon Musk’s SpaceX and Jeff Bezos’s Blue Origin, have flown, or are planning flights, to the International Space Station orbiting about 250 miles above Earth. Artemis is Nasa’s first deep-space exploration project for decades and relies heavily on outside contractors and international partners. SLS is designed and manufactured by Boeing. The Orion crew capsule is the brainchild of Lockheed Martin. And the European Space Agency supplies the service module, the powerhouse of the spacecraft for its lunar journey once the powerful solid rocket boosters and core stage of SLS have placed it beyond Earth’s gravitational pull. The ESM will push Orion farther from Earth than any human-rated space vehicle has ever flown before, providing electricity, water, oxygen and nitrogen and keeping the capsule on course and at the correct temperature before separating and burning up in the atmosphere on its return to Earth.