A fuel leak and then an engine problem during final liftoff preparations led NASA to clean up the launch of the new moon’s powerful rocket on Monday morning in a shakedown flight with three test dummies. The next launch attempt won’t take place until Friday at the earliest. As precious minutes ticked by, NASA repeatedly stopped and started fueling the Space Launch System rocket with nearly a million gallons of supercooled hydrogen and oxygen due to a leak of highly explosive hydrogen at the same spot it had seen leak during a dress rehearsal. back in the spring. Then NASA ran into a new problem when it was unable to properly cool one of the rocket’s four main engines, officials said. Engineers continued to work to collect data and identify the source of the problem after the launch postponement was announced. The rocket was about to take off on a mission to put a crew capsule into orbit around the moon. The launch represents a milestone in America’s effort to return astronauts to the lunar surface for the first time since the Apollo program ended 50 years ago. The 322-foot (98-meter) spacecraft is the most powerful rocket ever built by NASA, surpassing even the Saturn V that carried the Apollo astronauts to the moon. As for when NASA might make another launch attempt, launch commentator Derrol Nail said the problem is still being analyzed and “we have to wait and see what shakes out of their test data.” No astronauts were inside the rocket’s Orion capsule. Instead, test dummies, equipped with sensors to measure vibrations, cosmic radiation and other conditions, were strapped in for the six-week mission, which was scheduled to end with the capsule’s descent into the Pacific in October. Although no one was on board, thousands of people blocked the shore to watch the rocket soar. US Vice President Kamala Harris was expected among the VIPs. The launch, when it happens, will be the first flight in NASA’s 21st century lunar exploration program, named Artemis after Apollo’s mythological twin sister. Assuming the test goes well, astronauts will board the craft for the second flight and fly around the moon and return as soon as 2024. A two-man landing on the moon could follow by the end of 2025. The problems seen Monday were reminiscent of NASA’s space shuttle era, when hydrogen fuel leaks interrupted the countdown and delayed a series of launches in the 1990s. Later in the morning, NASA officials also spotted what they feared was a crack or other defect in the center stage — the large orange fuel tank with four main engines on it — but later said it appeared to be just a build-up of frost. Launch manager Charlie Blackwell-Thompson and her team also had to deal with a communication problem involving the Orion capsule. Engineers were trying to figure out an 11-minute delay in the communication lines between launch control and Orion that appeared late Sunday. Although the problem was cleared up by Monday morning, NASA needed to know why it happened before committing to a launch. —— The Associated Press Health and Science Section is supported by the Howard Hughes Medical Institute Science Education Division. AP is solely responsible for all content