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The quick repair fixed the leak, allowing hydrogen to resume flowing into the rocket. But then a Space Force radar tracking site went down because of a bad ethernet switch, leading to yet another scramble. The problems pushed the launch into the wee hours of Wednesday, as the countdown clocks held at the 10-minute mark.

“We are slipping indefinitely into the launch window,” said NASA launch commentator Derrol Nail.

“uel leaks plagued the first two attempts in late summer, then a pair of hurricanes caused more delays. While engineers never pinpointed the cause of the escaping hydrogen, they altered the fueling process to minimize leakage and expressed confidence that all the plumbing in the 322-foot (98-meter) rocket would remain tight and intact.

NASA added an hour to the operation to account for the slower fill-up, vital for reducing pressure on the fuel lines and keeping the seals in place. It seemed to work, but an intermittent hydrogen leak cropped up near the end of the six-hour operation. This particular leaky valve is on the launch platform, not the rocket, officials stressed, and is needed to replenish liquid hydrogen as it dissipates from the core stage.

The rocket was gassed up with nearly 1 million gallons (3.7 million liters) of super-cold hydrogen and oxygen, when the latest leak occurred.

NASA expected 15,000 to jam Kennedy Space Center for the launch in the wee hours of Wednesday morning, with thousands more lining the beaches and roads outside the gates. The space agency had two hours to get the rocket off, before standing down until Saturday.

The debut of the , known as SLS, had three test dummies but no astronauts inside the crew capsule on top, which NASA hoped to put into lunar orbit.

This first test flight was expected to last three weeks, ending with a splashdown in the Pacific. NASA’s top priority for the $4.1 billion mission is to verify the capsule’s heat shield during reentry, so four astronauts can strap in for the next moonshot in 2024. That would be followed by a two-person lunar landing in 2025.

NASA last sent astronauts to the moon in December 1972, closing out the Apollo program.

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