NASA postponed the launch of its new moon rocket on Monday due to hydrogen leaks and cooling issues.
As the 8:33 am EDT liftoff approached, NASA repeatedly stopped and started the fueling of the Space Launch System rocket because of a leak of highly explosive hydrogen.
The fueling already was running nearly an hour late because of thunderstorms off Kennedy Space Center at Cape Canaveral, Florida.
NASA encountered new trouble when it was unable to properly chill one of the rocket's four main engines, officials said.
Mission manager Mike Sarafin said the fault did not appear to be with the engine but with the plumbing leading to it.
As engineers were trying to troubleshoot that problem on the launch pad, another hydrogen leak developed, involving a vent valve higher up on the rocket, he said.
"The combination of not being able to get engine three chilled down and then the vent valve issue that they saw ... caused us to pause today," Sarafin said. "The team was tired at the end of the day, and we just decided that it was best to knock it off and to reconvene tomorrow."
Mechanical difficulties aside, thunderstorms ultimately would have prevented a liftoff, NASA said. Dark clouds and rain gathered over the launch site as soon as the countdown was halted.
NASA Administrator Bill Nelson said, "This is a very complicated machine, a very complicated system, and all those things have to work, and you don't want to light the candle until it's ready to go."
The 322-foot (98-meter) spaceship is the most powerful rocket ever built by NASA. The rocket was to carry a capsule without a crew. Dummies inside the Orion capsule were fitted with sensors to measure vibration, cosmic radiation and other conditions.
"It's just part of the space business and it's part of, particularly, a test flight," Nelson said of the setbacks.
The next launch attempt will not take place until Friday at the earliest and could be delayed until mid-September or later.
"Friday is definitely in play," Sarafin said at a news conference. "We just need a little bit of time to look at the data. But the team is setting up for a 96-hour recycle."
The mission will be the first flight in NASA's Artemis project, whose objective is to put astronauts back on the moon for the first time since the Apollo program ended 50 years ago. No US astronauts have been to the moon since Apollo 17 in December 1972.
"The world today is very different from the Apollo era when the last US heavy lift vehicle flew, but the capabilities to be demonstrated are crucial to US leadership in space," said George Washington University's Scott Pace, former deputy assistant to the president and executive secretary of the National Space Council during the Trump administration, according to gridnews.com.
NASA Watch Editor Keith Cowing is skeptical of the launch procedure.
"They are really whistling past the graveyard on this one to have only one test launch before putting people on a flight around the moon on the second launch," he told Grid. "They don't have any wiggle room for not having everything go right on this launch."