NASA: Artemis moon rocket's second launch attempt aborted

The US space agency has had to postpone the launch of its new Artemis I Moon rocket for the second time in a week.

Controllers were unable to stop the hydrogen leak on the vehicle since the start of Saturday's countdown process.

NASA now has another chance to launch the rocket on Monday or Tuesday.

The vehicle would then have to be returned to its assembly building for inspection and maintenance, which would mean further delays.

The Space Launch System is the most powerful rocket ever developed by NASA, and is designed to send astronauts and their instruments back to the lunar surface after a 50-year absence.

Most of its thrust comes from burning about three million liters of super-cold liquid hydrogen and oxygen in the four large engines under the vehicle.

But when controllers sent an order to fill the rocket's hydrogen tank early in the morning, an alarm sounded, indicating that a leak had occurred.

The problem was traced to the connection where hydrogen was being pumped into the vehicle.

The controllers tried a number of fixes, including allowing the hardware to warm up for a short period of time, in the hope that this might reset the seal. But without success.

The Artemis I mission is an unmanned demonstration, but NASA Administrator Bill Nelson said the rocket's future role in manned spaceflight means its operation still requires the utmost care.

"We'll go when it's ready," he insisted. "We don't go that far, and we make sure it's right before we put the humans on top of it."

Maybe NASA will try again in the next few days. But if further work needs to take the rocket back to the engineering building, it could be mid-October before we see it back on the pad.

Saturday's attempt to send a Space Launch System (SLS) rocket was scheduled for the start of a two-hour window beginning at 14:17 local time (19:17 BST; 18:17 GMT).

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The 100-metre-long vehicle was intended to throw a human-rated capsule in the direction of the Moon, which has not happened since Project Apollo ended in 1972.

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NASA earlier tried to launch the SLS on Monday, but that bid was eventually cleared because controllers could not ensure that the four large engines under the rocket's core-stage were properly prepared for flight.

When SLS fades away, it's sure to be a spectacular sight.

"It's going to be a 'Shuttle on steroids,'" said Doug Hurley, who was the pilot on the last Shuttle mission in 2011.

The former astronaut now works for Northrop Grumman building the large white solid boosters on the sides of the SLS.

"What I always thought was the best thing about Shuttle launch was that you saw it lift off and it was well clear of the tower before you heard anything, and then it was before you felt it." It was a little long," he explained.

"Weight-wise, the SLS is pretty close to the Shuttle. Apollo's Saturn V rocket was quite different. I've never seen it personally but it came clean off the pad. For the Shuttle, it looked like it took a moment." , almost as soon as the boosters were lit. The SLS is what it should be," he told BBC News.

The first powered phase of SLS's ascent will last just over eight minutes.

This will engage the rocket's upper-stage with the Orion capsule still attached, in a highly elliptical orbit that will see them both crash back to Earth without any further effort.

So, the upper-stage would have to raise and round off the orbit before propelling Orion in the direction of the Moon.

Confirmation that the capsule is on track on its own and should come two hours and five minutes after launch at 30,000 km/h (19,000 mph) through space.

The planned mission length is just under 38 days, much longer than the 21 days that capsule manufacturer Lockheed Martin says is the maximum time astronauts should spend in the spacecraft.