NASA has announced that a third attempt to launch its new lunar rocket will not occur in the coming days, after a fuel leak caused a second launch attempt to be halted earlier today.

The current launch period for the Artemis 1 mission "ends on Tuesday. We will not be launching in this launch period," said Jim Free, associate administrator for Exploration Systems Development at NASA.

Earlier, NASA called off its second effort to get the powerful new rocket off the ground and send its uncrewed test capsule toward the Moon.

It came after engineers detected a fuel leak near the base of the rocket was found as ultra-cold liquid hydrogen was being pumped in.

NASA said engineers would "stop flowing liquid hydrogen to the tank, close the valve used to fill and drain it," then try to reseal it.

But the space agency later confirmed there would be a second delay in the Artemis programme - following Monday's aborted effort - after a "no go" recommendation from the launch director.

Today's launch of the massive Space Launch System (SLS) had been scheduled for 7:17 pm (Irish time) from Kennedy Space Center in Florida.

News media in Florida has been preparing for the Artemis 1 rocket Moon mission launch

If it does not launch in the coming days, then the next launch window will not be until 19 September, due to the Moon's position.

The initial launch attempt was halted after engineers detected a fuel leak and a sensor showed that one of the rocket's four main engines was too hot.

Both issues have since been resolved, the launch team said.

Shortly before 11am today, launch director Charlie Blackwell-Thompson had given the go-ahead to start filling the rocket's tanks with cryogenic fuel.

About three million liters of ultra-cold liquid hydrogen and oxygen was expected to be pumped into the spacecraft.

The purpose of the Artemis 1 mission is to verify that the Orion capsule, which sits atop the SLS rocket, is safe to carry astronauts in the future.

Mannequins equipped with sensors are standing in for astronauts on the mission and will record acceleration, vibration and radiation levels.

It will take several days for the spacecraft to reach the Moon, flying around 100km at its closest approach.

The weather conditions are favourable at Kennedy Space Center in Florida

The trip is expected to last around six weeks and one of its main objectives is to test the capsule's heat shield, which at almost five metres in diameter, is the largest ever built.

On its return to Earth's atmosphere, the heat shield will have to withstand speeds of 40,000km per hour and a temperature of 2,760C - roughly half as hot as the Sun.

Artemis is named after the twin sister of the Greek god Apollo, after whom the first Moon missions were named.

Unlike the Apollo missions, which sent only white men to the Moon between 1969 and 1972, Artemis missions will see the first person of color and the first woman step foot on the lunar surface.

The next mission, Artemis 2, will take astronauts to the Moon without landing on its surface.

The crew of Artemis 3 is to land on the Moon in 2025 at the earliest, with later missions envisaging a lunar space station and a sustainable presence on the lunar surface.

According to NASA chief Bill Nelson, a crewed trip to the red planet aboard Orion, which would last several years, could be attempted by the end of the 2030s.