Fuel leak delays NASA's mega-rocket moon mission

Houston has a problem.

Once again, NASA's new mega-rocket has suffered a significant leak of explosive hydrogen propellant during a countdown rehearsal.

It means plans to launch four astronauts on a mission around the moon have been delayed until March.

Lift-off had been scheduled for as soon as Sunday. But the space agency says the delay will give engineers extra time to resolve the issue.

Everything you need to know about Artemis II

The so-called "wet" dress rehearsal at Kennedy Space Centre in Florida was a critical pre-launch test of the rocket, which has only flown once before.

It's a run-through of all the events running up to launch, including fuelling the rocket.

But the countdown was paused twice because hydrogen was found to be leaking from the seal between the fuelling hose and the rocket.

Engineers thought they had resolved the issue and finished filling up the two-million-litre hydrogen tank.

But after entering the "replenish phase", when the tank is kept topped up, the hydrogen leak was once again found to exceed safety limits with just over five minutes left on the countdown.

Hydrogen is a notoriously difficult propellant to handle. The molecule is extremely small, making it hard to contain. It's also pumped into the rocket as a liquid at high pressure and at -253C it's so cold that seals can become unreliable.

The first - uncrewed - test flight of the Artemis rocket in 2022 was delayed by three months because of a series of problems, including hydrogen leaks.

The rocket was twice rolled back to its maintenance hangar for repairs.

NASA had hoped the fuelling issues had been resolved this time around.

With humans on board for this flight, they are taking no chances.

The astronauts have been released from quarantine in Houston, but will once again begin shielding from infections around two weeks before the next launch date, currently due to be 6 March.

Read more from Sky News:
Stunning aurora filmed from ISS
Mysterious iron 'bar' in space
Tim Peake on the new space race

?Listen to The World with Richard Engel and Yalda Hakim on your podcast app?

The delay to the launch isn't a huge surprise because it is a new rocket.

But there is another countdown in the minds of the NASA and White House administrations.

China hopes to land taikonauts on the lunar surface by 2030 and the United States wants to be there first.

This flight around the moon is designed to test the rocket and the Orion crew capsule ahead of a moon landing, optimistically scheduled for 2028.

Engineers will be under pressure to find a fix.

(c) Sky News 2026: Fuel leak delays NASA's mega-rocket moon mission