NASA delays launch of giant Moon rocket

NASA called off a test flight of its largest-ever rocket in a setback to the ambitious program to send humans back to the Moon and eventually to Mars.

"We don't launch until it's right," NASA administrator Bill Nelson said after an engine temperature issue forced liftoff from Kennedy Space Centre to be scrubbed.

"This is a very complicated machine," Nelson said. "You don't want to light the candle until it's ready to go."

Alternative dates for launch of the US space agency's uncrewed Artemis 1 mission are Friday and next Monday.

Blastoff was cancelled because of a temperature problem with one of the four RS-25 engines on the 98-metre Space Launch System (SLS) rocket.

NASA said a test to get one of the engines to the proper temperature range for liftoff was not successful.

It said the SLS rocket and Orion crew capsule which sits on top "remain in a safe and stable configuration."

The goal of the flight is to test the SLS and Orion crew capsule. Mannequins equipped with sensors are standing in for a crew for the mission.

The rocket's Orion capsule is to orbit the Moon to see if the vessel is safe for people in the near future. At some point, Artemis aims to put a woman and a person of colour on the Moon for the first time.

Tens of thousands of people had gathered near the Kennedy Space Centre in Florida to watch the launch, which comes 50 years after Apollo 17 astronauts last set foot on the Moon.