Boeing’s latest attempt to launch astronauts into space has ended in failure after a last-minute problem.

Two Nasa astronauts were strapped in to the company’s Starliner capsule when the countdown was halted at three minutes and 50 seconds by the computer system that controls the final moments before lift-off.

There was no time to work out the cause of the latest trouble and everything was called off.

Launch controllers were evaluating the data, a spokesman for United Launch Alliance said.

It is possible the team could try again as soon as Sunday, depending on what went wrong.

Technicians raced to the pad to help astronauts Butch Wilmore and Suni Williams out of the capsule on the fully fuelled Atlas V rocket at Cape Canaveral Space Force Station. Within an hour of the launch being aborted, the hatch was reopened.

It was the second launch attempt. The first try on May 6 was delayed for leak checks and rocket repairs.

Nasa wants a back-up to SpaceX, which has been flying astronauts since 2020.

Boeing should have launched its first crew around the same time as SpaceX but its first test flight with no one on board in 2019 was plagued by severe software issues and never made it to the space station.

Another attempt in 2022 fared better but parachute problems caused more delays. A small helium leak in the capsule’s propulsion system last month came on top of a rocket valve issue.

More valve trouble cropped up two hours before Saturday’s planned lift-off but the team used a back-up circuit to get the ground-equipment valves working to top off the fuel for the rocket’s upper stage.

Launch controllers were relieved to keep pushing ahead but the computer system known as the ground launch sequencer ended the effort.

“Of course, this is emotionally disappointing,” Nasa astronaut Mike Fincke, the back-up pilot, said from the neighbouring Kennedy Space Centre.

But he said delays are part of spaceflight. “We’re going to have a great launch in our future,” he added.