Last-minute computer trouble nixed Saturday's launch attempt for Boeing's first astronaut flight, the latest in a string of delays over the years.

Two NASA astronauts were strapped in the company's Starliner capsule when the countdown automatically was halted at 3 minutes and 50 seconds by the computer system that controls the final minutes before liftoff.

With only a split second to take off, there was no time to work the latest problem and the launch was called off.

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

The team can't get to the computers to troubleshoot the problem until the rocket is drained of all its fuel, said Tory Bruno, CEO for the rocket maker, United Launch Alliance.

Bruno said one of the three redundant computers located near the rocket at the pad was sluggish. All three must work properly to proceed with a launch, he said.

Depending on what needs to be fixed, the next launch attempt could be as early as Wednesday. If it doesn't blast off this coming week, then that would be it until mid-June in order to move the rocket off the pad and replace batteries.

"This is the business that we're in," Boeing's Mark Nappi said. "Everything's got to work perfectly."

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

NASA wants a backup 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.

A redo in 2022 fared better, but parachute problems and flammable later 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 liftoff, but the team used a backup 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 backup pilot, said from neighboring Kennedy Space Center shortly after the countdown was halted.

But he said delays are part of spaceflight. "We're going to have a great launch in our future."