A last-minute problem 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 computer system automatically halted the countdown at 3 minutes and 50 seconds before liftoff.

With only a split second to take off, there was no time to work the latest trouble and everything was called off. It was not immediately clear why the computers aborted the countdown.

Launch controllers were evaluating the data, said United Launch Alliance’s Dillon Rice. But it’s 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 atop the fully fueled Atlas V rocket at Cape Canaveral Space Force Station. Within an hour of the launch abort, 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 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 tape 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.

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