CAPE CANAVERAL, Fla. (AP) — Boeing geared up again Wednesday for its first astronaut launch, held up for years by safety concerns.

It was the third launch attempt for NASA test pilots Butch Wilmore and Suni Williams in Boeing’s Starliner capsule. Rocket-related trouble thwarted the first two countdowns.

The astronauts will test Starliner’s systems on the way to the International Space Station, where they'll spend at least a week before aiming for a touchdown in the western U.S.

NASA hired Boeing along with SpaceX after the space shuttles retired to transport astronauts to and from the space station. SpaceX has been ferrying astronauts since 2020.

Boeing's capsule rocketed into orbit in 2019 without a crew, but that test flight was cut short by software problems. Boeing had better luck on the do-over mission in 2022, but parachute and other issues later were discovered, delaying Starliner's crew debut even further.

Minutes before Saturday's planned liftoff, a computer's power unit failed at the pad that had to be replaced by rocket maker United Launch Alliance. And a bad valve inside the Atlas V rocket scrapped the launch attempt in early May.

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