Boeing's Starliner spacecraft atop the United Launch Alliance Atlas V rocket rolls out in Florida on Thursday, May 30, 2024.

Boeing 's first Starliner flight with astronauts on board was called off in the final minutes on Saturday.

The company was targeting a launch on June 1 at 12:25 p.m. ET of its capsule, which is carrying astronauts to the International Space Station for the first time in a final major test of the system.

The launch's hold was automatically issued for an unspecified reason, NASA said on its broadcast, with under four minutes remaining in the countdown. Holds in a rocket launch countdown – as well as "scrubs," indicating a launch delay – are a common occurrence in the industry. The crew on board are safe and will disembark.

Two NASA astronauts are aboard the Starliner capsule, which would be carried by United Launch Alliance's Atlas V rocket to the International Space Station.

Boeing already has backup launch dates scheduled, including Sunday at 12:03 p.m. EDT. Depending on the cause of the launch scrub, Boeing and NASA can reschedule the launch for another attempt 24 hours later, or target alternative launch dates of June 5th or June 6th.

NASA and Boeing called off a launch attempt in early May due to an issue detected with the rocket. ULA, a joint venture of Boeing and Lockheed Martin , replaced the rocket's problematic valve.

After calling off the May attempt, NASA and Boeing found a "small" helium leak in Starliner, causing the agency and company to perform another series of assessments. After analysis, NASA and Boeing believe the source of the leak is in the spacecraft's helium propulsion system. But officials said last week that the leak is "stable" and "not a safety of flight issue."

Starliner's crew debut has been delayed by years, with SpaceX's competing Dragon capsule flying astronauts for NASA regularly since 2020 under the agency's Commercial Crew program. To date, Boeing has eaten $1.5 billion in costs due to Starliner setbacks and nearly $5 billion of NASA development funds.

The spacecraft was once seen as a competitor to SpaceX's Dragon. However, various setbacks and delays have steadily slipped Starliner into a backup position for NASA, with the agency taking the rare step of reassigning astronauts off the first Boeing crew flights in 2021. Boeing is under contract to fly six operational Starliner missions to the ISS. Saturday's crew flight test represents the final major step before receiving NASA certification to begin regular missions.