Boeing Starliner to make another attempt at crewed flight test Friday

May 7 (UPI) -- Starliner, the spacecraft Boeing designed to ferry astronauts to and from the International Space Station, is set to possibly take off Friday after a mechanical issue scrubbed Monday's attempt to take off.

A launch is set to possibly take place on Friday at 9 p.m. EDT barring any unforeseen issues.

Boeing's long-delayed first crewed Starliner mission was scheduled to launch Monday night at 10:34 p.m. EDT from Florida's Cape Canaveral Space Force Station for a 10-day test flight to certify the spacecraft for future manned space missions.

It was called off two hours before launch, over concerns about an oxygen relief valve. The launch was canceled "over an abundance of caution."

"That procedure takes several days," United Launch Alliance CEO Tory Bruno said about the likelihood of replacing the oxygen valve if needed, adding how "it's unlikely we would be prepared to make another attempt before Sunday."

Astronauts Suni Williams, 58, and Butch Wilmore, 61, were strapped into the Starliner capsule and ready for their journey to the ISS when the launch was called off.

In early April, NASA had delayed the Starliner launch to "no sooner than May 6" in order to better optimize the space station's "schedule of activities planned toward the end of April, including a cargo spacecraft undocking and a crew spacecraft port relocation required for Starliner docking."

Safety concerns had forced Boeing to delay Starliner's June 2023 spacecraft mission.

The Starliner's first manned mission originally was planned to occur four years earlier, but a 2019 test mission had failed to reach the International Space Station.

A 2022 test flight accomplished that feat, but neither of those test flights carried a flight crew. But Monday's failed launch was to be the first to have humans on board.