Boeing's Starliner spacecraft launch to the ISS has been postponed due to a malfunctioning rocket valve, specifically a faulty oxygen relief valve.

The rescheduled launch is now set for Friday at 9 p.m. EDT, following an initial delay in April aimed at optimizing the space station's schedule.

The upcoming mission is pivotal as it will be Starliner's first with a human crew, provided it can overcome technical hurdles including the possibility of replacing the oxygen relief valve.

Boeing has faced several setbacks with Starliner, including a 2019 test mission failure and previous delays in 2023 due to safety concerns.

Starliner is contracted for at least six more crewed missions for NASA, pending the success of this launch.

Elon Musk of SpaceX has publicly criticized Boeing's delays and technical issues, comparing SpaceX's earlier and cheaper success in reaching the ISS.

Space industry commentators suggest Boeing's challenges may be due to adapting to the fixed-price model of commercial spaceflight, in contrast to SpaceX's quicker adjustment and industry leadership.

Boeing and SpaceX are both integral to NASA's Commercial Crew Program, which seeks to involve private companies in space missions.