New Delhi, May 18 : Boeing Starliner's historic crewed manned mission has been delayed yet again over a helium leak detected in one of the capsule's thrusters, said NASA on Saturday.

The spacecraft, aiming to carry NASA astronauts Butch Wilmore and Indian-Origin Sunita Williams to the space station, is expected to fly on May 25.

"NASA, @BoeingSpace, and @ulalaunch are now targeting no earlier than 3:09 pm ET May 25 for the launch of the agency's Boeing Crew Flight Test mission," NASA said in a post on X.com

"Teams will use the additional time to finalise next steps that address a stable helium leak on the #Starliner service module," it added.

After facing several delays over the years, Starliner's first crewed mission was planned on May 7.

However, it was scrubbed two hours before launch, due to a valve issue on the upper stage of the United Launch Alliance Atlas V rocket.

The mission then slipped to May 10, and later May 21, due to a helium leak.

NASA officials performed a pressure testing on May 15 on the Starliner's helium system, which showed that 'the leak in the flange is stable and would not pose a risk at that level during the flight'.

"The testing also indicated the rest of the thruster system is sealed effectively across the entire service module," NASA said.

Boeing said its "teams are working to develop operational procedures to ensure the system retains sufficient performance capability and appropriate redundancy during the flight".

Meanwhile, the ULA Atlas V rocket and Boeing's Starliner that was rolled back from the launch pad, remain in the Vertical Integration Facility at Space Launch Complex-41 on Cape Canaveral Space Force Station in Florida.

The astronauts Wilmore and Williams will remain quarantined in Houston as pre-launch operations progress.

The Starliner mission aims to carry astronauts and cargo for future NASA missions to low Earth orbit, and beyond.

/IANS