*

Mission scrubbed due to ground system issue

*

Next launch opportunity is no earlier than Thursday,

pending

review

*

An 8-day stay for astronauts has turned into nine months

in

space

*

Astronauts had been expected to leave space station on

Sunday

(Adds reason for scrubbing the launch, new date of launch,

paragraph 3-4)

By Joey Roulette

March 12 (Reuters) - SpaceX on Wednesday scrubbed the

expected launch of a replacement crew of four astronauts to the

International Space Station that would have set in motion the

long-awaited homecoming of U.S. astronauts Butch Wilmore and

Suni Williams, who have been stuck in space for nine months

after a trip on Boeing's ( BA ) faulty Starliner.

NASA had been set to launch a SpaceX rocket from Florida

carrying a replacement crew for the International Space Station

in a mission that would set up the return to Earth of Wilmore

and Williams - stuck in space for nine months after a trip on

Boeing's ( BA ) faulty Starliner.

The launch was called off due to a hydraulic system issue with a

ground support clamp arm for the Falcon 9 rocket, NASA said in a

statement.

NASA said the next available launch opportunity is no

earlier than 7:26 p.m. EDT (2326 GMT) Thursday, pending review

of the issue. With a Thursday Crew-10 launch, the Crew-9 mission

would depart the space station on Monday, March 17, it said.

The U.S. space agency had moved up the mission by two weeks

after President Donald Trump and his adviser Elon Musk, CEO of

SpaceX, called for Wilmore and Williams to be brought back

earlier than NASA had planned.

A planned eight-day stay on the orbiting station has dragged

on for Wilmore and Williams, a pair of veteran astronauts and

U.S. Navy test pilots. Starliner returned to Earth without them

last year.

SpaceX's rocket had been scheduled to blast off from the

Kennedy Space Center in Cape Canaveral at 7:48 p.m. ET (2348

GMT) with a crew of two U.S. astronauts and one astronaut each

from Japan and Russia.

Wilmore and Williams have been working on research and

maintenance with the space station's other astronauts and have

remained safe, according to NASA. Williams told reporters in a

March 4 call that she is looking forward to seeing her family

and pet dogs upon returning home.

"It's been a roller coaster for them, probably a little bit

more so than for us," Williams said of her family. "We're here,

we have a mission - we're just doing what we do every day, and

every day is interesting because we're up in space and it's a

lot of fun."

The flight, known as Crew-10, normally would be considered a

routine astronaut rotation. Instead, it has become entangled in

politics as Trump and Musk have sought - without offering

evidence - to blame former President Joe Biden for the delayed

return of Wilmore and Williams.

The demands by Trump and Musk for an earlier return were an

unusual intervention in NASA's human spaceflight operations. The

mission previously had a target date of March 26, but NASA

swapped a delayed SpaceX capsule with a different one that would

be ready sooner.

When the new crew arrives aboard the station, Wilmore,

Williams and two others - NASA astronaut Nick Hague and Russian

cosmonaut Aleksandr Gorbunov - can return to Earth in a capsule

that has been attached to the station since September, as part

of the prior Crew-9 mission.

Wilmore and Williams cannot leave until the new Crew-10 craft

arrives in order to keep the ISS staffed with enough U.S.

astronauts for maintenance, according to NASA.

Wilmore and Williams flew to the station in June as the

first test crew of Boeing's ( BA ) Starliner, which suffered propulsion

system issues in space. NASA deemed it too risky for the

astronauts to fly home on the Boeing ( BA ) craft. This led to the

current plan to bring them home in a SpaceX capsule.

Boeing ( BA ) built Starliner under a $4.5 billion contract with

NASA to compete with SpaceX's Crew Dragon capsule, which since

2020 has been the U.S. space agency's only vehicle for sending

ISS crew members to orbit from American soil. Last year's

mission had marked Starliner's first test flight with astronauts

aboard, a requirement before NASA could certify the capsule for

routine astronaut missions.

Starliner's development has been plagued with engineering

issues and cost overruns since 2019, putting it far behind

SpaceX's Crew Dragon, which was developed under a similar NASA

contract worth at least $4 billion.