*

Stuck NASA astronauts left ISS on Tuesday morning

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Crew splashed down off Florida coast around 5:57 p.m. ET

(2157

GMT)

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Homecoming of Butch Wilmore and Suni Williams caps end to

nine-month mission

(Updates with crew return process, splashdown)

By Joey Roulette

WASHINGTON, March 18 (Reuters) - NASA astronauts Butch

Wilmore and Suni Williams returned to Earth in a SpaceX capsule

on Tuesday with a soft splashdown off Florida's coast, nine

months after their faulty Boeing Starliner craft upended

what was to be a week-long stay on the International Space

Station.

Their return caps a protracted space mission that was

fraught with uncertainty and technical troubles and turned a

rare instance of NASA's contingency planning - and the latest

failures of Boeing's ( BA ) Starliner - into a global spectacle.

Wilmore and Williams, two veteran NASA astronauts and

retired U.S. Navy test pilots, had strapped inside their Crew

Dragon spacecraft along with two other astronauts and undocked

from the orbiting laboratory of the ISS at 1.05 a.m. ET (0505

GMT) to embark on a 17-hour trip to Earth.

The four-person crew, formally part of NASA's Crew-9

astronaut rotation mission, re-entered Earth's atmosphere around

5:45 p.m. ET. Using Earth's atmosphere and two sets of

parachutes, the craft slowed its orbital speed of roughly 17,000

miles per hour to a soft 17 miles per hour at splashdown.

Dressed in re-entry suits, boots and helmets, the astronauts

were seen earlier on NASA's live footage laughing, hugging and

posing for photos with their colleagues from the station shortly

before they were shut into the capsule for two hours of final

pressure, communications and seal tests.

The astronaut pair had launched into space as Starliner's

first crew in June for what was expected to be an eight-day test

mission. But issues with Starliner's propulsion system led to

cascading delays to their return home, culminating in a NASA

decision last year to have them take a SpaceX craft back this

year as part of the agency's crew rotation schedule.

The mission has captured the attention of U.S. President

Donald Trump, who upon taking office in January called for a

quicker return of Wilmore and Williams and alleged without

evidence that former President Joe Biden "abandoned" them on the

ISS for political reasons.

SpaceX CEO Elon Musk, a close adviser to Trump, echoed

his call for an earlier return. SpaceX's Crew Dragon is the

United States' only orbital-class crew spacecraft, which Boeing ( BA )

had hoped its Starliner would compete with before the mission

with Wilmore and Williams threw its development future into

uncertainty.

After the splashdown, the astronauts will be flown to their

crew quarters at the space agency's Johnson Space Center in

Houston for several days of health checks, per routine for

astronaut returns, before NASA flight surgeons approve they can

go home to their families.

Living in space for months can affect the human body in

multiple ways, from muscle atrophy to possible vision

impairment.

Wilmore and Williams have logged 286 days in space on the

mission - longer than the average six-month ISS mission length,

but far short of U.S. record holder Frank Rubio. His continuous

371 days in space, ending in 2023, were the unexpected result of

a coolant leak on a Russian spacecraft.

Williams, capping her third spaceflight, has tallied 608

cumulative days in space, the second most for any U.S. astronaut

after Peggy Whitson's 675 days. Russian cosmonaut Oleg Kononenko

set the world record last year at 878 cumulative days.

REPLACEMENT CREW

Swept up in NASA's routine astronaut rotation schedule,

Wilmore and Williams could not begin their return to Earth until

their replacement crew arrived, in order to maintain adequate

U.S. staffing levels, according to NASA.

Their replacements arrived on Friday night - four astronauts

as part of NASA's Crew-10 mission that briefly put the station's

headcount at 11.

"We came prepared to stay long, even though we planned to

stay short," Wilmore told reporters from space earlier this

month, adding that he did not believe NASA's decision to keep

them on the ISS until Crew-10's arrival had been affected by

politics.

"That's what your nation's human spaceflight program's all

about," he said. "Planning for unknown, unexpected

contingencies. And we did that."

Wilmore and Williams had been doing scientific research and

conducting routine maintenance with the station's other five

astronauts. Williams had performed two six-hour spacewalks for

maintenance outside the ISS, including one with Wilmore.

The ISS, about 254 miles (409 km) in altitude, is a football

field-sized research lab that has been housed continuously by

international crews of astronauts for nearly 25 years, a key

platform of science diplomacy managed primarily by the U.S. and

Russia.

Williams told reporters earlier this month that she was

looking forward to returning home to see her two dogs and

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

bit more so than for us," she said.