March 18 (Reuters) - NASA astronauts Butch Wilmore and

Suni Williams are about to return to Earth from the

International Space Station, where they have been living for

nine months in a drawn-out mission fraught with technical

challenges, schedule changes and politics.

Here is a timeline of their novel journey:

June 2022: Wilmore and Williams are locked in as Boeing

Starliner's first crew after several unexpected changes.

2024

June 5: Wilmore and Williams launch to space as Starliner's

first crew, after several delays triggered by scrutiny of

propulsion system issues and a helium leak. Their mission is

expected to last roughly eight days.

June 6: Starliner crew safely arrives at the space station

following a 27-hour flight that included failures of five of the

spacecraft's thrusters used for in-space maneuvering - the

latest glitches in Starliner's troubled development history.

June 11: NASA delays Wilmore and Williams' return to Earth

aboard Starliner to June 18 as it investigates propulsion system

issues, as well as leaks of helium, which is used to give

pressure to the thrusters.

June 21: NASA again delays Wilmore and Williams' return

without stating a specific date.

June 26: A third delay to the astronauts' return begins to

raise deeper questions about the nature of Starliner's technical

problems, how Wilmore and Williams will get home and whether

SpaceX's Crew Dragon - the only active U.S. orbital crew

spacecraft - will need to play a role.

June 27: An old Russian satellite breaks into more than 100

pieces of orbital debris that fly near the ISS, forcing all

astronauts to enter their spacecraft and prepare for an

emergency exit. Wilmore and Williams rush inside Starliner

despite its propulsion system issues, which Boeing ( BA ) at the time

said validated the craft's readiness as an emergency return

option. The debris subsided and astronauts resumed normal ISS

life.

June 28: Wilmore and Williams' return to Earth becomes more

opaque. The length of their ISS stay, NASA said, hinges on

results of ground testing that Boeing ( BA ) was doing with thruster

mockups, as it scrambled to build evidence that Starliner was

safe to return the astronauts to Earth.

July 21: Wilmore and Williams reach 45 days on the ISS - the

maximum nominal duration Starliner was approved to stay on the

station - as NASA and Boeing ( BA ) continue experimenting with

propulsion system studies and software changes.

August 7: After more than a month of simulations and

technical investigation, Boeing ( BA ) and senior NASA officials debate

the severity of Starliner's problems and how best to bring

Wilmore and Williams home. The agency is increasingly concerned

Starliner will not be safe enough for their return, though

Boeing ( BA ) argues it is.

August 24: NASA opts to bring Wilmore and Williams back to

Earth on a SpaceX Crew Dragon capsule due for launch the

following month as a routine astronaut rotation mission, Crew-9.

This commits Wilmore and Williams to NASA's astronaut rotation

schedule and, in all, an eight-month stay on the ISS, as the

Crew-9 return date at the time was February 2025 - also the

expected arrival of the next rotation mission, Crew-10.

September 6: Starliner returns to Earth without any

astronauts on board, landing safely at the White Sands Missile

Range in New Mexico. NASA, which stood by its safety risk

tolerance approach, had deemed the spacecraft's risk level too

high for its astronauts to ride.

September 29: Two astronauts in NASA's Crew-9 mission launch

to the ISS using the SpaceX Crew Dragon capsule that will get

Wilmore and Williams home the following year. Normally with four

astronauts, two seats were left empty for Wilmore and Williams.

December 17: NASA delays the launch of Crew-10, the rotation

mission that will allow Wilmore and Williams to come home. The

agency said the mission, planned for February, would launch in

late March due to delays in SpaceX's production of a new Crew

Dragon capsule that was to be used for the flight.

2025

January 29: President Donald Trump, a week into his second

term, publicly asks his close adviser, SpaceX CEO Elon Musk, to

quickly retrieve Wilmore and Williams from the ISS, accusing

without evidence former President Joe Biden of having "virtually

abandoned" them in space for political reasons. Musk accepts the

request and says he will get them home "as soon as possible,"

raising questions about whether the White House intervened in

NASA's planned operation to bring the astronauts back.

January 30: NASA, in a statement after Trump's request to

Musk, affirms its original plan to bring Wilmore and Williams

home on Crew-10.

February 11: NASA changes its plan to return Wilmore and

Williams home after Trump and Musk's public urging, swapping the

Crew Dragon capsule delayed in SpaceX production with a

different one that has flown three times previously. This

changes the Crew-10 launch date by two weeks from March 26 to

March 12.

March 4: As allegations by Trump and Musk prompt questions

about the agency's decision-making, Wilmore tells reporters in a

space-to-ground news conference he did not believe politics

played a role in NASA's decision to have him and Williams stay

on the ISS for nine months. They prepared for the prospect of an

extended mission by nature of being an astronaut, he added.

March 12: A launchpad issue triggers a two-day delay in the

launch of Crew-10, the mission that opens the door to Wilmore

and Williams' departure for Earth.

March 14: Crew-10 launches to the ISS, bringing Wilmore and

Williams one step closer to home.

March 16: Crew-10 crew arrives on the ISS, greeted by its

seven astronauts including Wilmore and Williams.

March 18: Wilmore and Williams, along with NASA astronaut

Nick Hague and Russian cosmonaut Aleksandr Gorbunov, undock from

the ISS, beginning a 17-hour trip to Earth.

(Compiled by Joey Roulette; Editing by Jamie Freed)