The NASA astronauts who have remained in space for months longer than planned are finally headed back to Earth.

Barry “Butch” Wilmore and Sunita “Suni” Williams performed the first astronaut-crewed flight of Boeing’s Starliner capsule to the International Space Station (ISS) in June 2024.

However, what was supposed to be a mission lasting about one week turned into a nine-month stay aboard the ISS due to several issues with Starliner.

Issues with the spacecraft prompted NASA and Boeing to send Starliner back to Earth uncrewed and keep Wilmore and Williams onboard the ISS until early 2025, when they would return home on a SpaceX Crew-9 Dragon spacecraft once Crew-10 arrived at the ISS.

SpaceX Crew-9 is finally set to undock in the early hours of Tuesday, March 18, and deorbit in the afternoon, returning to Earth in the evening.

Here’s a timeline of the Starliner mission:

April 2, 2024

NASA officials say the target date for the Boeing Starliner’s first crewed flight test is no earlier than May 6.

May 6, 2024

Starliner’s first attempted launch is scrubbed after a problem with an oxygen valve is found on the rocket that launches the spacecraft into orbit.

May 7, 2024

NASA, Boeing and United Launch Alliance Starliner rocket – say they’re targeting a launch date no earlier than May 10.

May 14, 2024

Officials say a new pressure regulation valve has been replaced and tested successfully, and that the new Starliner launch target date will be no earlier than May 21.

May 23, 2024

NASA announces a new target Starliner launch date of June 1. A launch date had been set for May 25 but a small helium leak was discovered in the service module, which contains support systems and instruments for operating a spacecraft.

June 1, 2024

Officials scrub Starliner’s launch just a few minutes before liftoff due to a computer ground launch sequencer not loading properly. A backup date of June 2 is also canceled.

June 2, 2024

NASA and Boeing officials say they are targeting a June 5 launch date for Starliner.

June 5, 2024

After several delays, Starliner launches, lifting off at 10:52 a.m. ET from Florida’s Cape Canaveral Space Force Station Wilmore and Williams are scheduled to return to Earth aboard Starliner on June 14.

June 6, 2024

Starliner successfully docks at the ISS after helium leaks and a thruster issue threatened to delay the docking.

June 11, 2024

NASA says Starliner has five “small” helium leaks and that the astronauts’ ISS mission will be extended to June 18, pending weather and Starliner’s readiness to return them home.

June 14, 2024

NASA and Boeing announce they are targeting June 22 for Starliner’s crewed return to Earth.

June 18, 2024

NASA delays the astronauts’ return until June 26 while the team troubleshoots some of Starliner’s issues, including the helium leaks and thruster failures.

June 21, 2024

The astronauts’ return date is canceled again due to conflicts with previously planned spacewalks. Mission officials continue to review Starliner data.

June 28, 2024

NASA and Boeing officials say during a press conference that additional testing is being conducted on the spacecraft’s propulsion system before Starliner can be undocked.

July 10, 2024

Wilmore and Williams say they feel “confident” Starliner can bring them home safely.

Aug 7, 2024

During a press conference, NASA officials say Wilmore and Williams may have to come home on a spacecraft other than Starliner.

Aug. 24, 2024

NASA officials confirm that the astronauts will have to return home on a different spacecraft in 2025 and that Starliner will return to Earth uncrewed.

Aug. 29, 2024

NASA and Boeing officials say they will proceed with undocking Starliner no earlier than the evening of Sept. 6.

Sept. 7, 2024

Starliner lands uncrewed at White Sands Space Harbor in New Mexico.

Sept. 13, 2024

During a press conference, Wilmore and Williams say they don’t feel “let down” by not returning on Boeing’s Starliner or by the delay in their mission.

March 12, 2024

NASA’s SpaceX Crew-10 mission is canceled less than 45 minutes before liftoff due to a hydraulic system issue.

March 14, 2024

Members of the Crew-10 mission successfully launch aboard a SpaceX Dragon spacecraft from the Kennedy Space Center in Florida.

March 16, 2024

Crew-10 successfully docks at the ISS, bringing four new astronauts to work on the floating lab and setting up the return to Earth of Wilmore and Williams, as well as another NASA astronaut and a Russian cosmonaut.

ABC News’ Faith Abubey, Matthew Glasser, Leah Sarnoff and Gina Sunseri contributed to this report.