Why NASA's Starliner astronauts spent 9 months in space on a 10-day mission: A timeline

NASA astronauts Barry "Butch" Wilmore and Sunita "Suni" Williams are finally headed back to Earth.

The duo launched to the International Space Station (ISS) last June on the first-ever crewed mission of Boeing's new Starliner capsule. Their mission was supposed to last just 10 days or so, but they ended up staying aloft for more than nine months.

Here's a rundown of Butch and Suni's surprisingly long, and unexpectedly controversial, time in space, which will end with a splashdown this evening (March 18) off the Florida coast.

June 5, 2024: Starliner takes to the skies

Starliner lifted off June 5 atop a United Launch Alliance Atlas V rocket from Cape Canaveral Space Force Station in Florida on its debut crewed mission, with the ISS as the destination.

Wilmore and Williams, both former U.S. Navy test pilots, expected to remain in orbit for about 10 days on the mission, which was called Crew Flight Test (CFT). The main goal was to show that Starliner is ready to carry astronauts to and from the ISS, so that the spacecraft can start flying operational, long-duration missions in the near future.

Related: Starliner: Boeing's next-generation spaceship for astronauts

June 6: Starliner docks with the ISS after thruster issues

Starliner arrived at the ISS on June 6, on its second try. Five of Starliner's 28 reaction-control system (RCS) thrusters malfunctioned during its pursuit of the orbital lab, thwarting its first docking attempt on that same day

The mission team revived four of the five problematic thrusters before clearing Starliner to approach the ISS on its second time around. Once aboard, Wilmore and Williams were greeted by Expedition 71's seven-member crew.

June 18: Starliner's return date delayed

NASA began to push back the date for Starliner's return to Earth to troubleshoot the thruster problem, marking June 26 as a touchdown target. Additional issues soon cropped up as well, however, and the mission was further extended.

NASA noted a small helium leak in Starliner's propulsion system before launch and decided it wasn't a serious concern. But a few more leaks occurred after the Atlas V deployed the capsule, which the space agency wanted to look into before Starliner returned home.

July 2: NASA extends CFT mission past 45-day limit

NASA originally set the maximum duration for CFT at 45 days. But in early July, the agency deemed Starliner's performance in orbit to be good enough to exceed that limit, giving mission team members more time to test and analyze the thruster issues and the helium leaks before Starliner came home. NASA set a tentative return date for later that summer.

July 2024: Starliner tests thrusters at ISS as NASA reviews options

Engineers performed an in-space test on Starliner's RCS thrusters in preparation for a wider NASA review. This would determine if the capsule would be safe enough to carry Wilmore and Williams home.

By that time, the NASA astronauts, who had set out for 10 days in space, had been living on the ISS for more than 55 days. The agency still hoped to return them to Earth sometime in August.

Aug. 24: NASA says Starliner will return without crew

On Aug. 24, NASA and Boeing finally announced that Starliner would return to Earth without the CFT astronauts. The agency said Boeing's capsule would land at White Sands Space Harbor in New Mexico, while Wilmore and Williams would continue living on board the ISS until February 2025 at the earliest.

The Starliner duo would return to Earth aboard the Crew Dragon capsule flying SpaceX's Crew-9 astronaut mission, which was expected to launch to the station in late September.

Aug 30: NASA cuts 2 from Crew-9 mission to make room for Starliner astronauts

Crew Dragon usually carries four astronauts to and from the orbiting lab. But on Aug. 30, NASA announced that it would take two of its astronauts off Crew-9 — mission commander Zena Cardman and mission specialist Stephanie Wilson — so that the Dragon would have room for Wilmore and Williams on the ride back to Earth.

Sept. 7: Starliner returns to Earth without crew

Nearly three months later than originally expected, Starliner came home. It touched down in New Mexico at 12:01 a.m. EDT (0401 GMT) on Sept. 7 without anyone on board. The desert landing went off without a hitch.

Sept. 13: 'We just ran out of time:' Butch and Suni give teleconference from ISS

While Starliner landed sans crew, the outcome could've been different if NASA had more time, its former crewmembers said. "The timeline came to the point where we had to decide, is Starliner coming back with us or without us?" Wilmore said during a call with reporters that he and Williams held from the ISS on Sept. 13.

"We just did not have enough time to get to the end of that runway where we could say that we were going to come back with it. I think we'd have gotten there, but we just ran out of time," he added.

Sept. 22: Suni Williams takes command of ISS

After more than three months aboard the ISS, Williams assumed command of the orbiting lab on Sept. 22, taking the reins from departing Russian cosmonaut Olog Kononenko. He landed back on Earth Sept. 23 along with two crewmates in the Soyuz MS-25 spacecraft.

Sept. 28: Crew-9 launches to the ISS

A Crew Dragon capsule carrying the two Crew-9 astronauts — NASA's Nick Hague and cosmonaut Aleksandr Gorbunov — lifted off atop a SpaceX Falcon 9 rocket from Space Launch Complex-40 at Cape Canaveral Space Force Station on Sept. 28. This was the first crewed launch from the upgraded pad. The two empty seats on the capsule were reserved for Wilmore and Williams.

Nov. 12: Suni Williams refutes health claims

After tabloid speculation that Suni Williams' health was suffering due to her unexpectedly long space stay, the ISS commander dispelled the rumors, saying she was fine and that she'd kept up a healthy workout routine.

"I'm the same weight that I was when I got up here," Williams said on Nov. 12 in a video interview from the ISS, in response to a question from the New England Sports Network.

Dec. 17: NASA announces that Butch and Suni are staying up until March 2025

Crew-9 could not come home until its replacement, SpaceX's Crew-10 mission, made it to the ISS. Crew-10 was supposed to launch in February, but SpaceX encountered delays with that mission's Crew Dragon, a new capsule that had not yet flown. On Dec. 17, NASA announced that those delays had pushed Crew-10's launch — and, therefore, Crew-9's return to Earth — until late March at the earliest.

Jan. 28, 2025: President Trump asks Elon Musk to 'go get' Butch and Suni

Butch and Suni's situation generated a great deal of media attention from the beginning, but President Donald Trump made the spotlight shine much brighter shortly after his inauguration. On Jan. 28, the president announced that he had asked SpaceX founder and CEO Elon Musk to "go get" Butch and Suni from the ISS, claiming they had been "virtually abandoned in space by the Biden administration." Musk affirmed that he would indeed do so, saying it was "terrible that the Biden administration left them there so long."

This was a bit puzzling for most space observers, as the plan for SpaceX to bring Butch and Suni down had been in place for five months at this point.

Related: 'Stuck' NASA astronauts on ISS grilled on Earthly politics as long 9-month mission nears end. 'From my standpoint, politics is not playing into this at all.'

Jan. 30: Suni Williams sets spacewalk record

Suni Williams set the record for the most total time by a woman spent performing EVAs (extravehicular activities) after she and Wilmore removed a faulty radio communications unit during their 5.5-hour spacewalk on Jan. 30. The astronauts succeeded in the removal after two failed attempts during previous spacewalks. Williams has now accumulated a total of 62 hours and six minutes of spacewalking time.

Feb. 11: NASA moves Butch and Suni's return date up to mid-March

On Feb. 11, NASA announced something unusual: Butch and Suni would actually be coming home earlier than expected. The agency said it would go with a flight-proven Crew Dragon, the capsule Endurance, on Crew-10 rather than wait for SpaceX to finish work on the new spacecraft. As a result, Crew-10 could launch in mid-March, allowing Crew-9 to return to Earth shortly thereafter.

March 14, 2025: Crew-10 launches to relieve Crew-9

The four-astronaut Crew-10 ended up launching atop a Falcon 9 rocket from NASA's Kennedy Space Center in Florida on March 14, making it to the ISS 28 hours later.

Endurance's arrival officially cleared the way for Crew-9's Dragon, named Freedom, to return to Earth with Williams, Wilmore, Hague and Gorbunov. The quartet departed the ISS on Tuesday (March 18) at 1:05 a.m. EDT (0505 GMT) and are scheduled to splash down off the Florida coast at 5:57 p.m. EDT (2157 GMT) that same day.