A live-stream from NASA showed the SpaceX shuttle splashing down off the coast of Tallahassee, Florida, US.

The SpaceX crew monitoring the splashdown erupted in cheers as the shuttle landed.

“On behalf of SpaceX, welcome home,” the ground crew told the four astronauts aboard.

The journey home from space took about 17 hours, with the astronauts now waiting about 30 minutes for recovery ships to reach them.

Butch Wilmore and Suni Williams bid farewell to the ISS overnight, departing aboard a SpaceX capsule alongside two other astronauts.

The shuttle was pristine white when it departed the ISS, but landed in the ocean discoloured and scorched after re-entry.

Recovery boats tested the shuttle for hypergolic fumes – a combination of a fuel and an oxidizer that ignites immediately upon contact – and began the process of preparing the vessel for removal from the oval.

The parachutes were also recovered.

The astronauts remain inside the shuttle while awaiting recovery, but are kept cool by an on-board air conditioner and remain in contact with the outside world through their communications system.

The two NASA pilots expected to be gone just a week or so after launching on Boeing’s new Starliner crew capsule on June 5.

So many problems cropped up on the way to the space station that NASA eventually sent Starliner back empty and transferred the test pilots to SpaceX, pushing their homecoming into February.

Then SpaceX capsule issues added another month’s delay.

Sunday’s arrival of their relief crew meant Wilmore and Williams could finally leave.

They checked out with NASA’s Nick Hague and Russia’s Alexander Gorbunov, who arrived in their own SpaceX capsule last fall with two empty seats reserved for the Starliner duo.

“We’ll miss you, but have a great journey home,” NASA’s Anne McClain called out from the space station as the capsule pulled away 418km above the Pacific.

While other astronauts had logged longer spaceflights over the decades, none had to deal with so much uncertainty or see the length of their mission expand by so much.

Wilmore and Williams quickly transitioned from guests to full-fledged station crew members, conducting experiments, fixing equipment and even spacewalking together.

With 62 hours over nine spacewalks, Williams set a new record: the most time spent spacewalking over a career among female astronauts.

Both had lived on the orbiting lab before and knew the ropes, and brushed up on their station training before rocketing away.

Williams became the station’s commander three months into their stay and held the post until earlier this month.

Both retired Navy captains, Wilmore and Williams stressed they didn’t mind spending more time in space — a prolonged deployment reminiscent of their military days.

But they acknowledged it was tough on their families.

Wilmore, 62, missed most of his younger daughter’s senior year of high school; his older daughter is in college.

Williams, 59, had to settle for internet calls from space to her mother.

They’ll have to wait until they’re off the SpaceX recovery ship and flown to Houston before the long-awaited reunion with their loved ones.