Two Nasa astronauts are on the last leg of their journey home as they prepare to make the first splashdown return to Earth in 45 years.
Robert Behnken and Douglas Hurley left the International Space Station after two months on the orbiting laboratory.
The pair are expected to land in the ocean off the coast of Florida at around 7.48pm on Sunday.
Mr Behnken and Mr Hurley made history on May 30 when they became the first people to launch into low-Earth orbit on a commercial spacecraft, built by SpaceX.
Their mission, named Demo-2, also marked the first time Nasa had launched astronauts from US soil in nine years.
SpaceX’s astronaut carrier, the Crew Dragon, is expected to land in the water off Pensacola, western Florida.
The US space agency said this location is far away from Hurricane Isaias, which is expected to hit the eastern part of the state.
The last time astronauts made an ocean landing was on July 1975 during an Apollo mission.
Since then, they have always landed on terra firma, using Nasa’s Space Shuttle or the Russian space agency’s Soyuz capsules.
If all goes to plan, the splashdown will usher in a new era for Nasa, which will have at least one commercial spacecraft ready to launch astronauts into space from US soil.
The splashdown is the final step in the mission designed to test SpaceX’s human spaceflight system – including launch, docking, splashdown and recovery operations.
In a post-launch conference back in May, Elon Musk – the founder of SpaceX – said he was not keen to “declare victory yet”, emphasising that the “return can be more dangerous than the ascent”.
Mr Musk said at the time: “We need to bring them home safely and make sure that we are doing everything we can to minimise that risk of re-entry.”
Crew Dragon’s flight back to Earth with @AstroBehnken and @Astro_Doug remains on track; targeting splashdown off the coast of Pensacola, Florida in the Gulf of Mexico at 2:48 p.m. EDT today https://t.co/bJFjLCzWdK— SpaceX (@SpaceX) August 2, 2020
The Crew Dragon performed manoeuvres to lower the capsule’s orbit and get it closer to the splashdown zone.
The spacecraft is expected to perform another manoeuvre, known as de-orbit burn, which will place it on a trajectory for splashdown, travelling at about 17,500mph.
On entering the Earth’s atmosphere, the Crew Dragon will face temperatures of around 1,900C as it deploys parachutes to slow its speed to around 119mph.
At the point of splashdown, the capsule will be descending at around 15mph.
The re-entry will create a communications blackout, caused by an envelope of hot air surrounding the capsule, which is expected to last about six minutes.
GO Navigator makes its way to the primary splashdown zone off the coast of Pensacola, Florida for @AstroBehnken and @Astro_Doug's return. 👨🚀🪂🌊🚢— NASA's Johnson Space Center (@NASA_Johnson) August 2, 2020
Listen in to learn how the recovery vessel will hoist @SpaceX #CrewDragon Endeavour with our astronauts inside 👇 pic.twitter.com/CF4iVVAzCr
A SpaceX recovery ship called Go Navigator – made up of spacecraft engineers, recovery experts and medical professionals – will be waiting to pull the capsule aboard and help the astronauts get out as they begin readjusting to gravity.
The re-entry will mark the end of SpaceX’s human spaceflight demonstration mission.
The aerospace company’s first operational flight is expected to take place in September, where a second Crew Dragon spacecraft will carry four astronauts to the space station.
The capsule that carried Mr Hurley and Mr Behnken into space will be refurbished and launched on SpaceX’s second operational crewed mission, Crew 2, due to take place early next year.
Another aerospace company, Boeing, is also developing spacecraft to ferry astronauts to the space station, as part of Nasa’s Commercial Crew Programme.