On Friday the Crew Dragon capsule will detach from the International Space Station (ISS) 400km above Earth and begin a fiery journey back through the atmosphere, ending in a splashdown 450km off the coast of Florida.
If all goes according to plan, it will wrap up the first complete test mission of the Crew Dragon spacecraft, which is expected to carry its first astronauts into orbit by the middle of this year.
While Crew Dragon will be recovered from the ocean this time, the spacecraft was designed with the ability to make powered landings using its four side-mounted “Super Draco” thrusters.
These thrusters are also designed to fire and lift the spacecraft away from danger in any emergency during launch.
Video footage of tests show the thrusters allowing a tethered capsule to hover in mid air.
However, powered landings were ruled out for the time being in 2017 amid safety concerns and time constraints, so parachutes will be used for the foreseeable future.
In 2014, Nasa awarded Elon Musk’s SpaceX and Boeing a combined $6.8bn to build competing spacecraft to carry astronauts into orbit from the United States.
No human spaceflight has launched from America since the retirement of the Space Shuttle in 2011, and Nasa has relied on Russian Soyuz modules to ferry astronauts to and from the ISS in the intervening years.
Crew Dragon docked at the ISS on Sunday, 27 hours after blasting off from the Kennedy Space Center in Florida last Saturday.
The spaceship carried 180kg of supplies and test equipment, including a crash test dummy named Ripley, after Sigourney Weaver’s character in Alien.