The US space agency Nasa is all set to bring home its Orion capsule.
The spaceship, which has been on a three-week journey around the Moon, is targeting a splashdown in the Pacific Ocean off California.
Uncrewed for this test flight, the capsule is expected to carry astronauts on its next outing, assuming everything works as planned in the coming hours.
The parachute-assisted drop into the sea should occur at about 09:40 local time (17:40 GMT).
The incoming velocity will be extremely high. The capsule will be moving at 40,000km/h (25,000mph) – or 32 times the speed of sound – when it touches the top of our planet’s atmosphere.
Friction and pressure on Orion’s forward-facing surface will generate temperatures likely to reach close to 3,000C (5,000F).
The shielding that covers this part of the spacecraft has to handle this challenge if Orion is ever to be trusted to carry astronauts in the future.
The exercise is part of Nasa’s Artemis programme, a quest to take people back to the lunar surface later this decade.
Fittingly, Sunday marks exactly 50 years since this feat was last achieved by the crew of Apollo 17.