WASHINGTON, United States (AFP) — After making a close pass at the Moon and venturing further into space than any previous habitable spacecraft, National Aeronautics and Space Administration's Orion capsule is due to splash down Sunday in the final test of a high-stakes mission called Artemis.

As it hurtles into Earth's atmosphere at a speed of 40,000 kilometers per hour, the gumdrop-shaped traveler will have to withstand a temperature of 2,800 degrees Centigrade — about half that of the surface of the sun.

Splashdown in the Pacific off the Mexican island of Guadalupe is scheduled for 9:39 a.m. local time.

Achieving success in this mission of just over 25 days is key for NASA, which has invested tens of billions of dollars in the Artemis program due to take people back to the Moon and prepare for an onward trip, someday, to Mars.

So far the first test of this uncrewed spacecraft has gone very well.

But it is only in the final minutes of this voyage that the true challenge comes: seeing if Orion's heat shield, the biggest ever built, actually holds up.

"It is a safety-critical piece of equipment. It is designed to protect the spacecraft and the passengers, the astronauts on board. So the heat shield needs to work," Artemis mission manager Mike Sarafin said.

Choppers, divers and boats

A United States Navy ship, the USS Portland, has been positioned in the Pacific to recover the Orion capsule. Helicopters and inflatable boats will also be deployed for this task.

The falling spacecraft will be slowed first by the Earth's atmosphere and then a web of 11 parachutes until it eases to a speed of 30 kilometers per hour when it finally hits the blue waters of the Pacific.

Once it is there, NASA will let Orion float for two hours — a lot longer than if astronauts were inside — so as to collect data.