SpaceX's first crewed mission is headed back to Earth. Here's every step that must go perfectly for 2 NASA astronauts to come home safely.

SpaceX

• NASA, SpaceX, and two veteran astronauts are about to finish the first-ever crewed commercial spaceflight mission.
• Astronauts Bob Behnken and Doug Hurley climbed back aboard the Crew Dragon from the International Space Station on Saturday, and they are preparing to weather a fiery fall through Earth's atmosphere on Sunday afternoon.
• The spaceship's successful splashdown would mark the beginning of a new era in which commercial spacecraft regularly ferry humans to and from space.
• Here's how the return trip will work.
• Visit Business Insider's homepage for more stories.

Two NASA astronauts are currently orbiting Earth in a SpaceX spaceship and about to embark on a fiery fall through the atmosphere, into the ocean.

Bob Behnken and Doug Hurley became the first people to fly SpaceX's brand-new spaceship, the Crew Dragon, on May 30. It was the first crewed launch from American soil since July 2011 and the first-ever launch of a commercial spacecraft with humans inside. The ship docked to the International Space Station the next day, and Behnken and Hurley have since been conducting science experiments and spacewalks there.

But now comes the hard part: bringing them back to Earth.

Behnken and Hurley must hurtle back through the atmosphere — a voyage that will require the spacecraft to weather temperatures up to 3,500 degrees Fahrenheit. You can watch the process live here.

SpaceX CEO Elon Musk has said the fall to Earth is what worries him most about the Demo-2 mission.

Here's how each step of the return trip must play out to bring the astronauts home safely.

The Demo-2 return began on Saturday, when Behnken and Hurley climbed back into the Crew Dragon capsule, which they've named Endeavour.

NASA and SpaceX had been watching the weather closely to make sure it would be safe for the capsule to splash down in at least two preselected sites. If winds get too strong or waves are too high, the spaceship has up to 60 hours in Earth's orbit before it must land.

But as of 12:55 p.m. ET on Sunday, NASA reported calm weather and smooth seas.

"It looks like glass. It's awesome," one mission controller said on NASA's live feed.

If the Crew Dragon safely brings the men back to Earth, the culmination of the mission will officially kick off a new era of commercial spaceflight.

NASA plans to use commercial providers like SpaceX to launch and bring home astronauts — not just on missions to the ISS, but soon to the moon and eventually to Mars.

"This is the next era in human spaceflight, where NASA gets to be the customer," NASA Administrator Jim Bridenstine said during Sunday's live feed of the astronauts' return journey.

Behnken and Hurley have been in space since May 30, when a Falcon 9 rocket carried them into Earth's orbit in the Crew Dragon spaceship.

See Also:

• NASA astronaut Megan McArthur, whose husband just flew on SpaceX's Crew Dragon, will pilot the spaceship in the spring
• Watch live: 2 NASA astronauts just made a fiery return to Earth aboard SpaceX's new Crew Dragon ship
• Elon Musk's Starlink satellites photobombed Comet Neowise in a photographer's striking image

SEE ALSO: NASA just launched its Mars alien-hunting Perseverance rover into deep space with a drone tucked under its belly

DON'T MISS: NASA just picked astronaut Megan McArthur, whose husband launched aboard SpaceX's Crew Dragon, to pilot the spaceship in spring