SpaceX is launching 4 people on a risky mission to fly through radiation belts and do the first commercial spacewalk

They’re scheduled to spend about five days in space, soaring further from Earth than anybody has gone since the Apollo era more than 50 years ago.

As they travel up to 1,400 kilometers (870 miles) from Earth’s surface, they should pass through the Van Allen radiation belts, which are two donuts of intense radiation surrounding Earth.

A Dragon spaceship has never been opened up to the vacuum of space like that.

“You are taking on a lot of risk at that point,” Isaacman said, adding that he thought SpaceX had mitigated the risks well through testing and spaceship upgrades.

He said the spacewalk was the main focus of the mission preparations, almost to the point that he worried about being “way too focused” on it. SpaceX also subjected every part of the mission to “paranoia reviews,” starting over to double-check everything, he said.

When astronauts conduct spacewalks from the space station, they do a “pre-breathe” process: They breathe pure oxygen for a few hours to pull nitrogen out of their bloodstream. Otherwise, the decrease in air pressure from the spacewalk could cause the nitrogen to form bubbles in their blood and give them a dangerous condition called the “bends.”

Polaris Dawn also plans to do a pre-breathe, but stretch it over 48 hours as they slowly depressurize the cabin. They’ve already practiced this in a two-day simulation on the ground.

Starship, which stands taller than the Statue of Liberty, flew to space and returned in one piece for the first time in June. It has many more test flights ahead before SpaceX plans to put a Polaris crew on board.