SpaceX is about to send four people on a wild — and risky — mission into the radiation belts.

Polaris Dawn crew will travel into an oval-shaped orbit that extends as high as 870 miles (1,400 kilometers) from Earth. That’s well into the inner band of Earth’s Van Allen radiation belts, which begin at around 600 miles (1,000 kilometers) in altitude…

The International Space Station orbits about 250 miles (400 kilometers) above Earth. The Hubble Space Telescope, which NASA astronauts have conducted spacewalks to repair, orbits about 320 miles (515 kilometers) high.