Polaris Dawn, a private space mission that aims to complete the first-ever civilian spacewalk, is expected to launch this week. On X, SpaceX said it’s targeting Tuesday August 27 at 3:38AM ET for liftoff of the Falcon 9 rocket that will carry the Polaris Dawn crew to orbit. Led by billionaire Jared Isaacman, Polaris Dawn plans to send its crew of four private citizens as far as 870 miles from Earth — farther than any human has traveled since the Apollo program. The spacewalk, in which two of the crew members will step outside the SpaceX Dragon capsule, will take place at an altitude of 435 miles above Earth.

The Polaris Dawn crew includes Isaacman, CEO of Shift4, as commander, retired Air Force Lieutenant Colonel Scott “Kidd” Poteet as its pilot, and SpaceX engineers Sarah Gillis and Anna Menon as mission specialists. Menon will also serve as the medical officer. The mission is expected to last about five days.

While only two crew members will actually leave the spacecraft during the flight, all will be exposed to the vacuum of space when the hatch opens — the Dragon capsule doesn’t have an airlock. It’ll be a critical test for SpaceX’s new Extravehicular Activity space suits, which the entire Polaris Dawn crew will have to wear to keep them safe. In an interview with Florida Today ahead of the mission, Menon said the suits have gone through extensive testing on the ground and expressed confidence in their performance. “We absolutely know the suits can pressurize there,” Menon said, adding that the team has “spent a lot of time pressurizing the suits at this point.”

Polaris Dawn will also put Starlink laser-based communications to the test in space for the first time, and gather data to support research into the effects of spaceflight on human health. The mission comes several years in the making and is the first of three planned Polaris spaceflights.