POLARIS DAWN: One of the most adventurous human spaceflights since Apollo may launch tonight.

During the initial hours of the spaceflight, the crew will seek to fly in a highly elliptical orbit, reaching an altitude as high as 1,400 km (870 miles) above the planet’s surface. This will be the highest Earth-orbit mission ever flown by humans and the farthest any person has flown from Earth since the Apollo Moon landings more than half a century ago. This will expose the crew to a not insignificant amount of radiation, and they will collect biological data to assess harms.

The Resilience spacecraft will then descend toward a more circular orbit about 700 km above the Earth’s surface. Assuming a launch on Tuesday, the crew will don four spacesuits on Friday and open the hatch to the vacuum of space. Then Isaacman, followed by mission specialist Sarah Gillis, will each briefly climb out of the spacecraft into space.

Isaacman’s interest in performing the first private spacewalk accelerated, by years, SpaceX’s development of these spacesuits. This really is just the first generation of the suit, and SpaceX is likely to continue iterating toward a spacesuit that has its own portable life support system (PLSS). This is the “backpack” on a traditional spacesuit that allows NASA astronauts to perform spacewalks untethered to the International Space Station.

The general idea is that, as the Starship vehicle makes the surface of the Moon and eventually Mars more accessible to more people, future generations of these lower-cost spacesuits will enable exploration and settlement. That journey, in some sense, begins with this mission’s brief spacewalks, with Isaacman and Gillis tethered to the Dragon vehicle for life support.

Godspeed…