Led by Shift4 Payments CEO Jared Isaacman, the four-member crew aims to journey farther into the cosmos than any other manned mission in more than half a century, since the end of the Apollo era.

On the mission's first day, they will soar to a peak altitude of 870 miles (1,400 kilometers) before returning into a lower orbit.

"Dragon will travel repeatedly through the orbital altitudes of over 10 thousand satellites and bits of space debris," SpaceX founder CEO Elon Musk wrote on X. "No room for error in our calculations."

The highlight of the voyage is slated for as early as Thursday: the first ever spacewalk by civilians, outfitted in sleek, newly developed SpaceX extravehicular activity (EVA) suits with heads-up displays, helmet cameras and an advanced joint mobility system.

SpaceX has scheduled the EVA for 0623 GMT on Thursday, with a backup window on Friday at the same time.

Since the Crew Dragon capsule lacks an airlock, the entire crew will be exposed to the vacuum of space for the duration of the spacewalk, as two venture out, tethered to the spaceship.

"I think the world is a more interesting place when you can journey among the stars," Isaacman said in a video message released by SpaceX.

"We will develop technologies and test technologies that will help SpaceX ultimately achieve its long-term ambitions of making human life interplanetary."

- High radiation zone -

The capsule blasted off early Tuesday atop a Falcon 9 rocket from the Kennedy Space Center in Florida.

Applause broke out across the mission control center as it separated successfully from the main engine and the first glimpses of Earth came into view.

Musk joined in the celebrations, a photo reposted by him on X showed.

At its upper altitudes, the capsule will enter the Van Allen radiation belt, a region teeming with high-energy charged particles that can pose health risks to humans over extended periods.

While the crew will orbit nearly three times higher than the International Space Station, they won't surpass the record-setting distance of 248,000 miles achieved by the Apollo 13 crew in 1970.

The Apollo 13 astronauts reached that distance as they slingshot around the Moon after an explosion forced an emergency return to Earth.

- Two years' preparation -

Isaacman has remained tight-lipped on his total investment in the project, though reports suggest he paid around $200 million for the SpaceX Inspiration4 mission in September 2021, the first all-civilian orbital mission.

Rounding out the team are mission pilot Scott Poteet, a retired US Air Force lieutenant colonel; mission specialist Sarah Gillis, a lead space operations engineer at SpaceX; and mission specialist and medical officer Anna Menon, also a lead space operations engineer at SpaceX.

The quartet underwent more than two years of training in preparation for the landmark mission, logging hundreds of hours on simulators as well as skydiving, centrifuge training, scuba diving, and summiting an Ecuadoran volcano.

Splashdown should take place around five or six days out from launch.

Polaris Dawn is the first of three missions under the Polaris program, a collaboration between Isaacman and SpaceX.

The final mission is slated to be the first crewed flight of SpaceX's Starship prototype -- the rocket it envisions as the key to future Mars colonization.

In addition to their spacewalk, the crew will test laser-based satellite communications between the spacecraft and Starlink's satellite constellation, aiming to enhance space communication speeds.

They'll also carry out 36 scientific experiments, including tests on contact lenses with embedded microelectronics to monitor changes in eye pressure and shape -- adding to the growing body of space research aimed at advancing human exploration beyond Earth.

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