The first-of-its-kind Polaris Dawn space mission concluded Sunday with the return to Earth of four private sector astronauts in a Crew Dragon capsule that had lifted off five days earlier atop a SpaceX Falcon 9 rocket.

SpaceX founder and CEO Elon Musk noted the completion of the mission with a post on the X social network (formerly Twitter): "Polaris crew is home safe & sound!"

The signature accomplishment of Polaris Dawn's time on orbit was a spacewalk on Thursday by two members of the crew, the first such extravehicular activity to be performed by astronauts in a commercial venture rather than as an undertaking by a government-backed agency such as NASA or its counterparts in Russia and China. 

"It is critical for the commercial industry to have the tools and experience for spacewalk operations and the suit we tested is just the first step in that journey," Mission Commander Jared Isaacman said on X in a Sunday post recapping the mission. "Along the way, we've learned a lot about the technical disciplines related to EVA operations."

The mission was a follow-up of sorts to a 2021 private mission called Inspiration4. Both were backed by Isaacman, the billionaire founder and chief executive of the data company Shift4. Polaris Dawn has been in the works for several years; at one point, there was talk of sending a crew to boost the life of the Hubble space telescope. 

This new mission wasn't that. Instead, the crew used spacesuit technology developed by SpaceX for its spacewalk activities. They also tested laser-based communications with satellite broadband provider Starlink as part of an effort to pave the way for travel to places including Mars. Starlink is a subsidiary of SpaceX, which is owned by Tesla CEO Elon Musk.

The risks weren't negligible: The crew also achieved the highest orbit of Earth ever recorded and passed through heavy radiation and areas at higher risk of damage from small space rocks and debris.

"It's not easy to travel that far into space," Isaacman said in his Sunday X post. "The environment is harsh, with increased radiation, more micrometeoroid debris, and no nearby safe havens in case of trouble. We went there to study the radiation environment, gather data on its impact on systems and human health, and to explore areas we know less about, where we can learn new problem-solving methods that will help in future missions."  

Who flew on the mission?

The crew comprised four members. They are:

Jared Isaacman, the Shift4 CEO, who's said to be spending hundreds of millions of dollars on the mission, in addition to serving as mission commander. Isaacman was on the Inspiration4 mission in 2021 as well.

Sarah Gillis, SpaceX's senior operations engineer, who's trained NASA astronauts and who served as mission specialist for Polaris Dawn. Along with Isaacman, she was one of the two crew members who performed the spacewalk.

Scott Poteet, who served as mission director of Inspiration4, is a former fighter jet pilot for the US Air Force. He did communications and spacewalk assistance on the mission.

Anna Menon, a lead space operations engineer at SpaceX, was in charge of the crew's health during Polaris Dawn.

What did they accomplish on this mission?

On Thursday, two crew members exited the spacecraft to conduct the first spacewalks by members of a commercial venture.

"SpaceX, back at home we all have a lot of work to do, but from here, Earth sure looks like a perfect world," Isaacman said from an open hatch. The mission team shared that moment in a video posted to social media Thursday as SpaceX marked the completion of that excursion.

In addition to the spacewalk, which Isaacman and Gillis were the first private astronauts to perform, the mission is tested laser communications with Starlink and performed a series of biology and human endurance tests, according to the Polaris Dawn website.

The spacecraft traveled to an orbit of about 870 miles above the Earth, just past the altitude record of 853 miles set by the Gemini XI mission in 1966, according to The New York Times. For comparison, the International Space Station orbits at roughly 250 miles.

Polaris Dawn is expected to be the first of three missions, the next two of which would use SpaceX's new Starship rocket. 

What took so long with the Polaris Dawn launch?

The Falcon 9 rocket blasted off from NASA's Kennedy Space Center in Cape Canaveral, Florida, at 5:23 a.m. ET on Tuesday, Sept. 10, following two weeks of postponements. SpaceX marked the occasion with a short, to-the-point message on X: "Liftoff of Polaris Dawn!" Shortly afterward, the first-stage booster returned, landing on its target droneship as the spacecraft continued its ascent. Within 15 minutes, the crew was in orbit.

Tuesday's launch window was the latest in a series of opportunities that had come and gone since late August. "Targeting no earlier than Tuesday, Sept. 10 for Falcon 9's launch of the Polaris Dawn mission," SpaceX said in a post on X late on Monday, Sept. 9. "Weather is currently 40% favorable for liftoff, and conditions at the possible splashdown sites for Dragon's return to Earth remain a watch item."

The original launch date in the last week of August was scrubbed to allow for "a closer look at a ground-side helium leak on the Quick Disconnect umbilical," SpaceX said at the time in an X post. A day later, the Polaris Dawn team stood down again "due to unfavorable weather in Dragon's splashdown area off the coast of Florida," the company said. Isaacman had earlier posted on X that the launch team would assess conditions day by day. 

"Crew safety is absolutely paramount and this mission carries more risk than usual, as it will be the furthest humans have traveled from Earth since Apollo and the first commercial spacewalk!" Musk posted in late August on X, which he owns. "If any concerns arise, the launch will be postponed until those concerns are addressed."

Correction, Aug. 28: An earlier version of this article incorrectly stated the name of Jared Isaacman's company. He's CEO of Shift4.