A crew of four private astronauts made history in the early hours of Thursday morning when they opened the hatch of their SpaceX Dragon capsule and conducted the first commercial spacewalk.

The spacewalk, the riskiest part of the five-day Polaris Dawn mission, began at 6:12 a.m. ET as oxygen began flowing into the astronauts’ spacesuits. Only two of the four crew members actually exited the vehicle, but all four had to don SpaceX’s new suits because the Dragon capsule has no airlock. That meant the entire spacecraft had to be depressurized.

During a spacewalk, also known as an extravehicular activity, astronauts leave the relative safety of their spacecraft and head into the void of space. In the history of human spaceflight, spacewalks have only been performed by government astronauts, who used them as an opportunity to perform repairs, maintenance, or scientific experiments. Spacewalks by NASA astronauts typically last between five and eight hours.

Billionaire mission leader Jared Isaacman was the first to leave the Dragon capsule. After his return, SpaceX engineer Sarah Gillis went into the vacuum of space. They used a special ladder called the “Skywalker,” which SpaceX had attached to the Dragon capsule specifically for this purpose, to help them exit the capsule. The pair were connected to the spacecraft by umbilical cords and maintained contact with the ladder the entire time. The spacewalk was very quick, with each person outside the spacecraft for less than ten minutes. During this time, Isaacman and Gillis performed a series of movements to test the mobility and performance of the suits.

“We all have a lot to do at home, but from here it looks like a perfect world,” Isaacman said.

SpaceX’s spacesuits are significantly lighter than the heavy white suits worn by NASA astronauts, and the company said they were designed “with mobility in mind.”

One of the biggest differences between NASA’s spacesuits and SpaceX’s is the lack of the bulky white backpack called the primary life support system. Instead of a backpack, the main life support systems are powered by the 12-foot umbilical cord connected to the spacecraft.

As the two took turns exiting the spacecraft, the rest of the crew, former US Air Force pilot Scott “Kidd” Poteet and SpaceX engineer Anna Menon, carefully monitored their progress. After Gillis closed the hatch, the spacecraft was gradually repressurized. The entire process took less than two hours.

This remarkable achievement is a huge boon to SpaceX’s private spaceflight ambitions, which most notably include a private manned mission to Mars. If SpaceX can pull it off, the suits worn by humans traveling to the Red Planet will likely have their origins in the spacesuits worn by Isaacman and his crewmates on Polaris Dawn.

“Although Polaris Dawn will be the first time the SpaceX EVA suit will be deployed in low Earth orbit, its ultimate fate lies much farther from our home planet,” the company said in May. “Building a base on the Moon and a city on Mars will require developing a scalable design for the millions of spacesuits needed to support life on multiple planets.”

This is not the first milestone for the Polaris Dawn mission. After launching on a SpaceX Falcon 9 rocket early Tuesday morning, the capsule fired its engines and carried the crew to an altitude of 1,400 kilometers – higher than any other human aircraft since the Apollo 17 moon mission in 1972.

With the two major milestones now behind them, the Polaris Dawn crew will spend their remaining days in orbit conducting a range of science experiments and continuing to test laser communications between the capsule and the Starlink internet satellites. The crew will likely return in the early hours of Sunday morning, splashing down off the coast of Florida, although SpaceX has not yet released a firm timetable for their return to Earth.