On Saturday, SpaceX is taking its most ambitious step yet toward launching people into space. It’s not sending anyone with a pulse just yet, but this upcoming launch is still a high-consequence event. In the wee hours of the morning on March 2, SpaceX’s shiny new astronaut taxi—dubbed Crew Dragon—will take to the skies, bound for the International Space Station.

The flight, officially known as Demo Mission-1 (or DM-1), stars an upgraded version of SpaceX’s Dragon cargo craft. SpaceX has always intended for its Dragon capsules to ferry humans, but every SpaceX Dragon capsule launched so far has only shuttled cargo to and from the ISS. The upgraded version, debuting on DM-1, will feature new crew life-support systems, seats, control panels, and a propulsion system that can be used to keep the crew safe during a launch emergency. But it won’t carry people; before astronauts can climb aboard, SpaceX has to prove Dragon is ready.

That doesn’t mean that the craft will be empty. SpaceX says Dragon will carry supplies for the crew currently on the space station, a radiation experiment, and a mannequin similar to the Starman that flew on board the first Falcon Heavy mission. Perched in one of the craft’s seats, the faux astronaut will be suited up in a custom flight suit that will let SpaceX collect data on the capsule’s environment.

Saturday’s mission—which will last approximately five days—is a shortened version of the ones that future crews will complete. That’s because its purpose is to provide critical data about how Crew Dragon performs in space. “Demo-1 is a flight test but also a real mission, a very critical mission,” Bill Gerstenmaier, associate administrator for NASA’s human spaceflight program, said in a news briefing last week.

“It’s a test flight, but it’s more than a test flight,” he added. “It’s a mission to the International Space Station.”

Following a Saturday launch, Crew Dragon is expected to arrive on Sunday morning at the International Space Station, where one of its key tasks will be to show NASA that it can safely dock with the space station—a first for Dragon. To date, all Dragon cargo crafts have berthed it instead: The spacecraft approaches the station and waits for a crew member to grapple it with one of the station’s robotic arms, securing it into place. With this Crew Dragon, the craft’s onboard computers will undertake the riskier maneuver of guiding it in to dock itself.

"We need to make sure that it can safely go rendezvous and dock with the space station, and undock safely, and not pose a hazard to the International Space Station," Kathy Lueders, manager of NASA's Commercial Crew Program, said during the same briefing.

The domed black-and-white capsule can accommodate up to seven passengers, and represents not only the next big step in SpaceX’s evolution but also NASA’s dependence on a commercial space industry. Saturday’s mission will be the first time that a private company launches a crew-ready US vehicle since the final flight of the space shuttle Atlantis eight years ago. (Currently NASA and others around the world depend on pricey Russian rockets to send crew to and from the ISS.)

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Following the shuttle program’s end, NASA put its faith in the commercial sector, selecting two companies to build its future space taxis: SpaceX and Boeing. These two companies have worked since 2014 to build a spacecraft capable of carrying crew under a contract worth $6.8 billion. Their vehicles—SpaceX’s Crew Dragon and Boeing’s CST-100 Starliner—will be the agency’s primary means of ferrying astronauts to space.