Virgin Galactic flew an experimental spacecraft to the edge of space on Thursday morning, passing an important milestone as the orbital-tourism company prepares to carry paying customers into space.

The complex test-flight began at approximately 7 a.m. PST at the Mojave Air and Space Port in California's Mojave Desert. Virgin Galactic's four-engine transport plane Eve—named for Eve Branson, mother of Virgin founder Richard Branson—took off with the 60-foot-long spacecraft Unity under its center wing. Unity was thus named by the late physicist Stephen Hawking; the spacecraft's nose art includes a depiction of Hawking's iris.

The twin-fuselage Eve slowly climbed past 43,000 feet. Aboard Unity, test pilots Mark Stucky and C.J. Sturckow—a former NASA test pilot and NASA astronaut, respectively—began pre-flight checks.

Unity fell away from Eve. A few seconds later Stucky and Sturckow ignited Unity’s hybrid rocket motor, which consumes a combination of solid fuel and liquid oxidizer. Unity arced toward space, quickly accelerating past the speed of sound.

The Thursday test was a critical one for Virgin Galactic. An earlier test of the company’s spacecraft in October 2014 ended in disaster when Unity’s sister ship Enterprise broke apart mid-flight, killing co-pilot Michael Alsbury and injuring pilot Peter Siebold.

The National Transportation Safety Board (NTSB) concluded that Alsbury had unlocked Enterprise’s “feathers”—a kind of air brake—too early, catastrophically stressing the airframe.

The NTSB blamed human error but also warned about the risk inherent in the rapid development of the space tourism industry. Several companies are working on orbital and near-orbital craft for paying customers. In September, Elon Musk’s rocket company SpaceX announced that Japanese businessman Yusaku Maezawa would travel around the moon atop one of the company's so-called “Big Fucking Rockets” as early as 2023.

But SpaceX’s own rockets still fail on occasion. On Dec. 5, a reusable Falcon 9 rocket malfunctioned and missed its landing zone at Cape Canaveral in Florida, instead splashing down in the Atlantic Ocean a few miles offshore.

“Commercial space transportation must continue to evolve and mature,” NTSB investigator Christopher Hart warned.

Virgin Galactic CEO George Whitesides signaled caution in the months before the December test. “We’ll do a variety of different things as we expand the envelope and try to understand abort scenarios and other things,” Whitesides said. “We have a lot of work still to go, but we’re making good progress.”

If the December flight was a success, Virgin Galactic would continue expanding its testing and building more spacecraft. “We have a vision of building out a fleet of spaceships over time,” Whitesides said.

At the time of Unity’s flight, The Spaceship Company, which builds spacecraft for Virgin Galactic, was assembling two more vehicles similar to Unity. “That will take some time to do, but we’re really looking forward to getting the next vehicle into service when it’s ready to start test flights,” Whitesides said.

NASA signaled confidence in the December test. For the first time, it offered monitoring gear for installation on a Virgin Galactic spacecraft. “Payloads on the flight will collect valuable data to improve technologies for future missions,” the space agency tweeted.

High over Mojave, Unity accelerated and climbed. As the vehicle sped past Mach 2.5, Stucky and Sturckow shut off the rocket motor. Unity continued to pick up speed, peaking at Mach 2.9 before beginning a gradual descent and deceleration.

Virgin Galactic tweeted the final figures. Unity climbed to 271,268 feet, or 82.7 kilometers. While some scientists insist that “space” begins as high as 100 kilometers, astrophysicist Jonathan McDowell argued in a 2018 paper that 80 kilometers, or around 50 miles, is the “more appropriate boundary.” NASA awards astronaut wings to its crew who reach 80 kilometers of altitude.

“Welcome to space,” Virgin Galactic tweeted.

Stucky and Sturckow extended Unity’s feathers. The spacecraft slowed as it spiraled downward. Unity safely landed around 8:48 a.m. PST. NASA tweeted congratulations. “With a good rocket motor burn, the mission went beyond the 50-mile altitude target.”

Virgin Galactic has not said when it plans to begin carry tourists into space. But Thursday's successful flight brought that date much closer. “The peak for humans traveling to space was 1985 when 63 humans flew to space in one year,” Virgin Galactic tweeted. “That’s 33 years ago! Excited to be working towards increasing that number.”