The world’s largest airplane took flight for the first time ever on Saturday morning. Built by rocket launch company Stratolaunch, the 500,000-pound plane with a 385-foot wingspan lifted off shortly after 10AM ET from Mojave Air and Space Port in Mojave, California. It was a critical first test flight for the aircraft, designed to launch rockets into orbit from the air. The inaugural flight lasted for 150 minutes, according to the company, after which the plane safely landed.

The dual-fuselage Stratolaunch is designed to fly to an altitude of 35,000 feet, where it can drop rockets that ignite their engines and boost themselves into orbit around the planet. There is no rocket on this particular flight. But the company has already signed at least one customer, Northrop Grumman, which plans to use Stratolaunch to send its Pegasus XL rocket into space.

“It was an emotional moment for me, personally, to watch this majestic bird take flight,” said Stratolaunch CEO Jean Floyd. The aircraft performed as expected, reaching a maximum speed of 175 miles per hour and a peak altitude of 15,000 feet.

“The flight itself was smooth, which is exactly what you want a first flight to be,” said test pilot Evan Thomas. During the first phase of the flight, Stratolaunch tested the airplane’s handling qualities. “It flew very much like we had simulated and like we predicted,” he said. According to Stratolaunch, the plane’s systems “ran like a watch” and that the aircraft landed “on the mark” after a few low passes.

Today’s flight comes just three months after Stratolaunch laid off “more than 50” employees and canceled efforts to develop its own rockets. Originally, the company had planned to build a whole suite of rockets, including a spaceplane. The change in plans was reportedly sparked by the death of Microsoft co-founder Paul Allen, who started Stratolaunch in 2011.

Allen’s name came up frequently during today’s press call “Without a doubt, he would have been exceptionally proud to see his aircraft take flight,” said Floyd. “Even though he wasn’t there today, I did whisper a ‘thank you.’’

Stratolaunch did not take questions during the press call and made no mention of what comes next for the aircraft.

The road to today’s launch involved a number of incremental tests over the last few years, including the initial rollout and an engine test in 2017, and a number of taxis down the runway in Mojave at various speeds.

With reporting from Loren Grush

Update April 13th 2:20PM ET: The article has been updated to reflect that the Stratolaunch plane safely landed after its inaugural flight with executive comments from a press call.