Stratolaunch, the world’s biggest airplane, hit a new milestone recently, taxiing down the runway at 46 mph. While that may not sound like much, it’s worth watching the video to see this 500,000-pound beast with twin fuselages and a wingspan of 385 feet lumbering down the concrete. The chase cars look like Micro Machines next to this thing.

It’s a big improvement over a low-speed test conducted last December, in which the Stratolaunch traveled down a runway at just 28 mph. Previously, the massive aircraft successfully conducted a test of its six turbofan engines at the Mojave Air and Space Port in California. All of these incremental milestones are said to be leading up to the Stratolaunch’s first test flight in 2019.

Stratolaunch is a private space company helmed by Microscoft co-founder Paul Allen. The goal is to use the airplane as a platform for lifting rockets into the stratosphere before launching them into space. Some see it as a cheaper, more reliable route to low Earth orbit — the sweet spot for many kinds of satellites. Thanks to its massive size, the plane is capable of carrying payloads up to 550,000 pounds.

Air launching rockets isn’t a new thing. Orbital ATK’s Pegasus XL rocket is capable of launching from air. And while the Pegasus is a fairly small rocket, capable of launching satellites weighing up to 1,000 pounds, the rocket-maker signed a deal with Stratolaunch last year. NASA and Richard Branson’s Virgin Group have similar projects under development, as does the Defense Advanced Research Projects Agency.

The key test will be the first flight next year. This will determine whether Stratolaunch has a commercial future, or whether it will end up in a museum alongside the Spruce Goose, Howard Hughes’ behemoth flying boat that only took to the skies once.