Watch the world's largest plane hit 46MPH in latest taxi tests

While Stratolaunch didn't meet its original 2016 launch goal, the company has been putting its massive plane through one test after another over the past year. During its most recent tests, the 500,000-pound aircraft with a 385-foot wingspan has successfully reached a top taxi speed of 46MPH. It still hasn't taken to skies, but that's a huge improvement over the 28MPH it hit during the first taxi tests the space transportation company conducted in December.

According to Stratolaunch chief Paul Allen, his team has also verified that they can steer and stop the aircraft -- another success, since the tests' purpose is actually to certify that operators can control the largest plane in the world. The company hasn't revealed what other tests will need to be conducted before its new target launch date in 2020 and whether reaching 46MPH on the ground means we'll see it fly soon. But the hope is that once development is finished and it's been thoroughly tested, Stratolaunch will serve an affordable way to ferry small satellites to Low Earth Orbit.

The plane will do so by attaching the payload and its launch vehicle companion to its belly. It will then fly into the stratosphere before letting the vehicle go, so it can make its way to space. Stratolaunch shares a similar two-fuselage combination with Virgin Orbit's LauncherOne, which Richard Branson's Virgin Group is also developing for satellite launches. It's much bigger than the LauncherOne, which can only carry up to 500 pounds of payload. Stratolaunch, on the other hand, will be able to carry as much as 500,000 pounds.