The Stratolaunch, which is so big that it requires two cockpits and six jet engines, will be sent on a test flight this summer, if all goes to plan.
The plane has a wingspan which is longer than a football field at 385 feet and will eventually be used to transport rockets carrying satellites and astronauts into Earth’s upper atmosphere.
Dreamt up by Microsoft co-founder Paul Allen, the Stratolaunch reached a maximum speed of 46 miles per hour in two previous ground tests.
However, if the Stratolaunch is to take to the skies the aircraft will need to reach a speed of 138 miles per hour.
George Bugg, aircraft program manager at Stratolaunch, said of the ground: “This was another exciting milestone for our team and the program.
“Our crew was able to demonstrate ground directional control with nose gear steering, and our brake systems were exercised successfully on the runway.
“Our first low speed taxi test is a very important step toward first flight. We are all proud and excited.”
Mr Allen wants Stratolaunch to act as a type of launchpad in the sky, allowing rockets to take off from it to release satellites in to space.
He added he would like to follow in a similar manner to Elon Musk’s SpaceX and use re-usable rockets to minimise the cost.
In an interview with the Washington Post, Mr Allen said: “I would love to see us have a full reusable system and have weekly, if not more often, airport-style, repeatable operations going.”
Stratolaunch could also be used to launch a top-secret shuttle-sized rocket called ‘Black Ice’ – which could be launched from the plane, with Stratolaunch landing safely back to the ground.
Mr Allen said: “If you caught the bug back in the Mercury era, of course it’s in the back of your mind.
“But I think you’re seeing right now, other than [space station] resupply missions, most spaceflights are about launching satellites. That’s the reality.
“As well as sending cargo to space, the plane could be used to launch a secretive Shuttle-sized rocket codenamed ‘Black Ice’, according to its creator.
“And they are extremely important for everything from television to data all over the world. You can get data in the Kalahari Desert because there’s a satellite up there.”