Stratolaunch's rocket-launching mothership was driven down the runway for the first time this past weekend.

The double-bodied jet —which has the largest wingspan of any aircraft in the world —has been undergoing tests at Stratolaunch's facility at the Mojave Air and Space Port in California. The latest phase in this process was testing the aircraft's steering and stopping capabilities.

Video footage of the taxi test showed the plane rolling along at a slow speed. Afterward, Stratolaunch officials said the vehicle's steering, braking, anti-skid and telemetry systems all operated as anticipated.

"Our crew was able to demonstrate ground directional control with nose gear steering, and our brake systems were exercised successfully on the runway,"George Bugg, Stratolaunch's aircraft program manager, said in a statement. "Our first low speed taxi test is a very important step toward first flight. We are all proud and excited." [Supersonic! The 11 Fastest Military Airplanes]

The private spaceflight company Stratolaunch is the brainchild of Microsoft co-founder Paul Allen. The carrier plane is designed to make a runway-style takeoff and then, at cruising altitude, deploy rockets that can launch small satellites into low-Earth orbit.

The monster jet was only rolled out from its scaffolding in May. This weekend's latest milestone comes three months after the company successfully tested the six engines on the colossal airplane for the first time. Stratolaunch officials have said they hope to have the aircraft in flight by the end of the decade, and the Mojave Air and Space Port will eventually be the company's center of operations.

The aircraft weighs 500,000 lbs. (227,000 kilograms), and it can carry another 550,000 lbs. (almost 250,000 kg) with up to three rockets under the conjoined wing at the center of the vehicle. Its wingspan is longer than a football field, measuring 386 feet (118 meters) across.

The aircraft was built by Scaled Composites, the Mojave-based aerospace company founded by spaceship builder Burt Rutan. Scaled Composites is also behind the design for White Knight Two, the mothership built to launch Virgin Galactic’s tourist-carrying space plane.

Original article on Live Science.