Last week, Stratolaunch founder Paul Allen tweeted that the company’s signature plane, the largest in the world, reached a new top taxi speed of 46 miles per hour. The team has also shown for the first time that it can steer and stop the plane.

In May 2017, the Stratolaunch plane rolled out of its hangar in California for the first time to begin fuel tests. In the fall, Stratolaunch transitioned to stationary engine tests. These were incremental, with the engine’s power gradually increasing over time.

The plane is propelled by six jet engines which have been salvaged from two 747s. Additional components from the 747s were also utilized, including landing gear, windows, avionics, and actuators.

The aircraft is 238 ft. from nose to tail and stands 50 ft. tall from the ground to the top of the vertical tail. The airplane’s largest parts are four wing spars that are each more than 62 meters long. A team of 300 engineers and fabricators designed, built, and hand assembled the twin fuselage vehicle as an air launch platform with a payload capacity of about 550,000 lbs. The jet’s airframe is made mostly of CFRP, and due to the aicraft’s historic size, Stratolaunch has a building dedicated just to making the CFRP components.

While both fuselages on the carrier have windows, the three-person crew will fly in the right fuselage. The left fuselage is not human rated and thus will only house electronics.

Once operational, the Stratolaunch carrier aircraft will serve as a mobile launch platform for rockets including Orbital ATK’s Pegasus XL. It will carry the Pegasus from a carbon fiber aircraft designed by Scaled Composites – the same company that built WhiteKnightTwo (WK2) for Virgin Galactic.

While the next step in the timeline for Stratolaunch development is not yet known, as of last year, 2019 was cited as the target for the first launch. For more information, visit