The Stratolaunch aircraft, the world's largest aircraft by wingspan, started the latest phase of taxi testing last month in California, reaching a top speed 46 mph (74 km/h).
The aircraft uses six Pratt & Whitney turbofan engines, features a payload capacity of over 500,000 lbs (226.79 tonnes) and has an operational range of approximately 2,000 nautical miles. The aircraft has a wingspan of 385 ft (117.3 m) and a length of 238 ft (72.5 m).
The first low-speed taxi tests were completed in December 2017 and tested the aircraft's ability to steer and stop. The ground team monitored a number of the systems including steering, braking, anti-skid and telemetry.
Since the first engine runs in September, Stratolaunch has performed a series of engine tests from the Stratolaunch Mission Control Center (MCC), located at the Mojave Air & Space Port. The MCC serves as Stratolaunch's hub for communications testing and will eventually be the centre of its aircraft and launch operations.
Stratolaunch aims to be fully operational by the end of this decade and will serve as a mobile launch platform for rockets.