Scaled Composites’ Stratolaunch is the largest airplane in existence by wingspan, which is an insane 385 feet. It needs to be this big because this twin-fusalage’d aircraft isn’t really an aircraft at all—it’s an airborne rocket launching pad. This taxi test of the plane gives a good sense of just how huge this thing is.
It looks like it should be CGI, right? Look how tiny that chase truck is there.
The Stratolauncher is capable of holding a 550,000 pound payload in the section between the two fuselages (only the right one is pressurized and carries crew; the left one is unpressurized and mostly empty save for flight data systems). That payload will most likely be a Pegasus XL rocket, which can launch payloads into low earth orbit.
Interestingly, much of the Stratolauncher’s systems are adapted from a Boeing 747-400, which is where the engines, avionics, landing gear, flight deck, and other systems are adapted from.
The Stratolauncher essentially takes the place of an expensive, normally non-reusable first stage, getting the rocket to an altitude high enough to allow smaller rocket stages to complete the job effectively. Currently, this role is being played by a Lockheed L-1011, but the new Stratolauncher should provide much more capability.
But, for the moment, it’s just taxi-ing across a runway, looking massive and strange.