Its latest outing has seen the team clock the gargantuan dual-fuselage plane at speeds approaching those typically needed for regular aircraft to lift-off on the runway.

With a massive wingspan of 385 ft (117 m), the Stratolaunch plane tips the scales at 500,000 lb (226,000 kg) and is built to accommodate payloads up to 550,000 lb (249,476 kg). If it does eventually take flight it will be the largest plane ever to do so, and its creators hope it can become the first commercial air-launch vehicle capable of delivering small payloads to various Earth orbits.

This would work in a similar way to Virgin Orbit's Cosmic Girl aircraft, which is also making promising strides, heading upward to a designated altitude before firing a separate launch vehicle into orbit and then returning to the runway for another mission.