WhiteKnightTwo (WK2, also dubbed "EVE" by Virgin Galactic's Sir Richard Branson), which will serve as the launch vehicle for Virgin Galactic's SpaceShipTwo (SS2), has expanded its flight envelope with a third test flight that took the aircraft to 140 knots and 18,000 feet. The flight also tested engine thrust asymmetry parameters and in-flight engine restarts. Burt Rutan, founder of Scaled Composites, which has been instrumental in the development of the vehicles, believes WK2 will ultimately find niche applications "beyond the initial requirements of Virgin Galactic." Powered by four Pratt & Whitney Canada PW308A engines and slung below a 140-foot carbon composite wing spar, WK2 is designed for a payload capacity of more than 37,000 pounds and a "coast-to-coast" range. Tests to 50,000 feet (SS2's launch altitude) are expected to take place during the next few months. As for the huge aircraft's flight characteristics, pilot Peter Siebold commented that the aircraft "might look unique from the ground" but "it is not strange to fly" and is "in fact a great piloting experience." Rutan believes the capabilities of WK2 will find it work outside of space tourism, as well.

WK2 "has the power, strength and maneuverability to provide for pre space-flight, positive G force and zero G astronaut training as well as a lift capability which is over 30% greater than that represented by a fully crewed SpaceShipTwo," according to a press release from Virgin Galactic. The company suggests that some other missions for which WK2's unique design might be well-suited include launching satellites into low Earth orbit via unmanned rockets that WK2 would carry aloft. For its role carrying space tourists aboard SS2, the aircraft will need to take off from a normal runway and carry SS2 to an altitude of about 50,000 feet, where that vehicle will initiate its launch.