With its successful maiden flight on 21 December 2008 Scaled Composites WhiteKnightTwo mothership is expected to start carrier flight tests with its SpaceShipTwo (SS2) payload later in 2009.

The WK2 design, an all-composite airframe with a 42.7m wingspan, booms that give it a length of 23.7m and a tail height of 7.62m, was unveiled in January 2008. The experimental WK2 prototype was rolled out at Scaled Composites’ Mojave air and spaceport facility on 28 July.

Using four Pratt & Whitney Canada PW308A engines WK2 has a payload capacity of 17,000kg (37,400lb) to 50,000ft, a range of 4,200km (2,270nm) with SS2 attached, and will be capable of a Viking departure without it.

WhiteKnightTwo’s four engines are to ensure a take-off capability while carrying SS2 even with an engine out.

The WK2 mothership uses the same cabin design as SS2, allowing for pilots and space tourists to prepare for flights in the spaceship. The mothership’s two pilots will operate the aircraft from the right fuselage's cabin, looking at WK2 from a plan view, while passengers could one-day travel in the left fuselage to watch SS2 launches.

Designed for spaceline Virgin Galactic’s proposed suborbital service that is to begin in 2010 from New Mexico’s Spaceport America, it will take-off from a normal runway and carry the SS2 to around 50,000ft, release it and then return to the spaceport.