This is an injection-plastic jet aircraft model kit.
From the manufacturer:
The White Knight airplane was developed in 2002 by Scaled Composites Company as a jet-powered carrier of the SpaceShipOne (SS-1) experimental spacecraft. The SS-1 manned suborbital nonexpendable spacecraft was built one year later. Both air vehicles have been built almost completely from composite materials. Flight starts with a jet-powered carrier takeoff, and it climbs until 15km, where the passenger spacecraft is drop-released. SS-1 straightens itself out about 10 s. and siwtches its rocket engine on after that. That brings the spacecraft nearly vertical, with an acceleration lasting a little bit more than 1 minute. During that period, its maximum speed reaches 3,500km/h. At 100 km altitude, when the fuel is burned out, the SS-1 continues free flight. After that it experiences free fall, then gliding flight and glides down to a horizontal landing at the runway.