The vehicle in the accident, VSS Enterprise, registration N339SS, was the sole Scaled Composites Model 339 SpaceShipTwo test vehicle.[3] It was the first of the five SpaceShipTwo craft planned by Virgin Galactic.[4] Since October 2010, VSS Enterprise had flown 20 captive flights while remaining attached to its WhiteKnightTwo carrier aircraft, 31 unpowered glide-to-landing tests, and three rocket-powered test flights.[citation needed] There were several performance issues during the ship engine's development in 2012 and 2013.[5][6]