Friday's flight marked the 55th for SpaceShipTwo, which was intended to be the first of a fleet of craft. This was only the fourth flight to include a brief rocket firing.
The rocket fires after the spacecraft is released from the underside of a larger carrying plane. During other flights, the craft either was not released from its mother ship or functioned as a glider after release.
The spacecraft broke up after being released from a carrier aircraft at high altitude, according to Ken Brown, a photographer who witnessed the accident.
SpaceShipTwo is based on aerospace design maverick Burt Rutan's award-winning SpaceShipOne prototype, which became the first privately financed manned rocket to reach space in 2004. Three people died in a blast at the Mojave Air and Space Port in 2007 while testing a rocket motor for SpaceShipTwo.
