A rocket plane is an aircraft that uses a rocket for propulsion, possibly in addition to jet engines. Rocket planes can achieve much higher speeds than similarly-sized jet aircraft, but for much shorter periods of operation, typically only a few minutes. Because of the expense and the various practical difficulties of operating rockets, these are poor choices for most aviation needs, and so are invariably specialised, mostly experimental, aircraft.
The first rocket-powered aircraft was the Lippisch Ente, flown in 1928. The only rocket plane ever to be mass-produced was the Messerschmitt Me 163 in 1944, one of several German World War II attempts at rocket-powered aircraft.
The first truly successful rocket plane was the North American X-15, which was used for several years and eventually broke Mach 6.0.
The development of SpaceShipOne, first flown in 2003, suggests that rocket planes may become more common, as spaceplanes are one of very few practical ways to reach space.
