Aerospace manufacturing is a high-technology industry that produces "aircraft, guided missiles, space vehicles, aircraft engines, propulsion units, and related parts". Most of the industry is geared toward governmental work. Aerospace engineers may develop new technologies for use in aviation, defense systems, and spacecraft. They often specialize in areas such as aerodynamic fluid flow; structural design; guidance, navigation, and control; instrumentation and communication; robotics; and propulsion and combustion.