In general terms, propulsion is the act of changing the motion of a body with respect to an inertial reference frame. Propulsion systems provide forces that either move bodies initially at rest or change their velocity or that overcome retarding forces when bodies are propelled through a viscous medium. The word propulsion comes from the Latin propulsus, which is the past participle of the verb propellere, meaning “to drive away.” Jet propulsion is a type of motion whereby a reaction force is imparted to a vehicle by the momentum of ejected matter.

Rocket propulsion is a class of jet propulsion that produces thrust by ejecting matter, called the working fluid or propellant, stored entirely in the flying vehicle. Duct propulsion is another class of jet propulsion and it includes turbojets and ramjets; these engines are more commonly called air‐breathing engines. Duct propulsion devices mostly utilize their surrounding medium as the propellant, energized by its combustion with the vehicle's stored fuel. Combinations of rockets and duct propulsion devices have been attractive for some applications, and one is briefly described in this chapter.

The energy source most commonly used in rocket propulsion is chemical combustion. Energy can also be supplied by solar radiation and by a nuclear reactor. Accordingly, the various propulsion devices in use can be divided into chemical propulsion, nuclear propulsion, and solar propulsion. Table 1–1 lists many important ...

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