- Propulsion comes from a greek word propellene which means Push
- Theory of rocket is different from theory of bullet fired from a gun in such a way that as the rocket propels , it burns the fuel and gets lighter and faster.
Basic principles of propulsion
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
propulsion concepts according to their energy source and type of propellant. Radiant
energy may originate from sources other than the sun and theoretically includes the
transmission of energy by ground-based microwaves and laser beams. Nuclear energy
originates in transformations of mass within atomic nuclei and is generated by either
fission or fusion. Energy sources are central to rocket performance and several kinds,
both within and external to the vehicle, have been investigated.
The useful energy input modes in rocket propulsion systems are either heat or electricity. Useful output
thrust comes from the kinetic energy of the ejected matter and from the propellant
pressure on inner chamber walls and at the nozzle exit; thus, rocket propulsion systems primarily convert input energies into the kinetic energy of the exhausted gas.
The ejected mass can be in a solid, liquid, or gaseous state. Often, combinations of
two or more phases are ejected. At very high temperatures, ejected matter can also
be in a plasma state, which is an electrically conducting gas
Alpha Rocketry 