The Cambridge Dictionary of Space Technology defines a rocket as a propulsive device using a mixture of propellants which, upon ignition, provide a reaction force to propel a vehicle such as a missile, aircraft or spacecraft.

Typically, two separate chemical propellants are used, a fuel (such as liquid hydrogen or kerosene), and an oxidizer (such as liquid oxygen or nitrous oxide), which provides the oxygen to sustain a burning reaction. Rockets differ from similar propulsion systems such as gas turbine engines (jets) in that they carry both their fuel and oxidizer on board, thereby needing no intake oxygen to operate. Also, the performance possible with rockets make them ideal for vehicles such as spacecraft, which need to achieve large changes in momentum and high final velocities.

A rocket operates according to Newton’s third law of motion, which states, generally, that for every action there is an equal and opposite reaction. In a chemical rocket, the fuel and oxidizer are combined in a combustion chamber, where they are exposed to a source of ignition, causing a violent chemical reaction which produces hot, rapidly expanding gases. These gases are accelerated through a throat and nozzle, where they are ejected at very high velocity, thereby imparting a change of momentum to the vehicle.

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by Robert C. Truax, January 1999

Copyright © 2000 Aerospace America.   Reprinted with permission.

The story of turbopump rocket development is an interesting one of trial and error. Many sidelines were explored before the objectives of light weight and high performance were finally attained with the main engines for the Shuttle. Russian rocket development followed a somewhat similar path, and the end result was very similar: a topping cycle with high combustion chamber pressures.

But turbopump engines, whether high pressure or low, were a mistake from the very beginning. They simply are not worth what they cost in time and money. In all the early development efforts, pump-fed systems were preceded by a pressure-fed version. In every case, the mission was accomplished and the program goals met before the development of the pump system was completed. After the X-I broke the sound barrier with its pressure-fed rocket engine, who ever heard of the D-558-2 — powered by a pump-fed engine?

Technically simple two-stage launchers with pressure-fed engines and ocean recovery offer the economical operations that have escaped our high-technology turbopump rockets for more than four decades.

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