The classification of liquid propellants has been given in Section 6.1 of the preceding chapter. In this chapter we discuss properties, performance, and characteristics of selected common liquid propellants. These characteristics affect the engine design, test facilities, propellant storage and handling. Today we commonly use three liquid bipropellant combinations. Each of their propellants will be described further in this chapter. They are: (1) the cryogenic oxygen-hydrogen propellant system, used in upper stages and sometimes booster stages of space launch vehicles; it gives the highest specific impulse for a non-toxic combination, which makes it best for high vehicle velocity missions; (2) the liquid oxygen-hydrocarbon propellant combination, used for booster stages (and a few second stages) of space launch vehicles; its higher average density allows a more compact booster stage, when compared to the first combination; also, historically, it was developed before the first combination and was originally used for ballistic missiles; (3) several storable propellant combinations, used in large rocket engines for first and second stages of ballistic missiles and in almost all bipropellant low-thrust, auxiliary or reaction control rocket engines (this term is defined below); they allow long-term storage and almost instant readiness to start without the delays and precautions that come with cryogenic propellants. In Russia the nitric acid-hydrocarbon combination was used in ballistic missiles many years ago. Today Russia and China favor nitrogen tetroxide-unsymmetrical dimethylhydrazine or UDMH for ballistic missiles and auxiliary engines. The USA started with nitrogen tetroxide and a fuel mixture of 50% UDMH with 50% hydrazine in the Titan missile. For auxiliary engines in many satellites and upper stages the USA has used the bipropellant of nitrogen tetroxide with monomethylhydrazine. The orbit maneuvering system of the Space Shuttle uses it. Alternatively, many US satellites have used monopropellant hydrazine for auxiliary engines.
A comparative listing of various performance quantities for a number of propellant combinations is given in Table 5-5 and in Ref. 7-1. Some important physical properties of various propellants are given in Table 7-1. For comparison water is also listed. Specific gravities and vapor pressures are shown in Figs. 7-1 and 7-2.
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