PROPELLANT SELECTION

Current common practice is to divide chemical propellants into four classes liquids, solids, hybrids and thixotropes or gels. 

Traditionally the liquid systems are considered to be either bipropellants or mono-propellants although as discussed in later sections multicomponent systems are feasible. The most common liquid systems are the bipropellant ones in which the fuel and oxidizer are introduced separately into the rocket combustion chamber. 

The monopropellants are liquids which can undergo controlled exothermix decomposition, or combustion, reactions. As the prefix implies, only one liquid is injected into the combustion chamber. Various types of monopropellants are  

1) Single compounds which decompose exothermically such as hydrazine, -hydrogen peroxide, ethylene oxide, acetylene, etc. 

2) Single compounds which contain both fuel and oxidizing elements in a stable form at most ambient conditions but which decompose at elevated temperature into oxidizing and reducing fragments which subsequently react exothermically. Propyl nitrate falls into this class. 

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Solid Propellant Selection and Characterisation, Space Vehicle Design Criteria, Monograph no. SP 8064, NASA, Airport, Md., 1971. 

Monographs on rockets and rocket propellants by the National Aeronautics and Space Administration (NASA), Lewis Research Center, Cleveland. These iaclude the foUowiag Solid Propellant Selection and Characteri tion, Report SP-8064,1971 Solid Rocket Motor Peformance, Report SP-8039,1971 Solid Rocket Motor Igniters, Report SP-8051,1971 Solid Rocket Motor Metal Cases, Report SP-8025, 1970, and Captive Eire Testing of Solid Rocket Motors, Report SP-8041,1971. 

Adams, G. K., and Wiseman, L. A., The Combustion of Double-Base Propellants, Selected Combustion Problems, Butter-worth s Scientific Publications, London, 1954, pp. 277-288. 

The requirements for selecting a fuel and oxidizer as a liquid bipropellant system are usually a compromise between the demands of the vehicle system, the propulsion system, and the propellants themselves. The vehicle and propulsion system will determine performance levels, physical property requirements, thermal requirements, auxiliary combustion requirements, degree of storability and package-ability, hypergolicity, etc. The final propellant selection must not only satisfy such requirements but is also dictated by thermochemical demands which the fuel and oxidizer make on each other. Frequently, specifically required properties are achieved through the use of chemical additives and/or propellant blending. 

Gun propellants are manufactured by three different methods (i) solvent method (ii) semi-solvent method and (iii) solventless method. The solvent method is that most commonly used for the manufacture of gun propellants. Selection of the method for manufacture basically depends on the properties of the raw materials and the propellant formulation. While there are limitations for the manufacture of gun propellants by solventless and semi-solvent methods, the solvent method may be applied for almost every gun propellant formulation. The solid-liquid ratio of the ingredients and the type of nitrocellulose used usually decide the feasibility of manufacture by the solventless method. Some characteristics of solid gun propellants are given in Table 4.1. 

The specimen shall consist of a portion of propellant selected in accordance with the applicable propellant specification, and weighed in accordance with the test method used. 

In addition to specific impulse, the vehicle requirements usually influence propellant selection in terms of storability, density, toxicity, and other hazards, and other application-sensitive factors, including exhaust plume properties and radar cross section and radiation emissions. Other factors being essentially equal, the higher the heat of reaction of a propellant (or combination). Hie more attractive die propellant. Sharp exceptions to this rule occur in some missiles because of volume limitations, the need for smokeless exhaust or similar restraints. 

Propellant selection then should consider density, as well as specific impulse. For pure terrestrial weapon systems other considerations such as reliability, readibili-ty, cost, are also of importance. Other desirable properties of propellants are detailed below. 

Propellant selection for arcjet propulsion devices is likely to be made on the basis of availability rather than maximum performance. Arcjet propulsors have the uncommon characteristic of operational capability using practically any material as the propellant. Because of the high temperatures of operation, all propellants which might be used would be reduced largely to atomic species in the arc chamber. 

In combustion rockets, the combustion temperature is not directly available as a design parameter but rather is determined by the propellant selection, mixture ratio and combustion pressure. In heat transfer rockets however, the initial temperature of the propellant, that is, the stagnation temperature of the propellant, is available as a design parameter. It is probably sufficient to say that the propellant stagnation temperature should be maximized for maximum performance. 

Titan I utilized kerosene and LOX as propellant the Titan II ICBM development required earth-storable propellant selection. 

Bombelli, V, Maree, T., and Caramelli, F., Non-toxic liquid propellant selection method—A requirement-oriented approach, in 41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Tucson, AZ July 2005 (AIAA 2005-4453). 

Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

R. A. McKay,M Study of Selected Parameters in S olid Propellant Processing,]et Propulsion Lab, Pasadena, Calif., Aug. 1986 J. L. Brown and co-workers. Manufacturing Technologyfor SolidPropellantIngredients/Preparation Reclamation, Morton Thiokol, Inc., Brigham City, Utah, Apt. 1985 W. P. Sampson, Eow Cost Continuous Processing of Solid Rocket Propellant, Al-TR-90-008, Astronautics Laboiatoiy/TSTR, Edwards AEB, Oct. 1990. 

W. P. Killian, "Loading Composite Sohd Propellant Rockets—Cuiient Technology," Proceedings Symposium on Selected Topics in Aerospace Chemistry, 64th National Meeting AlCE, Odando, Fla., 1968. 

F. A. Warren, "SoHd Propellant Technology," ia R. A. Gess, ed.. Selected Reprint Series, AIAA, New York, 1970. 

Most schemes that have been proposed to propel starships involve plasmas. Schemes differ both in the selection of matter for propulsion and the way it is energi2ed for ejection. Some proposals involve onboard storage of mass to be ejected, as in modem rockets, and others consider acquisition of matter from space or the picking up of pellets, and their momentum, which are accelerated from within the solar system (184,185). Energy acquisition from earth-based lasers also has been considered, but most interstellar propulsion ideas involve nuclear fusion energy both magnetic, ie, mirror and toroidal, and inertial, ie, laser and ion-beam, fusion schemes have been considered (186—190). 

Propeller size, pitch, and rotational speed may be selected by model tests, by experience with similar operations, or, in a few cases, by published correlations of performance data such as mixing time or heat transfer. The propeller diameter and motor power should be the minimum which meet process requirements. 

FIG. 23-30 Basic stirred tank design and selected lands of impellers, (h) Propeller, (c) Turbine, (d) Hollow, (e) Anchor,... 

In order to reduce or eliminate off-line sample preparation, multidimensional chromatographic techniques have been employed in these difficult analyses. LC-GC has been employed in numerous applications that involve the analysis of poisonous compounds or metabolites from biological matrices such as fats and tissues, while GC-GC has been employed for complex samples, such as arson propellants and for samples in which special selectivity, such as chiral recognition, is required. Other techniques include on-line sample preparation methods, such as supercritical fluid extraction (SFE)-GC and LC-GC-GC. In many of these applications, the chromatographic method is coupled to mass spectrometry or another spectrometiic detector for final confirmation of the analyte identity, as required by many courts of law. 

Propeller/paddle mixers are used to blend or agitate liquid mixtures in tanks, pipelines, or vessels. Figure 38.1 illustrates a typical top-entering propeller/paddle mixer. This unit consists of an electric motor, a mounting bracket, an extended shaft, and one or more impeller(s) or pro-peller(s). Materials of construction range from bronze to stainless steel, which are selected based on the particular requirements of the application. 

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