Other propulsion systems

Several other types of propulsion systems have been proposed which do not fall logically into the preceding categories. Photon rockets would produce thrust at 

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Assuming that the current programs in electric propulsion are successful, and that the required efficiencies and specific weights are attained, what are the advantages of this propulsion system over others such as chemical or nuclear rockets Using the trajectory theories [2, 3,16], the initial weights and payloads for a number of missions have been estimated and compared with those needed with other propulsion systems. 

Furthermore, three practical examples of application can be named for traction batteries with economic use compared to other propulsion systems ... 

The improvement of human control over inanimate forms of energy, put to use to military ends, has improved the logistics and coordination aspects of armies and navies, and increased the overall destructive capacity of humanity. Energy-efficient propulsion systems have reduced the costs and increased the ranges of various forms of transportation, both militai y and civilian. For the militai y, energy is both a blessing and a vulnerability, requiring ever-more-specialized soldiers and more expensive equipment to remain effective in the face of competition from other modern military forces. 

Only chemical propulsion will be further discussed, and in particular, that associated with liquid, solid, and hybrid motors and engines. These motors and engines are uniquely different from other chemical propulsion systems in that they carry on board the necessary propellants, as contrasted to jet engines that rely on atmospheric oxygen for combustion of the fuel. 

The prediction of burning-rate characteristics, on the other hand, has not been possible. This has caused rocket designers to adopt a trial-and-error approach to the development of specific propellants to meet specific mission requirements. In an effort to reduce the large development effort required for each new propulsion system, considerable basic research effort has been directed toward the definition and quantitative characterization of propellant combustion mechanisms. The ultimate objective of this effort is to provide methods for predicting the burning-rate characteristics of particular propellant formulations. 

Besides fuel-cell (electric) vehicles (FCV), there are other vehicle concepts under development, which are also based on electric drives ranked by increasing battery involvement in the propulsion system, and thus extended battery driving range, these are hybrid-electric vehicles (HEV), plug-in hybrid-electric vehicles (PHEV) - which both incorporate an ICE - and, finally, pure battery-electric vehicles (BEV), without an ICE. While electric mobility in its broadest sense refers to all electric-drive vehicles, that is, vehicles with an electric-drive motor powered by batteries, a fuel cell, or a hybrid drive train, the focus in this chapter is on (primarily) battery-driven vehicles, i.e., BEV and PHEV, simply referred to as electric vehicles in the following. 

In standard internal combustion engine drive trains, about 60% of the added value results from the vehicle industry. This share may be reduced to only 10% for fuel-cell drive trains if the outsourcing potential is fully exploited. This shift is because the components of the fuel-cell propulsion system are not suited to current production structures in the automobile industry. Therefore, it can initially be assumed that they will be manufactured by other sectors. However, if there is a breakthrough of fuel cells, it is possible that the automobile industry will start to manufacture many of the components that are assigned to other sectors in Figure 13.13. 

Other applications include car rental, shared-car ownership or public transport -these transfer the risk of ownership of a vehicle with a new propulsion system away from the private person. Once established, these niche applications can help to raise the profile of the new technology, increase public acceptance and provide opportunities for feedback that can lead to technology improvement. Once their commercial viability in the niche market has been proved, the vehicles can expand into wider markets. Particularly suitable for introducing hydrogen (or other alternative fuels) are buses, fleet vehicles and rental vehicles (Smith, 2001). 

Although several different system configurations have been simulated, the focus of this paper will be on the unsteady, compressible, multiphase flow in an axisymmetric ramjet combustor. After a brief discussion of the details of the geometry and the numerical model in the next section, a series of numerical simulations in which the physical complexity of the problem solved has been systematically increased are presented. For each case, the significance of the results for the combustion of high-energy fuels is elucidated. Finally, the overall accomplishments and the potential impact of the research for the simulation of other advanced chemical propulsion systems are discussed. 

Cesium is used as a getter in electron tubes. Other applications are in photoelectric cells ion propulsion systems heat transfer fluid in power generators and atomic clocks. The radioactive Cs-37 has prospective applications in sterilization of wheat, flour, and potatoes. 

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. 

Other MAF fuels, MAF-1 (DETA-UDMH-acetonitrile, 50-40-10), and MAF-3 (UDMH-DETA, 20-80) were formulated primarily to increase density. These formulations were based on density impulse requirements of various prepackaged propulsion systems as well as to maintain the freezing point and viscosity characteristics of the UDMH. 

As a result of this constant evaluation and compromise between the demands of the vehicle and propulsion systems and the current propellant technology, various liquid propellant systems have been developed and are being applied in current vehicle systems (Table IV). In Table IV thrust level is used to demonstrate the size of the propulsion system. Some of the systems in this table have been phased out, while others are still in development. However, Table IV does represent the current status of operational liquid bipropellant systems. 

Status of Technology. At present only one heterogeneous fuel, aluminum in gelled hydrazine (42), has been thoroughly developed and evaluated extensively in a static propulsion system. Other metal-containing fuels are being developed, but fuels based on the metal hydrides are... 

Thirdly, if new molecules could be synthesized which were to maximize properties and energy, such molecules could be useful even if costly. Much effort has been expended toward synthesizing new compounds for use as liquid propellants. Since that area of the propellant industry is the subject of two other chapters in this volume, I will avoid any detailed discussion of this area. However, in many tactical weapons systems, propellants can be used whose costs would normally be considered prohibitive for a propulsion application. This results from the fact that the rest of the missile propulsion, guidance, and warhead systems are so expensive and the amount of propellant so small that propellants costs become unimportant. The larger the missile becomes, and the more propellant it contains, the greater becomes the consideration of propellant cost. However, the fact that propellant cost may not be crucial has justified much research to prepare new propellants. In fact, several new propellant or propellant ingredients have been synthesized and will find their way into propulsion systems. 

Most of the propulsion systems recorded in Tables 73 and 74 are only suggestions for the future or in development. Some of them would require chemicals which are produced only on a laboratory scale. Others would need chemicals whose properties and methods of production are often insufficiently known. 

According to Refs 1,2 and 4, Aerozine-50 (UDMH/hydrazine—50/50 wt %) is used as the first stage fuel in the ICB Titan Missile system. This fuel provides a minimal make-ready and launch time as compared to a solid propint system. However, since 1975 there have been 125 reported accidents involving complete missile systems using this fuel. Indeed, ref 3 reports that, Two airmen have been killed and nearly 80 injured, some seriously, as the result of leaks in the missiles fuel and propulsion systems and other accidents. 

Compared with the almost limitless number of chemical compounds that exist or can be formed, the number of chemical propellants in common use is relatively few. This situation arises from criteria including costs, source availability, toxicity, resistance to shock, and other requirements imposed by the vehicle application and the propulsion system design. Another practical reason is that extensive overlap of physical, chemical, and economic properties are displayed by many of the theoretically possible propellants. During the 1960s, the universities, industry, and government in the United States pursued extensive research programs for synthesizing new chemical compounds viewed as candidate propellants,... 

The advantages of a monopropellant over a bipropellant combination result primarily from a substantial reduction in the number of components in the tankage and flow hardware. The attractive simplications in the propulsion system resulting from the use of monopropellants are obtained only at the expense of a reduced specific impulse. The resulting implied trade-off between simplicity and propellant performance limits the attractiveness of monopropellants to propulsion systems where a simplicity and the usually associated reliability which comes with simplicity are premium desired characteristics. Typical applications have included attitude control rockets, vernier rockets for mid-course trajectory corrections, and other low thrust propulsors, especially those having a requirement for pulsed operation or repeated restarts. Monopropellants also find application as a source of relatively low temperature working fluids, as for driving gas turbines. 

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