Thermal rockets

The thermal rockets, other than chemical rockets,. currently at the furthest state of development are surface heat transfer rockets. The term surface heat transfer is used to imply that thermal energy is transferred to the propellant through a material wall. Many sources of the thermal energy are possible and include solid core nuclear reactors, radioisotopes, electrical resistance heaters, and solar heaters. 

As for chemical thermal rockets, the performance of the rocket vehicle depends strongly upon propellant specific impulse which in turn is dependent upon the enthalpy change during the expansion process. 

Species Molecular Weight Enthalpy (h°-h2ge) kcal/gm 2000°K 3000°K 4000°K  

The enthalpy contents of some candidate heat transfer rocket propellants are presented in table IV. E. 1. These enthalpies are referenced to the enthalpy of the same specie at the standard conditions of one atmosphere pressure and 298°K. 

This case represents frozen composition expansion in the nozzle. The enthalpy contents of some candidate heat transfer rocket propellants in their respective equilibrium compositions at a pressure of one atmosphere and selected temperatures are recorded in table IV.E. 2. The enthalpies of this table are referenced to the enthalpy the propellant would have at its equilibrium composition at the standard conditions of one atmosphere pressure and 298°K. This case is that of equilibrium composition expansion in the nozzle. 

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Direct heating thermal rockets are distinguished from heat transfer thermal rockets in that the energy transfer does not occur through a material wall. Such devices include the arcjet, which already has been mentioned, liquid and gaseous core nuclear rockets, and nuclear bomb propulsion. Most of the previous discussion applies directly to the selection of a propellant for an arcjet propulsion device. In reality even the arcjet performance is temperature limited--except in this case the propellant acts to heat the wall rather than the reverse. 

A thermal rocket of recent development which produces low thrust and specific impulse for satellite control purposes is the subliming propellant rocket. In this rocket the propellant is ordinarily a high vapor pressure solid. Propellant flow rate is controlled by the addition of heat to the subliming propellant. Desirable properties of propellants for such rockets is stability in the solid phase, high vapor pressure, and, as for all thermal rocket propellants, low molecular weight of the vapor produced. 

In principle, emission spectroscopy can be applied to both atoms and molecules. Molecular infrared emission, or blackbody radiation played an important role in the early development of quantum mechanics and has been used for the analysis of hot gases generated by flames and rocket exhausts. Although the availability of FT-IR instrumentation extended the application of IR emission spectroscopy to a wider array of samples, its applications remain limited. For this reason IR emission is not considered further in this text. Molecular UV/Vis emission spectroscopy is of little importance since the thermal energies needed for excitation generally result in the sample s decomposition. 

Carbon—carbon composites for rocket nozzles or exit cones are usually made by weaving a 3D preform composed of radial, axial, and circumferential carbon or graphite fibers to near net shape, followed by densification to high densities. Because of the high relative volume cost of the process, looms have been designed for semiautomatic fabrication of parts, taking advantage of selective reinforcement placement for optimum thermal performance. 

The reaction with fluorine occurs spontaneously and explosively, even in the dark at low temperatures. This hydrogen—fluorine reaction is of interest in rocket propellant systems (99—102) (see Explosives and propellants, propellants). The reactions with chlorine and bromine are radical-chain reactions initiated by heat or radiation (103—105). The hydrogen-iodine reaction can be carried out thermally or catalyticaHy (106). 

Because of the use of ammonium perchlorate as a soHd oxidizer for rocket propeUants, the thermal decomposition has been much studied (29—32). Three separate activation energies have been observed for AP decompositions an activation energy of 123.8 kJ/mol (29.6 kcal/mol) is found below 240°C of 79.1 kj/mol (18.9 kcal/mol) above 240°C and finally, of 307.1 kj/mol (73.4 kcal/mol) between 400—440°C (33,34). Below 300°C, the equation... 

A siHcon carbide-bonded graphite material in which graphite particles are distributed through the siHcon carbide matrix has high thermal shock resistance and is suitable for appHcations including rocket nose cones and nozzles and other severe thermal shock environments (155) (see Ablative materials). 

Pyrolytic graphite was first produced in the late 1800s for lamp filaments. Today, it is produced in massive shapes, used for missile components, rocket nozzles, and aircraft brakes for advanced high performance aircraft. Pyrolytic graphite coated on surfaces or infiltrated into porous materials is also used in other appHcations, such as nuclear fuel particles, prosthetic devices, and high temperature thermal insulators. 

In contrast, there is also current interest in investigating PAN-based fibers in low thermal conductivity composites [62], Such fibers are carbonized at low temperature and offer a substitute to rayon-based carbon fibers in composites designed for solid rocket motor nozzles and exit cones. 

The first experiments with the thermal electric engine were conducted in Russia in 1929 by its inventor, Valentin P. Glushko, who later became a world-famous authority in rocket propulsion. For more than forty years, the United States and Russia have devoted many resources to research and development of various kinds of EREs. First tested in space by the Russians in 1964, these engines have found some limited applications in modern space technology. For more than two decades Russian weather and communication satellites have regularly used electric rocket engines for orbital stabilization. The first spacecraft to employ ERE for main propulsion was the American asteroid exploration probe Deep Space 1, launched in 1998. The performance of... 

Plastics will continue to be required in space applications from rockets to vehicles for landing on other planets. The space structures, reentry vehicles, and equipment such as antennas, sensors, and an astronaut s personal communication equipment that must operate outside the confines of a spaceship will encounter bizarre environments. Temperature extremes, thermal stresses, micrometeorites, and solar radiation are sample conditions that are being encountered successfully that include the use of plastics. 

Moorite Propellant. A series of rocket proplnts submitted to PicArsn for evaluation in 1949. They consisted of an oxidizer (such as K perchlorate) 70, and a cured rubber hydrocarbon plus accelerators, 30%. Although the examined samples proved to possess desirable props for rocket proplnt use, their thermal stability was poor and their press exponent undesirably high. It was concluded that further work was required on the method of prepn to eliminate these defects... 

Dynamic differential thermal analysis is used to measure the phase transitions of the polymer. IR is used to determine the degree of unsaturation in the polymer. Monitoring of the purity and raw is done commercially using gas phase chromatography for fractionization and R1 with UV absorption at 260 nanometers for polystyrene identification and measurement Polystyrene is one of the most widely used plastics because of fabrication ease and the wide spectrum of properties possible. Industries using styrene-based plastics are packaging, appliance, construction, automotive, radio and television, furniture, toy, houseware and baggage. Styrene is also used by the military as a binder in expls and rocket propints... 

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