Study of the Factors Affecting the Efficiency in Thermal Acceleration of Propellants

The report describes the experimental and analytical work conducted to study the various influences affecting the operating characteristics of electrothermal accelerators. A survey of the testing facilities, including vacuum systems, resistance heaters, and liquid metal heaters is given. The experimental work conducted with hydrogen, helium, ammonia, nitrogen, oxygen, and argon at temperatures ranging from 300K to 3000K is described. Conical and annular nozzles are compared with simple cylindrical throats, and the experimental and analytical expressions relative to their behavior are included. Outlined are the development of low pressure arc heaters and the experiments which led, for the first time, to the attainment of specific impulse levels of over 10,000 seconds using hydrogen. Performance comparisons between resistance and arc heating and associated anomalies using ammonia are also discussed. The behavior of self-magnetic fields in the arc heater is explained, together with the effects of externally applied magnetic fields ranging from 500 to 12,000 gauss. Included are operation at low mass flow rates and the development of arc heaters working without propellant throughput using electrode vapors or residual ambient gas as the working fluid.