Energy End-Use Efficiency, Policy and Economics

Project Title:
Integrating power conversion and electric propulsion

Principle Investigator(s):
Raymond Sedwick (Aerospace Eng.)

Abstract:
The use of electric propulsion in space is often limited more by inefficiencies in the power convesion system than by inefficiencies in the propulsion system itself. Examples include photovoltaic conversion (18-25%), thermoelectric conversion (10-15%) and thermodynamic conversion (25-30%). In the last case, the limiting factor is the desire to minimize system mass, typically by allowing the radiator to run at a higher temperature than otherwise desirable. If one considers the cases of solar thermal or chemical propulsion systems, a favorable condition occurs where there exists both a high temperature heat source (concentrated solar flux or chemical combustion) and a low temperature heat sink (propellant flow from tank). If sufficient mass flow exists, then an efficient power cycle can be operated between these reservoirs, with the resulting electrical power used to enhance operation as an electrothermal arcjet. In addition, the waste heat of the cycle appears in the propellant stream, so that while the conversion efficiency of the cycle is only 80-90%, the theoretical conversion efficiency of the system is 100%.

Figure 1. Direct use of waste heat in a solar thermal thruster (left)
and dual mode chemical/electrical thruster (right)

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