Preliminary design of a space propulsion system utilizing stored thermal energy

Abstract

A space propulsion system utilizing stored thermal energy is analyzed with emphasis on the preliminary design of the heat exchanger and on the general performance of engines incorporating this concept. A highenergy propellant is developed by heat transfer from a phase-change material (Si) to a low-density gas (H2) through a concentric cylinder heat exchanger. The phase-change material is heated by a radioisotope (PoGd) over a period of time which is significantly longer than the firing time. It is shown that such an engine can most efficiently operate just above and just below a propellant flow regime defined by gradual flow transition in the heat exchanger. Two designs are developed to illustrate each distinct operating scenario. A 10-N engine utilizing laminar flow is shown to be an attractive alternative to chemical and electric systems for the maneuvering of a vehicle in the vicinity of a larger space structure. A 450-N engine utilizing primarily turbulent heat transfer is shown to be an alternative to other systems for orbit transfer. Rapid cooling of the thermal storage material in the entrance region of the heat exchanger, which can be mitigated by varying the flow area or increasing the length of the engine, is a primary limitation on an engine utilizing thermal storage.