Analysis of solar and microwave thermal propulsion systems.

摘要

Theoretical models are developed to assess the conceptual feasibility of employing solar and microwave energy to heat a propellant gas and generate thrust. Both these advanced electrothermal propulsion concepts promise high specific impulses and are, therefore, being considered as alternatives to chemical propulsion for space-based applications. The present research addresses two major feasibility issues: (1) the efficient coupling of electromagnetic energy to the propellant, and (2) the performance capabilities of these systems.; Physical modeling of the direct absorption of solar radiation in gases involves the solution of the thermal radiation problem within the thruster. The absorption of the incident beam is modeled by a ray-tracing technique while the reradiation of the heated gas is treated by a thick-thin model. The thick-thin model is calibrated by the P-1 model and an exact integral method. Spectral dependence of the radiative properties is handled by a band model. Results for different thruster sizes indicate that high energy conversion efficiencies are possible if a combination of direct and indirect heating is used; part of the incident radiation is absorbed directly by the gas while the remainder is absorbed on a regeneratively cooled wall. Performance predictions for the thruster indicate specific impulses in the range of 500 to 650 s for moderate gas pressures (1 to 10 atm); at higher pressures, better performance is possible but structural considerations are likely to play a limiting role.; The analysis of the microwave problem involves the coupled solution of the Navier-Stokes equations for the gasdynamics and the Maxwell equations for the microwaves. Time-marching techniques are employed for the solution of both equation sets. Local thermal equilibrium is assumed for the plasma. Computational results are in good agreement with experimental data for resonant cavity plasmas--peak plasma temperatures are between 9000 and 10,000 K and high coupling efficiencies (up to 100%) are predicted. Parametric studies are performed to extend the results to high power and high pressure regimes.