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NASA Glenn Research Center and the Department of Energy (DOE) are developing a Stirling converter for an advanced radioisotope power system to provide spacecraft on-board electric power for NASA deep space missions. NASA Glenn is addressing key technology issues through the use of two NASA Phase II SBIRs with Stirling Technology Company (STC) of Kennewick, WA. Under the first SBIR, STC demonstrated a parallel connection of two thermodynamically independent free-piston Stirling converters and a 40 to 50 fold reduction in vibrations compared to an unbalanced converter. The second SBIR is for the development of an Adaptive Vibration Reduction System (AVRS) that will practically eliminate vibrations over an entire mission lifetime, even with one failed converter. This paper discusses the status and results for these two SBIR projects and also presents results for characterizing the friction factor of high-porosity random fiber regenerators that were evaluated for this application.

An efficient finite difference (FD) computational code has been developed for the analysis and design of circular sector radiators for linear alternator output “Free Piston Stirling Engine” space power systems utilizing a radioisotope Pu-238 General Purpose (GPHS) heat source. The code calls on a subroutine developed by the author to solve the second order, fourth degree, ordinary differential equation (ODE) of a fin (extended heat transfer surface) radiating to the space environment. Although the code was originally written for a rectangular coordinates system, it was transcribed into polar (cylindrical) coordinates for the present application. The circular sector radiator panel analyzed has an embedded heat pipe at an arbitrary radial location conducting cycle reject heat from the Stirling engine cold end to the radiator.

This paper presents an update on the NASA Lewis Stirling component technology program. The component technology program has been organized as part of the NASA Lewis effort to develop Stirling converter technology for space power applications. The Stirling space power program is part of the High Capacity Power element of the NASA Civil Space Technology Initiative (CSTI). Lewis is also providing technical management of a DOE-funded project to develop Stirling converter systems for distributed dish solar terrestrial power applications. The Lewis component technology program is coordinated with the primary contract efforts of these projects but is aimed at longer term issues, advanced technologies, and independent assessments. Topics to be discussed include bearings, linear alternators, controls and load interaction, materials/life assessment, and heat exchangers.

A Stirling engine digital computer model developed at NASA Lewis Research Center has been configured to predict the performance of the GPU-3 single-cylinder rhombic drive engine. Revisions to the basic equations and assumptions previously reported on are discussed. Initial comparisons of the model predictions with the early results of the Lewis Research Center GPU-3 tests are made.