Maurice A. White

Technology demonstration of a free-piston stirling advanced radioisotope space power system

Free-piston Stirling convertors (Stirling engine with integral linear alternator) are a mature technology with demonstrated long-life, maintenance-free, degradation-free operation exceeding 46,000 hours (5+ years) on one unit. Tens of thousands of hours have been accumulated on numerous systems in beta trials, plus more than 8 million flexure-hours (900 flexure-years) on the most critical component (flexure bearings), all with no failures when operated within specifications. Vibration is a key concern for Stirling convertors in space. Recent tests have demonstrated a factor of 50 reduction in vibration, relative to a single convertor, by coupling two convertors mechanically and electrically. Even though the measured vibration level is below Jet Propulsion Laboratory (JPL) specified vibration objectives, demonstration of an additional factor of 10 vibration reduction is pending with an active vibration reduction system. Stirling cycle efficiency is well established. A four-convertor 150-W(e) end of mission...

Technology development for a Stirling radioisotope power system

NASA Glenn Research Center and the Department of Energy are developing a Stirling convertor 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 synchronous connection of two thermodynamically independent free-piston Stirling convertors and a 40 to 50 fold reduction in vibrations compared to an unbalanced convertor. The second SBIR is for the development of an Adaptive Vibration Reduction System (AVRS) that will essentially eliminate vibrations over the mission lifetime, even in the unlikely event of a failed convertor. This paper presents the status and results for these two SBIR projects and also discusses a new NASA Glenn in-house project to provide supporting technology for the overall Stirling radioisotope power system development. Tasks for this new effort include convertor performance verification, controls development, heater head structural life assessment, magnet characterization and thermal aging tests, FEA analysis for a lightweight alternator concept, and demonstration of convertor operation under launch and orbit transfer load conditions.

Developing a Free-Piston Stirling Convertor for advanced radioisotope space power systems

The Department of Energy (DOE) has selected Free-Piston Stirling Convertors as a technology for future advanced radioisotope space power systems. In August 2000, DOE awarded competitive Phase I, Stirling Radioisotope Generator (SRG) power system integration contracts to three major aerospace contractors, resulting in SRG conceptual designs in February 2001. All three contractors based their designs on the Technology Demonstration Convertor (TDC) developed by Stirling Technology Company (STC) for DOE. The contract award to a single system integration contractor for Phases II and III of the SRG program is anticipated in late 2001. The first potential SRG mission is targeted for a Mars rover. This paper provides a description of the Flight Prototype (FP) Stirling convertor design as compared to the previous TDC design. The initial flight prototype units are already undergoing performance tuning at STC. The new design will be hermetically scaled and will provide a weight reduction from approximately 4.8 kg to...

Technology Development for a Stirling Radioisotope Power System for Deep Space Missions

Abstract NASA Glenn Research Center and the Department ofEnergy (DOE) are developing a Stirling convertor for anadvanced radioisotope power system to provide spacecrafton-board electric power for NASA deep space missions.NASA Glenn is addressing key technology issues throughthe use of two NASA Phase II SBIRs with Stirling Tech-nology Company (STC) of Kennewick, WA. Under thefirst SBIR, STC demonstrated a 40 to 50 fold reduction invibrations, compared to an unbalanced convertor, with asynchronous connection of two thermodynamically inde-pendent free-piston Stirling convertors. The second SBIRis for the development of an Adaptive Vibration Reduc-tion System (AVRS) that will essentially eliminate vibra-tions over a mission lifetime, even in the unlikely eventof a failed convertor. This paper discusses the status andresults for these two SBIR projects and also presents re-suits for characterizing the friction factor of high-porosityrandom fiber regenerators that are being used for thisapplication.

Stirling convertor performance mapping test results

The Department of Energy (DOE) has selected Free-Piston Stirling Convertors as a technology for future advanced radioisotope space power systems. In August 2000, DOE awarded competitive Phase I, Stirling Radioisotope Generator (SRG) power system integration contracts to three major aerospace contractors, resulting in SRG conceptual designs in February 2001. All three contractors based their designs on the Technology Demonstration Convertor (TDC) developed by Stirling Technology Company (STC) for DOE. The contract award to a single system integration contractor for Phases II and III of the SRG program is anticipated in late 2001. The first potential SRG mission is targeted for a Mars rover. Recent TDC performance data are provided in this paper, together with predictions from Stirling simulation models.

Preliminary test results from a free-piston Stirling engine technology demonstration program to support advanced radioisotope space power applications

Free-piston Stirling engines offer a relatively mature, proven, long-life technology that is well-suited for advanced, high-efficiency radioisotope space power systems. Contracts from DOE and NASA are being conducted by Stirling Technology Company (STC) for the purpose of demonstrating the Stirling technology in a configuration and power level that is representative of an eventual space power system. The long-term objective is to develop a power system with an efficiency exceeding 20% that can function with a high degree of reliability for up to 15 years on deep space missions. The current technology demonstration convertors (TDC’s) are completing shakedown testing and have recently demonstrated performance levels that are virtually identical to projections made during the preliminary design phase. This paper describes preliminary test results for power output, efficiency, and vibration levels. These early results demonstrate the ability of the free-piston Stirling technology to exceed objectives by appro...

Preliminary Design Of An Advanced Stirling System For Terrestrial Solar Energy Conversion

A preliminary design was generated for an Advanced Stirling Conversion System (ASCS) that will be capable of delivering about 25 kW of electric power to an electric utility grid. The Department of Energys (DOE) Solar Thermal Technology Program, Sandia National Laboratories (SNLA) is evaluating Stirling engines for terrestrial solar applications. As part of the DOE program, which is managed by NASA Lewis Research Center, a two-year task to complete detailed design, fabrication, assembly and testing of an ASCS prototype began in April, 1990. The ASCS is designed to deliver maximum power per year over a range of solar inputs with a design life of 30 years (60,000 hours). The ASCS has a long term cost goal of about

Status update of a free-piston Stirling convertor for radioisotope space power systems

450 per kilowatt, exclusive of the 11-meter parabolic dish concentrator. Ile proposed system includes a Stirling engine with high-pressure hydraulic output, coupled with a bent axis variable displacement hydraulic motor and a rotary induction generator. This paper describes the major thrusts of the preliminary design, which include: 1) material selection for the hot end components, 2) heat transport system (reflux pool boiler) design, 3) system thermal response, 4) improved manufacturability, 5) FMECA/FTA analysis, 6) updated manufacturing cost estimate and 7) predicted system performance.

Assessment of 25 kW free-piston Stirling technology alternatives for solar applications

Free-piston Stirling engines offer a relatively mature technology that is well-suited for advanced, high-efficiency radioisotope space power systems. This paper updates results from a combination of DOE and NASA contracts with Stirling Technology Company (STC). These contracts have demonstrated STC’s Stirling convertor technology in a configuration and power level representative of a space power system. Based on demonstrated performance, long-life maintenance-free technology heritage, and success with aggressively imposed vibration testing. DOE has awarded system integration contracts to Boeing, Lockheed Martin and Teledyne Energy Systems. The objectives of these competitive Phase I contracts are to develop complete spacecraft power system conceptual designs based on the STC Stirling convertor, and to plan subsequent phases for two launches. Performance results for the DOE 55-W(e) Technology Demonstration Convertors (TDC’s) have met original projections. Although the TDC’s were intended only for technolog...

Measurement Considerations for Dynamic Testing of STC Stirling Convertors

The final design, construction, and testing of a 25-kW free-piston advanced Stirling conversion system (ASCS) are examined. The final design of the free-piston hydraulic ASCS consists of five subsystems: heat transport subsystem (solar receiver and pool boiler), free-piston hydraulic Stirling engine, hydraulic subsystem, cooling subsystem, and electrical and control subsystem. Advantages and disadvantages are identified for each technology alternative. Technology alternatives considered are gas bearings vs flexure bearings, stationary magnet linear alternator vs moving magnetic linear alternator, and seven different control options. Component designs are generated using available in-house procedures to meet the requirements of the free-piston Stirling convertor configurations.