SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS

A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 9 - MAY 5, 2006

20 SPACECRAFT PROPULSION AND POWER
Includes main propulsion systems and components, e.g., rocket engines; and spacecraft auxiliary power sources.

For related information see also 07 Aircraft Propulsion and Power, 28 Propellants and Fuels, 15 Launch Vehicles and Launch Operations, and 44 Energy Production and Conversion.

20060011233NASA Glenn Research Center, Cleveland, OH, USA

Calculation of Thermally-Induced Displacements in Spherically Domed Ion Engine Grids

Soulas, George C.; March 2006; 27 pp.; In English; 29th International Electric Propulsion Conference, 31 Oct. - 4 Nov. 2005,Princeton, NJ, USA; Original contains black and white illustrationsContract(s)/Grant(s): WBS 22-512-50-04-19Report No.(s): NASA/TM-2006-214046; IEPC-2005-248; E-15403; No Copyright; Avail.: CASI: A03, Hardcopy

An analytical method for predicting the thermally-induced normal and tangential displacements of spherically domed ionoptics grids under an axisymmetric thermal loading is presented.Afixed edge support that could be thermally expanded is usedfor this analysis. Equations for the displacements both normal and tangential to the surface of the spherical shell are derived.A simplified equation for the displacement at the center of the spherical dome is also derived. The effects of plate perforationon displacements and stresses are determined by modeling the perforated plate as an equivalent solid plate with modified, oreffective, material properties. Analytical model results are compared to the results from a finite element model. For the solidshell, comparisons showed that the analytical model produces results that closely match the finite element model results. Thesimplified equation for the normal displacement of the spherical dome center is also found to accurately predict thisdisplacement. For the perforated shells, the analytical solution and simplified equation produce accurate results for materialswith low thermal expansion coefficients.Author

Ion Engines; Thermal Expansion; Ion Optics; Spherical Shells; Finite Element Method; Temperature Effects

20060011236 NASA Glenn Research Center, Cleveland, OH, USA

A Comparison of Fission Power System Options for Lunar and Mars Surface Applications

Mason, Lee S.; February 2006; 21 pp.; In English; Space Technology and Applications International Forum (STAIF-2006),12-16 Feb. 2006, Albuquerque, NM, USA; Original contains color illustrationsContract(s)/Grant(s): WBS 22-982-10-30Report No.(s): NASA/TM-2006-214120; E-15455; No Copyright; Avail.: CASI: A03, Hardcopy

This paper presents a comparison of reactor and power conversion design options for 50 kWe class lunar and Mars surfacepower applications with scaling from 25 to 200 kWe. Design concepts and integration approaches are provided for threereactor-converter combinations: gas-cooled Brayton, liquid-metal Stirling, and liquid-metal thermoelectric. The studyexamines the mass and performance of low temperature, stainless steel based reactors and higher temperature refractoryreactors. The preferred system implementation approach uses crew-assisted assembly and in-situ radiation shielding viainstallation of the reactor in an excavated hole. As an alternative, self-deployable system concepts that use earth-delivered,on-board radiation shielding are evaluated. The analyses indicate that among the 50 kWe stainless steel reactor options, theliquid-metal Stirling system provides the lowest mass at about 5300 kg followed by the gas-cooled Brayton at 5700 kg andthe liquid-metal thermoelectric at 8400 kg. The use of a higher temperature, refractory reactor favors the gas-cooled Braytonoption with a system mass of about 4200 kg as compared to the Stirling and thermoelectric options at 4700 and 5600 kg,respectively. The self-deployed concepts with on-board shielding result in a factor of two system mass increase as comparedto the in-situ shielded concepts.Author

Fission; Mars Surface; Lunar Surface; Brayton Cycle; Thermoelectricity; Reactor Design; Liquid Metals; Stainless Steels

20060012148 NASA Glenn Research Center, Cleveland, OH, USA

Stirling Convertor Fasteners Reliability Quantification

Shah, Ashwin R.; Korovaichuk, Igor; Kovacevich, Tiodor; Schreiber, Jeffrey G.; April 2006; 18 pp.; In English; ThirdInternational Energy Conversion Engineering Conference, 15-18 Aug. 2005, San Francisco, CA, USA; Original contains colorillustrationsContract(s)/Grant(s): NAS3-03064; WBS 22-972-20-01Report No.(s): NASA/TM-2006-213992; AIAA Paper 2005-5507; E-15316; No Copyright; Avail.: CASI: A03, Hardcopy

Onboard Radioisotope Power Systems (RPS) being developed for NASA s deep-space science and exploration missionsrequire reliable operation for up to 14 years and beyond. Stirling power conversion is a candidate for use in an RPS becauseit offers a multifold increase in the conversion efficiency of heat to electric power and reduced inventory of radioactivematerial. Structural fasteners are responsible to maintain structural integrity of the Stirling power convertor, which is criticalto ensure reliable performance during the entire mission. Design of fasteners involve variables related to the fabrication,manufacturing, behavior of fasteners and joining parts material, structural geometry of the joining components, size andspacing of fasteners, mission loads, boundary conditions, etc. These variables have inherent uncertainties, which need to beaccounted for in the reliability assessment. This paper describes these uncertainties along with a methodology to quantify thereliability, and provides results of the analysis in terms of quantified reliability and sensitivity of Stirling power conversionreliability to the design variables. Quantification of the reliability includes both structural and functional aspects of the joiningcomponents. Based on the results, the paper also describes guidelines to improve the reliability and verification testing.Author

Stirling Cycle; Energy Conversion Efficiency; Reliability Analysis; Design Analysis

20060012149 NASA Glenn Research Center, Cleveland, OH, USA

Single Phase Passive Rectification Versus Active Rectification Applied to High Power Stirling Engines

Santiago, Walter; Birchenough, Arthur G.; March 2006; 19 pp.; In English; Third International Energy ConversionEngineering Conference, 15-18 Aug. 2005, San Francisco, CA, USA; Original contains color illustrationsContract(s)/Grant(s): WBS 22-319-20-M1Report No.(s): NASA/TM-2006-214045; AIAA Paper 2005-5687; E-15402; No Copyright; Avail.: CASI: A03, Hardcopy

Stirling engine converters are being considered as potential candidates for high power energy conversion systems requiredby future NASA explorations missions. These types of engines typically contain two major moving parts, the displacer andthe piston, in which a linear alternator is attached to the piston to produce a single phase sinusoidal waveform at a specificelectric frequency. Since all Stirling engines perform at low electrical frequencies (less or equal to 100 Hz), space explorationsmissions that will employ these engines will be required to use DC power management and distribution (PMAD) systeminstead of an AC PMAD system to save on space and weight. Therefore, to supply such DC power an AC to DC converteris connected to the Stirling engine. There are two types of AC to DC converters that can be employed, a passive full bridgediode rectifier and an active switching full bridge rectifier. Due to the inherent line inductance of the Stirling Engine-LinearAlternator (SE-LA), their sinusoidal voltage and current will be phase shifted producing a power factor below 1. In order tokeep power the factor close to unity, both AC to DC converters topologies will implement power factor correction. This paperdiscusses these power factor correction methods as well as their impact on overall mass for exploration applications.Simulation results on both AC to DC converters topologies with power factor correction as a function of output power andSE-LA line inductance impedance are presented and compared.Author

Rectifiers; Stirling Engines; NASA Programs; Spacecraft Power Supplies

20060012152 NASA Glenn Research Center, Cleveland, OH, USA

Grid Gap Measurement for an NSTAR Ion Thruster

Diaz, Esther M.; Soulas, George C.; April 2006; 18 pp.; In English; 29th International Electric Propulsion Conference, 31 Oct. - 4 Nov. 2005, Princeton, NJ, USA; Original contains color and black and white illustrations Contract(s)/Grant(s): WBS 22-800-92-71 Report No.(s): NASA/TM-2006-214249; E-15494; IEPC-2005-244; No Copyright; Avail.: CASI: A03, Hardcopy

The change in gap between the screen and accelerator grids of an engineering model NSTAR ion optics assembly was measured during thruster operation with beam extraction. The molybdenum ion optics assembly was mounted onto an engineering model NSTAR ion thruster. The measurement technique consisted of measuring the difference in height of an alumina pin relative to the downstream accelerator grid surface. The alumina pin was mechanically attached to the center aperture of the screen grid and protruded through the center aperture of the accelerator grid. The change in pin height was monitored using a long distance microscope coupled to a digital imaging system. Transient and steady-state hot grid gaps were measured at three power levels: 0.5, 1.5 and 2.3 kW. Also, the change in grid gap was measured during the transition between power levels, and during the startup with high voltage applied just prior to discharge ignition. Performance measurements, such as perveance, electron backstreaming limit and screen grid ion transparency, were also made to confirm that this ion optics assembly performed similarly to past testing. Results are compared to a prior test of 30 cm titanium ion optics. Author

Extraction; Ion Optics; Ion Propulsion; Metal Ions; Molybdenum; Rocket Engines

Source: NASA