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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1992

Photovoltaic Array Space Power flight experiment plus diagnostics (PASP+) modules

The Photovoltaic Array Space Power Plus Diagnostics flight experiment (PASP+) subsumes twelve solar array modules which represent the state of the art in the space photovoltaic array industry. Each of the twelve modules individually feature specific photovoltaic technologies such as advanced semiconductor materials, multi-bandgap structures, lightweight array designs, advanced interconnect technologies, or concentrator array designs. This paper will describe each module in detail including the configuration, components, materials, anticipated on orbit performance, and some of the aspects of each array technology. The layout of each module and the photovoltaic cells or array cross section will be presented graphically. A discussion on the environmental constraints and materials selection will be included as well as a delineation of the differences between the modules and the baseline array configuration in its intended application.

Cooley, William T.↗
NASA NTRS1994

Solar Photovoltaic Array With Mini-Dome Fresnel Lenses

Mini-dome Fresnel lenses concentrate sunlight onto individual photovoltaic cells. Facets of Fresnel lens designed to refract incident light at angle of minimum deviation to minimize reflective losses. Prismatic cover on surface of each cell reduces losses by redirecting incident light away from metal contacts toward bulk of semiconductor, where it is usefully absorbed. Simple design of mini-dome concentrator array easily adaptable to automated manufacturing techniques currently used by semiconductor industry. Attractive option for variety of future space missions.

Piszczor, Michael F., Jr.↗
NASA NTRS1994

Aromatic Polyimides With Low Dielectric Constants

Linear aromatic polyimides developed containing dimethylsilane linkages in dianhydride portions of molecules and at least one trifluoromethyl group in each of diamine portions. Polyimides offer advantages of thermal stability, low density, resistance to ionizing radiation, toughness, flexibility, and exhibit lower dielectric constants. Also polyimides nearly transparent and colorless; an advantage in protective coating of solar photovoltaic cells, optical components, and antennas.

St. Clair, Anne K.↗
NASA NTRS1994

Effect of power system technology and mission requirements on high altitude long endurance aircraft

An analysis was performed to determine how various power system components and mission requirements affect the sizing of a solar powered long endurance aircraft. The aircraft power system consists of photovoltaic cells and a regenerative fuel cell. Various characteristics of these components, such as PV cell type, PV cell mass, PV cell efficiency, fuel cell efficiency, and fuel cell specific mass, were varied to determine what effect they had on the aircraft sizing for a given mission. Mission parameters, such as time of year, flight altitude, flight latitude, and payload mass and power, were also altered to determine how mission constraints affect the aircraft sizing. An aircraft analysis method which determines the aircraft configuration, aspect ratio, wing area, and total mass, for maximum endurance or minimum required power based on the stated power system and mission parameters is presented. The results indicate that, for the power system, the greatest benefit can be gained by increasing the fuel cell specific energy. Mission requirements also substantially affect the aircraft size. By limiting the time of year the aircraft is required to fly at high northern or southern latitudes, a significant reduction in aircraft size or increase in payload capacity can be achieved.

Colozza, Anthony J.↗
NASA NTRS1994

Fiber Optical Solar Simulator

A new solar simulator is described whose output closely matches a desired solar spectrum for testing photovoltaic cells. The accurate simulation of the spectrum is attained by combining three light beams, each tailored to have suitable spectral content. The three light beams, derived from two sources, are filtered and 'mixed' by means of a trifurcated, randomized fiber cable so that when superimposed they add up to the desired solar spectrum. The fiber optic solar simulator (FOSS) simplifies solar cell testing by greatly reducing measurement time, obviating need for spectral mismatch corrections, and improving the accuracy of measurement. Other applications of FOSS are also described.

Sopori, Bhushan L.↗
NASA NTRS1993

Impact of LDEF photovoltaic experiment findings upon spacecraft solar array design and development requirements

Photovoltaic cells (solar cells) and other solar array materials were flown in a variety of locations on the Long Duration Exposure Facility (LDEF). With respect to the predicted leading edge, solar array experiments were located at 0 degrees (row 9), 30 degrees (row 8) and 180 degrees (row 3). Postflight estimates of location of the experiments with respect to the velocity vector add 8.1 degrees to these values. Experiments were also located on the Earth end of the LDEF longitudinal axis. Types and magnitudes of detrimental effects differ between the locations with some commonality. Postflight evaluation of the solar array experiments reveal that some components/materials are very resistant to the environment to which they were exposed while others need protection, modification, or replacement. Interaction of materials with atomic oxygen (AO), as an area of major importance, was dramatically demonstrated by LDEF results. Information gained from the LDEF flight allows array developers to set new requirements for on-going and future technology and flight component development.

Young, Leighton E.↗
NASA NTRS1995

Coatings Would Protect Polymers Against Atomic Oxygen

Proposed interposition of layers of silver oxide tens to hundreds of angstroms thick between polymeric substrates and overlying films helps protect substrates against chemical attack by monatomic oxygen. In original application, polymer substrate would be, sheet of polyimide supporting array of solar photovoltaic cells on spacecraft in low orbit around Earth. Concept also applicable to protection of equipment in terrestrial laboratory and industrial vacuum and plasma chambers in which monatomic oxygen present.

Banks, Bruce A.↗
NASA NTRS1995

Polyimides Made From PDMDA

Thermally stable linear aromatic polyimides with improved optical, electrical, and processing characteristics made from 3,3'-bis(3,4-dicarboxyphenoxy)diphenylmethane dianhydride (PDMDA). Made in form of powders that can be dissolved to cast thin films. Potentially useful as coating and matrix materials. Films made vary from transparent to pale yellow. Greater degrees of transparency and lower dielectric constants make these polyimides more suitable for use in some electronic and optical applications; e.g., as insulating materials on wires and protective films on solar photovoltaic cells.

St. Clair, Anne K.↗
NASA NTRS1995

High efficiency radioisotope thermophotovoltaic prototype generator

A radioisotope thermophotovoltaic generator space power system (RTPV) is lightweight, low-cost alternative to the present radioisotope thermoelectric generator system (RTG). The fabrication of such an RTPV generator has recently become feasible as the result of the invention of the GaSb infrared sensitive photovoltaic cell. Herein, we present the results of a parametric study of emitters and optical filters in conjuction with existing data on gallium antimonide cells. We compare a polished tungsten emitter with an Erbia selective emitter for use in combination with a simple dielectric filter and a gallium antimonide cell array. We find that the polished tungsten emitter is by itself a very selective emitter with low emissivity beyond 4 microns. Given a gallium antimonide cell and a tungsten emitter, a simple dielectric filter can be designed to transmit radiant energy below 1.7 microns and to reflect radiant energy between 1.7 and 4 microns back to the emitter. Because of the low long wavelength emissivity associated with the polished tungsten emitter, this simple dielectric filter then yields very respectable system performance. Also as a result of the longer wavelength fall-off in the tungsten emissivity curve, the radiation energy peak for a polished tungsten emitter operating at 1300 K shifts to shorter wavelengths relative to the blackbody spectrum so that the radiated energy peak falls right at the gallium antimonide cell bandedge. The result is that the response of the gallium antimonide cell is well matched to a polished tungsten emitter. We propose, therefore, to fabricate an operating prototype of a near term radioisotope thermophotovoltaic generator design consisting of a polished tungsten emitter, standard gallium antimonide cells, and a near-term dielectric filter. The Jet Propulsion Laboratory will design and build the thermal cavity, and JX Crystals will fabricate the gallium antimonide cells, dielectric filters, and resultant receiver panels. With 250 Watts of heat input, we expect this prototype to produce over 300 Watts of electrical energy output for a system energy conversion efficiency of over 12%. This low risk, near term design provides advances relative to present radioisotope thermophotovoltaic generators and has the additional advantage of allowing component and system development and testing to begin immediately. Improved cells and filters can easily be incorporated in this baseline system if they should become available in the future.

Avery, James E.↗
NASA NTRS1996

Parameter Design and Optimal Control of an Open Core Flywheel Energy Storage System

In low earth orbit (LEO) satellite applications spacecraft power is provided by photovoltaic cells and batteries. To overcome battery shortcomings the University of Maryland, working in cooperation with NASA/GSFC and NASA/LeRC, has developed a magnetically suspended flywheel for energy storage applications. The system is referred to as an Open Core Composite Flywheel (OCCF) energy storage system. Successful application of flywheel energy storage requires integration of several technologies, viz. bearings, rotor design, motor/generator, power conditioning, and system control. In this paper we present a parameter design method which has been developed for analyzing the linear SISO model of the magnetic bearing controller for the OCCF. The objective of this continued research is to principally analyze the magnetic bearing system for nonlinear effects in order to increase the region of stability, as determined by high speed and large air gap control. This is achieved by four tasks: (1) physical modeling, design, prototyping, and testing of an improved magnetically suspended flywheel energy storage system, (2) identification of problems that limit performance and their corresponding solutions, (3) development of a design methodology for magnetic bearings, and (4) design of an optimal controller for future high speed applications. Both nonlinear SISO and MIMO models of the magnetic system were built to study limit cycle oscillations and power amplifier saturation phenomenon observed in experiments. The nonlinear models include the inductance of EM coils, the power amplifier saturation, and the physical limitation of the flywheel movement as discussed earlier. The control program EASY5 is used to study the nonlinear SISO and MIMO models. Our results have shown that the characteristics and frequency responses of the magnetic bearing system obtained from modeling are comparable to those obtained experimentally. Although magnetic saturation is shown in the bearings, there are good correlations between the theoretical model and experimental data. Both simulation and experiment confirm large variations of the magnetic bearing characteristics due to air gap growth. Therefore, the gap growth effect should be considered in the magnetic bearing system design. Additionally, the magnetic bearing control system will be compared to other design methods using not only parameter design but H-infinity optimal control and mu synthesis.

Pang, D.↗
NASA NTRS1995

Nanosatellite Power System Considerations

The capability to build complex electronic functions into compact packages is opening the path to miniature satellites on the order of 1 kg mass, 10 cm across, packed with the computing processors, motion controllers, measurement sensors, and communications hardware necessary for operation. Power generation will be from short strings of silicon or gallium arsenide-based solar photovoltaic cells with the array power maximized by a peak power tracker (PPT). Energy storage will utilize a low voltage battery with nickel cadmium or lithium ion cells as the most likely selections for rechargeables and lithium (MnO2-Li) primary batteries for one shot short missions.

Robyn, M.↗
NASA NTRS1998

A Review of Recent Thermophotovoltaic Energy Conversion Technology Development at NASA Lewis Research Center

NASA Lewis Research Center (LeRC) has had an ongoing research program in TPV since the late 1980's. This effort has included both in-house research programs on critical components such as photovoltaic cells (PV) and emitter materials, as well as an active contracting effort directed toward system, and component development. Of particular note is the in-house development of thin film selective emitters fabricated from rare-earth yttrium aluminum garnets (YAG). Also developed at LeRC is a Monolithic Interconnect Module (MIM) consisting of many small InGaAs cells series interconnected on a single InP substrate. An infrared reflector placed on the rear surface of the substrate returns unabsorbed photons to the emitter for recycling. The current contracted efforts include two TPV system developments by Tecogen, Inc., a solar powered TPV system development, a GaInAsSb cell development and several emitter development efforts (plasma-sprayed selective emitters, flexible SiC and a selective emitting light pipe).

Wilt, David M.↗
NASA NTRS1995

Thermophotovoltaic Generators Using Selective Metallic Emitters

In the literature to date on thermophotovoltaic (TPV) generators, two types of infrared emitter's have been emphasized : gray body emitters and rare earth oxide selective emitters. The gray body emitter is defined as an emitter with a spectral emissivity independent of wavelength whereas the rare earth oxide selective emitter is idealized as a delta function emitter with a high emissivity at a select wavelength and a near zero emissivity at all other wavelengths. Silicon carbide is an example of a gray body emitter and ER-YAG is an example of a selective emitter. The Welsbach mantle in a common lantern is another example of an oxide selective emitter. Herein, we describe an alternative type of selective emitter, a selective metallic emitter. These metallic emitters are characterized by a spectral emissivity curve wherein the emissivity monotonically increases with shorter infrared wavelengths as is shown. The metal of curve "A", tungsten, typifies this class of selective metallic emitter's. In a thermophotovoltaic generator, a photovoltaic cell typically converts infrared radiation to electricity out to some cut-off wavelength. For example, Gallium Antimonide (GaSb) TPV cells respond out to 1.7 microns. The problem with gray body emitters is that they emit at all wavelengths. Therefore, a large fraction of the energy emitted will be outside of the response band of the TPV cell. The argument for the selective emitter is that, ideally, all the emitted energy can be in the cells response band. Unfortunately, rare earth oxide emitters are not ideal. In order to suppress the emissivity toward zero away from the select wavelength, the use of thin fiber's is necessary. This leads to a fragile emitter typical of a lantern mantle. Even given a thin ER-YAG emitter, the measured emissivity at the select wavelength of 1.5 microns has been reported to be 0.6 while the off wavelength background emissivity falls to only 0.2 at 5 microns. This gives a selectivity ratio of only 3. Another problem with a delta function selective emitter is its low power density at practical temperatures because of its narrow emission bandwidth. The concept of selectivity can be generalized by noting that we simply wish to maximize the ratio of in-cell-band power to out-of-cell-band power. Using this generalized selectivity concept and assuming a GaSb cell covered by a simple dielectric filter, we note that the emissivity selectivity ratio for tungsten is 0.3 (at 1.5 microns) / 0.07 (at 5 microns) = 4.3. In the folloy4ng sections, we note that the selective metallic emitters can be valuable in both radioisotope TPV generators in space and in hydrocarbon fired TPV generators here on earth.

Fraas, Lewis M.↗
NASA NTRS2002

The Stretched Lens Array (SLA): A Low-Risk, Cost-Effective Array Offering Wing-Level Performance of 180 W/KG and 300 W/M2 at 300 VDC

At IECEC 2001, our team presented a paper on the new stretched lens array (SLA), including its evolution from the successful SCARLET array on the NASA/JPL Deep Space 1 spacecraft. Since that conference, the SLA team has made significant advances in the SLA technology, including component-level improvements, array-level optimization, space environment exposure testing, and prototype hardware fabrication and evaluation. This paper describes the evolved version of the SLA, highlighting recent improvements in the lens, solar cell, photovoltaic receiver, rigid panel structure, and complete solar array wing.

ONeill, Mark↗
NASA NTRS2003

Monolithic Interconnected Modules (MIMs) for Thermophotovoltaic Energy Conversion

Monolithic Interconnected Modules (MIM) are under development for thermophotovoltaic (TPV) energy conversion applications. MIM devices are typified by series-interconnected photovoltaic cells on a common, semi-insulating substrate and generally include rear-surface infrared (IR) reflectors. The MIM architecture is being implemented in InGaAsSb materials without semi-insulating substrates through the development of alternative isolation methodologies. Motivations for developing the MIM structure include: reduced resistive losses, higher output power density than for systems utilizing front surface spectral control, improved thermal coupling and ultimately higher system efficiency. Numerous design and material changes have been investigated since the introduction of the MIM concept in 1994. These developments as well as the current design strategies are addressed.

Wilt, David↗
NASA NTRS2004

ITO-MgF2 Film Development for PowerSphere Polymer Surface Protection

Multi-kilogram class microsatellites with a PowerSphere electric power system are attractive for fulfilling a variety of potential NASA missions. However, PowerSphere polymer surfaces must be coated with a film that has suitable electrical sheet resistivity for electrostatic discharge control, be resistant to atomic oxygen attack, be transparent to ultraviolet light for composite structure curing and resist ultraviolet light induced darkening for efficient photovoltaic cell operation. In addition, the film must be tolerant of polymer layer folding associated with launch stowage of PowerSphere inflatable structures. An excellent film material candidate to meet these requirements is co-sputtered, indium oxide (In2O3) - tin oxide (SnO2), known as 'ITO', and magnesium fluoride (MgF2). While basic ITO-MgF2 film properties have been the subject of research over the last decade, further research is required in the areas of film durability for space-inflatable applications and precise film property control for large scale commercial production. In this paper, the authors present film durability results for a folded polymer substrate and film resistance to vacuum UV darkening. The authors discuss methods and results in the area of film sheet resistivity measurement and active control, particularly dual-channel, plasma emission line measurement of ITO and MgF2 plasma sources. ITO-MgF2 film polymer coupon preparation is described as well as film deposition equipment, procedures and film characterization. Durability testing methods are also described. The pre- and post-test condition of the films is assessed microscopically and electrically. Results show that an approx. 500A ITO-18vol% MgF2 film is a promising candidate to protect PowerSphere polymer surfaces for Earth orbit missions. Preliminary data also indicate that in situ film measurement methods are promising for active film resistivity control in future large scale production. Future film research plans are also discussed.

Hambourger, Paul D.↗
NASA NTRS1996

SCARLET Solar Array Delivered for METEOR Mission

Solar Concentrator Array with Refractive Linear Element Technology (SCARLET) is a joint NASA Lewis Research Center/Ballistic Missile Defense Organization program to develop advanced photovoltaic array technology for future space missions. This advanced power system technology uses a unique refractive concentrator design to focus sunlight onto a line of photovoltaic cells located below the optical element. The concentrator design is based on previous work conducted at Lewis under a Small Business Innovation Research Program (SBIR) with Entech, Inc.

Source record↗
NASA NTRS1997

SCARLET Photovoltaic Concentrator Array Selected for Flight Under NASA's New Millennium Program

The NASA Lewis Research Center continues to demonstrate its expertise in the development and implementation of advanced space power systems. For example, during the past year, the NASA New Millennium Program selected the Solar Concentrator Array with Refractive Linear Element Technology (SCARLET) photovoltaic array as the power system for its Deep Space-1 (DS-1) mission. This Jet Propulsion Laboratory (JPL) managed DS-1 mission, which represents the first operational flight of a photovoltaic concentrator array, will provide a baseline for the use of this technology in a variety of future government and commercial applications. SCARLET is a joint NASA Lewis/Ballistic Missile Defense Organization program to develop advanced photovoltaic array technology that uses a unique refractive concentrator design to focus sunlight onto a line of photovoltaic cells located below the optical element. The general concept is based on previous work conducted at Lewis under a Small Business Innovation Research (SBIR) contract with AEC-Able Engineering, Inc., for the Multiple Experiments to Earth Orbit and Return (METEOR) spacecraft. The SCARLET II design selected by the New Millennium Program is a direct adaptation of the smaller SCARLET I array built for METEOR. Even though SCARLET I was lost during a launch failure in October 1995, the hardware (designed, built, and flight qualified within 6 months) provided invaluable information and experience that led to the selection of this technology as the primary power source for DS-1.

Piszczor, Michael F., Jr.↗