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NASA NTRS2018

High Efficiency Quantum Well Waveguide Solar Cells and Methods for Constructing the Same

Photon absorption, and thus current generation, is hindered in conventional thin-film solar cell designs, including quantum well structures, by the limited path length of incident light passing vertically through the device. Optical scattering into lateral waveguide structures provides a physical mechanism to increase photocurrent generation through in-plane light trapping. However, the insertion of wells of high refractive index material with lower energy gap into the device structure often results in lower voltage operation, and hence lower photovoltaic power conversion efficiency. The voltage output of an InGaAs quantum well waveguide photovoltaic device can be increased by employing a III-V material structure with an extended wide band gap emitter heterojunction. Analysis of the light IV characteristics reveals that non-radiative recombination components of the underlying dark diode current have been reduced, exposing the limiting radiative recombination component and providing a pathway for realizing solar-electric conversion efficiency of 30% or more in single junction cells.

Welser, Roger E.↗

NASA NTRS1977

High-temperature, high-power-density thermionic energy conversion for space

Theoretic converter outputs and efficiencies indicate the need to consider thermionic energy conversion (TEC) with greater power densities and higher temperatures within reasonable limits for space missions. Converter-output power density, voltage, and efficiency as functions of current density were determined for 1400-to-2000 K emitters with 725-to-1000 K collectors. The results encourage utilization of TEC with hotter-than-1650 K emitters and greater-than-6W sq cm outputs to attain better efficiencies, greater voltages, and higher waste-heat-rejection temperatures for multihundred-kilowatt space-power applications. For example, 1800 K, 30 A sq cm TEC operation for NEP compared with the 1650 K, 5 A/sq cm case should allow much lower radiation weights, substantially fewer and/or smaller emitter heat pipes, significantly reduced reactor and shield-related weights, many fewer converters and associated current-collecting bus bars, less power conditioning, and lower transmission losses. Integration of these effects should yield considerably reduced NEP specific weights.

Morris, J. F.↗

NASA NTRS2019

Evaluation of Electrical System Requirements for Implementing Turbine Electrified Energy Management

Turbine Electrified Energy Management (TEEM) is a concept concerned with the management of energy in an electrified propulsion system. The management of energy in the hybrid-electric architecture has potential to benefit the turbomachinery and the aircraft it powers. The concept is particularly useful for improving operability during transient operation and could be leveraged to design a better performing engine. The concept utilizes electric machines coupled to the engine shafts and an electric power distribution system that includes energy storage. A controller is used to decide when and how energy is moved around the electrified propulsion system, particularly when considering energy conversion between mechanical and electrical forms. Prior work has shown that the electric machines can be used to supply/or extract supplemental power to/from the engine shafts to improve their operability and achieve or enable propulsion efficiency and performance benefits. However, the previous studies did not consider the practical constraints of the electrical machines and energy storage devices that are required for implementing the TEEM system architecture concept. This paper presents an integrated engine and electrical system model that is used to evaluate the electrical system requirements. The model captures the physics of the conceptual, Advanced Geared Turbofan 30,000lbf (AGTF30) engine, which features advanced technologies such as a compact gas turbine and a variable area fan nozzle. For this work, the engine is augmented with electrical system components that allow for the implementation of the TEEM concept. The evaluation presented suggests the potential of the TEEM concept to provide performance benefits for a turbofan engine.

electrified↗

NASA NTRS2019

Evaluation of Electrical System Requirements for Implementing Turbine Electrified Energy Management

hybrid electric propulsion↗

NASA NTRS1981

Study of the effects of impurities on the properties of silicon materials and performance of silicon solar cell

The effect of silicon film thickness on the energy conversion efficiency of a back surface field solar cell is investigated. A computer-aided design study on the dependence of efficiency peaks on the concentrations of the recombination and dopant impurities is presented. The illuminated current voltage characteristics of over 100 cell designs were obtained using the transmission line circuit model to numerically solve the Shockley Equations. Using an AM1 efficiency of 17% as a target value, it is shown that the efficiency versus thickness dependence has a broad maximum which varies less than 1% over more than three-to-one range of cell thickness from 30 to 100 microns. Optical reflecting back surface will give only a slight improvement of AM1 efficiency, about 0.7%, in this thickness range. The sensitive dependence of efficiency on patchiness across the back surface field, low high junction in thin cells is noted.

Sah, C. T.↗

NASA NTRS2009

2-Micron Laser Transmitter for Coherent CO2 DIAL Measurement

Carbon dioxide (CO2) has been recognized as one of the most important greenhouse gases. It is essential for the study of global warming to accurately measure the CO2 concentration in the atmosphere and continuously record its variation. A high repetition rate, highly efficient, Q-switched 2-micron laser system as the transmitter of a coherent differential absorption lidar for CO2 measurement has been developed in NASA Langley Research Center. This laser system is capable of making a vertical profiling of CO2 from ground and column measurement of CO2 from air and space-borne platform. The transmitter is a master-slave laser system. The master laser operates in a single frequency, either on-line or off-line of a selected CO2 absorption line. The slave laser is a Q-switched ring-cavity Ho:YLF laser which is pumped by a Tm:fiber laser. The repetition rate can be adjusted from a few hundred Hz to 10 kHz. The injection seeding success rate is from 99.4% to 99.95%. For 1 kHz operation, the output pulse energy is 5.5mJ with the pulse length of ~50 ns. The optical-to-optical efficiency is 39% when the pump power is 14.5W. A Ho:YLF laser operating in the range of 2.05 micrometers can be tuned over several characteristic lines of CO2 absorption. Experimentally, a diode pumped Ho:Tm:YLF laser has been successfully used as the transmitter of coherent differential absorption lidar for the measurement of CO2 with a repetition rate of 5 Hz and pulse energy of 75 mJ. For coherent detection, high repetition rate is required for speckle averaging to obtain highly precise measurements. However, a diode pumped Ho:Tm:YLF laser can not operate in high repetition rate due to the large heat loading and up-conversion. A Tm:fiber laser pumped Ho:YLF laser with low heat loading can operate in high repetition rate. A theoretical model has been established to simulate the performance of Tm:fiber laser pumped Ho:YLF lasers. For continuous wave (CW) operation, high pump intensity with small beam size is suitable for high efficiency. For Q-switched operation, the optimal energy extraction relies on the pump intensity, pump volume, and pump duration which is inversely proportion to the repetition rate. CW and Q-switched Ho:YLF lasers with different linear cavity configurations have been designed and demonstrated for a 30 W Tm:fiber pump laser. The CW Ho laser slope efficiency and optical-to-optical efficiencies reach 65% and 55%, respectively. The pulsed laser efficiency depends on the repetition rate. For 1 kHz operation, the optical-to-optical efficiency is 39% when the pump power is 14.5W. Currently, the injection seeding success rate is between 99.4% and 99.95%. After a ten thousand pulses, the standard deviation of the laser frequency jitter is about 3 MHz. It meets the requirements of highly precise CO2 concentration measurement. In conclusion, an injection seeded, high repetition rate, Q-switched Ho:YLF laser has been developed for a coherent CO2 differential absorption lidar. This master-slave laser system has high optical-to-optical efficiency and seeding success rate. It can potentially meet the requirements of the coherent detection of CO2 concentration by a differential absorption lidar technique.

Singh, Upendra N.↗

NASA NTRS1998

Prelaunch Calibrations of the Clouds and the Earth's Radiant Energy System (CERES) Tropical Rainfall Measuring Mission and Earth Observing System Morning (EOS-AM1) Spacecraft Thermistor Bolometer Sensors

The Clouds and the Earth's Radiant Energy System (CERES) spacecraft scanning thermistor bolometer sensors measure earth radiances in the broadband shortwave solar (O.3 - 5.0 micron and total (0.3 to 100 microns) spectral bands as well as in the 8-12 microns water vapor window spectral band. On November 27, 1997, the launch of the Tropical Rainfall Measuring Mission (TRMM) spacecraft placed the first set of CERES sensors into orbit, and 30 days later, the sensors initiated operational measurements of the earth radiance fields. In 1998, the Earth Observing System morning (EOS-AM1) spacecraft will place the second and third sensor sets into orbit. The prelaunch CERES sensors' count conversion coefficients (gains and zero-radiance offsets) were determined in vacuum ground facilities. The gains were tied radiometrically to the International Temperature Scale of 1990 (ITS-90). The gain determinations included the spectral properties (reflectance, transmittance, emittance, etc.) of both the sources and sensors as well as the in-field-of-view (FOV) and out-of-FOV sensor responses. The resulting prelaunch coefficients for the TRMM and EOS-AM1 sensors are presented. Inflight calibration systems and on-orbit calibration approaches are described, which are being used to determine the temporal stabilities of the sensors' gains and offsets from prelaunch calibrations through on-orbit measurements. Analyses of the TRMM prelaunch and on-orbit calibration results indicate that the sensors have retained their ties to ITS-90 at accuracy levels better than /- 0.3% between the 1995 prelaunch and 1997 on-orbit calibrations.

Lee, Robert B., III↗

NASA NTRS1991

Condenser design for AMTEC power conversion

The condenser and the electrodes are the two elements of an alkali metal thermal-to-electric conversion (AMTEC) cell which most greatly affect the energy conversion performance. A condenser is described which accomplishes two critical functions in an AMTEC cell: management of the fluid under microgravity conditions and optimization of conversion efficiency. The first function is achieved via the use of a controlled surface shape, along with drainage grooves and arteries to collect the fluid. Capillary forces manage the fluid in microgravity and dominate hydrostatic effects on the ground so the device is ground-testable. The second function is achieved via a smooth film of highly reflective liquid sodium on the condensing surface, resulting in minimization of parasitic heat losses due to radiation heat transfer. Power conversion efficiencies of 25 percent to 30 percent are estimated with this condenser using present technology for the electrodes.

Crowley, Christopher J.↗

NASA NTRS1991

Final design of a free-piston hydraulic advanced Stirling conversion system

Under the US Department of Energy's (DOEs) Solar Thermal Technology Program, Sandia National Laboratories is evaluating heat engines for solar distributed receiver systems. The final design is described of an engineering prototype advanced Stirling conversion system (ASCS) with a free-piston hydraulic engine output capable of delivering about 25 kW of electric power to a utility grid. The free-piston Stirling engine has the potential for a highly reliable engine with long life because it has only a few moving parts, has noncontacting bearings, and can be hermetically sealed. The ASCS is designed to deliver maximum power per year over a range of solar input with a design life of 30 years (60,000 h). The system includes a liquid Nak pool boiler heat transport system and a free-piston Stirling engine with high-pressure hydraulic output, coupled with a bent axis variable displacement hydraulic motor and a rotary induction generator.

Wallace, D. A.↗

NASA NTRS2007

Space and Terrestrial Power System Integration Optimization Code BRMAPS for Gas Turbine Space Power Plants With Nuclear Reactor Heat Sources

In view of the difficult times the US and global economies are experiencing today, funds for the development of advanced fission reactors nuclear power systems for space propulsion and planetary surface applications are currently not available. However, according to the Energy Policy Act of 2005 the U.S. needs to invest in developing fission reactor technology for ground based terrestrial power plants. Such plants would make a significant contribution toward drastic reduction of worldwide greenhouse gas emissions and associated global warming. To accomplish this goal the Next Generation Nuclear Plant Project (NGNP) has been established by DOE under the Generation IV Nuclear Systems Initiative. Idaho National Laboratory (INL) was designated as the lead in the development of VHTR (Very High Temperature Reactor) and HTGR (High Temperature Gas Reactor) technology to be integrated with MMW (multi-megawatt) helium gas turbine driven electric power AC generators. However, the advantages of transmitting power in high voltage DC form over large distances are also explored in the seminar lecture series. As an attractive alternate heat source the Liquid Fluoride Reactor (LFR), pioneered at ORNL (Oak Ridge National Laboratory) in the mid 1960's, would offer much higher energy yields than current nuclear plants by using an inherently safe energy conversion scheme based on the Thorium --> U233 fuel cycle and a fission process with a negative temperature coefficient of reactivity. The power plants are to be sized to meet electric power demand during peak periods and also for providing thermal energy for hydrogen (H2) production during "off peak" periods. This approach will both supply electric power by using environmentally clean nuclear heat which does not generate green house gases, and also provide a clean fuel H2 for the future, when, due to increased global demand and the decline in discovering new deposits, our supply of liquid fossil fuels will have been used up. This is expected within the next 30 to 50 years, as predicted by the Hubbert model and confirmed by other global energy consumption prognoses. Having invested national resources into the development of NGNP, the technology and experience accumulated during the project needs to be documented clearly and in sufficient detail for young engineers coming on-board at both DOE and NASA to acquire it. Hands on training on reactor operation, test rigs of turbomachinery, and heat exchanger components, as well as computational tools will be needed. Senior scientist/engineers involved with the development of NGNP should also be encouraged to participate as lecturers, instructors, or adjunct professors at local universities having engineering (mechanical, electrical, nuclear/chemical, and/or materials) as one of their fields of study.

Juhasz, Albert J.↗

NASA NTRS1991

Light-emitting diodes as a radiation source for plants

Development of a more effective radiation source for use in plant-growing facilities would be of significant benefit for both research and commercial crop production applications. An array of light-emitting diodes (LEDs) that produce red radiation, supplemented with a photosynthetic photon flux (PPF) of 30 micromoles s-1 m-2 in the 400- to 500-nm spectral range from blue fluorescent lamps, was used effectively as a radiation source for growing plants. Growth of lettuce (Lactuca sativa L. Grand Rapids') plants maintained under the LED irradiation system at a total PPF of 325 micromoles s-1 m-2 for 21 days was equivalent to that reported in the literature for plants grown for the same time under cool-white fluorescent and incandescent radiation sources. Characteristics of the plants, such as leaf shape, color, and texture, were not different from those found with plants grown under cool-white fluorescent lamps. Estimations of the electrical energy conversion efficiency of a LED system for plant irradiation suggest that it may be as much as twice that published for fluorescent systems.

NASA Discipline Number 61-10↗

NASA NTRS2012

Comparison of Square and Radial Geometries for High Intensity Laser Power Beaming Receivers

In an effort to further advance a realizable form of wireless power transmission (WPT), high intensity laser power beaming (HILPB) has been developed for both space and terrestrial applications. Unique optical-to-electrical receivers are employed with near infrared (IR-A) continuous-wave (CW) semiconductor lasers to experimentally investigate the HILPB system. In this paper, parasitic feedback, uneven illumination and the implications of receiver array geometries are considered and experimental hardware results for HILPB are presented. The TEM00 Gaussian energy profile of the laser beam presents a challenge to the effectiveness of the receiver to perform efficient photoelectric conversion, due to the resulting non-uniform illumination of the photovoltaic cell arrays. In this investigation, the geometry of the receiver is considered as a technique to tailor the receiver design to accommodate the Gaussian beam profile, and in doing so it is demonstrated that such a methodology is successful in generating bulk receiver output power levels reaching 25 W from 7.2 sq cm of photovoltaic cells. These results are scalable, and may be realized by implementing receiver arraying and utilizing higher power source lasers to achieve a 1.0 sq m receiver capable of generating over 30 kW of electrical power. This type of system would enable long range optical "refueling" of electric platforms, such as MUAV s, airships, robotic exploration missions and provide power to spacecraft platforms which may utilize it to drive electric means of propulsion. In addition, a smaller HILPB receiver aperture size could be utilized to establish a robust optical communications link within environments containing high levels of background radiance, to achieve high signal to noise ratios.

Raible, Daniel E.↗

NASA NTRS1983

Air Force Logistics Command (AFLC) solar thermal plant

The plant proved its capability to deliver the desired energy product in a USAF industrial environment. The collector proved capable of energy conversion at insolation levels up to 25% below design minimum. The plant and the project were negatively affected by severe winter weather, with total insolation during the test period 60 percent less than the expected value. Environmental effects reduced plant availability to 55 percent. Only five, minimally good operating days were experienced during the test period. The subsequent lack of performance data prohibits the drawing of general conclusions regarding system performance. System operability was rated generally high. The only inhibiting factor was the difficulty in procuring replacement parts for rapid repair under USAF stockage and procurement policies. No inherently serious system failures were recorded, although a thermostatic valve malfunction in the freeze protection system ultimately took 30 days to repair.

Source record↗

NASA NTRS1976

Mineralogy of the Ibitira eucrite and comparison with other eucrites and lunar samples

The mineralogy of the Ibitira meteorite is studied using single-crystal X-ray and energy-dispersive electron-probe techniques. It is shown that this strongly metamorphosed unbrecciated vesicular eucrite has a primary variolitic and secondary hornfelsic texture dominated by equant grains of pale-brown pyroxene (60%) set in an irregular matrix of plagioclase (30%). Minor phases are detected which indicate igneous crystallization, a prolonged metamorphic history, and vapor deposition. The following sequence of events is suggested as the simplest explanation for the mineralogical features observed: (1) crystallization of the meteorite in a lava flow; (2) prolonged annealing, reduction of primary spinel, and vapor deposition; (3) strong shock sufficient to modify the texture of the plagioclase grains; and (4) sufficient annealing to allow crystallization of the plagioclase as a subparallel mosaic and partial conversion to the low structural state. Evidence for this sequence is examined in detail, particularly in relation to the general features of eucrites, howardites, and mesosiderites

Steele, I. M.↗

NASA NTRS2010

Fuel-Cell Power Source Based on Onboard Rocket Propellants

The use of onboard rocket propellants (dense liquids at room temperature) in place of conventional cryogenic fuel-cell reactants (hydrogen and oxygen) eliminates the mass penalties associated with cryocooling and boil-off. The high energy content and density of the rocket propellants will also require no additional chemical processing. For a 30-day mission on the Moon that requires a continuous 100 watts of power, the reactant mass and volume would be reduced by 15 and 50 percent, respectively, even without accounting for boiloff losses. The savings increase further with increasing transit times. A high-temperature, solid oxide, electrolyte-based fuel-cell configuration, that can rapidly combine rocket propellants - both monopropellant system with hydrazine and bi-propellant systems such as monomethyl hydrazine/ unsymmetrical dimethyl hydrazine (MMH/UDMH) and nitrogen tetroxide (NTO) to produce electrical energy - overcomes the severe drawbacks of earlier attempts in 1963-1967 of using fuel reforming and aqueous media. The electrical energy available from such a fuel cell operating at 60-percent efficiency is estimated to be 1,500 Wh/kg of reactants. The proposed use of zirconia-based oxide electrolyte at 800-1,000 C will permit continuous operation, very high power densities, and substantially increased efficiency of conversion over any of the earlier attempts. The solid oxide fuel cell is also tolerant to a wide range of environmental temperatures. Such a system is built for easy refueling for exploration missions and for the ability to turn on after several years of transit. Specific examples of future missions are in-situ landers on Europa and Titan that will face extreme radiation and temperature environments, flyby missions to Saturn, and landed missions on the Moon with 14 day/night cycles.

Ganapathi, Gani↗

NASA NTRS1962

Study of Umbrella-Type Erectable Paraboloidal Solar Concentrators for Generation of Spacecraft Auxiliary Power

An investigation was made of some aspects of erectable umbrella-type paraboloidal solar-energy concentrators for use in spacecraft auxiliary power systems. An analysis is presented for the design of concentrators employing radial ribs and membrane-type coverings. The rib stiffness necessary to give a desired parabolic curvature upon erection is determined. Rib contour measurements were made in an upright and inverted position on an experimental 10-foot-diameter concentrator giving a focal length of 30.78 inches and 30.6 inches, respectively, as compared with a design focal length of 30 inches. Calorimetric tests employing spherical heat receivers showed a maximum geometrical concentrator efficiency of 75.3 percent with a concentration ratio of 92.2 at a focal length of approximately 30.5 inches. Within the scope of this investigation, it was found that, as the concentrator size increases, the weight per unit projected area increases, time to damp to one-half amplitude increases, and the natural frequency decreases. Umbrella-type solar concentrators appear to be feasible for power conversion systems using low concentration ratios; however, for large concentrators the time required to damp out disturbances may be a problem.

SPACECRAFT↗

NASA NTRS2010

Improved OTEC System for a Submarine Robot

An ocean thermal energy conversion (OTEC), now undergoing development, is a less-massive, more-efficient means of exploiting the same basic principle as that of the proposed system described in "Alternative OTEC Scheme for a Submarine Robot" (NPO-43500), NASA Tech Briefs, Vol. 33, No. 1 (January 2009), page 50. The proposed system as described previously would be based on the thawing-expansion/freezing-contraction behavior of a wax or perhaps another suitable phase-change material (PCM). The power generated by the system would be used to recharge the batteries in a battery- powered unmanned underwater vehicle [UUV (essentially, a small exploratory submarine robot)] of a type that has been deployed in large numbers in research pertaining to global warming. A UUV of this type travels between the ocean surface and depths, measuring temperature and salinity. At one phase of its operational cycle, the previously proposed system would utilize the surface ocean temperature (which lies between 15 and 30 C over most of the Earth) to melt a PCM that has a melting/freezing temperature of about 10 C. At the opposite phase of its operational cycle, the system would utilize the lower ocean temperature at depth (e.g., between 4 and 7 C at a depth of 300 m) to freeze the PCM. The melting or freezing would cause the PCM to expand or contract, respectively, by about 9 volume percent. The PCM would be contained in tubes that would be capable of expanding and contracting with the PCM. The PCM-containing tubes would be immersed in a hydraulic fluid. The expansion and contraction would drive a flow of the hydraulic fluid against a piston that, in turn, would push a rack-and-pinion gear system to spin a generator to charge a battery.

Chao, Yi↗

NASA NTRS1999

A Study of Mars Dust Environment Simulation at NASA Johnson Space Center Energy Systems Test Area Resource Conversion Test Facility

The dust environment on Mars is planned to be simulated in a 20 foot thermal-vacuum chamber at the Johnson Space Center, Energy Systems Test Area Resource Conversion Test Facility in Houston, Texas. This vacuum chamber will be used to perform tests and study the interactions between the dust in Martian air and ISPP hardware. This project is to research, theorize, quantify, and document the Mars dust/wind environment needed for the 20 foot simulation chamber. This simulation work is to support the safety, endurance, and cost reduction of the hardware for the future missions. The Martian dust environment conditions is discussed. Two issues of Martian dust, (1) Dust Contamination related hazards, and (2) Dust Charging caused electrical hazards, are of our interest. The different methods of dust particles measurement are given. The design trade off and feasibility were studied. A glass bell jar system is used to evaluate various concepts for the Mars dust/wind environment simulation. It was observed that the external dust source injection is the best method to introduce the dust into the simulation system. The dust concentration of 30 Mg/M3 should be employed for preparing for the worst possible Martian atmosphere condition in the future. Two approaches thermal-panel shroud for the hardware conditioning are discussed. It is suggested the wind tunnel approach be used to study the dust charging characteristics then to be apply to the close-system cyclone approach. For the operation cost reduction purpose, a dehumidified ambient air could be used to replace the expensive CO2 mixture for some tests.

Chen, Yuan-Liang Albert↗