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  • Other Sources  (118)
  • SPACECRAFT PROPULSION AND POWER  (118)
  • 1990-1994  (118)
  • 1970-1974
  • 1991  (118)
  • 1
    Publication Date: 2013-08-31
    Description: High efficiency, two terminal, multijunction AlGaAs/GaAs solar cells were reproducibly made with areas of 0.5 sq cm. The multiple layers in the cells were grown by Organo Metallic Vapor Phase Epitaxy (OMVPE) on GaAs substrates in the n-p configuration. The upper AlGaAs cell has a bandgap of 1.93 eV and is connected in series to the lower GaAs cell (1.4 eV) via a metal interconnect deposited during post-growth processing. A prismatic coverglass is installed on top of the cell to reduce obscuration caused by the gridlines. The best 0.5 sq cm cell has a two terminal efficiency of 23.0 pct. at 1 sun, air mass zero (AM0) and 25 C. To date, over 300 of these cells were grown and processed for a manufacturing demonstration. Yield and efficiency data for this demonstration are presented. As a first step toward the goal of a 30 pct. efficient cell, a mechanical stack of the 0.5 sq cm cells described above, and InGaAsP (0.95 eV) solar cells was made. The best two terminal measurement to date yields an efficiency of 25.2 pct. AM0. This is the highest reported efficiency of any two terminal, 1 sun space solar cell.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: NASA. Lewis Research Center, Space Photovoltaic Research and Technology Conference; 7 p
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  • 2
    Publication Date: 2019-07-13
    Description: A high-efficiency, lightweight space photovoltaic concentrator array is described. Previous work on the minidome Fresnel lens concentrator concept is being integrated with Boeing's 30 percent efficient tandem GaAs/GaSb concentrator cells into a high-performance photovoltaic array. Calculations indicate that, in the near term, such an array can achieve 300 W/sq m at a specific power of 100 W/kg. Emphasis of the program has now shifted to integrating the concentrator lens, tandem cell, and supporting panel structure into a space-qualifiable array. A description is presented of the current status of component and prototype panel testing and the development of a flight panel for the Photovoltaic Array Space Power Plus Diagnostics (PASP PLUS) flight experiment.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: IEEE Photovoltaic Specialists Conference; Oct 07, 1991 - Oct 11, 1991; Las Vegas, NV; United States
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  • 3
    Publication Date: 2019-08-28
    Description: Three experiments are proposed to demonstrate the feasibility of converting dc power into microwave or millimeter-wave beam and transmitting it to users through free space. The generator could be located on earth or on a utility power satellite. The received power would be converted back into dc or ac power. The success of the experiments could lead to the commercial use of this technology.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: International Symposium SPS 91 - Power from Space; Aug 27, 1991 - Aug 30, 1991; Gif-sur-Yvette; France
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  • 4
    Publication Date: 2013-08-29
    Description: The Advanced Photovoltaic Solar Array (APSA) design is reviewed. The testing results and performance estimates are summarized. The APSA design represents a critical intermediate milestone for the NASA Office of Aeronautics, Exploration, and Technology (OAET) goal of 300 W/kg at Beginning Of Life (BOL), with specific performance characteristics of 130 W/kg (BOL) and 100 W/kg at End Of Life (EOL) for a 10 year geosynchronous (GEO) 10 kW (BOL) space power system. The APSA wing design is scalable over a power range of 1 to 15 kW and is suitable for a full range of missions including Low Earth Orbit (LEO), orbital transfer from LEO to GEO and interplanetary out to 5 AU.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: ESA, European Space Power Conference. Volume 2: Photovoltaic Generators; p 675-680
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  • 5
    Publication Date: 2013-08-31
    Description: With the ever increasing demands on space power systems, it is imperative that low cost, lightweight, reliable photovoltaics be developed. One avenue of pursuit for future space power applications is the use of low cost, lightweight flexible PV cells and arrays. Most work in this area assumes the use of flexible amorphous silicon (a-Si), despite its inherent instability and low efficiencies. However, polycrystalline thin film PV such as copper-indium-diselenide (CIS) are inherently more stable and exhibit better performance than a-Si. Furthermore, preliminary data indicate that CIS also offers exciting properties with respect to space applications. However, CIS has only heretofore only produced on rigid substrates. The implications of flexible CIS upon present and future space power platforms was explored. Results indicate that space qualified CIS can dramatically reduce the cost of PV, and in most cases, can be substituted for silicon (Si) based on end-of-life (EOL) estimations. Furthermore, where cost is a prime consideration, CIS can become cost effective than gallium arsenide (GaAs) in some applications. Second, investigations into thin film deposition on flexible substrates were made, and data from these tests indicate that fabrication of flexible CIS devices is feasible. Finally, data is also presented on preliminary TCO/CdS/CuInSe2/Mo devices.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: NASA. Lewis Research Center, Space Photovoltaic Research and Technology Conference; 8 p
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  • 6
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    In:  Other Sources
    Publication Date: 2019-06-28
    Description: Emission spectroscopy measurements were made of the plasma flow inside the nozzle of a 1-kW-class arcjet thruster. The thruster propellant was a hydrogen-nitrogen mixture used to simulate fully decomposed hydrazine. Atomic electron-excitation, vibrational, and rotational temperatures were determined for the expanding plasma using relative line intensity techniques. The atomic excitation temperature decreased from 18,000 K at a location 3 mm downstream of the constrictor to 9000 K at a location 9 mm from the constrictor, while the molecular vibrational and rotational temperatures decreased from 6500 K to 2500 K and from 8000 K to 3000 K, respectively, between the same locations. The electron density, measured using hydrogen H-beta line Stark broadening, decreased from about 10 to the 15th cu cm to about 2 x 10 to the 14th cu cm during the expansion. The results show that the plasma is highly nonequilibrium throughout the nozzle, with most relaxation times equal or exceeding the particle residence time.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-2113
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  • 7
    Publication Date: 2019-06-28
    Description: Self-pressurization of cryogenic storage tanks due to heat leak through the thermal protection system is examined along with the performance of various pressure control technologies for application in microgravity environments. Methods of pressure control such as fluid mixing, passive thermodynamic venting, and active thermodynamic venting are analyzed using the homogeneous thermodynamic model. Simplified equations suggested may be used to characterize the performance of various pressure control systems and to design space experiments.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-2405
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  • 8
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    In:  Other Sources
    Publication Date: 2019-06-28
    Description: The performance of water-cooled and radiation-cooled arcjet thrusters operating on both 1:2 nitrogen/hydrogen mixtures at 1-2 kW and on pure hydrogen at 1-4 kW are compared. To investigate the effects of test facility background pressure on performance, data were taken for both thrusters operating on hydrogen/nitrogen mixtures at facility background pressures nominally at 0.20 Pa and 20 Pa. It is shown that increasing the background pressure decreased the thruster performance, and simple pressure area corrections alone could not account for the observed degradation in performance.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-2456
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  • 9
    Publication Date: 2019-06-28
    Description: The NASA Lewis Research Center conducts and directs an electric propulsion research and technology program aimed at providing high-performance electric propulsion system options for a broad range of near- and far-term missions. This evolutionary program emphasizes the development of propulsion systems for three classes of missions: (1) near-term auxiliary propulsion applications such as North-South Stationkeeping for next generation communications satellites and orbit maintenance for orbiting platforms such as Space Station Freedom; (2) advanced solar electric propulsion and SP-100-class nuclear electric propulsion (NEP) for earth-space orbit transfer and robotic planetary missions; and (3) very high power systems to support major space missions including the Space Exploration Initiative. To cover widely disparate mission requirements, the program includes research on electrothermal, electrostatic, and electromagnetic systems. This paper provides an overview of the program with a focus on recent progress.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: IAF PAPER 91-241
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  • 10
    Publication Date: 2019-06-28
    Description: An experimental investigation was performed to evaluate hydrogen arcjet operating characteristics in the range of 1 to 4 kW. A series of nozzles were operated in modular laboratory thrusters to examine the effects of geometric parameters such as constrictor diameter and nozzle divergence angle. Each nozzle was tested over a range of current and mass flow rates to explore stability and performance. In the range of mass flow rates and power levels tested, specific impulse values between 650 and 1250 sec were obtained at efficiencies between 30 and 40 percent. The performance of the two larger half angle (20, 15 deg) nozzles was similar for each of the two constrictor diameters tested. The nozzles with the smallest half angle (10 deg) were difficult to operate. A restrike mode of operation was identified and described. Damage in the form of melting was observed in the constrictor region of all the nozzle inserts tested. Arcjet ignition was also difficult in many tests and a glow discharge mode that prevents starting was identified.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-2227
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