Engineering topics

Landis, Geoffrey A.

Publications and source records attributed to Landis, Geoffrey A..

At least 199 records · Page 11

NASA NTRS1991

Tether methods for reactionless orbital propulsion

In space, limits on transportation effectiveness are set by requirements for reaction mass, since reaction mass must be carried on board and often comprises the majority of the launch mass of a space system. Thus, applications where a tether can be used for propulsion with no requirement of reaction mass are extremely attractive for space development. It is a remarkable fact that tethers can be used to increase orbital energy with no requirement for reaction mass.

Landis, Geoffrey A.↗

NASA NTRS1991

Photovoltaic power options for Mars

The performance of a photovoltaic array is considered in terms of the properties of the Martian surface. Attention is given to the low solar intensity and high temperatures of Mars and to the performance of different chemical structures for the cells such as GaAs and silicon cells. A sample case is examined and it is shown that certain variables are still not understood with respect to photovoltaic performance on other planets.

Landis, Geoffrey A.↗

NASA NTRS1991

Structural scaling approximations for solar arrays

General scaling rules for a photovoltaic array structure are required in order to compare the effectiveness of different cell technologies. Important evaluation criteria for an array are moment of inertia, resonant frequency of vibrational modes, stiffness against acceleration, and resistance losses in the wiring. Approximate scaling relationships for these parameters for a generic solar array structure are presented.

Landis, Geoffrey A.↗

NASA NTRS1991

In-situ carbon dioxide fixation on Mars

The authors examine several novel proposals for CO2 fixation through chemical, photochemical, and photoelectrochemical means. For example, the reduction of CO2 to hydrocarbons such as acetylene (C2H2) can be accomplished with hydrogen. Acetylene has a theoretical vacuum specific impulse of about 375 s. The authors also examine potential uses of CO, as obtained or further reduced to carbon, as a reducing agent in metal oxide processing to form metals or metal carbides for use as structural or power materials. The CO2 can be recycled to generate O2 and CO. In this study, the authors examine reaction schemes for processing in situ resources. The authors highlight chemistry with hydrogen and carbon monoxide to produce propellants and other necessities of manned exploration.

Hepp, Aloysius F.↗

NASA NTRS1991

Applications of thin-film photovoltaics for space

The authors discuss the potential applications of thin-film polycrystalline and amorphous cells for space. There have been great advances in thin-film solar cells for terrestrial applications. Transfer of this technology to space applications could result in ultra low-weight solar arrays with potentially large gains in specific power. Recent advances in thin-film solar cells are reviewed, including polycrystalline copper indium selenide and related I-III-VI2 compounds, polycrystalline cadmium telluride and related II-VI compounds, and amorphous silicon arrays. The possibility of using thin-film multi-bandgap cascade solar cells is discussed.

Landis, Geoffrey A.↗

NASA NTRS1991

Minority carrier lifetime in indium phosphide

Transient photoluminescence is used to measure the minority carrier lifetime on n-type and p-type InP wafers. The measurements show that unprocessed InP wafers have very high minority carrier lifetimes. Lifetimes of 200 ns and 700 ns were observed for lightly-doped p- and n-type material respectively. Lifetimes over 5 ns were found in heavily doped n-type material.

Jenkins, Phillip↗

NASA NTRS1991

Enhancing optical absorption in InP and GaAs utilizing profile etching

The current state of profile etching in GaAs and InP is summarized, including data on novel geometries attainable as a function of etchant temperature, composition, and rate; substrate orientation; carrier concentration; and oxide thickness between substrate and photoresist. V-grooved solar cells have been manufactured with both GaAs and InP, and the improved optical absorption demonstrated. Preferred parameters for various applications are listed and discussed.

Bailey, Sheila G.↗

NASA NTRS1991

Photovoltaic receivers for laser beamed power in space

There has recently been a resurgence of interest in the use of beamed power to support space exploration activities. One of the most promising beamed power concepts uses a laser beam to transmit power to a remote photovoltaic array. Large lasers can be located on cloud-free sites at one or more ground locations and illuminate solar arrays to a level sufficient to provide operating power. Issues involved in providing photovoltaic receivers for such applications are discussed.

Landis, Geoffrey A.↗

NASA NTRS1990

Satellite eclipse power by laser illumination

A method is proposed to eliminate the energy storage system required to power a satellite in geosynchronous orbit during eclipse. An array of high-power CW lasers is situated at one or more ground locations in line of sight of the satellite, preferably on mountaintops. The lasers are provided with a tracking system, and lenses or mirrors of sufficient size to reduce the beam spread due to diffraction. As the satellite enters eclipse, the laser arrays illuminate the solar arrays on the satellite to a level sufficient to provide operating power.

Landis, Geoffrey A.↗

NASA NTRS1990

Reactionless orbital propulsion using tether deployment

Examples of tether propulsion in orbit without the use of reaction mass are discussed. These include (1) using tether extension to reposition a satellite in orbit without fuel expenditure by extending a mass on the end of the tether; (2) using a tether for eccentricity pumping to add energy to the orbit for boosting and orbital transfer; and (3) length modulation of a spinning tether to transfer angular momentum between the orbit and tether spin, thus allowing changes in orbital angular momentum.

Landis, Geoffrey A.↗

NASA NTRS1990

Vision-21: Space Travel for the Next Millennium

The papers from this symposium, that was held at the NASA Lewis Research Center on April 3-4, 1990, are presented. The theme selected for the symposium was space travel for the next millennium. It was hoped that the participants would allow their focus to consider possible advances in technologies for space travel not just for currently envisioned projects, but for possibilities beyond the next generation and the next thousand years. About half of the contributed papers focussed on propulsion and the other half on other issues related to space travel.

Landis, Geoffrey A.↗

NASA NTRS1990

Reactionless propulsion using tethers

An orbiting tethered satellite can propel itself by reaction against the gravitational gradient, with expenditure of energy but with no use of on-board reaction mass. Energy can be added to the orbit by pumping the tether length in the same way as pumping a swing. Examples of tether propulsion in orbit without use of reaction mass are discussed, including: (1) using tether extension to reposition a satellite in orbit without fuel expenditure by extending a mass on the end of a tether; (2) using a tether for eccentricity pumping to add energy to the orbit for boosting an orbital transfer; and (3) length modulation of a spinning tether to transfer angular momentum between the orbit and tether spin, thus allowing changes in orbital angular momentum.

Landis, Geoffrey A.↗

NASA NTRS1990

Applications of thin film technology toward a low-mass solar power satellite

Previous concepts for solar power satellites have used conventional-technology photovoltaics and microwave tubes. The authors propose using thin film photovoltaics and an integrated solid state phased array to design an ultra-lightweight solar power satellite, resulting in a potential reduction in weight by a factor of ten to a hundred over conventional concepts for solar power satellites.

Landis, Geoffrey A.↗

NASA NTRS1990

Wide-bandgap epitaxial heterojunction windows for silicon solar cells

It is shown that the efficiency of a solar cell can be improved if minority carriers are confined by use of a wide-bandgap heterojunction window. For silicon (lattice constant a = 5.43 A), nearly lattice-matched wide-bandgap materials are ZnS (a = 5.41 A) and GaP (a = 5.45 A). Isotype n-n heterojuntions of both ZnS/Si and GaP/Si were grown on silicon n-p homojunction solar cells. Successful deposition processes used were metalorganic chemical vapor deposition (MO-CVD) for GaP and ZnS, and vacuum evaporation of ZnS. Planar (100) and (111) and texture-etched - (111)-faceted - surfaces were used. A decrease in minority-carrier surface recombination compared to a bare surface was seen from increased short-wavelength spectral response, increased open-circuit voltage, and reduced dark saturation current, with no degradation of the minority carrier diffusion length.

Landis, Geoffrey A.↗

NASA NTRS1990

Design considerations for lunar base photovoltaic power systems

A survey was made of factors that may affect the design of photovoltaic arrays for a lunar base. These factors, which include the lunar environment and system design criteria, are examined. A photovoltaic power system design with a triangular array geometry is discussed and compared to a nuclear reactor power systems and a power system utilizing both nuclear and solar power sources.

Hickman, J. Mark↗

NASA NTRS1990

An evolutionary path to satellite solar power systems

A difficulty with proposals for satellite solar power systems is the absence of a plausible evolutionary pathway to development of systems on the scale required. One possible pathway is discussed, where the required technologies are developed and refined on an incremental scale. The initial stages of the process are development of ground-based photovoltaic power and of beamed power systems for space use.

Landis, Geoffrey A.↗

NASA NTRS1990

Design considerations for lunar base photovoltaic power systems

A survey was made of factors that may affect the design of photovoltaic arrays for a lunar base. These factors, which include the lunar environment and system design criteria, are examined. A photovoltaic power system design with a triangular array geometry is discussed and compared to a nuclear reactor power system and a power system utilizing both nuclear and solar power sources.

Hickman, J. M.↗

NASA NTRS1990

Design considerations for Mars photovoltaic power systems

Considerations for operation of a photovoltaic power system on Mars are discussed with reference to Viking Lander data. The average solar insolation at Mars is 590 W/sq m, which is reduced yet further by atmospheric dust. Of major concern are dust storms, which have been observed to occur on local as well as on global scales, and their effect on solar array output. While atmospheric opacity may rise to values ranging from 3 to 9, depending on storm severity, there is still an appreciable large diffuse illumination, even at high opacities, so that photovoltaic operation is still possible. If the power system is to continue to generate power even on high-optical-opacity (i.e., dusty atmosphere) days, it is important that the photovoltaic system be designed to collect diffuse irradiance as well as direct. Energy storage will be required for operation during the night. Temperature and wind provide additional considerations for array design.

Landis, Geoffrey A.↗