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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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At least 991 records · Page 55

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NASA NTRS1984

NASA welding assessment program

A long duration test was conducted for comparing various methods of attaching electrical interconnects to solar cells for near Earth orbit spacecraft. Representative solar array modules were thermally cycled for 36,000 cycles between -80 and +80 C. The environmental stress of more than 6 years on a near Earth spacecraft as it cycles in and out of the earth's shadow was simulated. Evaluations of the integrity of these modules were made by visual and by electrical examinations before starting the cycling and then at periodic intervals during the cycling tests. Modules included examples of parallel gap and of ultrasonic welding, as well as soldering. The materials and fabrication processes are state of the art, suitable for forming large solar arrays of spacecraft quality. The modules survived this extensive cycling without detectable degradation in their ability to generate power under sunlight illumination.

Stofel, E. J.↗

NASA NTRS1984

Solar powered actuator with continuously variable auxiliary power control

A solar powered system is disclosed in which a load such as a compressor is driven by a main induction motor powered by a solar array. An auxiliary motor shares the load with the solar powered motor in proportion to the amount of sunlight available, is provided with a power factor controller for controlling voltage applied to the auxiliary motor in accordance with the loading on that motor. In one embodiment, when sufficient power is available from the solar cell, the auxiliary motor is driven as a generator by excess power from the main motor so as to return electrical energy to the power company utility lines.

Nola, F. J.↗

NASA NTRS1985

Anomalously high potentials observed on ISEE

Data from two electric field experiments and from the plasma composition experiment on ISEE-1 are used to show that the spacecraft charged to close to -70 V in sunlight at 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. The stringent electrostatic cleanliness specifications imposed on ISEE make the presence of differential charging unlikely. Modeling of this event is required to determine if the barrier was produced by the presence of space charge.

Whipple, E. C.↗

NASA NTRS1985

Radiation-dominated Snowmelt on Mars

A set of microclimatic conditions conducive to the generation of liquid water is being sought to see whether their requirements are any less stringent than those suggested by the global-climatic models. In particular, the melting of snow and ice in the equatorial zone (where the valley networks are preferentially situated) is investigated with a model that includes detailed infrared radiation transfer between the atmosphere and the snow, penetration of sunlight into the snow, sensible heat transfer to the atmosphere, and water vapor diffusion within the surface boundary layer. IR fluxes are calculated by using pressure and temperature dependent forms for the band absorptances of CO2 and H2O in the spectral range 50 to 2000/cm.

Clow, G. D.↗

NASA NTRS1983

Modelling of photodegradation in solar cell modules of substrate and superstrate design made with ethylene-vinyl acetate as pottant material

A computer model was developed which can generate realistic concentration versus time profiles of the chemical species formed during photooxidation of hydrocarbon polymers using as input data a set of elementary reactions with corresponding rate constants and initial conditions. The results of computer simulation have been shown to be consistent with the general experimental observations of the photooxidation of polyethylene exposed to sunlight at ambient temperatures. The useful lifetime (5% oxidation) of the unstabilized polyethylene is predicted to vary from a few months in hot weather (100 F) to almost two years in cool weather (45 F) with an apparent net activation energy of 10 kcal/mol. Modelling studies of alternate mechanisms for stabilization of clear, amorphous, linear polyethylene suggest that the optimum stabilizer would be a molecularly dispensed additive in very low concentration which can trap peroxy radicals and also decompose hydroperoxides.

Somersall, A. C.↗

NASA NTRS1984

NASA welding assessment program

A long duration test has been conducted for comparing various methods of attaching electrical interconnects to solar cells for near Earth orbit spacecraft. Representative solar array modules have been thermally cycled for 36,000 cycles between -80 and +80 C on this JPL and NASA Lewis Research Center sponsored work. This test simulates the environmental stress of more than 6 years on a near Earth spacecraft as it cycles in and out of the Earth's shadow. Evaluations of the integrity of these modules were made by visual and by electrical examinations before starting the cycling and then at periodic intervals during the cycling tests. Modules included examples of parallel gap and of ultrasonic welding, as well as soldering. The materials and fabrication processes are state of the art, suitable for forming large solar arrays of spacecraft quality. The modules survived his extensive cycling without detectable degradation in their ability to generate power under sunlight illumination.

Stofel, E. J.↗

NASA NTRS1985

Technical development to improve satellite sounding over radiatively complex terrain

High resolution topography was acquired and applied on the McIDAS system. A technique for finding the surface skin temperature in the presence of cloud and reflected sunlight was implemented in the ALPEX retrieval software and the variability of surface emissivity at microwave wavelength was examined. Data containing raw radiances for all HIRS and MSU channels for NOAA-6 and 7 were used. METEOSAT data were used to derive cloud drift and water vapor winds over the Alpine region.

Schreiner, A. J.↗

NASA NTRS1985

Voyage to Uranus

Preparations being made for the Voyager 2's encounter with the seventh planet, Uranus are discussed. Research activities involved with the methane in Uranus' atmosphere and its absorption of photons of sunlight are discussed.

Dalrymple, M.↗

NASA NTRS1985

Activity and accomplishments of dish/Stirling electric power system development

The development of the solar parabolic-dish/Stirling-engine electricity generating plant known as the dish/Stirling electric power system is described. The dish/Stirling electric power system converts sunlight to electricity more efficiently than any known existing solar electric power system. The fabrication and characterization of the test bed concentrators that were used for Stirling module testing and of the development of parabolic dish concentrator No. 2, an advanced solar concentrator unit considered for use with the Stirling power conversion unit is discussed.

Livingston, F. R.↗

NASA NTRS1985

Recombination phenomena in high efficiency silicon solar cells

The dominant recombination phenomena which limit the highest efficiency attainable in silicon solar cells under terrestrial sunlight are reviewed. The ultimate achievable efficiency is limited by the two intrinsic recombination mechanisms, the interband Auger recombination and interband Radiative recombination, both of which occur in the entire cell body but principally in the base layer. It is suggested that an optimum (26%) cell design is one with lowly doped 50 to 100 micron thick base, a perfect BSF, and zero extrinsic recombination such as the thermal mechanism at recombination centers the Shockley-Read-Hall process (SRH) in the bulk, on the surface and at the interfaces. The importance of recombination at the interfaces of a high-efficiency cell is demonstrated by the ohmic contact on the back surface whose interface recombination velocity is infinite. The importance of surface and interface recombination is demonstrated by representing the auger and radiative recombination losses by effective recombination velocities. It is demonstrated that the three highest efficiency cells may all be limited by the SRH recombination losses at recombination centers in the base layer.

Sah, C. T.↗

NASA NTRS1985

High Lifetime Solar Cell Processing and Design

In order to maximize efficiency a solar cell must: (1) absorb as much light as possible in electron-hole production, (2) transport as large a fraction as possible of the electrons to the n-type terminal and holes to the p-type terminal without their first recombining, and (3) produce as high as possible terminal voltage. Step (1) is largely fixed by the spectrum of sunlight and the fundamental absorption characteristics of silicon, although some improvements are possible through texturizing induced light trapping and back surface reflectors. Steps (2) and (3) are, however, dependent on the recombination mechanisms of the cell. The recombination, on the contrary, is strongly influenced by cell processing and design. Some of the lessons during the development of point-contact-cell are discussed. Cell dependence on recombination, surface recombination, and contact recombination are discussed. Results show the overwhelming influence of contact recombination on the operation of the cell when the other sources of recombination are reduced by careful processing.

Swanson, R. M.↗

NASA NTRS1985

Earth Albedo and the orbit of LAGEOS

The long-period perturbations in the orbit of the Lageos satellite due to the Earth's albedo have been found using a new analytical formalism. The Earth is assumed to be a sphere whose surface diffusely reflects sunlight according to Lambert's law. Specular reflection is not considered. The formalism is based on spherical harmonics; it produces equations which hold regardless of whether the terminator is seen by the satellite or not. Specializing to the case of a realistic zonal albedo shows that Lageos' orbital semimajor axis changes periodically by only the a few millimeters and the eccentricity by one part in 100,000. The longitude of the node increases secularly. The effect considered here can explain neither the secular decay of 1.1 mm/day in the semimajor axis nor the observed along-track variations in acceleration of order 2 x 10 to the minus 12 power/sq ms.

Rubincam, D. P.↗

NASA NTRS1984

Reference-cell calibration activities

The use of secondary calibration in large area pulsed solar simulators (LAPSS) is discussed. It is argued that primary calibration in sunlight is time consuming, that only a limited sun calibration of a set of primary reference cells is required, that the LAPSS light source is filtered to closely match the am 1.5 direct spectrum, and that the temperal stability of the filtered LAPSS is excellent. There is the possibility of a lower error rate. Lower costs are anticipated.

Mueller, R.↗

NASA NTRS1985

Volatiles on satellites of the outer solar system

Molecules of cosmochemically abundant elements can act as volatiles and hence play a dominant role in the climatic and surficial evolution of solid bodies. Examples on terrestrial planets are H2O on Earth and H2O and CO2 on Mars. Analogous processes in the outer solar system focussing on CH4, its associated hydrocarbons, and N2 on Titan and Triton, the large moons of Saturn and Neptune were explored. A kilometer-deep C2H6-CH4 ocean was proposed for the surface of Titan to reconcile data on the lower atmosphere with understanding of the photochemical conversion of methane to heavier hydrocarbons. If such ocean exists, then it has dissolved in it an amount of N2 equal to the present atmospheric abundance. Since N2 contributes with CH4 a substantial greenhouse effect, the atmospheric physical and chemical characteristics are strongly coupled to those of the ocean, which change with time as methane is photolyzed in the stratosphere. Some relationship exists to the runaway greenhouse model for primordial Venus and the possible climatic implications of the buffering of Earth's atmospheric CO2 by the oceans. Two important diagnostics, measurable in Titan's atmosphere, of the conditions under which icy satellites formed are the abundances of noble gases and the CHd/CH4 radio. Both of these indicators have been altered during the evolution of Titan's surface-atmosphere system, the former by interaction with the ocean and the latter by progressive photolysis of methane into heavier hydrocarbons. The physical state and composition of volatiles on the surface of Triton is controversial, but plausibly could include CH4 N2 and perhaps CO. If condensed CH4 and N2 are widespread, their transformation to and from the vapor phase dominates the surface energy balance with sunlight. The extreme seasonal modulation of subsolar latitude on Triton is thus primarily expressed by volatile transport rather than large teperature changes, with possibly drastic observational consequences. The presence of two volatile species differing greatly in their vapor pressures make Triton a crude analog of Mars. Triton might be more appropriately regarded as a deep-freeze version of Titan.

Lunine, J. I.↗

NASA NTRS1985

Solar Ultraviolet Spectral Irradiance Monitor (SUSIM)

The solar ultraviolet spectral irradiance monitor (SUSIM) measures the ultraviolet flux from the entire Sun with high absolute accuracy over the wavelength range 120 to 400 nm with a resolution of 0.1 nm. SUSIM consists of two identical double dispersion scanning spectrometers with 5 photodiodes, 2 photon counters, and a deuterium lamp calibration source, all sealed in a canister pressurized to 1.1 atmosphere of argon. One spectrometer is used almost continuously during sunlight, the other is used once per day as a calibration check. The observations will yield improved absolute measurements of the ultraviolet solar fluxes, provide an accurate reference for studies of variability of the solar fluxes on the time scales of the solar cycle and longer, and measure shorter term changes as well. These measurements complement the active cavity radiometer (ACR) measurements of the total solar irradiance. The data will be used to study the physical behavior of the Sun and the Earth's atmosphere, weather, and climate.

Moore, R. L.↗

NASA NTRS1983

HgCdTe infrared focal plane arrays for imaging spectrometer applications

It is pointed out that the development of two-dimensional infrared focal plane arrays (FPAs) offers new alternatives in imaging and remote sensing. Attention is given to an imaging spectrometer which represents a new concept exploiting two-dimensional arrays. This instrument is to be used for the remote sensing of the earth on the basis of a utilization of reflected sunlight in both the visible (VIS) and short wavelength infrared (SWIR). The imaging spectrometer concept is to make it possible to obtain contiguous spectral coverage at high resolution without having to use increasingly complex scanners. The concept utilizes a prism spectrometer to disperse the image of the slit across the area arrays in the focal plane. The focal plane consists of silicon CCDs for the VIS and near infrared portions of the spectrum and HgCdTe hybrid arrays for the SWIR.

Rode, J. P.↗

NASA NTRS1984

Control algorithms and computer simulation of a stand-alone photovoltaic village power system

At Stand-Alone Photovoltaic (SAPV) power systems increase in size and load diversity, the design and simulation of control subsystems takes on added importance. These SAPV systems represent 'mini utilities' with commensurate controls requirements, albeit with the added complexity of the energy source (sunlight received) being an uncontrollable variable. This paper briefly describes a stand-alone photovoltaic power/load system computerized simulation model. The model was tested against operational data from the Schuchuli stand-alone village photovoltaic system and has achieved acceptable levels of simulation accuracy. The model can be used to simulate system designs although with probable battery modification.

Groumpos, P. P.↗

NASA NTRS1984

A new interpretation of the Venera 11 spectra of Venus. I - The 0.94 micron water band

Detailed band models for CO2 and H2O absorption are used to reinterpret Venera 11 spectra of the transmitted sunlight at several levels in the Venus atmosphere. An effective path approximation is used to allow for scattering in the clouds. The atmospheric model has 10 layers and uses 211 CO2 and 15 H2O vibrational transitions at 5/cm resolution. The conclusion of Moroz et al. (1979) that the 0.94 micron feature of the spectra indicates a sharp maximum in the water-vapor profile near 50 km is confirmed. It is also confirmed that such a profile fails to account for the spectra in the 1.13 micron water bands.

Young, L. D. G.↗