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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Analysis of satellite servicing cost benefits

Under the auspices of NASA/JSC a methodology was developed to estimate the value of satellite servicing to the user community. Time and funding precluded the development of an exhaustive computer model; instead, the concept of Design Reference Missions was involved. In this approach, three space programs were analyzed for various levels of servicing. The programs selected fall into broad categories which include 80 to 90% of the missions planned between now and the end of the century. Of necessity, the extrapolation of the three program analyses to the user community as a whole depends on an average mission model and equivalency projections. The value of the estimated cost benefits based on this approach depends largely on how well the equivalency assumptions and the mission model match the real world. A careful definition of all assumptions permits the analysis to be extended to conditions beyond the scope of this study.

Builteman, H. O.↗
NASA NTRSDate not supplied

Modeling of A Large-Scale Liquid Oxygen Propellant Transfer Test

Current planned NASA missions to the Moon and Mars involve the transfer of cryogenic propellants in orbit. Correctly predicting the flow rate during the propellant transfer operation could help with planning these operations. In lieu of expensive tests conducted on-orbit, accurate predictive computational models of these propellant transfer processes can be used to predict the propellant transfer flow rate. To gain confidence in these computational models, appropriate anchoring and validation to experimental data can be performed. Ground tests conducted at SpaceX involving the transfer of liquid oxygen were carried out to investigate the effect of the thermodynamic conditions including inlet pressure and temperature and downstream pressure on the flow rate. The results from the test were compared against flow rate predictions from a commercially available two-phase flow software. On average the model predicted the flow rates within 10% of the experimentally observed flow rates for the full range of thermodynamic inlet and outlet conditions.

Daniel Hauser↗
NASA NTRS1980

Arctic and Antarctic climatology of a GLAS general circulation model

A Jan.-Feb. climatology model was constructed from the GLAS general circulation model by averaging eight 30-day means of periods from Jan. 15-Feb. 14. The position and intensity of the Aleutian and Icelandic lows in the winter, the central Arctic pressure distribution during winter and summer, and the summertime North Atlantic and North Pacific high pressure regimes were satisfactorily simulated; sensible and evaporative heat fluxes and radiation budget parameters were reasonable, although a rigorous comparison is difficult due to data deficiencies. The model is less successful in simulating the Southern Hemisphere climatology; the 500 mb circumpolar flow is adequate, but the stationary low pressure centers at the surface around the Antarctic continent are not well reproduced.

Herman, G. F.↗
NASA NTRS1991

Nonlinear time-series-based adaptive control applications

A control design methodology based on a nonlinear time-series reference model is presented. It is indicated by highly nonlinear simulations that such designs successfully stabilize troublesome aircraft maneuvers undergoing large changes in angle of attack as well as large electric power transients due to line faults. In both applications, the nonlinear controller was significantly better than the corresponding linear adaptive controller. For the electric power network, a flexible AC transmission system with series capacitor power feedback control is studied. A bilinear autoregressive moving average reference model is identified from system data, and the feedback control is manipulated according to a desired reference state. The control is optimized according to a predictive one-step quadratic performance index. A similar algorithm is derived for control of rapid changes in aircraft angle of attack over a normally unstable flight regime. In the latter case, however, a generalization of a bilinear time-series model reference includes quadratic and cubic terms in angle of attack.

Mohler, R. R.↗
NASA NTRS1986

Preliminary report on the geology and gold mineralization of the South Pass granite-greenstone terrain, Wind River Mountains, western Wyoming (US)

The South Pass granite-greenstone terrain lies near the southern tip of the Wind River Mountains of western Wyoming. This Archean supracrustal pile has been Wyoming's most prolific source of gold and iron ore. From 1962 to 1983, more than 90 million tons of iron ore were recovered from oxide-facies banded iron formation, and an estimated 325,000 ounces of gold were mined from metagreywacke-hosted shears and associated placers. Precambrian rocks at South Pass are unconformably overlain by Paleozoic sediments along the northeast flank, and a Tertiary pediment buries Archean supracrustals on the west and south. To the northwest, the supracrustals terminate against granodiorite of the Louis Lake batholith; to the east, the supracrustals terminate against granite of the Granite Mountains batholith. The Louis Lake granodiorite is approximately 2,630 + or - 20 m.y. old, and the Granite Mountains granite averages 2,600 m.y. old. The geometry of the greenstone belt is best expressed as a synform that has been modified by complex faulting and folding. Metamorphism is amphibolite grade surrounding a small island of greenschist facies rocks. The younger of the Archean supracrustal successions is the Miners Delight Formation. This unit yielded a Rb-Sr isochron of 2,800 m.y. A sample of galena from the Snowbird Mine within the Miners Delight Formation yielded a model age averaging 2,750 m.y. The Snowbird mineralization appears to be syngenetic and is hosted by metavolcanics of calc-alkaline affinity. Discussion follows.

Hausel, W. D.↗
NASA NTRS2019

Estimating Total Open Heliospheric Magnetic Flux

Over the solar-activity cycle, there are extended periods where significant discrepancies occur between the spacecraft-observed total (unsigned) open magnetic flux and that determined from coronal models. In this article, the total open heliospheric magnetic flux is computed using two different methods and then compared with results obtained from insitu interplanetary magnetic-field observations. The first method uses two different types of photospheric magnetic-field maps as input to the Wang–Sheeley–Arge (WSA) model: i) traditional Carrington or diachronic maps, and ii) Air Force Data Assimilative Photospheric Flux Transport model synchronic maps. The second method uses observationally derived helium and extreme-ultraviolet coronal-hole maps overlaid on the same magnetic-field maps in order to compute total open magnetic flux. The diachronic and synchronic maps are both constructed using magnetograms from the same source, namely the National Solar Observatory Kitt Peak Vacuum Telescope and Vector Spectromagnetograph. The results of this work show that the total open flux obtained from observationally derived coronal holes agrees remarkably well with that derived from WSA, especially near solar minimum. This suggests that, on average, coronal models capture well the observed large-scale coronal-hole structure over most of the solar cycle. Both methods show considerable deviations from total open flux deduced from spacecraft data, especially near solar maximum, pointing to something other than poorly determined coronal-hole area specification as the source of these discrepancies.

Wallace, S.↗
NASA NTRS2010

Abundances of Jupiter's Trace Hydrocarbons from Voyager and Cassini

The flybys of Jupiter by the Voyager spacecraft in 1979, and over two decades later by Cassini in 2000, have provided us with unique datasets from two different epochs, allowing the investigation of seasonal change in the atmosphere. In this paper we model zonal averages of thermal infrared spectra from the two instruments, Voyager 1 IRIS and Cassini CIRS, to retrieve the vertical and meridional profiles of temperature, and the abundances of the two minor hydrocarbons, acetylene (C2H2) and ethane (C2H6). The spatial variation of these gases is controlled by both chemistry and dynamics, and therefore their observed distribution gives us an insight into both processes, We find that the two gases paint quite different pictures of seasonal change. Whilst the 2-D cross-section of C2H6 abundance is slightly increased and more symmetric in 2000 (northern summer solstice) compared to 1979 (northern fall equinox), the major trend of equator to pole increase remains. For C2H2 on tile other hand, the Voyager epoch exhibits almost no latitudinal variation, whilst the Cassini era shows a marked decrease polewards in both hemispheres. At the present time, these experimental findings are in advance of interpretation, as there are no published models of 2-D Jovian seasonal chemical variation available for comparison.

Nixon, C. A.↗
NASA NTRS1992

A modeling study of the time-averaged electric currents in the vicinity of isolated thunderstorms

A thorough examination of the results of a time-dependent computer model of a dipole thunderstorm revealed that there are numerous similarities between the time-averaged electrical properties and the steady-state properties of an active thunderstorm. Thus, the electrical behavior of the atmosphere in the vicinity of a thunderstorm can be determined with a formulation similar to what was first described by Holzer and Saxon (1952). From the Maxwell continuity equation of electric current, a simple analytical equation was derived that expresses a thunderstorm's average current contribution to the global electric circuit in terms of the generator current within the thundercloud, the intracloud lightning current, the cloud-to-ground lightning current, the altitudes of the charge centers, and the conductivity profile of the atmosphere. This equation was found to be nearly as accurate as the more computationally expensive numerical model, even when it is applied to a thunderstorm with a reduced conductivity thundercloud, a time-varying generator current, a varying flash rate, and a changing lightning mix.

Driscoll, Kevin T.↗
NASA NTRS2022

Climate Change Penalty and Benefit on Surface Ozone: A Global Perspective Based on CMIP6 Earth System Models

This work presents an analysis of the effect of climate change on surface ozone discussing the related penalties and benefits around the globe from the global modelling perspective based on simulations with five CMIP6 (Coupled Model Intercomparison Project Phase 6) Earth System Models. As part of AerChemMIP (Aerosol Chemistry Model Intercomparison Project) all models conducted simulation experiments considering future climate (ssp370SST) and present-day climate (ssp370pdSST) under the same future emissions trajectory (SSP3-7.0). A multi-model global average climate change benefit on surface ozone of −0.96 ± 0.07 ppbv °C−1 is calculated which is mainly linked to the dominating role of enhanced ozone destruction with higher water vapour abundances under a warmer climate. Over regions remote from pollution sources, there is a robust decline in mean surface ozone concentration on an annual basis as well as for boreal winter and summer varying spatially from −0.2 to −2 ppbv °C−1, with strongest decline over tropical oceanic regions. The implication is that over regions remote from pollution sources (except over the Arctic) there is a consistent climate change benefit for baseline ozone due to global warming. However, ozone increases over regions close to anthropogenic pollution sources or close to enhanced natural biogenic volatile organic compounds emission sources with a rate ranging regionally from 0.2 to 2 ppbv C−1, implying a regional surface ozone penalty due to global warming. Overall, the future climate change enhances the efficiency of precursor emissions to generate surface ozone in polluted regions and thus the magnitude of this effect depends on the regional emission changes considered in this study within the SSP3_7.0 scenario. The comparison of the climate change impact effect on surface ozone versus the combined effect of climate and emission changes indicates the dominant role of precursor emission changes in projecting surface ozone concentrations under future climate change scenarios.

surface ozone↗
NASA NTRS2015

Physical Models of Layered Polar Firn Brightness Temperatures from 0.5 to 2 GHz

We investigate physical effects influencing 0.5-2 GHz brightness temperatures of layered polar firn to support the Ultra Wide Band Software Defined Radiometer (UWBRAD) experiment to be conducted in Greenland and in Antarctica. We find that because ice particle grain sizes are very small compared to the 0.5-2 GHz wavelengths, volume scattering effects are small. Variations in firn density over cm- to m-length scales, however, cause significant effects. Both incoherent and coherent models are used to examine these effects. Incoherent models include a 'cloud model' that neglects any reflections internal to the ice sheet, and the DMRT-ML and MEMLS radiative transfer codes that are publicly available. The coherent model is based on the layered medium implementation of the fluctuation dissipation theorem for thermal microwave radiation from a medium having a nonuniform temperature. Density profiles are modeled using a stochastic approach, and model predictions are averaged over a large number of realizations to take into account an averaging over the radiometer footprint. Density profiles are described by combining a smooth average density profile with a spatially correlated random process to model density fluctuations. It is shown that coherent model results after ensemble averaging depend on the correlation lengths of the vertical density fluctuations. If the correlation length is moderate or long compared with the wavelength (approximately 0.6x longer or greater for Gaussian correlation function without regard for layer thinning due to compaction), coherent and incoherent model results are similar (within approximately 1 K). However, when the correlation length is short compared to the wavelength, coherent model results are significantly different from the incoherent model by several tens of kelvins. For a 10-cm correlation length, the differences are significant between 0.5 and 1.1 GHz, and less for 1.1-2 GHz. Model results are shown to be able to match the v-pol SMOS data closely and predict the h-pol data for small observation angles.

layered polar firn emission↗
NASA NTRS1974

Regolith history from cosmic-ray-produced isotopes

A statistical model is given for soil development relating meteoroid impacts on the moon to cosmic-ray-produced isotopes in the soil. By means of this model, the average lunar mass loss rate during the past 1.4 aeons is determined to be 170g/sq cm aeon and the soil mixing rate to be approximately 200 cm/aeon from the gadolinium isotope data for the Apollo 15 and 16 drill stems. The isotope data also restrict the time variation of the meteoroid flux during the past 1.4 aeons.

Fireman, E. L.↗
NASA NTRS1976

Maximum likelihood convolutional decoding (MCD) performance due to system losses

A model for predicting the computational performance of a maximum likelihood convolutional decoder (MCD) operating in a noisy carrier reference environment is described. This model is used to develop a subroutine that will be utilized by the Telemetry Analysis Program to compute the MCD bit error rate. When this computational model is averaged over noisy reference phase errors using a high-rate interpolation scheme, the results are found to agree quite favorably with experimental measurements.

Webster, L.↗
NASA NTRS1975

Sequential decoding in the presence of a noisy carrier reference

A new model for predicting the computational performance of a sequential decoder operating in a noisy carrier reference environment is described. The major difference between this model and previous models is that the new model characterizes the number of computations per frame as the sum of the computations resulting from a number of independent searches. This number of independent searches can then be considered as an effective frame length. When this computational model is averaged over noisy reference phase errors using a medium-rate interpolation scheme, the results are found to agree quite favorably with experimental measurements.

Lesh, J. R.↗
NASA NTRS1975

Sequential decoding in the presence of a noisy carrier reference

A new model for predicting the computational performance of a sequential decoder operating in a noisy carrier reference environment is described. The major difference between this model and previous models is that the new model characterizes the number of computations per frame as the sum of the computations resulting from a number of independent searches. This number of independent searches can then be considered as an effective frame length. When this computational model is averaged over noisy reference phase errors using a medium-rate interpolation scheme, the results are found to agree quite favorably with experimental measurements.

Lesh, J. R.↗
NASA NTRS1977

Analysis of torsional spectra of molecules with two C3v internal rotors. IV - The torsional potential function for propane-d0 and -d3

The Raman spectra of gaseous propane-d0 and -d3 have been recorded between 50 and 3500 cm. Considerable torsional data are reported and used to characterize the torsional potential function based on a semirigid model. The average 'effective' V3 for the propanes is found to be 1139 plus or minus 10/cm. The sine-sine coupling term is similar in magnitude but opposite in sign to the cosine-cosine coupling term in propane-d0.

Durig, J. R.↗
NASA NTRS1977

Analysis of torsional spectra of molecules with two internal C/3v/ rotors. III - Far-infrared and gas phase Raman spectra of dimethylamine-d0, -d3, and -d6

The Raman spectra of gaseous dimethylamine-d0, -d3, and -d6 have been recorded between 0 and 4000/cm. The far-infrared spectra have been recorded between 300 and 100/cm. Considerable torsional data are reported and used to characterize the torsional potential function based on a semi-rigid model. The average effective V3 for the dimethylamines was found to be 1052 plus or minus 12/cm. The cos-cos coupling term was approximately 15% of the effective V3, whereas the sine-sine coupling term was of an order of magnitude smaller for (CH3)2NH and (CD3)2NH. However, for the mixed isotope the sine-sine term was found to be negligible and the cos-cos about one-half the value obtained for the other two isotopes.

Durig, J. R.↗
NASA NTRS1978

Development and evaluation of a hybrid averaged orbit generator

A rapid orbit generator based on a first-order application of the Generalized Method of Averaging has been developed for the Research and Development (R&D) version of the Goddard Trajectory Determination System (GTDS). The evaluation of the averaged equations of motion can use both numerically averaged and recursively evaluated, analytically averaged perturbation models. These equations are numerically integrated to obtain the secular and long-period motion. Factors affecting efficient orbit prediction are discussed and guidelines are presented for treatment of each major perturbation. Guidelines for obtaining initial mean elements compatible with the theory are presented. An overview of the orbit generator is presented and comparisons with high precision methods are given.

Mcclain, W. D.↗