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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 541 records · Page 30

Data on incident solar energy

Instrumentation for solar irradiance monitoring, and radiation scales are discussed in a survey of incident solar energy data. The absolute accuracy and intrinsic reliability of the values of the solar constant and zero air mass solar spectrum proposed by the Institute of Environmental Sciences as an ASTM standard are evaluated. Extraterrestrial observations are used for deriving solar irradiance data at ground level for widely varying atmospheric parameters, with special reference to air pollution. The effects of diffuse sky radiance and those of varying slopes of the solar energy collecting surface are examined. Average values of solar energy available at different locations in the United States are included.

Thekaekara, M. P.↗

The structure of clusters of galaxies observed with Einstein

Imaging observations from the Einstein Observatory are used to determine properties of galactic clusters and the intracluster gas. The hydrostatic-isothermal gas model is applied to obtain the cluster core radius, the limiting slope of the X-ray surface brightness distribution, and the presence and magnitude of a central luminosity excess above that predicted from the model when fit to the outer regions of the cluster. It is concluded that clusters can be divided into two basic families, one with small core radii and X-ray emission centered on a central dominant galaxy, and one with larger core radii and generally no central, stationary bright galaxy. The former type probably begins to form in the early stages of a cluster's dynamical evolution. The intracluster gas has a larger scale height than that of the galaxies based on the fit of the hydrostatic-isothermal model to the X-ray surface brightness profiles.

Jones, C.↗

An assessment of the crustal remelting hypothesis for volcanism in the Freyja Montes deformation zone

The linear mountain belts of Ishtar Terra on Venus are notable for their topographic relief and slope and for the intensity of surface deformation. The mountains surround the highland plain Lakshmi Planum, the site of two major paterae and numerous other volcanic features and deposits, and evidence is widespread for volcanism within the mountains and in terrain immediately outward of the mountain belt units. While two hypotheses for magmatism can be distinguished on the basis of the chemistry of the melts, chemical data are presently lacking for the Ishtar region. The competing hypotheses for magmatism in Western Ishtar Terra can also be tested with thermal models, given a kinematic or dynamic model for the evolution of the region. The crustal remelting hypothesis is assessed, using the kinematic scenario of Head for the evolution of Freyja Montes. In that scenario, Freyja Montes formed by a sequence of large scale underthrusts of the lithosphere of the North Polar Plains beneath Ishtar Terra, with successive blocks of underthrust crust sutured in imbricate fashion onto the thickened crust of Lakshmi Planum and the mantle portion of underthrusting lithosphere episodically detached. The numerical experiments thus show that volcanic activity associated with the formation of the Frejya Montes deformation zone can be explained by crustal melting, due either to direct contact of crustal material with the hot asthenosphere or to heat generation in a thickened crustal layer.

Namiki, Noriyuki↗

Measurements of the interaction of wave groups with shorter wind-generated waves

Fields of statistically steady wind-generated waves produced in a wind wave facility were perturbed by the injection of groups of longer, mechanically generated waves with various slopes. The time histories of the surface displacements were measured at four fetches in ensembles consisting of 100 realizations of each set of experimental conditions; the data were stored and analyzed digitally. Four distinct stages in the overall interaction are identified and characterized. The properties of the wave energy front are documented, and a preliminary discussion is given of the dynamic processes involved in its formation.

Chu, Jacob S.↗

Eddy and wave dynamics in the South Atlantic as diagnosed from Geosat altimeter data

The characteristics of the sea surface height variability in the South Atlantic are investigated on the basis of almost 3 yr of Geosat data. The nature of the sea surface height field is shown to be nonstationary, heterogeneous, and anisotropic. The wavenumber spectral characteristics of the sea surface height field, such as spectral slopes, shape, breaks in spectral slopes, and energy density values, vary with latitude and longitude within the basin. The spectral slopes exhibit a spectral dependence approaching k exp -5 in the high-energy areas and k exp -3 in the low-energy areas. Along-track characteristic wavelengths are found to decrease from north to south and from west to east. The energy exhibits maximum values in the highly energetic eddy-shedding regions of the Malvinas-Brazil confluence and the Agulhas leakage region.

Forbes, Cristina↗

Mars Delay-Doppler Radar Observations With GSSR: Global Analysis for Landing Site Selection and Characterization

Earth-based radar data remain an important part of the information set used to select and certify spacecraft landing sites on Mars. Constraints on robotic landings on Mars include: terrain elevation, radar reflectivity. regional and local slopes, rock distribution and coverage, and surface roughness, all of which are addressed by radar data. Indeed, the usefulness of radar data for Mars exploration has been demonstrated in the past. Radar data were critical in assessing the Viking Lander I site, and more recently, the Mars Pathfinder landing site.

Haldemann, A. F. C.↗

Global Database of GSSR Mars Delay-Doppler Radar Obsevations: Analysis for Landing Site Characterization and Rover Trafficability

Earth-based radar data remain an important part of the information set used to select and certify spacecraft landing sites on Mars. Constraints on robotic landings on Mars include: terrain elevation, radar reflectivity, regional and local slopes, rock distribution and coverage, and surface roughness, all of which are addressed by radar data. Indeed, the usefulness of radar data for Mars exploration has been demonstrated in the past. Radar data were critical in assessing the Viking Lander, and more recently, the Mars Pathfinder landing.

Haldemann, A. F. C.↗

Global Database of GSSR Mars Delay-Doppler Radar Observations: Analysis for Landing Site Characterization and Rover Trafficability

Earth-based radar data remain an important part of the information set used to select and certify spacecraft landing sites on Mars. Constraints on robotic landings on Mars include: terrain elevation, radar reflectivity, regional and local slopes, rock distribution and coverage, and surface roughness, all of which are addressed by radar data. Indeed, the usefulness of radar data for Mars exploration has been demonstrated in the past. Radar data were critical in assessing the Viking Lander 1 site, and more recently, the Mars Pathfinder landing site.

Haldemann, A. F. C.↗

Greenland Glacier Albedo Variability

The program for Arctic Regional Climate Assessment (PARCA) is a NASA-funded project with the prime goal of addressing the mass balance of the Greenland ice sheet. Since the formal initiation of the program in 1995, there has been a significant improvement in the estimates of the mass balance of the ice sheet. Results from this program reveal that the high-elevation regions of the ice sheet are approximately in balance, but the margins are thinning. Laser surveys reveal significant thinning along 70 percent of the ice sheet periphery below 2000 m elevations, and in at least one outlet glacier, Kangerdlugssuaq in southeast Greenland, thinning has been as much as 10 m/yr. This study examines the albedo variability in four outlet glaciers to help separate out the relative contributions of surface melting versus ice dynamics to the recent mass balance changes. Analysis of AVHRR Polar Pathfinder albedo shows that at the Petermann and Jakobshavn glaciers, there has been a negative trend in albedo at the glacier terminus from 1981 to 2000, whereas the Stor+strommen and Kangerdlugssuaq glaciers show slightly positive trends in albedo. These findings are consistent with recent observations of melt extent from passive microwave data which show more melt on the western side of Greenland and slightly less on the eastern side. Significance of albedo trends will depend on where and when the albedo changes occur. Since the majority of surface melt occurs in the shallow sloping western margin of the ice sheet where the shortwave radiation dominates the energy balance in summer (e.g. Jakobshavn region) this region will be more sensitive to changes in albedo than in regions where this is not the case. Near the Jakobshavn glacier, even larger changes in albedo have been observed, with decreases as much as 20 percent per decade.

Source record↗

Summer Dust Aerosols Detected from CALIPSO Observations over the Tibetan Plateau

Summertime Tibetan dust aerosol plumes are detected from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. CALIPSO reveals that dust storms occur 4 times more frequently than previously found from Tibetan surface observations because few surface sites were available over remote northwestern Tibet. The Tibetan dust aerosol is characterized by column-averaged depolarization and color ratios around 21% and 0.83, respectively. The dust layers appear most frequently around 4-7 km above mean sea level. The depolarization ratio for about 90% of the dust particles is less than 10% at low altitudes (3-5 km), while only about 50% of the particles have a greater depolarization ratio at higher altitudes (7-10 km) suggesting a separation of larger irregular particles from smaller, near spherical ones during transport. The 4-day back trajectory analyses show that these plumes probably originate from the nearby Taklimakan desert surface and accumulate over the northern slopes of the Tibetan Plateau. These dust outbreaks can affect the radiation balance of the atmosphere of Tibet because they both absorb and reflect solar radiation.

Huang, Jianping↗

Limitations of Lifting-Line Theory for Estimation of Aileron Hinge-Moment Characteristics

Hinge-moment parameters for several typical ailerons were calculated from section data with the aspect-ratio correction as usually determined from lifting-line theory. The calculations showed that the agreement between experimental and calculated results was unsatisfactory. An additional aspect-ratio correction, calculated by the method of lifting-surface theory, was applied to the slope of the curve of hinge-moment coefficient against angle of attack at small angles of attack. This so-called streamline-curvature correction brought the calculated and experimental results into satisfactory agreement.

ATI-13584↗

Autonomous Off-road Navigation over Extreme Terrains with Perceptually-challenging Conditions

We propose a framework for resilient autonomous navigation in perceptuallychallenging unknown environments with mobility-stressing elements such asuneven surfaces with rocks and boulders, steep slopes, negative obstacles like cliffsand holes, and narrow passages. Environments are GPS-denied and perceptuallydegradedwith variable lighting from dark to lit and obscurants (dust, fog, smoke).Lack of prior maps and degraded communication eliminates the possibility of prioror off-board computation or operator intervention. This necessitates real-time onboardcomputation using noisy sensor data. To address these challenges, we proposea resilient architecture that exploits redundancy and heterogeneity in sensing modalities.Further resilience is achieved by triggering recovery behaviors upon failure.We propose a fast settling algorithm to generate robust multi-fidelity traversabilityestimates in real-time. The proposed approach was deployed on multiple physicalsystems including skid-steer and tracked robots, high-speed RC car and legged robotsand as a part of Team CoSTAR’s effort to theDARPASubterranean Challenge, wherethe team won 2nd and 1st place in the Tunnel and Urban Circuit, respectively.

Agha-mohammadi, Ali-akbar↗

Leveraging VIPER Geotechnical and Mobility Insights for Endurance Rover and Traverse Development

A new generation of lunar surface rover exploration is rapidly approaching. This is evidenced by the rise of commercially developed rovers from private companies (e.g., Lunar Outpost’s MAPP) and government agencies, like NASA’s Volatiles Investigating Polar Exploration Rover (VIPER), the Lunar Terrain Vehicle (LTV), and the Endurance/Intrepid rover concepts, and the INSPIRE mission concept. The drive distance requirements for off-world vehicles are also rapidly increasing. For example, LTV driving requirements dictate a 20 km range on a single battery charge, with an overall lifetime requirement of 13,000 km over a minimum 10-year service life. Similarly, NASA's Endurance-A mission concept requires a 2000 km vehicle traverse distance, which is nearly 50 times further than the USSR's Lunokhod 2, the longest lunar rover mission to date. Previous planetary surface missions on the Moon and Mars have revealed harsh mobility conditions: aggressive rocky terrains on Mars severely damaged the Curiosity rover’s wheels, soft lunar regolith caused the Lunokhod 2 rover to sink and NASA’s Apollo 15 LRV (Lunar Roving Vehicle) spun out due to poor traction, which required manual correction. This demonstrates that mobility challenges like wheel degradation and soft soil driving performance must be accounted for in a mission’s design phase to meet increasingly aggressive mission durations and mobility goals. The success of these long duration missions requires highly reliable and durable mobility platforms in conjunction with a more developed understanding of the geotechnical properties of the lunar surface. The VIPER mission is uniquely posed to inform future missions about mobility performance, wheel durability, and lunar surface soil mechanics of sunlit and shadowed regions through use of data streams that already exist for other mission purposes. VIPER’s mission to the lunar south pole will provide a new perspective into off-world mobility challenges including traversal into permanently shadowed regions. Mobility data from VIPER’s mission will represent a first glimpse into the surface mobility challenges of the lunar South Pole. Utilization of VIPER’s existing capabilities including cameras, inertial measurement unit (IMU) data, motor currents/torque, drill data, and the rover’s suspension state and kinematics provide the opportunity to determine potentially useful information for future rover and traverse designs, as well as on-Earth testing practices. Data products collected during VIPER’s mission could inform design considerations for the Endurance rover much earlier than NASA’s standard “lessons learned” approach as VIPER has a highly tactical mission operations structure. This work outlines the specific links between possible data products from the VIPER mission and their potential impact on the Endurance/Intrepid mission concepts in their early design phases. From VIPER, we will also gain insights for future development of onboard mobility software as VIPER is a way-point driven rover which requires more constant human operation on Earth than some other rover missions (non-lunar surface). Primary VIPER data products and insights of interest include wheel sinkage, wheel slip, wheel degradation, surface soil shear strength, and terrain slope estimation. VIPER data products will be made available via the Planetary Data System’s Geosciences and Cartography and Imaging Sciences nodes, conforming to the PDS4 standard.

mobility↗

Methane emission hotspots in a boreal forest-fen mosaic potentially linked to deep taliks

Permafrost thaw is transforming boreal forests into mosaics of wetlands and drier uplands. Topographic controls on hydrological and ecological conditions impact methane (CH 4 ) fluxes, contributing to uncertainty in local and regional CH 4 budgets and underlying drivers. The objective of this study was to explore CH 4 fluxes and their drivers in a transitioning boreal forest-fen ecosystem (Goldstream Valley, Alaska, USA). This landscape is characterized by thawing discontinuous permafrost and heterogeneous mosaics of fens, collapse-scar channels, and small mounds of permafrost soils. From a survey in July 2021, observed chamber CH4 fluxes included fen areas with intermediate to very high emissions (29.8–635.3 mg CH 4 m −2 d −1 ), clustered locations with CH 4 uptake (−2.11 to −0.7 mg CH 4 m −2 d −1 ), and three anomalous emission hotspots (342.4–772.4 mg CH 4 m −2 d −1 ) that were located near samples with lower emissions. Some surface and near-surface variables partially explained the spatial variation in CH 4 flux. Log-transformed CH 4 flux had a positive linear relationship with soil moisture at 20 cm depth ( R 2 = 0.31, p -value < 1e-5) and negative linear relationships with microtopography ( R 2 = 0.13, p -value < 0.006) and slope ( R 2 = 0.28, p -value < 2e-5). Methane emissions generally occurred in flat, wet, graminoid-dominated fens, whereas CH 4 uptake occurred on permafrost mounds dominated by feather mosses and woody vegetation. However, the CH 4 hotspots occurred on drier, slightly sloped locations with low or undetectable near-surface methanogen abundance, suggesting that CH 4 was produced in deeper soils. When the hotspot samples were omitted, log-transformed CH 4 flux had a positive linear relationship with near-surface methanogen abundance ( R 2 = 0.29, p -value = 0.0023), and stronger linear relationships with soil moisture, slope, and soil macronutrient concentrations. Our findings suggest that some CH 4 emission hotspots could arise from CH 4 in deep taliks. The inference that methanogenesis occurs in deep taliks was strengthened by the identification of intrapermafrost taliks across the study area using low-frequency geophysical induction. This study assesses surface spatial heterogeneity in the context of subsurface permafrost conditions and highlights the complexity of CH 4 flux patterns in transitioning forest-wetland ecosystems. To better inform regional CH 4 budgets, further research is needed to understand the spatial distribution of terrestrial CH 4 hotspots and to resolve their surface, near-surface, and subsurface drivers.

boreal↗

Spatial variation of sea surface temperature and flux-related parameters measured from aircraft in the JASIN experiment

Spatial variation of some parameters measured on two aircraft flying 100-km box and 200-km triangular patterns at low levels in the atmospheric boundary layer during the Joint Air Sea Interaction Experiment in the North Atlantic was studied. The variation should be representative of summer conditions in mid-latitude oceans. The variance density of remotely sensed sea surface temperature, corrected for sky reflection, is found to depend on the one-dimensional wave number raised to the power of approximately -5/3. Nonuniform clouds add low-frequency variance to observations of a downward looking radiometer and result in steeper slope of the spectra of uncorrected sea surface temperature. Turbulent fluxes of momentum, sensible heat, and moisture were determined with the bulk formulae from the parameters (wind speed, temperature, specific humidity, and sea surface temperature) measured from the aircraft. The averages of these fluxes over each flight leg were compared with the fluxes determined from the parameters averaged over the same leg. The difference is negligible, showing that spatially averaged observations, such as those from spaceborne sensors, can be used in the bulk formulae to evaluate the fluxes.

Liu, W. T.↗

The Spatial Coherence of Interannual Temperature Variations in the Antarctic Peninsula

Over 50 years of observations from climate stations on the west coast of the Antarctic Peninsula show that this is a region of extreme interannual variability in near-surface temperatures. The region has also experienced more rapid warming than any other part of the Southern Hemisphere. In this paper we use a new dataset of satellite-derived surface temperatures to define the extent of the region of extreme variability more clearly than was possible using the sparse station data. The region in which satellite surface temperatures correlate strongly with west Peninsula station temperatures is found to be quite small and is largely confined to the seas just west of the Peninsula, with a northward and eastward extension into the Scotia Sea and a southward extension onto the western slopes of Palmer Land. Correlation of Peninsula surface temperatures with surface temperatures over the rest of continental Antarctica is poor confirming that the west Peninsula is in a different climate regime. The analysis has been used to identify sites where ice core proxy records might be representative of variations on the west coast of the Peninsula. Of the five existing core sites examined, only one is likely to provide a representative record for the west coast.

King, John C.↗

Variable-Domain Displacement Transfer Functions for Converting Surface Strains into Deflections for Structural Deformed Shape Predictions

Variable-Domain Displacement Transfer Functions were formulated for shape predictions of complex wing structures, for which surface strain-sensing stations must be properly distributed to avoid jointed junctures, and must be increased in the high strain gradient region. Each embedded beam (depth-wise cross section of structure along a surface strain-sensing line) was discretized into small variable domains. Thus, the surface strain distribution can be described with a piecewise linear or a piecewise nonlinear function. Through discretization, the embedded beam curvature equation can be piece-wisely integrated to obtain the Variable-Domain Displacement Transfer Functions (for each embedded beam), which are expressed in terms of geometrical parameters of the embedded beam and the surface strains along the strain-sensing line. By inputting the surface strain data into the Displacement Transfer Functions, slopes and deflections along each embedded beam can be calculated for mapping out overall structural deformed shapes. A long tapered cantilever tubular beam was chosen for shape prediction analysis. The input surface strains were analytically generated from finite-element analysis. The shape prediction accuracies of the Variable- Domain Displacement Transfer Functions were then determined in light of the finite-element generated slopes and deflections, and were fofound to be comparable to the accuracies of the constant-domain Displacement Transfer Functions

displacement transfer functions↗

Solar concentrator advanced development project

A solar dynamic concentrator design developed for use with a solar-thermodynamic power generation module intended for the Space Station is considered. The truss hexagonal panel reflector uses a modular design approach and is flexible in attainable flux profiles and assembly techniques. Preliminary structural, thermal, and optical analysis results are discussed. Accuracy of the surface reflectors should be within 5 mrad rms slope error, resulting in the need for close fabrication tolerances. Significant fabrication issues to be addressed include the facet reflective and protective coating processes and the surface specularity requirements.

Corrigan, Robert D.↗