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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The shadow wind in high-mass X-ray binaries

We present hydrodynamic simulations of the most X-ray luminous high-mass X-ray binary systems, such as Cen X-3 and SMC X-1. These models illustrate the presence of both a normal radiatively driven wind confined to the X-ray shadow of the primary star -- a shadow wind -- and a thermally driven wind excited by the X-ray heating of the primary's stellar surface -- an X-ray-excited wind. The X-ray flux in these systems is sufficiently intense that any circumstellar gas exposed to the X-ray source will be highly photoionized. These extreme ionization conditions prevent the formation of a normal radiatively driven wind from the irradiated surface of the primary, but such a wind can still form on the shadowed side of the primary. Orbital rotation can then bring this shadow wind into the line of sight toward the X-ray source, enhancing the column density of the wind seen near eclipse egress. Furthermore, such a high X-ray flux can also excite a thermal wind from the irradiated surface of the primary. Again, orbital rotation tends to deflect the wind, this time leading to an enhanced column density near eclipse ingress.

Blondin, John M.↗
NASA NTRS1995

Analysis of shadowing effects on MIR photovoltaic and solar dynamic power systems

The NASA Lewis Research Center is currently working with RSC-Energia, the Russian Space Agency, and Allied Signal in developing a flight demonstration solar dynamic power system. This type of power system is dependent upon solar flux that is reflected and concentrated into a thermal storage system to provide the thermal energy input to a closed-cycle Brayton heat engine. The solar dynamic unit will be flown on the Russian Mir space station in anticipation of use on the International Space Station Alpha. By the time the power system is launched, the Mir will be a spatially complex configuration which will have, in addition to the three-gimbaled solar dynamic unit, eleven solar array wings that are either fixed or track the Sun along one axis and a variety or repositionable habitation and experiment modules. The proximity of arrays to modules creates a situation which makes it highly probable that there will be varying solar flux due to shadowing on the solar dynamic unit and some of the arrays throughout the orbit. Shadowing causes fluctuations in the power output from the arrays and the solar dynamic power system, thus reducing the energy capabilities of the spacecraft. An assessment of the capabilities of the power system under these conditions is an important part in influencing the design and operations of the spacecraft and predicting its energy performance. This paper describes the results obtained from using the Orbiting Spacecraft Shadowing Analysis Station program that was integrated into the Station Power Analysis for Capability Evaluation (SPACE) electrical power system computer program. OSSA allows one to consider the numerous complex factors for analyzing the shadowing effects on the electrical power system including the variety of spacecraft hardware geometric configurations, yearly and daily orbital variations in the vehicle attitude and orbital maneuvers (for communications coverage, payload pointing requirements and rendezvous/docking with other vehicles). The geometric models of the MIR with a solar dynamic power unit that were used in performing shadowing analyses are described. Also presented in this paper are results for individual orbits for several flight attitude cases which include assessments of the shadowing impacts upon the solar dynamic unit and the solar arrays. These cases depict typical MIR flight attitudes likely to have shadowing impact. Because of the time varying nature of the Mir orientation with respect to the Sun and the lack of knowledge of the precise timing of the attitude changes, strategies must be devised to assess and depict the shadowing impacts on power generation throughout the year. To address this, the best, nominal and worst impacts of shadowing considering a wide possible range of parameter changes for typical mission operation period are shown.

Fincannon, James↗
NASA NTRS2023

Neural Radiance Fields for Shadow Removal and Relighting of Satellite Imagery

Multi-view stereo photogrammetric techniques have been conventionally utilized to generate Global Digital Elevation Models (GDEM) of planetary and lunar surfaces. However, these methods, relying on conventional feature detectors, are often subject to inaccuracies caused by changes in lighting conditions, including diffuse reflection and harsh shading. This has limited the ability of these methods to accurately reconstruct shadowed regions in orbital imagery, such as highly shaded urban areas and the permanently shadowed regions (PSRs) located in the lunar surface, which are critical targets for NASA's Artemis program. Neural Radiance Fields (NeRFs) offer a novel solution to these limitations by breaking away from traditional photogrammetric assumptions of ridged, opaque surfaces. NeRFs are capable of reconstructing 3D objects with variably transmissive properties, such as fluids, PSRs, and reflective surfaces. In this work, we demonstrate the robustness of NeRFs in generating high-fidelity 3D models of terrain from highly shaded orbital imagery acquired from small satellites in low earth orbit (LEO). Our results showcase the ability of NeRF to overcome the limitations of traditional photogrammetric methods and provide a promising solution for reconstructing complex scenes in challenging lighting conditions.

Caleb Ashmore Adams↗
NASA NTRS2008

Automatic Hazard Detection for Landers

Unmanned planetary landers to date have landed 'blind'; that is, without the benefit of onboard landing hazard detection and avoidance systems. This constrains landing site selection to very benign terrain,which in turn constrains the scientific agenda of missions. The state of the art Entry, Descent, and Landing (EDL) technology can land a spacecraft on Mars somewhere within a 20-100km landing ellipse.Landing ellipses are very likely to contain hazards such as craters, discontinuities, steep slopes, and large rocks, than can cause mission-fatal damage. We briefly review sensor options for landing hazard detection and identify a perception approach based on stereo vision and shadow analysis that addresses the broadest set of missions. Our approach fuses stereo vision and monocular shadow-based rock detection to maximize spacecraft safety. We summarize performance models for slope estimation and rock detection within this approach and validate those models experimentally. Instantiating our model of rock detection reliability for Mars predicts that this approach can reduce the probability of failed landing by at least a factor of 4 in any given terrain. We also describe a rock detector/mapper applied to large-high-resolution images from the Mars Reconnaissance Orbiter (MRO) for landing site characterization and selection for Mars missions.

hazard detection↗
NASA NTRS2006

NASA Tech Briefs, September 2006

Topics covered include: Improving Thermomechanical Properties of SiC/SiC Composites; Aerogel/Particle Composites for Thermoelectric Devices; Patches for Repairing Ceramics and Ceramic- Matrix Composites; Lower-Conductivity Ceramic Materials for Thermal-Barrier Coatings; An Alternative for Emergency Preemption of Traffic Lights; Vehicle Transponder for Preemption of Traffic Lights; Automated Announcements of Approaching Emergency Vehicles; Intersection Monitor for Traffic-Light-Preemption System; Full-Duplex Digital Communication on a Single Laser Beam; Stabilizing Microwave Frequency of a Photonic Oscillator; Microwave Oscillators Based on Nonlinear WGM Resonators; Pointing Reference Scheme for Free-Space Optical Communications Systems; High-Level Performance Modeling of SAR Systems; Spectral Analysis Tool 6.2 for Windows; Multi-Platform Avionics Simulator; Silicon-Based Optical Modulator with Ferroelectric Layer; Multiplexing Transducers Based on Tunnel-Diode Oscillators; Scheduling with Automated Resolution of Conflicts; Symbolic Constraint Maintenance Grid; Discerning Trends in Performance Across Multiple Events; Magnetic Field Solver; Computing for Aiming a Spaceborne Bistatic- Radar Transmitter; 4-Vinyl-1,3-Dioxolane-2-One as an Additive for Li-Ion Cells; Probabilistic Prediction of Lifetimes of Ceramic Parts; STRANAL-PMC Version 2.0; Micromechanics and Piezo Enhancements of HyperSizer; Single-Phase Rare-Earth Oxide/Aluminum Oxide Glasses; Tilt/Tip/Piston Manipulator with Base-Mounted Actuators; Measurement of Model Noise in a Hard-Wall Wind Tunnel; Loci-STREAM Version 0.9; The Synergistic Engineering Environment; Reconfigurable Software for Controlling Formation Flying; More About the Tetrahedral Unstructured Software System; Computing Flows Using Chimera and Unstructured Grids; Avoiding Obstructions in Aiming a High-Gain Antenna; Analyzing Aeroelastic Stability of a Tilt-Rotor Aircraft; Tracking Positions and Attitudes of Mars Rovers; Stochastic Evolutionary Algorithms for Planning Robot Paths; Compressible Flow Toolbox; Rapid Aeroelastic Analysis of Blade Flutter in Turbomachines; General Flow-Solver Code for Turbomachinery Applications; Code for Multiblock CFD and Heat-Transfer Computations; Rotating-Pump Design Code; Covering a Crucible with Metal Containing Channels; Repairing Fractured Bones by Use of Bioabsorbable Composites; Kalman Filter for Calibrating a Telescope Focal Plane; Electronic Absolute Cartesian Autocollimator; Fiber-Optic Gratings for Lidar Measurements of Water Vapor; Simulating Responses of Gravitational-Wave Instrumentation; SOFTC: A Software Correlator for VLBI; Progress in Computational Simulation of Earthquakes; Database of Properties of Meteors; Computing Spacecraft Solar-Cell Damage by Charged Particles; Thermal Model of a Current-Carrying Wire in a Vacuum; Program for Analyzing Flows in a Complex Network; Program Predicts Performance of Optical Parametric Oscillators; Processing TES Level-1B Data; Automated Camera Calibration; Tracking the Martian CO2 Polar Ice Caps in Infrared Images; Processing TES Level-2 Data; SmaggIce Version 1.8; Solving the Swath Segment Selection Problem; The Spatial Standard Observer; Less-Complex Method of Classifying MPSK; Improvement in Recursive Hierarchical Segmentation of Data; Using Heaps in Recursive Hierarchical Segmentation of Data; Tool for Statistical Analysis and Display of Landing Sites; Automated Assignment of Proposals to Reviewers; Array-Pattern-Match Compiler for Opportunistic Data Analysis; Pre-Processor for Compression of Multispectral Image Data; Compressing Image Data While Limiting the Effects of Data Losses; Flight Operations Analysis Tool; Improvement in Visual Target Tracking for a Mobile Robot; Software for Simulating Air Traffic; Automated Vectorization of Decision-Based Algorithms; Grayscale Optical Correlator Workbench; "One-Stop Shopping" for Ocean Remote-Sensing and Model Data; State Analysis Database Tool; Generating CAHV and CAHVOmages with Shadows in ROAMS; Improving UDP/IP Transmission Without Increasing Congestion; FORTRAN Versions of Reformulated HFGMC Codes; Program for Editing Spacecraft Command Sequences; Flight-Tested Prototype of BEAM Software; Mission Scenario Development Workbench; Marsviewer; Tool for Analysis and Reduction of Scientific Data; ASPEN Version 3.0; Secure Display of Space-Exploration Images; Digital Front End for Wide-Band VLBI Science Receiver; Multifunctional Tanks for Spacecraft; Lightweight, Segmented, Mostly Silicon Telescope Mirror; Assistant for Analyzing Tropical-Rain-Mapping Radar Data; and Anion-Intercalating Cathodes for High-Energy- Density Cells.

Source record↗
NASA NTRS2016

Surface Water-Ice Deposits in the Northern Shadowed Regions of Ceres

Ceres, a dwarf planet located in the main asteroid belt, has a low bulk density, and models predict that a substantial amount of water ice is present in its mantle and outer shell. The Herschel telescope and the Dawn spacecraft have observed the release of water vapor from Ceres, and exposed water ice has been detected by Dawn on its surface at mid-latitudes. Water molecules from endogenic and exogenic sources can also be cold-trapped in permanent shadows at high latitudes, as happens on the Moon and Mercury. Here we present the first image-based survey of Ceres's northern permanent shadows and report the discovery of bright deposits in cold traps. We identify a minimum of 634 permanently shadowed craters. Bright deposits are detected on the floors of just 10 of these craters in multiscattered light. We spectroscopically identify one of the bright deposits as water ice. This detection strengthens the evidence that permanently shadowed areas have preserved water ice on airless planetary bodies.

Surface Water↗
NASA NTRS2005

The Variation of Hydrocarbon Abundances with Latitude and Season in Saturn's Stratosphere

We have developed a realistic, time-variable, one-dimensional, seasonal model for stratospheric photochemistry on Saturn using the Caltech/ JPL KINETICS code [1,2,3]. The model accounts for variations in ultraviolet flux due to orbital position, solar-cycle variations, and ring-shadowing effects. The results for two Saturnian years, starting at Ls = 0 in 1950 and running until the upcoming northern vernal equinox in 2009, are presented for numerous latitudes. The same two model years are run over and over again until the model convergences to make sure that high-altitude effects have had a chance to propagate down through the atmosphere. We use the SOLAR2000 model [4,5], in combination with the spectra presented in [6], to predict the ultraviolet flux at any wavelength and any point in time during the simulation. Saturn's orbital position during the simulation was taken from the ephemeris calculator at http://ssd.jpl.nasa.gov/horizons.html [7]. The photochemical model is derived from "Model C" of [8] and uses a hydrocarbon reaction list that has been extensively updated from that presented in [3].

Moses, J. I.↗
NASA NTRSDate not supplied

New Constraints on the Volatile Deposit in Mercury’s North Polar Crater, Prokofiev

There is strong evidence from multi-wavelength, multi-instrument observations and thermal models for the presence of ice and other volatiles in Mercury’s north polar permanently shadowed regions (PSRs)[1-6]. Ground-based radar measurements identified bright regions in some polar craters interpreted to be water ice on or near the surface[1]. The MESSENGER spacecraft found that some radar-bright deposits appeared bright in the optical and near-infrared while others appeared dark[4-6]. The bright regions were interpreted to be exposed surface ice while the dark regions were hypothesized to be complex organic volatile lag deposits overlaying buried ice[3]. One example of the former is in the 112 km diameter crater, Prokofiev, for which the Mercury Dual Imaging System (MDIS) acquired broadband images while in Sun shadow but illuminated by scattered light from the crater walls[5]. These images revealed a relatively high-albedo region spatially correlated with the PSR. Subsequent work[7] found a small offset between the boundary of the radar-bright region and that of the PSR predicted by an illumination model based on the polar digital elevation model (DEM)from the Mercury Laser Altimeter (MLA). Such an offset, if true, could have implications for the ice properties and its delivery and destruction mechanisms. However, the low resolution (1 km/pix) of the polar MLA DEM precluded a definitive conclusion. In the present work, we build new higher-resolution topographic, illumination, and thermal models of Prokofiev to place stronger constraints on its PSR and volatile deposits. We also study the MLA reflectance data in this crater to quantitatively estimate the ice abundance.

Michael K Barker↗
NASA NTRS2015

Earth-Facing Antenna Characterization in a Complex Ground Plane/Multipath Rich Environment

The Space Communications and Navigation (SCAN) Testbed was a Software Defined Radio (SDR)-based payload launched to the International Space Station (ISS) in July of 2012. The purpose of the SCAN Testbed payload was to investigate the applicability of SDRs to NASA space missions in an operational space environment, which means that a proper model for system performance in said operational space environment is a necessary condition. The SCAN Testbed has line-of-sight connections to various ground stations with its S-Band Earth-facing Near-Earth Network Low Gain Antenna (NEN-LGA). Any previous efforts to characterize the NEN-LGA proved difficult, therefore, the NASA Glenn Research Center built its own S-Band ground station, which became operational in 2015, and has been successfully used to characterize the NEN-LGAs in-situ pattern measurements. This methodology allows for a more realistic characterization of the antenna performance, where the pattern oscillation induced by the complex ISS ground plane, as well as shadowing effects due to ISS structural blockage are included into the final performance model. This paper describes the challenges of characterizing an antenna pattern in this environment. It will also discuss the data processing, present the final antenna pattern measurements and derived model, as well as discuss various lessons learned.

software defined radio↗
NASA NTRS2015

Earth-Facing Antenna Characterization in Complex Ground Plane/Multipath Rich Environment

The Space Communications and Navigation (SCAN) Testbed was a Software Defined Radio (SDR)-based payload launched to the International Space Station (ISS) in July of 2012. The purpose of the SCAN Testbed payload was to investigate the applicability of SDRs to NASA space missions in an operational environment, which means that a proper model for system performance in said operational space environment is a necessary condition. The SCAN Testbed has line-of-sight connections to various ground stations with its S-Band Earth-facing Near-Earth-Network Low Gain Antenna (NEN-LGA). Any previous efforts to characterize the NEN-LGA proved difficult, therefore, the NASA Glenn Research Center built its own S-Band ground station, which became operational in 2015, and has been used successfully to characterize the NEN-LGA's in-situ pattern measurements. This methodology allows for a more realistic characterization of the antenna performance, where the pattern oscillation induced by the complex ISS ground plane, as well as shadowing effects due to ISS structural blockage are included into the final performance model. This paper describes the challenges of characterizing an antenna pattern in this environment. It will also discuss the data processing, present the final antenna pattern measurements and derived model, as well as discuss various lessons learned

ground station↗
NASA NTRS1979

Some techniques for reducing the tower shadow of the DOE/NASA mod-0 wind turbine tower

Wind speed profile measurements to measure the effect of a wind turbine tower on the wind velocity are presented. Measurements were made in the wake of scale models of the tower and in the wake of certain full scale components to determine the magnitude of the speed reduction (tower shadow). Shadow abatement techniques tested on the towers included the removal of diagonals, replacement of diagonals and horizontals with round cross section members, installation of elliptical shapes on horizontal members, installation of airfoils on vertical members, and application of surface roughness to vertical members.

Burley, R. R.↗
NASA NTRS1990

Functional relation among subpixel canopy cover, ground shadow, and illuminated ground at large sampling scales

The functional relation among subpixel canopy cover, illuminated soil, and shadowed soil, which progressively develops with increasing pixel size, is investigated for Poisson distributed plants using a geometric canopy simulation model. An analytical relation among cover components is shown to be applicable when the scale of the pixel is much larger than the scale of the plant and ground shadow. The analysis is facilitated through the use of a nondimensional solar-geometric similarity parameter, eta, equal to the ratio of the area of one plant canopy to its associated ground shadow area, as viewed from nadir. A sampling scale ratio, defined as the ratio of the area of the pixel to the mean area of a single plant shadow, is tested as a quantitative criterion to evaluate when the functional relation among subpixel components occurs. The results of a remote sensing experiment over a natural conifer landscape provide preliminary confirmation of the theoretical analysis.

Jasinski, Michael F.↗
NASA NTRS1994

Accretion disk coronae in high-luminosity systems

We present the results of self-consistent models of Compton-heated accretion disk coronae. The models are calculated using a new method for computing monochromatic radiative transfer n two dimensions. The method splits the radiation into direct and scattered components. The direct radiation is computed by calculating the optical depth along rays, while transfer of the scattered radiation is approximated by flux-limited diffusion. The resulting code agrees with more accurate treatments to within 50%, and is highly efficient, making it practical for use in large hydrodynamic simulations. The coronal models are used to confirm the results of earlier work, and to extend it to higher luminosities. In contrast to earlier work, which found the outer disks to be shadowed by the inner corona at high luminosities, we find our results to form an almost continuous extension of the models at lower luminosities. This is due to the presence of multiply scattered radiation, which acts to partially offset the loss of direct radiation from the central source. Although the analytic methods derived at lower luminosities cannot be used to derive the coronal structure for L/L(sub Edd) approx. greater than 0.1, the results of the models are amenable to semiempirical fits. We also discuss possible observational consequences of the results for coronal veiling and line fluorescence from the disk.

Murray, Stephen D.↗
NASA NTRS2010

Illumination Conditions of the Lunar Polar Regions Using LOLA Topography

We use high-resolution altimetry data obtained by the Lunar Orbiter Laser Altimeter instrument onboard the Lunar Reconnaissance Orbiter to characterize present illumination conditions in the polar regions of the Moon. Compared to previous studies, both the spatial and temporal extent of the simulations are increased significantly, as well as the coverage (fill ratio) of the topographic maps used, thanks to the 28 Hz firing rate of the five-beam instrument. We determine the horizon elevation in a number of directions based on 240 m-resolution polar digital elevation models reaching down to 75 latitude. The illumination of both polar regions extending to 80 can be calculated for any geometry from those horizon longitudinal profiles. We validated our modeling with recent Lunar Reconnaissance Orbiter Wide-Angle Camera images. We assessed the extent of permanently shadowed regions (PSRs, defined as areas that never receive direct solar illumination), and obtained total areas generally larger than previous studies (12,866 and 16,055 sq. km, in the north and south respectively). We extended our direct illumination model to account for singly-scattered light, and found that every PSR does receive some amount of scattered light during the year. We conducted simulations over long periods (several 18.6-years lunar precession cycles) with a high temporal resolution (6 h), and identified the most illuminated locations in the vicinity of both poles. Because of the importance of those sites for exploration and engineering considerations, we characterized their illumination more precisely over the near future. Every year, a location near the Shackleton crater rim in the south polar region is sunlit continuously for 240 days, and its longest continuous period in total darkness is about 1.5 days. For some locations small height gains ( 10 m) can dramatically improve their average illumination and reduce the night duration, rendering some of those particularly attractive energy-wise as possible sites for near-continuous sources of solar power.

E. Mazarico↗
NASA NTRS1988

The cosmogonic shadow effect

The paper reviews the two-thirds fall-down mechanism and presents an approximate model for the dust distribution and neutralization at the '2/3' points along a given field line. The relationship between the charge on a dust particle and the ratio of dust to plasma density was obtained from the current (ions plus electrons) balance to the surface of the grain. Consideration is also given to the conditions under which rigid notation of a quasi-neutral plasma in thermal equilibrium is possible in a slightly perturbed magnetic dipole field.

Azar, Michel↗
NASA NTRS1980

Measurements of NO, O3, and temperature at 19.8 km during the total solar eclipse of 26 February 1979

Local measurements of stratospheric NO and O3 mixing ratios and air temperature were made during the total solar eclipse of 26 February 1979. The instrumentation was carried aboard a U-2 aircraft flown at an altitude of 19.8 km in the region near 47 deg N, 112 deg W. Eclipse maximum occurred approximately in the middle of the 2-3/4-hr measurement period. The NO mixing ratio was reduced at least a factor of 25 at the maximum of the eclipse. The decrease and recovery of NO during the passage of the Moon's shadow over the measurement region follows approximately the predictions of two independent models. No change was observed in either the O3 mixing ratio or the air temperature that could be attributed to the eclipse.

Starr, W. L.↗
NASA NTRS2022

New Constraints on the Volatile Deposit in Mercury’s North Polar Crater, Prokofiev

We present new high-resolution topographic, illumination, and thermal models of Mercury’s 112 km-diameter north polar crater, Prokofiev. The new models confirm previous results that water ice is stable at the surface within the permanently shadowed region (PSR) of Prokofiev for geologic timescales. The largest radar-bright region in Prokofiev is confirmed to extend up to several kilometers past the boundary of its PSR making it unique on Mercury for hosting a significant radar-bright area outside a PSR. The near-infrared normal albedo distribution of Prokofiev’s PSR suggests the presence of a darkening agent rather than pure surface ice. Linear mixture models predict at least roughly half of the surface area to be covered with this dark material. Using improved altimetry in this crater, we place an upper limit of 26 m on its ice deposit thickness. The 1 km-baseline topographic slope and roughness of the radar-bright deposit are lower than the non-radar-bright floor although the difference is not statistically significant when compared to the non-radar-bright floor’s natural topographic variations. These results place new constraints on the nature of Prokofiev’s volatile deposit that will inform future missions, such as BepiColombo.

Michael K Barker↗