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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Parameterizing Spectral Surface Reflectance Relationships for the Dark Target Aerosol Algorithm Applied to A Geostationary Imager

Originally developed for the Moderate Resolution Imaging Spectroradiometer (MODIS) in polar, sun-synchronous low-earth orbit (LEO), the Dark Target (DT) aerosol retrieval algorithm relies on the assumption of a Surface Reflectance Parameterization (SRP) over land surfaces. Specifically for vegetated and dark-soiled surfaces, values of surface reflectance in blue and red visible-wavelength bands are assumed to be nearly linearly related to each other and to the value in a shortwave infrared (SWIR) wavelength band. This SRP also includes dependencies on scattering angle and a normalized difference vegetation index computed from two SWIR bands (NDVISWIR). As the DT retrieval algorithm is being ported to new sensors to continue and expand the aerosol data record, we assess whether the MODIS-assumed SRP can be used for these sensors. Here, we specifically assess SRP for the Advanced Baseline Imager (ABI) aboard, the Geostationary Operational Environmental Satellite (GOES)-16/East (ABIE). First, we find that using MODIS-based SRP leads to higher biases and artificial diurnal signatures in aerosol optical depth (AOD)retrievals from ABIE. The primary reason appears to be that geostationary orbit (GEO) encounters an entirely different set of observation geometry than does LEO, primarily with regards to solar angles coupled with fixed view angles. Therefore, we have developed a new SRP for GEO that draws the angular shape of the surface bidirectional reflectance. We also introduce modifications to the parametrization of both red-SWIR and blue-red spectral relationships to include additional information.The revised Red-SWIR SRP includes solar zenith angle, NDVISWIR, and land-type percentage from an ancillary database. The blue-red SRP adds dependencies on the scattering angle and NDVISWIR. The new SRPs improve the AOD retrieval of ABIE in terms of overall less bias and mitigation of the overestimation around local noon. The average bias of DT AOD compared to AERONET AOD shows a reduction from 0.08 to 0.03, while the bias of local solar noon decreases from 0.12 to 0.03.The agreement between DT and AERONET AOD is established through regression slope of 1.06 and y-intercept of 0.01with correlation coefficient is0.74. By using the new SRP, the percentage of data falling within the expected error range (±0.05 + 15%) is notably risen from 54% to 78%.

Mijin Kim↗
NASA NTRS1978

Critical issues in viscous flow computations

In developing computer programs to numerically solve the Navier-Stokes equations, the purpose of the computation must be clearly kept in mind. In the Air Force, the purpose is to provide design information on non-linear aerodynamic phenomenon for aircraft that perform throughout the flight corridor. This translates into the requirement for a computer program which can solve the time averaged compressible Navier-Stokes equations (with a turbulence model) in three dimensions for generalized geometries. The intended application of the results then controls the priorities in addressing critical issues. Recurrent problem areas encountered in the study of viscous flow include: (1) grid generation for arbitrary geometry; (2) numerical difficulties; (3) turbulence models; (4) accuracy and efficiency; and (5) smearing of discontinuities.

Hankey, W. L., Jr.↗
NASA NTRS1991

On the lack of a magnetic signature of Triton's magnetospheric interaction on the Voyager 2 flyby trajectory

There is strong, albeit indirect, evidence for a sub-Alfvenic and transonic interaction between Triton and the Neptunian magnetosphere. A new inspection of magnetic field data around Triton encounter shows no evidence for the interaction. It is shown that this is due to the geometry of Triton's Alfvenic wings, which were probably too far from the spacecraft during the encounter. The situation is complicated by finite ion gyroradius effects, which tend to smear out the simple Alfven wings such as encountered at Io.

Neubauer, F. M.↗
NASA NTRS2011

Contributions of TetrUSS to Project Orion

The NASA Constellation program has relied heavily on Computational Fluid Dynamics simulations for generating aerodynamic databases and design loads. The Orion Project focuses on the Orion Crew Module and the Orion Launch Abort Vehicle. NASA TetrUSS codes (GridTool/VGRID/USM3D) have been applied in a supporting role to the Crew Exploration Vehicle Aerosciences Project for investigating various aerodynamic sensitivities and supplementing the aerodynamic database. This paper provides an overview of the contributions from the TetrUSS team to the Project Orion Crew Module and Launch Abort Vehicle aerodynamics, along with selected examples to highlight the challenges encountered along the way. A brief description of geometries and tasks will be discussed followed by a description of the flow solution process that produced production level computational solutions. Four tasks conducted by the USM3D team will be discussed to show how USM3D provided aerodynamic data for inclusion in the Orion aero-database, contributed data for the build-up of aerodynamic uncertainties for the aero-database, and provided insight into the flow features about the Crew Module and the Launch Abort Vehicle.

Mcmillin, Susan N.↗
NASA NTRS2013

Low Velocity Difference Thermal Shear Layer Mixing Rate Measurements

Current CFD modeling techniques are known to do a poor job of predicting the mixing rate and persistence of slot film flow in co-annular flowing ducts with relatively small velocity differences but large thermal gradients. A co-annular test was devised to empirically determine the mixing rate of slot film flow in a constant area circular duct (D approx. 1ft, L approx. 10ft). The axial rate of wall heat-up is a sensitive measure of the mixing rate of the two flows. The inflow conditions were varied to simulate a variety of conditions characteristic of moderate by-pass ratio engines. A series of air temperature measurements near the duct wall provided a straightforward means to measure the axial temperature distribution and thus infer the mixing rate. This data provides a characterization of the slot film mixing rates encountered in typical jet engine environments. The experimental geometry and entrance conditions, along with the sensitivity of the results as the entrance conditions vary, make this a good test for turbulence models in a regime important to modern air-breathing propulsion research and development.

Bush, Robert H.↗
NASA NTRS1984

Cosmic Ray Exposure & Linear-Energy-Transfer Evaluations for the COBE Mission

Magnetospherically attenuated, orbit integrated, surface incident cosmic ray fluxes of galactic origin were determined for the COBE mission. All heavy ions up to Nickel (z=28) were considered in this, evaluation. In order to provide worst case approximations, estimates were based on solar minimum conditions. Transport and material shielding calculations were then performed for these vehicle encountered particles, for a simple spherical 3-D aluminum geometry, and the materially attenuated cosmic ray distributions emerging behind selected shield thicknesses were obtained. Finally, Linear-Energy-Transfer (LET) spectra were evaluated for the energy spectra of each ion specie and these were, in turn, integrated into the sum-total LET distribution contained in this report. The results are presented in tabular and graphical form for eight (8) different shield thicknesses from.01 to 10.0 gm/cm2 of aluminum. They show most conclusively, and not unexpectedly, that material shielding has virtually no 'effect on the final LET spectrum, at least not for aluminum shields. This was predictable. Please note that in the LET graphs, two curves were plotted. Of these, please ignore the one labeled "grazing" and use only the one labeled "normal". Again, it should be remembered that the end results contain contributions from all elements up to Nickel (z=28).

Stassinopoulos, E. G.↗
NASA NTRS1977

Prediction and measurement results of radiation damage to CMOS devices on board spacecraft

All the currently available results of the flight experiment for all the individually instrumented 130 transistors, relating to both biased and unbiased n- and p-channel RCA and -channel AMI devices were presented. The predictions of dose levels based on a detailed analysis of the space radiation environment as encountered by Explorer-55 and calculated by one dimensional slab geometry, and three dimensional spherical geometry were cited.

Stassinopoulos, E. G.↗
NASA NTRS1984

Space Telescope mission planning

Planning and scheduling for the Space Telescope astronomy mission involves a combination of concerns regarding orbital environment constraints and spacecraft operational characteristics. In many cases proper selection or sequencing of observations can minimize the impact of disadvantageous orbital geometry with respect to targets of interest or of repeatedly encountered environmental factors such as spacecraft passages through high radiant regions on the earth's upper atmosphere. An overview is presented of the characteristics of viewing celestial targets from low earth orbit and the principal effects and operational considerations which constrain or restrict the scheduling of observations of them.

Sherrill, T. J.↗
NASA NTRS1985

Self-consistent simulation of plasma interactions with secondary-emitting insulators

A cylindrical particle-in-cell (PIC) plasma simulation code applicable to plasma densities encountered in low Earth orbit (LEO) is described. The simulated geometries include that of a plain disk and a disk surrounded by a dielectric. Both configurations are mounted upon a ground plate in contact with a plasma environment. Techniques allowing simulation of dielectric charging using PIC time scales are discussed. Current versus voltage characteristic curves are calculated and the results are compared to experimental data.

Brandon, S. T.↗
NASA NTRS1993

Magnetic pulsations from 0.1 to 4.0 Hz and associated plasma properties in the earth's subsolar magnetosheath and plasma depletion layer

AMPTE CCE magnetic field data acquired during periods of magnetospheric compressions when the spacecraft sampled the magnetosheath are analyzed on the basis of a dynamic spectral analysis covering frequencies 0.1 to 4.0 Hz. Ion and electron data are used to identify regions, to monitor the upstream shock geometry, and to evaluate moments of the proton distribution. Fourteen encounters representing 46 hr of observations are analyzed. A compilation of the temporal sequence of spectral structures shows that electromagnetic ion cyclotron (EMIC) waves occur next to the magnetopause, while mirror waves occur outside the region of EMIC waves. It is concluded that there is a close relationship between EMIC waves in the sheath and the plasma depletion layer. For quasi-parallel upstream conditions, the magnetic field power spectra often exhibit no band limited structures but only broadband noise.

Anderson, B. J.↗
DOE OSTI2025

A Domain-Decomposed A-ϕ Formulation Based on Lagrange Multipliers for Low-Frequency Problems

A domain-decomposed A-ϕ formulation based on Lagrange multipliers is proposed to simulate low-frequency elec- tromagnetic problems. This method partitions the computational domain into smaller subdomains, allowing each subdomain to be independently formulated using Lagrange multipliers as Dirichlet boundary conditions, while ensuring continuity of the fields across the interfaces. A mixed finite element method, utilizing both vector and scalar basis functions, is employed to discretize the formulation, resulting in a global system to be solved. The proposed method is validated using TEAM Problem 7 at 50 Hz, demonstrating its effectiveness in handling complex geometries and addressing the low-frequency breakdown issues commonly encountered in traditional finite element methods.

Hossain, Amzad↗
NASA NTRSDate not supplied

Increasing Flexibility of Polymers in the Application of Complex Space Craft Heat Shield Geometries

Highly crosslinked polymers, commonly utilized in spacecraft component fabrication, especially for heatshields, have historically encountered challenges due to their inherent brittleness. To overcome this issue, researchers have explored the incorporation of additives into the polymer backbone to enhance flexibility and durability. This study aims to improve the flexibility and durability of highly crosslinked polymers by introducing long-chain aliphatic silicon-based additives with varying molecular weights into the polymer backbone. By increasing the flexibility of these brittle polymers, they can be effectively employed in constructing intricate curvatures for heatshields, eliminating the need for gap fillers. In this study, we investigated six different additives, comparing them to a highly crosslinked high-temperature polymer used as a baseline. Various characterization techniques, including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dilatometry, dynamic mechanical analysis (DMA), nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopy (FTIR), were employed to assess the properties of the materials. The FTIR and NMR results indicated the successful incorporation of the silicon-based additives into the polymer backbone. Furthermore, thermal characterization results demonstrated that certain additives exhibited superior flexibility and lower densities compared to the baseline polymer.

Tane Boghozian↗
NASA NTRS1974

Low-speed wind-tunnel investigation of the aerodynamic and acoustic performance of a translating grid choked flow inlet

The aerodynamic and acoustic performance of a translating grid choked-flow inlet was determined in a low-speed wind tunnel at free-stream velocities of 24, 32, and 45 m/sec and incidence angles of 0, 10, 20, 30, 35, 40, 45, and 50 deg. The inlet was sized to fit a 13.97- centimeter-diameter fan with a design weight flow of 2.49 kg/sec. Measurements were made to determine inlet total pressure recovery, flow distortion, and sound pressure level for both choked and unchoked geometries over a range of inlet weight flows. For the unchoked geometry, inlet total pressure recovery ranged from 0.983 to 0.989 at incidence angles less than 40 deg. At 40 deg incidence angle, inlet cowl separation was encountered which resulted in lower values of pressure recovery and higher levels of fan broadband noise. For the choked geometry, increasing total pressure losses occurred with increasing inlet weight flow that prevented the inlet from reaching full choked conditions with the particular fan used. These losses were attributed to the high Mach number drag rise characteristics of airfoil grid. At maximum attainable inlet weight flow, the total pressure recovery at static conditions was 0.935. The fan blade passing frequency and other fan generated pure tones were eliminated from the noise spectrum, but the broadband level was increased.

Abbott, J. M.↗
NASA NTRS2002

Numerical Investigation of 'Transonic Resonance' with a Convergent-Divergent Nozzle

At pressure ratios lower than the design value, convergent-divergent (C-D) nozzles often undergo a flow resonance accompanied by the emission of acoustic tones. The phenomenon, driven by the unsteady shock within the divergent section of the nozzle, has been studied experimentally by Zaman et al. In this paper, the space-time conservation element solution element (CE/SE) method is employed to numerically investigate the phenomenon. The computations are performed for a given nozzle geometry for several different pressure ratios. Sustained 'limit cycle' oscillations are encountered in all cases. The oscillation frequencies, their variation with pressure ratio including a 'stage jump', agree well with the experimental results. The unsteady flow data confirm that stage 1 of the resonance (fundamental) involves a one-quarter standing wave while stage 2 (third harmonic) involves a three-quarter standing wave within the divergent section of the nozzle. Details of the shock motion, and the flow and near acoustic field, are documented for one case each of stages 1 and 2.

Loh, Ching Y.↗
NASA NTRS1983

Aerothermodynamic design considerations of an aerobraked spacecraft

The major aerothermodynamic design issues that influenced the VOIR (Venus Orbiting Image Radar) airbrake and mission design are discussed. In the discussion of aerobrake heating, it is pointed out that the heat transfer to the deployed aerobrake is a function of the flow regime encountered during the periapsis pass, the perapsis altitude, and the brake surface geometry. The discussion of spacecraft thermal protection encompasses separated flow heating, aerobrake backface radiation, total solar cell heating, and undeployed aerobrake effects. The aerobrake is designed to protect the spacecraft thermally by limiting the integrated entry heating to the critical solar cell arrays (located on three sides of the spacecraft) due to flow impingement heating, separated flow heating, and backface radiation heating. It is explained that these design considerations led to the selection of a flat-faced aerobrake design located on the front of the spacecraft to provide maximum spacecraft thermal protection. The 8.4-m equivalent diameter aerobrake eliminates direct flow impingement heating and lowers separated flow heating on the spacecraft.

Florence, D.↗
NASA NTRS1984

Coma morphology and dust-emission pattern of periodic Comet Halley. II - Nucleus spin vector and modeling of major dust features in 1910

The continuous ejection of dust from discrete emission sources on the rotating nucleus of the Comet Halley is modelled in order to explain the evolution of spiral jets which unwind from the nucleus condensation into envelopes or halos in the comet head. The model is applied to digitally processed images of three features of the comet taken from Mount Wilson plates during the 1910 fly-by. The model permits a determination of the motion and spin vector for each emission source, its cometocentric coordinates, and a function relating particle ejection velocity to the solar radiation pressure exerted on the ejecta. It is found that the obliquity of the comet orbit's plane to its equatorial plane is 45 deg, the axis of rotation period of 17.3 days. The derived function of particle ejection velocity to the solar radiation pressure implied no contribution from grains larger than 10 microns in radius. High dust loading of gas flows from the June 1910 emission sources is indicated. It is estimated that because of the favorable approach geometry of the Gioto spacecraft during its 1986 flyby, the likelihood of encountering dense jets of dust is small.

Sekanina, Z.↗
NASA NTRS1986

Gaseous jets in Comet P/Halley

Properties of the gas jets in P/Halley reported to exist in images taken in the light of CN are described. The jets also exist in the light of other radicals, specifically C2. The jets do not exist in the continuum images although it appears that one of the jets seen may come from the same area on the nucleus that produces much of the dust. The jets are seen to persist, although with varying geometry, for 2 months or more, from the time of the spacecraft encounters in March to the beginning of May. The strength of the jets is well correlated with fluctuations in the overall production rate of radicals by the comet.

Ahearn, Michael F.↗
NASA NTRS2002

Energy Dispersive Spectrometry and Quantitative Analysis Short Course. Introduction to X-ray Energy Dispersive Spectrometry and Quantitative Analysis

This course will cover practical applications of the energy-dispersive spectrometer (EDS) to x-ray microanalysis. Topics covered will include detector technology, advances in pulse processing, resolution and performance monitoring, detector modeling, peak deconvolution and fitting, qualitative and quantitative analysis, compositional mapping, and standards. An emphasis will be placed on use of the EDS for quantitative analysis, with discussion of typical problems encountered in the analysis of a wide range of materials and sample geometries.

Carpenter, Paul↗