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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 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

On the evaluation of expected performance cost for partially observed closed-loop stochastic systems

New methods are presented for evaluating the expected performance cost of partially observed closed-loop stochastic systems. When the variances of the process statistics are small, a linearized model of the closed-loop stochastic system is defined for which the expected cost can be evaluated by recursion on a set of purely deterministic difference equations. When the variances of the process statistics are large, the linearized model can be used in the control variate method of variance reduction for reducing the number of sample paths required for effective Monte Carlo estimation.

Bayard, D. S.↗
NASA NTRS1987

Short solar events with evidence of repetitive structures

Several short (less than 40 s) solar hard X-ray events (greater than 100 keV) have been observed simultaneously with identical instruments on the Venera 11, 12, 13, and 14 and Prognoz 7 (Franco-Soviet Signe experiments) spacecraft. High time resolution (equal to or greater than 2 ms) data were stored in memory when a trigger occurred. The observations reported here were made by Prognoz 7 and V12 which were closer to the sun at the time and provided good statistics. Observations of modulation with a period of 1.6 s for the event on 1978 December 3 are presented. Also presented is evidence for fast time fluctuations from an event on 1979 November 6, observed with Venera 12, and another on 1981 September 6, observed with the Solar Maximum Hard X-Ray Burst Spectrometer. Power spectrum analysis, epoch folding, and Monte Carlo simulation to evaluate the statistical significance of persistent time delays between features. The results are discussed in light of the MHD model proposed by Zaitsev and Stepanov (1982) and Zaitsev, Stepanov, and Chernov (1984).

Desai, Upendra D.↗
NASA NTRS1993

Computer simulation of initial events in the biochemical mechanisms of DNA damage

Understanding the systematic and quantitative correlation between the physical events of energy deposition by ionizing radiation and the ensuing chemical and biochemical processes leading to DNA damage is one of the goals in radiation research. Significant progress has been made toward achieving the stated goal by using theoretical modeling techniques. These techniques are strongly dependent on computer simulation procedures. A review of such techniques with details of various stages of simulation development, including a comparison with available experimental data, is presented in this article.

Non-NASA Center↗
NASA NTRS2005

Spaceborne Doppler Radar Measurements of Rainfall: Correction of Errors Induced by Pointing Uncertainties

In this paper a sea surface radar echo spectral analysis technique to correct for the rainfall velocity error caused by radar-pointing uncertainty is presented. The correction procedure is quite straightforward when the radar is observing a homogeneous rainfall field. When nonuniform beam filling (NUBF) occurs and attenuating frequencies are used, however, additional steps are necessary in order to correctly estimate the antenna-pointing direction. This new technique relies on the application of the combined frequency-time (CFT) algorithm to correct for uneven attenuation effects on the observed sea surface Doppler spectrum. The performance of this correction technique was evaluated by a Monte Carlo simulation of the Doppler precipitation radar backscatter from high-resolution 3D rain fields (either generated by a cloud resolving numerical model or retrieved from airborne radar measurements). The results show that the antenna-pointing-induced error can, indeed, be reduced by the proposed technique in order to achieve 1 m s(exp -1) accuracy on rainfall vertical velocity estimates.

remote sensing↗
NASA NTRS2011

Elemental Mercury Diffusion Processes and Concentration at the Lunar Poles

In 2009, the Lyman Alpha Mapping Project (LAMP) spectrograph onboard the Lunar Reconnaissance Orbiter (LRO) spacecraft made the first detection of element mercury (Hg) vapor in the lunar exosphere after the Lunar Crater Observing and Sensing Satellite (LCROSS) Centaur rocket impacted into the Cabeus crater in the southern polar region of the Moon. The lunar regolith core samples from the Apollo missions determined that Hg had a devolatilized pattern with a concentration gradient increasing with depth, in addition to a layered pattern suggesting multiple episodes of burial and volatile loss. Hg migration on the lunar surface resulted in cold trapping at the poles. We have modeled the rate at which indigenous Hg is lost from the regolith through diffusion out of lunar grains. We secondly modeled the migration of Hg vapor in the exosphere and estimated the rate of cold-trapping at the poles using a Monte Carlo technique. The Hg vapor may be lost from the exosphere via ionization, Jeans escape, or re-impact into the surface causing reabsorption.

Moxley, Frederick↗
NASA NTRS2015

Simulated Transmission of the Dengue Virus Across the US-Mexico Border Using Remotely Sensed and Ground Based Weather Data

Incidence of dengue fever, caused by a mosquito transmitted virus, have increased in the Americas during recent decades. In the US, local transmission has been reported in southern Texas and Florida. However, despite its close proximity to dengue endemic areas in Mexico and the presence of a primary mosquito vector, there are no reports of local transmission in Arizona. Many studies have demonstrated that weather influences dengue virus transmission by regulating vector development rates, vector habitat availability, and the duration of the virus extrinsic incubation period (EIP). The EIP, the period between mosquito infection and the ability for it to retransmit the virus, is especially important given its high sensitivity to temperature and the short lifespan of mosquitoes. Other studies, however, have suggested that human related factors such as socioeconomic status and herd immunity may explain much of the disparity in dengue incidence in the US‐Mexico border region. Using a meteorologically driven model of vector population dynamics and virus transmission we compare simulations of dengue fever cases in southern Arizona and northern Mexico. A Monte Carlo approach is employed to select parameter values by evaluating simulations in Hermosillo Mexico with reported dengue fever case data. Simulations that replicate the case data best are retained and rerun using remotely sensed climate data from other Arizona and Mexico locations to determine the relative influence of weather on virus transmission. Although human and environmental factors undoubtedly influence dengue transmission in the US‐Mexico border regions, weather is a major facilitator of the transmission process.

Dengue↗
NASA NTRS2018

Picometer Differential Wavefront Metrology by Nonlinear Zernike Wavefront Sensing for LUVOIR

We propose the Nonlinear Zernike wavefront sensor (NLZWFS) for out-of-band differential wavefront sensing to augment primary mirror stability on LUVOIR and similar mission concepts during exoplanet coronagraphy. This new data analysis paradigm involving a full polychromatic scalar physical optics model for the phase-shifting Zernike wavefront sensor removes the linearity assumptions which would otherwise prevent accurate sensing. We show Monte-Carlo simulations of NLZWFS and focus-diverse phase retrieval to understand the exposure times necessary to achieve picometer-level stability in the telescope wavefront.

Redding, David C.↗
NASA NTRS2004

Bounding the risk of crew loss following orbital debris penetration of the International Space Station at assembly stages 1J and 1E

Orbital debris impacts on the International Space Station occur frequently. To date, none of the impacting particles has been large enough to penetrate manned pressurized volumes. We used the Manned Spacecraft Crew Survivability code to evaluate the risk to crew of penetrations of pressurized modules at two assembly stages: after Flight 1J, when the pressurized elements of Kibo, the Japanese Experiment Module, are present, and after Flight 1E, when the European Columbus Module is present. Our code is a Monte-Carlo simulation of impacts on the Station that considers several potential event types that could lead to crew loss. Among the statistics tabulated by the program is the probability of death of one or more crew members in the event of a penetration, expressed as the risk factor, R. This risk factor is dependent on details of crew operations during both ordinary circumstances and decompression emergencies, as well as on details of internal module configurations. We conducted trade studies considering these procedure and configuration details to determine the bounds on R at the 1J and 1E stages in the assembly sequence. Here we compare the R-factor bounds, and procedures could that reduce R at these stages. Published by Elsevier Ltd on behalf of COSPAR.

Models, Theoretical↗
NASA NTRS1993

NTR plume modeling

Viewgraphs on nuclear thermal propulsion are presented. Topics covered include computational fluid dynamics (CFD) for plume analysis; molecular fluid dynamics; molecular CFD characteristics; direct-simulation Monte-Carlo (DSMC) method; integration of DSMC and Navier-Stokes computations; and density profiles.

Byers, D.↗
NASA NTRS1982

Transport processes on the lunar surface - Comparison of model calculations with radionuclides data

Descriptions are given of the experimental methods used in determining Al-26 and Mn-53 activities and of the possible improvements that can be expected in the near future. The results obtained for the seven lunar core sections where both Al-26 and Mn-53 are measured with good depth definition are discussed. It is then shown how meteoritic impacts and the secondary effects they induce modify the Al-26 and Mn-53 activities in a core. Using a Monte Carlo method, 150 possible depositional histories for a core are generated; from these the resulting activity profiles for both Al-26 and Mn-53 are computed, using several possible SCR energy spectra. These model-generated profiles are then compared with the experimental profiles in the seven cores, and plausible scenarios for the depositional history of each of the cores are tentatively inferred.

Langevin, Y.↗
NASA NTRS2004

Space Applications of the FLUKA Monte-Carlo Code: Lunar and Planetary Exploration

NASA has recognized the need for making additional heavy-ion collision measurements at the U.S. Brookhaven National Laboratory in order to support further improvement of several particle physics transport-code models for space exploration applications. FLUKA has been identified as one of these codes and we will review the nature and status of this investigation as it relates to high-energy heavy-ion physics.

Anderson, V.↗
NASA NTRSDate not supplied

Direct Simulation Monte Carlo Studies of the Gas Sampling for the VATMOS-SR Mission Concept

VATMOS-SR (Venus ATMOSpheric - Sample Return) is a small spacecraft mission concept which would return a gas sample from the upper atmosphere of Venus to Earth for scientific analysis. This could be the first sample return mission for an extra-terrestrial atmosphere, and potentially the first sample return from an Earth-sized planet. The VATMOS-SR mission concept consists of a SmallSat atmospheric sampling probe (45 deg. sphere/cone geometry, <1 m diameter) that is designed to skim through the Venus upper atmosphere and acquire gas samples below the homopause altitude (around ~110 km altitude), where the different atmospheric gases are mixed. The velocity of the spacecraft where sampling would occur is expected to be between ~10.5 km/s and ~13.1 km/s, depending on the trajectory chosen. This presentation will discuss hypervelocity sampling in the upper atmosphere of Venus, with respect to the VATMOS-SR mission concept. VATMOS-SR would enable critical atmospheric measurements to form a full picture of how, why, and when Venus evolved to be so different from Earth and Mars. The abundances and isotopic compositions of volatile elements (such as N, C, S, O and the noble gases) in planetary atmospheres record volatile delivery during accretion, outgassing from planetary interiors, and atmospheric loss to space. Precise and accurate determinations of atmospheric volatile signatures are the key to understanding the origins and geodynamical evolution of Venus compared to the other terrestrial planets. Hypersonic sampling poses unique technical and scientific challenges. To ensure it is possible to relate the composition of the sampled gases to the free stream atmospheric composition, large-scale numerical simulations are employed to model the flow through the VATMOS-SR sampling system. In particular, an emphasis is placed on quantifying noble gas isotopic fractionation that occurs during the sample acquisition and transfer process in order to determine how measured isotopic ratios of noble gases in the sample compare to actual isotopic ratios in the Venusian atmosphere. The Direct Simulation Monte Carlo (DSMC) code SPARTA, an open source software package developed by Sandia National Laboratories, is used in this work. SPARTA, based on Bird’s DSMC method, is a molecular-level gas-kinetic technique. As SPARTA is able to model hypervelocity reacting flows in strong chemical and thermal non-equilibrium, this software package is well suited to determine relevant flow properties for the VATMOS-SR mission concept, and to numerically quantify the expected level of elemental and/or isotopic fractionation in the sample acquired by VATMOS-SR. This presentation will show results from 3D simulations correlating the noble gas isotopic fractionation in the gas acquired at hypervelocity speeds to its ambient atmosphere value. In particular, emphasis will be placed at Xenon isotopes of masses 128 and 130, as precise measurements of that ratio would yield a comparison to Earth’s atmosphere. Additionally, sensitivity studies that quantify the uncertainties due to the freestream parameters as well as the modeling parameters will be performed.

direct simulation Monte Carlo↗
NASA NTRS2026

Diffusion Quantum Monte Carlo Calculation of the Austenite and Martensite Phases of NiTi

NiTi is a promising material for smart and active technologies due to its exhibition of the shape memory effect, superelasticity, and biocompatibility. The shape memory effect is tied to the reversible transition between the austenite and martensite phases. A major research direction is to alloy NiTi with Zr, Hf, Pd, Pt, etc., in order to tune the martensitic transition temperature (MTT). Modeling the MTT from first principles is challenging because the lattice dynamics is complicated by anharmonicity and various low-energy structures. Using density functional theory, the energy difference between the austenite and martensite phases of NiTi varies by up to 100 meV/atom depending on the choice of density functional, which is of the same order of the energy difference itself. Consequently, free energy calculations with different functionals can result in estimates of the MTT that vary by several hundred K. Using diffusion quantum Monte Carlo, we calculated the energy difference between the B2 and B19' structures of NiTi to be 70.9 +- 2.5 meV/atom.

Kevin K Ly↗
NASA NTRS1971

Study of automatic flare and decrab guidance and control system for the space shuttle

The automatic landing of an unpowered space shuttle vehicle was studied along with the design of the guidance and flight controls, selection of the ground reference component of the landing system (signals in space), and evaluation of the performance of the overall system. The study was carried out by means of an all-digital simulation which incorporated wind shears, gusts and error models for the hardware components. The performance of the landing system operating in winds and turbulence and with hardware errors was determined by Monte Carlo techniques. It was found that the interactions of turbulence and vehicle characteristics were the limiting factors on system performance. The touchdown errors due to the measurement errors of the ground reference system were less significant. The guidance designed was predictive in the longitudinal direction and fixed path in the lateral direction.

Cockayne, W.↗
NASA NTRS1981

Spatial aspects of electron energy degradation in atomic oxygen

Spatial (radial and longitudinal) yield spectra for electron energy degradation in atomic oxygen have been obtained using a Monte Carlo method for 25 eV to 10 keV incident electrons. Four-dimensional yield spectra have been analytically represented in terms of a model containing three simple microplumes. We find that the scaled spatial yield spectra for O is approximately the same as for N2. This feature provides a basis for inferring yield spectra for any atmosphere gas or mixture of gases.

Singhal, R. P.↗
NASA NTRS1982

Electromagnetic cascades in pulsars

The development of pair-photon cascades initiated by high energy electrons above a pulsar polar cap is simulated numerically. The calculation uses the energy of the primary electron, the magnetic field strength, and the period of rotation as parameters, and follows the curvature radiation emitted by the primary, the conversion of this radiation to e(+)e(-) pairs in the intense fields, and the quantized synchrotron radiation by the secondary pairs. A recursive technique allows the tracing of an indefinite number of generations using a Monte Carlo method. Gamma-ray and pair spectra are calculated for cascades in different parts of the polar cap and with different acceleration models. It is found that synchrotron radiation from secondary pairs makes an important contribution to the gamma-ray spectrum above 25 MeV, and that the final gamma-ray and pair spectra are insensitive to the height of the accelerating region, as long as the acceleration of the primary electrons is not limited by radiation reaction.

Daugherty, J. K.↗
NASA NTRS1984

An abrasion-ablation model description of galactic heavy-ion fragmentation

The fragmentation of high-energy galactic heavy ions by nuclear interactions with arbitrary target nuclei is described within the context of a simple abrasion-ablation fragmentation model. The abrasion part of the theory utilizes a quantum-mechanical formalism based upon an optical model potential approximation to the exact nucleus-nucleus multiple-scattering series. Nuclear charge distributions of the excited prefragments are calculated using either a hypergeometric distribution or a method based upon the zero-point oscillations of the giant dipole resonance. The excitation energy of the prefragment is estimated from the geometric clean-cut abrasion-ablation model. The decay probabilities for the various particle emission channels, in the ablation stage of the fragmentation, are obtained from the EVAP-4 Monte Carlo computer program. Elemental production cross sections for 1.88-GeV/nucleon iron colliding with carbon, silver, and lead targets are calculated and compared with experimental data and with the predictions from the semiempirical relations of Silberberg and Tsao.

Townsend, L. W.↗
NASA NTRS1984

Atmospheric transfer of radiation above an inhomogeneous non-Lambertian reflective ground. II - Computational considerations and results

The theoretical foundation for solution of the three-dimensional radiative transfer problem described in the preceding paper is reviewed. Practical considerations involved in implementing the Fourier transform/Gauss-Seidel method on a minicomputer are discussed, along with derivations of symmetry relations and approximations which can be used to enhance the computational efficiency. Model results for a surface whose albedo varies as a step function are presented and compared with published solutions obtained by using the Monte Carlo method.

Diner, D. J.↗