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NASA NTRS1999

An Analysis of Gravity-Field Estimation Based on Intersatellite Dual-1-Way Biased Ranging

The GRACE (Gravity Recovery And Climate Experiment) mission is designed to make global, highly accurate measurements of the Earth's gravity field with high spatial resolution. Ancillary GPS occultation measurements are also to be carried out for atmospheric monitoring. In the dual-1-way biased ranging of this mission, the range between two satellites separated by 100 to 200 km in nearly polar, coplanar, circular orbits, is measured to very high precision, to within an additive constant, through the exchange of K- and Ka-band sinusoidal signals. Such biased ranging data, along with GPS L-band range and phase data, can be processed and fit over successive multiday intervals to obtain accurate estimates of the Earth's gravity field. This report approximately models and analyzes this process, from the generation of the RF signals at the two satellites through the extraction of the geopotential. The steps include generation of the transmitted signals, processing the received signals to extract high-rate baseband phase, carrying out a dual-1-way combination of baseband phase to extract high-rate biased range for each band, combining K- and Ka-band ranges to correct for the ionosphere effect, and processing the resulting high-rate biased range values to extract three types of reduced-rate observables: biased range, range rate and range acceleration. The version of dual-1-way biased ranging developed by this report improves upon previous versions in a number of ways: highly accurate satellite-timetag corrections derived from concurrent GPS data, better baseband phase extraction using highly digital processing, highly accurate USO-rate calibration derived from concurrent GPS data, an improved method for extracting high-rate biased range from baseband phase, improved filtering for extracting reduced- rate observables from high-rate biased range, and parallel extraction of three observable types.

SINUSOIDAL SIGNALS↗

NASA NTRS1988

Observation of the Meissner effect in a lattice Higgs model

The lattice-regularized U(1) Higgs model in an external electromagnetic field is studied by Monte Carlo techniques. In the Coulomb phase, magnetic flux can flow through uniformly. The Higgs phase splits into a region where magnetic flux can penetrate only in the form of vortices and a region where the magnetic flux is completely expelled, the relativistic analog of the Meissner effect in superconductivity. Evidence is presented for symmetry restoration in strong external fields.

Damgaard, Poul H.↗

NASA NTRS1992

An optical study of grain formation: Casting and solidification technology (2-IML-1)

By studying the unidirectional growth of a metal-model material in microgravity, an attempt is made to characterize alloy solidification. Using holograms and supporting temperature measurements obtained during processing in the Fluids Experiment System (FES), the solute and thermal fields associated with the dendrite growth front and extraneous nucleation will be measured and compared to a theoretical (computational) model. Ground based supporting experiments include particle tracking to measure the velocity fields, and optical phase shift techniques (confocal optical signal processing, interferometry, and Schlieren) to study thermal and solutal fields.

Mccay, Mary H.↗

NASA NTRS1998

Preliminary Work for Modeling the Propellers of an Aircraft as a Noise Source in an Acoustic Boundary Element Analysis

An algorithm for generating appropriate velocity boundary conditions for an acoustic boundary element analysis from the kinematics of an operating propeller is presented. It constitutes the initial phase of Integrating sophisticated rotorcraft models into a conventional boundary element analysis. Currently, the pressure field is computed by a linear approximation. An initial validation of the developed process was performed by comparing numerical results to test data for the external acoustic pressure on the surface of a tilt-rotor aircraft for one flight condition.

Vlahopoulos, Nickolas↗

NASA NTRS1994

Temperature Field During Flame Spread over Alcohol Pools: Measurements and Modelling

A principal difference between flame spread over solid fuels and over liquid fuels is, in the latter case, the presence of liquid-phase convection ahead of the leading edge of the flame. The details of the fluid dynamics and heat transfer mechanisms in both the pulsating and uniform flame spread regimes were heavily debated, without resolution, in the 1960s and 1970s; recently, research on flame spread over pools was reinvigorated by the advent of enhanced diagnostic techniques and computational power. Temperature fields in the liquid, which enable determination of the extent of preheating ahead of the flame, were determined previously by the use of thermocouples and repetitive tests, and suggested that the surface temperature does not decrease monotonically ahead of the pulsating flame front, but that there exists a surface temperature valley. Recent predictions support this suggestion. However, others' thermocouple measurements and the recent field measurements using Holographic Interferometry (HI) did not find a similar valley. In this work we examine the temperature field using Rainbow Schlieren Deflectometry (RSD), with a measurement threshold exceeding that of conventional interferometry by a factor of 20:1, for uniform and pulsating flame spread using propanol and butanol as fuels. This technique was not applied before to flame spread over liquid pools, except in some preliminary measurements reported earlier. Noting that HI is sensitive to the refractive index while RSD responds to refractive index gradients, and that these two techniques might therefore be difficult to compare, we utilized a numerical simulation, described below, to predict and compare both types of field for the uniform and pulsating spread regimes. The experimental data also allows a validation of the model at a level of detail greater than has been attempted before.

Miller, Fletcher J.↗

NASA NTRS1990

Effects of large-scale wind driven turbulence on sound propagation

Acoustic measurements made in the atmosphere have shown significant fluctuations in amplitude and phase resulting from the interaction with time varying meteorological conditions. The observed variations appear to have short term and long term (1 to 5 minutes) variations at least in the phase of the acoustic signal. One possible way to account for this long term variation is the use of a large scale wind driven turbulence model. From a Fourier analysis of the phase variations, the outer scales for the large scale turbulence is 200 meters and greater, which corresponds to turbulence in the energy-containing subrange. The large scale turbulence is assumed to be elongated longitudinal vortex pairs roughly aligned with the mean wind. Due to the size of the vortex pair compared to the scale of the present experiment, the effect of the vortex pair on the acoustic field can be modeled as the sound speed of the atmosphere varying with time. The model provides results with the same trends and variations in phase observed experimentally.

Noble, John M.↗

NASA NTRS2017

The Substorm Cycle as Reproduced by Global MHD Models

Recently, Gordeev et al. (2015) suggested a method to test global MHD models against statistical empirical data. They showed that four community-available global MHD models supported by the Community Coordinated Modeling Center (CCMC) produce a reasonable agreement with reality for those key parameters (the magnetospheric size, magnetic field, and pressure) that are directly related to the large-scale equilibria in the outer magnetosphere. Based on the same set of simulation runs, here we investigate how the models reproduce the global loading-unloading cycle. We found that in terms of global magnetic flux transport, three examined CCMC models display systematically different response to idealized2 h north then 2 h south interplanetary magnetic field (IMF) Bz variation. The LFM model shows a depressed return convection and high loading rate during the growth phase as well as enhanced return convection and high unloading rate during the expansion phase, with the amount of loaded unloaded magnetotail flux and the growth phase duration being the closest to their observed empirical values during isolated substorms. Two other models exhibit drastically different behavior. In the BATS-R-US model the plasma sheet convection shows a smooth transition to the steady convection regime after the IMF southward turning. In the Open GGCM a weak plasma sheet convection has comparable intensities during both the growth phase and the following slow unloading phase. We also demonstrate potential technical problem in the publicly available simulations which is related to post processing interpolation and could affect the accuracy of magnetic field tracing and of other related procedures.

Gordeev, E.↗

NASA NTRS1973

Aspects of investigating STOL noise using large-scale wind-tunnel models.

The applicability of the NASA Ames 40- by 80-foot wind tunnel for acoustic research on STOL concepts has been investigated. The acoustic characteristics of the wind-tunnel test section have been studied with calibrated acoustic sources. Acoustic characteristics of several large-scale STOL models have been studied in both the free-field and wind-tunnel acoustic environments. The results of these studies indicate that the acoustic characteristics of large-scale STOL models can be measured in the wind tunnel if the test section acoustic environment and model acoustic similitude are taken into consideration. The reverberant field of the test section must be determined with an acoustically similar noise source. A directional microphone, a phased array of microphones, and extrapolation of near-field data to far-field are some of the techniques being explored as possible solutions to the directivity loss in a reverberant field. The model sound pressure levels must be of sufficient magnitude to be distinguishible from the wind-tunnel background noise.

Falarski, M. D.↗

NASA NTRS1995

Electrochromatographic separation of proteins

We have developed a modified electrochromatography system which minimizes Joule heating at electric field strengths up to 125 V/cm. A non-linear equilibrium model is described which incorporates electrophoretic mobility, hydrodynamic flow velocity, and an electrically induced concentration polarization at the surface of the stationary phase. This model is able to provide useful estimates of protein retention time and velocity in a column packed with Sephadex gel and subjected to an electric field. A correlation of electrophoretic mobility of peptide and proteins with respect to their charge, molecular mass, and asymmetry enables the selection of solute target molecules for electrochromatographic separations. Good separation of protein mixtures have been obtained.

NASA Discipline Life Support Systems↗

NASA NTRSDate not supplied

Going With the Flow: Using a Particle Dispersion Model to Reveal Links Between Ocean Ecosystems and Marine Aerosols

Marine biogenic particle contributions to atmospheric aerosol concentrations are not well understood though they are important for determining cloud optical and cloud nucleating properties. Here we examine the relationship between marine aerosol measurements with satellite and model fields of ocean biology and meteorological variables during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). NAAMES consisted of four field campaigns between November 2015 and April 2018 that aligned with the four major phases of the annual phytoplankton bloom cycle. The FLEXPART Lagrangian particle dispersion model is used to connect these variables spatiotemporally to ship-based aerosol. We find that correlations between some aerosol measurements with satellite measured and modelled variables increase with increasing trajectory length. This indicates biological and meteorological processes over the air mass history are influential to measured particle properties. For example, results show organic aerosol mass is driven by biogenic volatile organic compound (VOC) emissions from photosynthesis by phytoplankton stocks during advection into the region. In contrast, primary marine aerosol (PMA) concentrations showed better correlations to variables weighted with shorter air mass residence times, which reflects their localized origin as primary emissions. Evidence also suggest variability in PMA concentrations likely play an important role in VOC emission removal. The removal of VOCs lessen their impact on particle number and mass concentrations. The sensitivity of marine aerosols to the main ecosystem-atmosphere drivers and its dependence on air mass history are to be further discussed.

Kevin J Sanchez↗

NASA NTRS2015

Microstructural Influence on Deformation and Fatigue Life of Composites Using the Generalized Method of Cells

A fully coupled deformation and damage approach to modeling the response of composite materials and composite laminates is presented. It is based on the semi-‐analytical generalized method of cells (GMC) micromechanics model as well as its higher fidelity counterpart, HFGMC, both of which provide closed-form constitutive equations for composite materials as well as the micro scale stress and strain fields in the composite phases. The provided constitutive equations allow GMC and HFGMC to function within a higher scale structural analysis (e.g., finite element analysis or lamination theory) to represent a composite material point, while the availability of the micro fields allow the incorporation of lower scale sub‐models to represent local phenomena in the fiber and matrix. Further, GMC's formulation performs averaging when applying certain governing equations such that some degree of microscale field accuracy is surrendered in favor of extreme computational efficiency, rendering the method quite attractive as the centerpiece in a integrated computational material engineering (ICME) structural analysis; whereas HFGMC retains this microscale field accuracy, but at the price of significantly slower computational speed. Herein, the sensitivity of deformation and the fatigue life of graphite/epoxy PMC composites, with both ordered and disordered microstructures, has been investigated using this coupled deformation and damage micromechanics based approach. The local effects of fiber breakage and fatigue damage are included as sub‐models that operate on the microscale for the individual composite phases. For analysis of laminates, classical lamination theory is employed as the global or structural scale model, while GMC/HFGMC is embedded to operate on the microscale to simulate the behavior of the composite material within each laminate layer. A key outcome of this study is the statistical influence of microstructure and micromechanics idealization (GMC or HFGMC) on the overall accuracy of unidirectional and laminated composite deformation and fatigue response.

Microscale Models↗

NASA NTRS2018

The OpenSE Cookbook: A Practical, Recipe Based Collection of Patterns, Procedures, and Best Practices for Executable Systems Engineering for the Thirty Meter Telescope

The OpenSE Cookbook is an open-sourced collection of patterns, procedures, and best practices targeted for systems engineers who seek guidance on applying model-based and executable systems engineering (MBSE) using SysML. Its content has emerged from the system level modeling effort on the European Framework Program 6 (FP6) and the Thirty Meter Telescope (TMT). The TMT MBSE approach applied the Executable Systems Engineering Method (ESEM) and the open-source Engineering Environment (OpenMBEE) to specify, analyze, and verify requirements of TMT’s Alignment and Phasing System (APS) and the Narrow Field Infrared Adaptive Optics System (NFIRAOS). In these applications, implicit dependencies are made explicit in a formal model through the use of ESEM, OpenMBEE, and SysML modeling constructs. The value proposition for applying this MBSE approach was to establish precise requirements and fine-grained traceability to system designs, and to verify key requirements beginning early in development. The integration of ESEM and the OpenMBEE tooling infrastructure (providing linked-data and web-operability) is a significant added value for the MBSE approach. The APS is responsible for the overall pre-adaptive optics wavefront quality, using starlight to measure wavefront errors and align the TMT optics. In the formally integrated and executable SysML model, simulations are performed to analyze the impact of changed requirements and verify specified constraints for various operational scenarios. The APS team used several modeling patterns to capture information such as the requirements, the operational scenarios, involved subsystems and their interaction points, the estimated or required time durations, and the mass and power consumption. Adaptive optics systems are designed to sense real-time atmospheric turbulence and correct the telescope’s optical beam to remove its effect. The system model for the adaptive optics operational modes was developed to capture sequence behaviors and operational scenarios to run Monte-Carlo simulations for verifying acquisition time, observing efficiency, and operational behavior requirements. The model is particularly useful for investigating the effect of parallelization, identifying interface issues, and re-ordering sequence acquisition tasks. A former version of the Cookbook (which is now updated to MBSE challenges, goals, and lessons learned) included modeling guidelines and conventions for all system aspects, hierarchy levels, and views, which were developed during for the Active Phasing Experiment (APE), an opto-mechatronical system technology demonstrator for the Extremely Large Telescope (ELT). The Cookbook utilizes the above mentioned system models as real-world case-studies to demonstrate and document the applications of the recipes, providing also instructional examples and addressing the available tooling support. The Cookbook is accompanied by a number of SysML models and aodel libraries which facilitate model authoring and maintenance. The Cookbook covers the different aspects of Systems Engineering such as management of Requirements, Design (behavior and structure), Interfaces, Interdisciplinary Integration, Analysis, Trade Studies, and Technical Resources. This paper presents the background, motivation, architecture, and highlights some key content of the Cookbook. For example, interface management, error budget management, requirements verification, Monte Carlo driven analysis, and timing analysis of operational scenarios. The paper discusses how the capabilities of OpenMBEE contributed significantly to the adoption of executable systems engineering.

Brower, Eric↗

NASA NTRS2018

Infrared Computer-Generated Holograms: Design and Application for the WFIRST Grism Using Wavelength-Tuning Interferometry

Interferometers using computer-generated holograms (CGHs) have become the industry standard to accurately measure aspheric optics. The CGH is a diffractive optical element that can create a phase or amplitude distribution and can be manufactured with low uncertainty using modern lithographic techniques. However, these CGHs have conventionally been used with visible light and piezo-shifting interferometers. Testing the performance of transmissive optics in the infrared requires infrared CGHs and an infrared interferometer. Such an instrument is used in this investigation, which introduces its phase shift via wavelength-tuning. A procedure on how to design and manufacture infrared CGHs and how these were successfully used to model and measure the Wide-Field Infrared Survey Telescope grism elements is provided. Additionally, the paper provides a parametric model, simulation results, and calculations of the errors and measurements that come about when interferometers introduce a phase variation via wavelength-tuning interferometry to measure precision aspheres.

Communication↗

NASA NTRS1990

Development of advanced silicon solar cells for Space Station Freedom

This report describes the development of large area high efficiency wrapthrough solar cells for Space Station Freedom. The goal of this contract was the development and fabrication of 8 x 8 cm coplanar back contact solar cells with a minimum output of 1.039 watts/cell. The first task in this program was a modeling study to determine the optimum configuration of the cell and to study the effects of surface passivation, substrate resistivity, and back surface field on the BOL and EOL performance. In addition, the optical stack, including the cell cover, AR coatings, and Kapton blanket, was modeled to optimize 'on orbit' operation. The second phase was a manufacturing development phase to develop high volume manufacturing processes for the reliable production of low recombination velocity boron back surface fields, techniques to produce smooth, low leakage wrapthrough holes, passivation, photoresist application methods, and metallization schemes. The final portion of this program was a pilot production phase. Seven hundred solar cells were delivered in this phase. At the end of the program, cells with average efficiencies over 13 percent were being produced with power output in excess of 1.139 watts/cell, thus substantially exceeding the program goal.

Lillington, David R.↗

NASA NTRS1993

The Effects of Neutral Inertia on Ionospheric Currents in the High-Latitude Thermosphere Following a Geomagnetic Storm

Results of an experimental and theoretical investigation into the effects of the time dependent neutral wind flywheel on high-latitude ionospheric electrodynamics are presented. The results extend our previous work which used the National Center for Atmospheric Research Thermosphere/Ionosphere General Circulation Model (NCAR TIGCM) to theoretically simulate flywheel effects in the aftermath of a geomagnetic storm. The previous results indicated that the neutral circulation, set up by ion-neutral momentum coupling in the main phase of a geomagnetic storm, is maintained for several hours after the main phase has ended and may dominate height-integrated Hall currents and field-aligned currents for up to 4-5 hours. We extend the work of Deng et al. to include comparisons between the calculated time-dependent ionospheric Hall current system in the storm-time recovery period and that measured by instruments on board the Dynamics Explorer 2 (DE 2) satellite. Also, comparisons are made between calculated field-aligned currents and those derived from DE 2 magnetometer measurements. These calculations also allow us to calculate the power transfer rate (sometimes called the Poynting flux) between the magnetosphere and ionosphere. The following conclusions have been drawn: (1) Neutral winds can contribute significantly to the horizontal ionospheric current system in the period immediately following the main phase of a geomagnetic storm, especially over the magnetic polar cap and in regions of ion drift shear. (2) Neutral winds drive Hall currents that flow in the opposite direction to those driven by ion drifts. (3) The overall morphology of the calculated field-aligned current system agrees with previously published observations for the interplanetary magnetic field (IMF) B(sub Z) southward conditions, although the region I and region 2 currents are smeared by the TI(ICM model grid resolution. (4) Neutral winds can make significant contributions to the field-aligned current system when B(sub Z) northward conditions prevail following the main phase of a storm, but can account for only a fraction of the observed currents. (5) DE 2 measurements provide a demonstration of "local" (satellite-altitude) flywheel effects. (6) On the assumption that the magnetosphere acts as an insulator, we calculate neutral-wind-induced polarization electric fields of approx. 20-30 kV in the period immediately following the geomagnetic storm.

Deng, W.↗

NASA NTRS1989

Three-dimensional linear instability modeling of the cloud level Venus atmosphere

Based on the success of several two-dimensional (latitude, longitude) linear barotropic instability models at matching some of the observed characteristics of the cloud level, polar region of the Venus atmosphere, a more realistic, linear, three-dimensional (height, latitude and longitude) model has been developed to further test the hypothesis that the observed features can be described by linear instability theory. The approach taken is to vary the model input parameters to see whether it is possible to produce modes that resemble the observations of wave activity and to compare those input parameters with other observations of the mean state. Sensitivity studies show that in addition to a well-documented dependence on the mean zonal wind, the growth and propagation of unstable modes depends on the latitude variation of the mean temperature (and hence static stability). These studies have led to the specification of a model basic state wind and temperature field that produces modes which are matched to observations of spatial structure, preferred wavenumber and phase speed of the polar disturbances. Wavenumber 2 is found to have the shortest growth time and unlike the two-dimensional results, wavenumbers 1-3 share a nearly common period of about 3 days. The derived basic state has a temperature field that is quite similar to Pioneer Venus observations; however, in some regions the model basic state wind field departs from cyclostrophic values based on temperature observations.

Elson, Lee S.↗

NASA NTRS1978

Mars gravity field derived from Viking-1 and Viking-2 - The navigation result

Viking-1 and Viking-2 Doppler tracking data taken during orbit phases characterized by 1500 km subperiapse altitudes have provided a basis for a determination of the Martian gravity field. Navigation results show that the linear combination of short-arc gravity estimates is an acceptable technique for obtaining gravity models over multiple data arcs. An ensemble field composed of Viking data and Mariner-9 a priori retains the inherent local accuracy of its constituent fields. At the same time, the model can be made to be valid globally by careful weighting of a priori Mariner-9 data. The sixth degree and order model presented reduces the error concerning the change in period by more than an order of magnitude during the high altitude (1500 km) phases of the Viking mission. The resulting areoid deviates by no more than 150 m from the areoid produced by the a priori Mariner-9 field.

Christensen, E. J.↗

NASA NTRS2022

Probing the High-energy Gamma-Ray Emission Mechanism in the Vela Pulsar via Phase-resolved Spectral and Energy-dependent Light-curve Modeling

Recent kinetic simulations sparked a debate regarding the emission mechanism responsible for pulsed GeV γ-ray emission from pulsars. Some models invoke curvature radiation, while other models assume synchrotron radiation in the current sheet. We interpret the curved spectrum of the Vela pulsar as seen by H.E.S.S. II (up to ∼100 GeV) and the Fermi Large Area Telescope to be the result of curvature radiation due to primary particles in the pulsar magnetosphere and current sheet. We present phase-resolved spectra and energy-dependent light curves using an extended slot gap and current-sheet model, invoking a step function for the accelerating electric field as motivated by kinetic simulations. We include a refined calculation of the curvature radius of particle trajectories in the lab frame, impacting the particle transport, predicted light curves, and spectra. Our model reproduces the decrease of the flux of the first peak relative to the second one, evolution of the bridge emission, near-constant phase positions of peaks, and narrowing of pulses with increasing energy. We can explain the first of these trends because we find that the curvature radii of the particle trajectories in regions where the second γ-ray light-curve peak originates are systematically larger than those associated with the first peak, implying that the spectral cutoff of the second peak is correspondingly larger. However, an unknown azimuthal dependence of the E field, as well as uncertainty in the precise spatial origin of the GeV emission, precludes a simplistic discrimination of emission mechanisms.

Monica Barnard↗