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NASA NTRSDate not supplied

Integrated Modeling for Payload Test of the Roman Space Telescope

The Nancy Grace Roman Telescope (RST) is a NASA observatory designed to unravel the secrets of dark energy and dark matter, search for and image exoplanets, and explore many topics in infrared optics. Scheduled to launch in no earlier than October 2026, this 2.4 meter aperture telescope has a field of view 100 times greater than the Hubble Space Telescope. The mission is currently in its construction phase, where integrated modeling between thermal, structural, and optical models of the observatory is necessary to demonstrate science quality images over the range of operational parameters. This presentation discusses the most recent integrated modeling analysis cycle for Roman, including model correlation with our instrument level testing. We include a discussion on improved processes of the handling of the various flows of data between the modeling disciplines and discipline specific monte-carlo analysis predictions. We will finish with the predicted uncertainties and expected performance for our upcoming observatory alignment verification test using machine learning algorithms.

telescope↗

NASA NTRS2003

Self-Consistent Large-Scale Magnetosphere-Ionosphere Coupling: Computational Aspects and Experiments

Both external and internal phenomena impact the terrestrial magnetosphere. For example, solar wind and particle precipitation effect the distribution of hot plasma in the magnetosphere. Numerous models exist to describe different aspects of magnetosphere characteristics. For example, Tsyganenko has developed a series of models (e.g., [TSYG89]) that describe the magnetic field, and Stern [STER75] and Volland [VOLL73] have developed an analytical model that describes the convection electric field. Over the past several years, NASA colleague Khazanov, working with Fok and others, has developed a large-scale coupled model that tracks particle flow to determine hot ion and electron phase space densities in the magnetosphere. This model utilizes external data such as solar wind densities and velocities and geomagnetic indices (e.g., Kp) to drive computational processes that evaluate magnetic, electric field, and plasma sheet models at any time point. These models are coupled such that energetic ion and electron fluxes are produced, with those fluxes capable of interacting with the electric field model. A diagrammatic representation of the coupled model is shown.

Newman, Timothy S.↗

NASA NTRS1982

Computer simulation of inner magnetospheric dynamics for the magnetic storm of July 29, 1977

The Rice University convection model is applied to the early main phase of the July 29, 1977 magnetic storm through a computer implementation that self-consistently calculates electric fields, currents, and plasma distributions and velocities in the inner magnetosphere/ionosphere system. On the basis of solar wind parameters and AL index as inputs, the model predicts the injection of plasma sheet plasma to form a substantial storm time ring current whose total predicted strength agrees with the observed Dst index. The possibility that the magnetic field may be sufficiently inflated to make 60 deg field lines extend to the outer magnetosphere is examined. In the model, distortion of the plasma sheet inner edge by magnetospheric compression associated with the sudden commencement temporarily disrupts the normal Birkeland current pattern. Normal Birkeland currents and shielding reassert themselves in about an hour.

Wolf, R. A.↗

NASA NTRS1989

Formation of Fourier phase shifts in the solar Ni I 6768 A line

A formalism is developed to understand better how Doppler shifts of spectrum lines as inferred from phase shifts in the Fourier transforms of line profiles are related to the underlying velocity structures which they are intended to measure. With a standard model atmosphere and a simplified, quasi-LTE treatment of line formation, the formalism is applied to the Ni I 6768 A line, which has been selected for use with a network of imaging interferometers under development by the Global Oscillations Network Group for research in helioseismology. Fourier phase shifts are found to be a remarkably linear measure of velocity even in the presence of gradients and unresolved lateral variations in the assumed velocity field. An assumed outward increase in amplitude of a model oscillatory velocity is noticeably reflected in the center-to-limb behavior of the simulated velocity measure, and a sample model of solar granulation is found to have a strong influence on the formation of the Fourier phase.

Jones, Harrison P.↗

NASA NTRSDate not supplied

Characterization of Dendritic Spatially Extended 3D Patterns in Directional Solidification: Microgravity Experiments in DECLIC-DSI onboard ISS and 3D Phase-field Simulations

To clarify and characterize the fundamental physical mechanisms active in the dynamical formation of three-dimensional (3D) arrays of dendrites under diffusive growth conditions, in situ monitoring of series of experiments on transparent model alloy succinonitrile – 0.46 wt% camphor was carried out under low gravity in the DECLIC Directional Solidification Insert onboard the International Space Station. These experiments offer the very unique opportunity to observe in situ and characterize the dynamics of the microstructure formation and evolution in extended 3D patterns under microgravity environment. The analyses of the dendritic patterns for a broad range of growth velocities displaying different levels of sidebranching will be presented. Especially, the time evolution of primary spacing, in case of solidifications at constant pulling rate as well as for experiments with pulling rate jump, will be compared to 3D phase-field simulations, and the results will be discussed in terms of stable spacing range.

Kaihua Ji↗

NASA NTRSDate not supplied

Characterization of Dendritic Spatially Extended 3D Patterns in Directional Solidification: Microgravity Experiments in DECLIC-DSI Onboard ISS and 3D Phase-field Simulations

Kaihua Ji↗

NASA NTRS1981

A magnetospheric signature of some F layer positive storms

Calculations of electron density distributions in the global thermosphere-ionosphere system perturbed by high-latitude thermospheric heating are presented which indicate a link between the heating and magnetospheric plasma disturbances near the equator. The calculations were made using a self-consistent model of the global sunlit thermosphere-ionosphere system describing the evolution of equatorial plasma disturbances. The heat input is found to cause electron density enhancements that propagate along magnetic field lines from the F2 maximum over mid-latitudes to the equator in the magnetosphere and which correspond to the positive phase of an F layer storm. The positive phase is shown to be generated by the induction of equatorward winds that raise the mid-latitude F layer through momentum transfer from neutral atoms to ionospheric ions, which ions pull electrons with them. Model results are used to identify plasma signatures of equatorward winds and an intensified magnetospheric electric field in Explorer 45 and Arial 4 measurements taken during the positive phase of an F layer storm.

Miller, N. J.↗

NASA NTRS1982

Mode characteristics of nonplanar double-heterojunction and large-optical-cavity laser structures

Mode behavior of nonplanar double-heterojunction (DH) and large-optical-cavity (LOC) lasers is investigated using the effective index method to model the lateral field distribution. The thickness variations of various layers for the devices discussed are correlated with the growth characteristics of liquid-phase epitaxy over topographical features (channels, mesas) etched into the substrate. The effective dielectric profiles of constricted double-heterojunction (CDH)-LOC lasers show a strong influence on transverse mode operation: the fundamental transverse mode (i.e., in the plane perpendicular to the junction) may be laterally index-guided, while the first (high)-order mode is laterally index-antiguided. The analytical model developed uses a smoothly varying hyperbolic cosine distribution to characterize lateral index variations. The waveguide model is applied to several lasers to illustrate conditions necessary to convert leaky modes to trapped ones via the active-region gain distribution. Theoretical radiation patterns are calculated using model parameters, and matched to an experimental far-field pattern.

Butler, J. K.↗

NASA NTRS1983

Influence of modulation frequency in rubidium cell frequency standards

The error signal which is used to control the frequency of the quartz crystal oscillator of a passive rubidium cell frequency standard is considered. The value of the slope of this signal, for an interrogation frequency close to the atomic transition frequency is calculated and measured for various phase (or frequency) modulation waveforms, and for several values of the modulation frequency. A theoretical analysis is made using a model which applies to a system in which the optical pumping rate, the relaxation rates and the RF field are homogeneous. Results are given for sine-wave phase modulation, square-wave frequency modulation and square-wave phase modulation. The influence of the modulation frequency on the slope of the error signal is specified. It is shown that the modulation frequency can be chosen as large as twice the non-saturated full-width at half-maximum without a drastic loss of the sensitivity to an offset of the interrogation frequency from center line, provided that the power saturation factor and the amplitude of modulation are properly adjusted.

Audoin, C.↗

NASA NTRS1983

New observations of plasma vortices and insights into their interpretation

Two- and three-dimensional plasma measurements and three-dimensional magnetic field measurements made with the ISEE 1 and 2 satellites during sixteen plasma vortex occurrences in the magnetotail plasma sheet are used to develop a fuller description of the vortex phenomenon than has existed heretofore. The phase and energy propagation properties of the vortex waves was studied in particular. The rotation period of the vortices (T = 10 + or - 5 minutes) is apparently independent of location, while the wavelength (lambda not less than several Re) increases with increasing distance down the tail, pointing to a global mode of propagation in which effects of inhomogeneous equilibrium are important. The flow rotation can be explained by propagation of surface waves or resonant waves in a uniform medium. Other observed features, however, require a nonuniform model: nonuniform propagation properties and differences of the phase propagation speed calculated from different components of velocity or magnetic field.

Hones, E. W., Jr.↗

NASA NTRS2017

BrO and Inferred Bry Profiles over the Western Pacific: Relevance of Inorganic Bromine Sources and a Bry Minimum in the Aged Tropical Tropopause Layer

We report measurements of bromine monoxide (BrO) and use an observationally constrained chemical box model to infer total gas-phase inorganic bromine (Br(sub y)) over the tropical western Pacific Ocean (tWPO) during the CONTRAST field campaign (January-February 2014). The observed BrO and inferred Bry profiles peak in the marine boundary layer (MBL), suggesting the need for a bromine source from sea-salt aerosol (SSA), in addition to organic bromine (CBry ). Both profiles are found to be C-shaped with local maxima in the upper free troposphere (FT). The median tropospheric BrO vertical column density (VCD) was measured as 1.6 x 10(exp 13) molec cm(exp -2), compared to model predictions of 0.9 x 10(exp 13) molec cm(exp -2) in GEOS-Chem (CBr(sub y) but no SSA source), 0.4 x 10(exp 13) molec cm(exp -2) in CAM-Chem (CBr(sub y) and SSA), and 2.1 x 10(exp 13) molec cm(exp -2) in GEOS-Chem (CBry and SSA). Neither global model fully captures the Cshape of the Br(sun y) profile. A local Br(sub y) maximum of 3.6 ppt (2.9-4.4 ppt; 95% confidence interval, CI) is inferred between 9.5 and 13.5 km in air masses influenced by recent convective outflow. Unlike BrO, which increases from the convective tropical tropopause layer (TTL) to the aged TTL, gas-phase Br(sub y) decreases from the convective TTL to the aged TTL. Analysis of gas-phase Br(sub y) against multiple tracers (CFC-11, H2O/O3 ratio, and potential temperature) reveals a Br(sub y) minimum of 2.7 ppt (2.3-3.1 ppt; 95% CI) in the aged TTL, which agrees closely with a stratospheric injection of 2.6 +/- 0.6 ppt of inorganic Br(sub y) (estimated from CFC-11 correlations), and is remarkably insensitive to assumptions about heterogeneous chemistry. Bry increases to 6.3 ppt (5.6-7.0 ppt; 95% CI) in the stratospheric "middleworld" and 6.9 ppt (6.5-7.3 ppt; 95% CI) in the stratospheric "overworld". The local Br(sub y) minimum in the aged TTL is qualitatively (but not quantitatively) captured by CAM-Chem, and suggests a more complex partitioning of gas-phase and aerosol Br(sub y) species than previously recognized. Our data provide corroborating evidence that inorganic bromine sources (e.g., SSA-derived gas-phase Br(sub y) ) are needed to explain the gas-phase Br(sub y) budget in the upper free troposphere and TTL. They are also consistent with observations of significant bromide in Upper Troposphere-Lower Stratosphere aerosols. The total Br(sub y) budget in the TTL is currently not closed, because of the lack of concurrent quantitative measurements of gas-phase Br(sub y) species (i.e., BrO, HOBr, HBr, etc.) and aerosol bromide. Such simultaneous measurements are needed to (1) quantify SSA-derived Br(sub y) in the upper FT, (2) test Br(sub y) partitioning, and possibly explain the gas-phase Br(sub y) minimum in the aged TTL, (3) constrain heterogeneous reaction rates of bromine, and (4) account for all of the sources of Br(sub y) to the lower stratosphere.

Atmospheric Chemistry; bromine; troposphere; CONTR↗

NASA NTRS1982

The coronal field lines of an evolving bipolar magnetic region

A simple potential field model is presented to illustrate that loops of magnetic flux rise upward through the corona during the relatively short growth phase of a bipolar magnetic region but contract back to the sun's surface during the much longer decay phase of the photospheric region. To reconcile this behavior with the unidirectional, solar-wind-driven convection of flux outward from the sun, one must postulate the existence of an X-type neutral line in the middle corona where open field lines can be converted back to closed ones.

Sheeley, N. R., Jr.↗

NASA NTRS1973

Break-up characteristics of Chena River Basin

The author has identified the following significant results. Results from snowmelt model were obtained showing the decreasing changes in snow depth for four elevational ranges in the Chena River Basin. This model is based on the energy balance of the snowpack and the results are shown on attached figures. Also, the measured hydrographs for two stations on the Chena River are shown. The next phase of the study will be to analyze the model using both ERTS-1 imagery and measured field values.

Carlson, R. F.↗

NASA NTRS1977

Effect of haze absorption and scattering on radiative-convective-conductive heat flux divergence in Martian CO2 atmosphere and ground

The paper presents some guidelines of an improved numerical modeling effort developed to investigate the effect of an absorbing and scattering particulate phase on the temperature field of the Mars atmosphere and soil in its diurnal cycle and in response to a time-dependent convective heat transfer. Some guidelines are also formulated for the re-evaluation of Mariner 9 infrared radiometer or spectrometer inverted temperature measurements of the dust-laden atmosphere.

Pallmann, A. J.↗

NASA NTRS1981

Acoustic near field and local flow properties associated with broadband shock noise

Shock noise associated with unheated supersonic jets were investigated using a near field microphone array and a single sensor wedge shaped hot-film probe. Both over and underexpanded cases were investigated using Mach 1.5 and 2.0 convergent-divergent nozzles. Correlation measurements through each shock cell of a single underexpanded case with the Mach 1.5 nozzle were obtained between the hot-film probe and microphone array. The results show for the Mach number cases selected that the probe's response is primarily sensitive to velocity. The results of the hot-film near field microphone correlations show general agreement with certain theoretical models as to the location for shock noise production, although they demonstrate the existence of some large perhaps turbulent structure that collectively interacts and phases the motion of the downstream shocks. The near field microphone correlations demonstrate that downstream shocks dominate shock noise production, and suggests the existence of a Doppler effect in near field of the sources. In addition broadband shock noise is found to also propagate at small angles to the jet axis.

Seiner, J. M.↗

NASA NTRS1986

Characteristic recovery times of Forbush-type decreases in the cosmic radiation. I - Observations at earth at different energies

Data on 30 asymmetric Forbush decreases recorded by the IMP spacecraft at 1 AU and the Mt. Washington neutron monitor over the period 1972-84 are examined to characterize the recovery characteristics of cosmic rays after the events. The spacecraft data are concentrated at energies of 1.7 GV, while the terrestrial instruments recorded events at 5 GV. Attention is paid to the relative amplitudes of the recorded transient decreases, the characteristic recovery times, and the energy dependence of the amplitudes and recovery time. The recovery times were found to be equal at both energy levels, supporting a concept of energy independence for the recoveries. Also, no correlations were found between the recovery times and the occurrences of a solar magnetic field reversal or with phase in the solar modulation cycle. A time-dependent, two-dimensional model is defined, which expresses the cosmic ray particle distributions as a function of the decay of the disturbance, with a small dependence on the transport parameters of the cosmic rays.

Lockwood, J. A.↗

NASA NTRS1986

Aerothermal modeling program, phase 2

The main objective of the NASA sponsored Aerothermal Modeling Program, Phase 2--Element A, is to develop an improved numerical scheme for predicting combustor flow fields. This effort consists of the following three technical tasks. Task 1 involves the selection and evaluation of various candidate numerical techniques. Task 2 involves an in-depth evaluation of the selected numerical schemes. Task 3 involves the convection-diffusion scheme and the direct solver that will be incorporated in the NASA 3-D elliptic code (COM3S).

Karki, K. C.↗

NASA NTRS1995

Low velocity opposed-flow frame spread in a transport-controlled environment DARTFire

The overall objectives of the DARTFire project are to uncover the underlying physics and increase understanding of the mechanisms that cause flames to propagate over solid fuels against a low velocity of oxidizer flow in a low-gravity environment. Specific objectives are (1) to analyze experimentally observed flame shapes, measured gas-phase field variables, spread rates, radiative characteristics, and solid-phase regression rates for comparison with previously developed model prediction capability that will be continually extended, and (2) to investigate the transition from ignition to either flame propagation or extinction in order to determine the characteristics of those environments that lead to flame evolution. To meet the objectives, a series of sounding rocket experiments has been designed to exercise several of the dimensional, controllable variables that affect the flame spread process over PMMA in microgravity, i.e., the opposing flow velocity (1-20 cm/s), the external radiant flux directed to the fuel surface (0-2 W/cm(exp 2)), and the oxygen concentration of the environment (35-70%). Because radiative heat transfer is critical to these microgravity flame spread experiments, radiant heating is imposed, and radiant heat loss will be measured. These are the first attempts at such an experimental control and measurement in microgravity. Other firsts associated with the experiment are (1) the control of the low velocity, opposed flow, which is of the same order as diffusive velocities and Stefan flows; (2) state-of-the-art quantitative flame imaging for species-specific emissions (both infrared and ultraviolet) in addition to novel intensified array imaging to obtain a color image of the very dim, low-gravity flames.

West, Jeff↗