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NASA NTRS2001

Laboratory Experimentation Model of the 270 Degree Electron Tophat Analyzer

One of the most important space plasma measurements is that of a well-resolved low-energy (approximately 1 eV to 1 keV) electron spectrum. This range includes the regime where photoelectron and Auger processes are important as well as the very low energy range (down to 1 eV) where electron distributions of temperature 11,000 K are measurable. Knowledge of the structure (approx. eV scale) of the photoelectron spectrum can provide information on the composition of a planetary or cometary atmosphere. As evidence, scientists developing the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) Electron Spectrometer (ELS) flying on the European Space Agency (ESA) Mars Express Mission have adapted their electron instrument to increase energy resolution in the photoelectron energy region as a means of remotely sensing the Martian atmosphere; the idea being that the Martian magnetic field is so weak that electron interaction between the source and point of detection is nonexistent; the measured electrons are therefore reflective of the processes occurring in the Martian atmosphere.

Frahm, R. A.↗

NASA NTRS2002

Laboratory Experimentation Model of the 270 Degree Electron Tophat Analyzer

One of the most important space plasma measurements is that of a well-resolved low-energy (approx.1 eV to 1 keV) electron spectrum. This range includes the regime where photoelectron and Auger processes are important [Winningham et at., 1989] as well as the very low-energy range (down to 1 eV) where electron distributions of temperature 11,000 K are measurable. Knowledge of the structure (approx. eV scale) of the photoelectron spectrum can provide information on the composition of a planetary or cometary atmosphere. As evidence, scientists developing the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) Electron Spectrometer (ELS) flying on the European Space Agency (ESA) Mars Express Mission have adapted their electron instrument to increase energy resolution in the photoelectron energy region as a means of remotely sensing the Martian atmosphere; the idea being that the Martian magnetic field is so weak that electron interaction between the source and point of detection is nonexistent; the measured electrons are therefore reflective of the processes occurring in the Martian atmosphere.

Frahm, R. A.↗

NASA NTRS1962

Effect of Alpha-Particle Irradiation on Brain Glycogen in the Rat

The studies of Klatzo, Miquel, Tobias and Haymaker (1961) have shown that one of the earliest and most sensitive indications of the effects of alpha-particle irradiation on rat bran is the appearance of glycogen granules mainly in the neuroglia of the exposed area of the brain. Periodic acid-Schiff (PAS) positive, alpha-amylase soluble granules were demonstrated within 12 hr after irradiation, preceding by approximately 36 hr the first microscopically detectable vascular permeability disturbances, as shown by the fluorescein labeled serum protein technique. These studies suggested that the injurious effects of alpha-particle energy were on cellular elements primarily, according to the physical properties and distribution of the radiation in the tissue, and that the vascular permeability disturbances played a secondary role in pathogenesis. The purpose of this study was to correlate the histochemical observations on glycogen with a quantitative assessment of the glycogen in the irradiated brain tissue. It is felt that such a study may contribute to the understanding of radiation injury at the molecular level. A practical aspect of this problem is that the information on biological radiation effects due to accelerated particles from the cyclotron source, is employed in this study, is applicable to radiation from cosmic particles both in free space and entrapped in the Van Allen belts.

Wolfe, L. S.↗

NASA NTRS1986

Proton acceleration in gamma-ray bursts

Proton acceleration and subsequent secondary electron production are proposed as the process responsible for the radiation emission in gamma-ray bursts. In this mechanism electrons are naturally injected at energies much larger than m(e) x c-squared and emission above 10 MeV is expected to be one of their common features, in agreement with observations showing that most of the luminosity of these events is emitted in gamma-rays. This mode of injection guarantees copious e(+)-e(-) pair production at the source and implies a relationship between the luminosity and the spectra of the bursts, the soft bursts being, in general, the most (intrinsically) luminous and hence the most distant. This, in turn, implies that bursts with soft spectra should show a galactic distribution, a fact consistent with the limited available data. It is also argued that the observed red-shift of the e(+)-e(-) annihilation feature may not always be gravitational.

Kazanas, Demosthenes↗

NASA NTRS1992

Quasi-linear velocity space diffusion of heavy cometary pickup ions on bispherical diffusion characteristics

We consider an ion transport equation describing the source, convection, adiabatic acceleration, and quasi-linear velocity diffusion of cometary pickup ions. The equation is solved numerically along solar wind plasma flow lines for the environment of Comet Halley, to obtain distributions at positions on the Giotto spacecraft trajectory which may be compared with observations. We obtain full two-dimensional (pitch angle and velocity) numerical distributions which show pitch angle scattering about the wave scattering centers at +/- V(A), where V(A) is the Alfven wave speed in the solar wind frame. Peak ion phase-space densities approximately follow the bispherical shell geometry. The energy distributions F(v) agree well with Giotto observations at lower v, but in the high-energy tail there is evidence possibly for the first-order Fermi acceleration mechanism taking place in the Comet Halley foreshock region.

Huddleston, D. E.↗

NASA NTRS1987

Inverse Compton scattering of ambient radiation by a cold relativistic jet - A source of beamed, polarized continuum in blazars?

A general formalism is developed for computing the intensity and polarization of unpolarized radiation scattered by a group of electrons with a specified distribution of momenta. The case of isotropic incident radiation with a power-law spectrum is addressed, and the 'head-on' approximation is developed to describe the nearly unidirectional character of the incident radiation in the electron rest frame. The formalism is implemented numerically, verifying the validity of the 'head-on' approximation and illustrating the polarization and intensity properties of radiation scattered by jets with different electron momentum distribution. The results are placed in an astrophysical setting, determining the optical depths and kinetic energies required for the scattered radiation to dominate over the isotropic component in blazars. It is argued that Comptonization of unbeamed AGN radiation by a relativistic jet can account for the polarization and the overall spectral shape of the IR-optical continuum in blazars.

Begelman, Mitchell C.↗

NASA NTRS1991

HF radar observations of Pc 5 field line resonances in the midnight/early morning MLT sector

The technique of F region sounding by HF coherent radar is applied to the study of field line resonances equatorward of a region of shear flow in the early morning sector. The motions were predominantly in the geomagnetic east-west direction, indicating north-south electric fields. These oscillations had pronounced peaks in their latitudinal power distribution. For the pulsation at 1.95 mHz, a latitudinal phase shift of 180 deg was observed across the peaks in all the look directions of the radar, and a longitudinal wavelength corresponding to an m value of 3 was obtained. For the 2.6-mHz pulsation, the phase shifts across the peaks had a variation with a look direction that indicated a significant longitudinal as well as latitudinal variation; for this activity, an m value of about 16 is estimated. These features are interpreted in terms of the field line resonance theory, and the possible sources of the pulsation energy are discussed.

Ruohoniemi, J. M.↗

NASA NTRS2018

1-Watt Radioisotope Power System for Small Spacecraft

A variety of mission concepts have been studied by NASA and the U. S. Department of Energy that would utilize low power Radioisotope Power Systems (RPS) for small probes, landers, rovers, and communication repeaters. These missions would contain science measuring instruments that could be distributed across planetary surfaces for operation in temporarily or permanently shadowed regions. High efficiency dynamic RPS could be mission enabling for science measurements on the moon, such as collecting real-time, event-based, or cumulative space radiation measurements including primary galactic cosmic rays (GCR), solar particle events (SPE), and secondary particles liberated during atmospheric and/or surface reactions. Small RPS would use fractional versions of the General Purpose Heat Source (GPHS) or Light Weight Radioisotope Heater Units (LWRHU), to heat the power conversion technologies. Capable of three to four times higher conversion efficiency than static technologies, dynamic RPS would provide an equal amount of power using less fuel or more power using an equal amount of fuel. Providing spacecraft with more power could decrease duty cycling of basic functions and increase the quality and abundance of science data. Low power Stirling convertors are being developed at NASA Glenn Research Center (GRC) to provide future micro spacecraft with electrical power by converting heat from one or more LWRHUs. An initial concept would convert eight Watts of heat to one Watt of electrical power output for science instruments and communication. The initial design, called Small Stirling Technology Exploration Power (smallSTEP), is 11 cm diameter X 32 cm long, weighs around 3 kg, and could be used to charge batteries or capacitors for higher power burst usage. Development of the 1-watt RPS includes maturation of a Stirling engine and linear alternator, an electronics controller, and an evacuated metal foil insulation package. Test hardware and facilities are being prepared for initial demonstration of the subassemblies in a laboratory environment.

Wilson, Scott↗

NASA NTRS1983

The low-energy plasma in the Jovian magnetosphere

Burke and Franklin (1955) discovered radio emissions from Jupiter at 22.2 MHz. Subsequent observations established the strong control of the decametric emissions by the satellite Io. The Voyager encounters with Jupiter in 1979 have resulted in a dramatic increase in detailed knowledge of the plasma properties of the Jovian magnetosphere. The Io plasma torus is discussed, taking into account the Voyager plasma science experiment, positive-ion temperatures in the torus, electron distribution functions in the torus, elementary-charge concentrations in the torus, positive-ion composition in the torus, and plasma velocities in the torus. The Io flux tube is considered along with the middle magnetosphere and the outer magnetosphere. Attention is given to the sources of plasma, aspects of diffusive transport, questions of inertial loading, and the existence of nonazimuthal flow velocities in the middle magnetosphere.

Belcher, J. W.↗

NASA NTRS1981

Optical spectral variability of the N galaxies 3C 382 and 3C 390.3

Multichannel spectrophotometry data acquired from 1969 to 1980 are used to study the absolute energy distribution and emission line variability of the N galaxies 3C 382 and 3C 390.3. It is shown that: (1) the continuum spectra can be decomposed into a nuclear nonthermal component of constant spectral shape and a constant elliptical galaxy component; (2) apparent visual magnitudes within a 10 arcsec aperture are derived for underlying galaxies, 3C 382 being 15.27 and 3C 390.3, 16.04; (3) forbidden lines and narrow Balmer lines do not change with the central continuum, but (4) the intensity variations of the broad Balmer lines are correlated nonlinearly with changes in the luminosity of the central continuum source. This correlation can be explained by a time-lag effect if there are two components of broad-line emission, one varying on a time scale of a few months and the other over a few years.

Yee, H. K. C.↗

NASA NTRS2012

The Aerosol-Monsoon Climate System of Asia

In Asian monsoon countries such as China and India, human health and safety problems caused by air-pollution are worsening due to the increased loading of atmospheric pollutants stemming from rising energy demand associated with the rapid pace of industrialization and modernization. Meanwhile, uneven distribution of monsoon rain associated with flash flood or prolonged drought, has caused major loss of human lives, and damages in crop and properties with devastating societal impacts on Asian countries. Historically, air-pollution and monsoon research are treated as separate problems. However a growing number of recent studies have suggested that the two problems may be intrinsically intertwined and need to be studied jointly. Because of complexity of the dynamics of the monsoon systems, aerosol impacts on monsoons and vice versa must be studied and understood in the context of aerosol forcing in relationship to changes in fundamental driving forces of the monsoon climate system (e.g. sea surface temperature, land-sea contrast etc.) on time scales from intraseasonal variability (~weeks) to climate change (~ multi-decades). Indeed, because of the large contributions of aerosols to the global and regional energy balance of the atmosphere and earth surface, and possible effects of the microphysics of clouds and precipitation, a better understanding of the response to climate change in Asian monsoon regions requires that aerosols be considered as an integral component of a fully coupled aerosol-monsoon system on all time scales. In this paper, using observations and results from climate modeling, we will discuss the coherent variability of the coupled aerosol-monsoon climate system in South Asia and East Asia, including aerosol distribution and types, with respect to rainfall, moisture, winds, land-sea thermal contrast, heat sources and sink distributions in the atmosphere in seasonal, interannual to climate change time scales. We will show examples of how elevated absorbing aerosols (dust and black carbon) may interact with monsoon dynamics to produce feedback effects on the atmospheric water cycle, leading to in accelerated melting of snowpacks over the Himalayas and Tibetan Plateau, and subsequent changes in evolution of the pre-monsoon and peak monsoon rainfall, moisture and wind distributions in South Asia and East Asia.

Lau, William K. M.↗

NASA NTRS2016

Optimized Heat Pipe Backup Cooling System Tested with a Stirling Convertor

Advanced Stirling Radioisotope Generator (ASRG) is an attractive energy system for select space missions, and with the addition of a VCHP, it becomes even more versatile. The ASRG is powered through thermal energy from decaying radioisotopes acting as General Purpose Heat Sources (GPHS). A Stirling engine converts the thermal energy to electrical energy and cools the GPHS [2]. The Stirling convertor must operate continuously to maintain acceptable temperatures of the GPHS and protect their cladding. The addition of alkali metal VCHP allows the Stirling to cycle on and off during a mission and can be used as a backup cooling system. The benefits of being able to turn the Stirling off are: allowing for a restart of the Stirling and reducing vibrations for sensitive measurements. The VCHP addition should also increase the efficiency of the Stirling by providing a uniform temperature distribution at the heat transfer interface into the heater head.

Stirling Radioisotope Generator↗

NASA NTRS2011

An Examination of the Spatial Distribution of Carbon Dioxide and Systematic Errors

The industrial period and modern age is characterized by combustion of coal, oil, and natural gas for primary energy and transportation leading to rising levels of atmospheric of CO2. This increase, which is being carefully measured, has ramifications throughout the biological world. Through remote sensing, it is possible to measure how many molecules of CO2 lie in a defined column of air. However, other gases and particles are present in the atmosphere, such as aerosols and water, which make such measurements more complicated1. Understanding the detailed geometry and path length of the observation is vital to computing the concentration of CO2. Comparing these satellite readings with ground-truth data (TCCON) the systematic errors arising from these sources can be assessed. Once the error is understood, it can be scaled for in the retrieval algorithms to create a set of data, which is closer to the TCCON measurements1. Using this process, the algorithms are being developed to reduce bias, within.1% worldwide of the true value. At this stage, the accuracy is within 1%, but through correcting small errors contained in the algorithms, such as accounting for the scattering of sunlight, the desired accuracy can be achieved.

Carbon Dioxide (CO2)↗

NASA NTRS1986

The Jet Propulsion Laboratory low-cost solar array project, 1974-1986

The overall objective of the photovoltaic program is to ensure that photovoltaic conversion systems play a significant role in the nation's energy supply by stimulating an industry capable of providing approximately 50 GWe of installed electricity generating capacity by the year 2000. In order to achieve this overall objective, several time-phased program goals have been defined. Near-term goals are to achieve photovoltaic flat-plate module or concentrator array prices of $2 per peak watt (1975 dollars) at an annual production rate of 20 peak megawatts in 1982. At this price level, energy costs should range from 100 to 200 mills/kwh. Mid-term goals are to achieve photovoltaic flat-plate module or concentrator array prices of $0.50 per peak watt (in 1975 dollars), and an annual production rate of 500 peak megawatts in 1986. Studies project that photovoltaic systems will begin to compete for both distributed and larger load-center utility-type applications and thereby open up significant markets for large-scale photovoltaic systems. Far term goals are to achieve the photovoltaic flat-plate module or concentrator array price goal of $0.10 to $0.30 per peak watt in 1990 (in 1975 dollars), and an annual production rate of 10 to 20 peak gigawatts in 2000. At this price range, energy cost should be in the range of 40 to 60 mills. kwh and be cost effective for utility applications. Achievement of these goals can make photovoltaic systems economically competitive with other energy sources for dispersed on-site applications as well as for central power generation.

Maycock, P. D.↗

NASA NTRS1994

The tropical water and energy cycles in a cumulus ensemble model. Part 1: Equilibrium climate

A cumulus ensemble model is used to study the tropical water and energy cycles and their role in the climate system. The model includes cloud dynamics, radiative processes, and microphysics that incorporate all important production and conversion processes among water vapor and five species of hydrometeors. Radiative transfer in clouds is parameterized based on cloud contents and size distributions of each bulk hydrometeor. Several model integrations have been carried out under a variety of imposed boundary and large-scale conditions. In Part 1 of this paper, the primary focus is on the water and heat budgets of the control experiment, which is designed to simulate the convective - radiative equilibrium response of the model to an imposed vertical velocity and a fixed sea surface temperature at 28 C. The simulated atmosphere is conditionally unstable below the freezing level and close to neutral above the freezing level. The equilibrium water budget shows that the total moisture source, M(sub s), which is contributed by surface evaporation (0.24 M(sub s)) and the large-scale advection (0.76 M(sub s)), all converts to mean surface precipitation bar-P(sub s). Most of M(sub s) is transported verticaly in convective regions where much of the condensate is generated and falls to surface (0.68 bar-P(sub s)). The remaining condensate detrains at a rate of 0.48 bar-P(sub s) and constitutes 65% of the source for stratiform clouds above the melting level. The upper-level stratiform cloud dissipates into clear environment at a rate of 0.14 bar-P(sub s), which is a significant moisture source comparable to the detrained water vapor (0.15 bar-P(sub s)) to the upper troposphere from convective clouds. In the lower troposphere, stratiform clouds evaporate at a rate of 0.41 bar-P(sub s), which is a more dominant moisture source than surface evaporation (0.22 bar-P(sub s)). The precipitation falling to the surface in the stratiform region is about 0.32 bar-P(sub s). The associated latent heating in the water cycle is the dominant source in the heat budget that generates a net upward motion in convective regions, upper stratiform regions (above the freezing level), and a downward motion in the lower stratiform regions. The budgets reveal a cycle of water and energy resulted from radiation-dynamic-convection interactions that maintain equilibrium of the atmosphere.

Sui, C. H.↗

NASA NTRS1993

Diffusion of Na and K in the uppermost regolith of Mercury

We examine the conditions under which ions impacting the Hermean surface can act as a regional source of enhanced atmospheric column through ion implantation and subsequent release at the surface. At most latitudes, energetic (a few keV) Na or K ions which impact the nightside surface, are released quickly (well before noon) upon warming of the surface. We show that the relative sunrise/sunset difference produced by ion implantation is ((n)(sub SR) - (n)(sub SS)/(n)(sub Ave) = f, where f is the fraction of the photo-ions recycled, (n)(sub SR) is the average zenith column above the sunrise portion of the illuminated hemisphere, (n)(sub SS) is the average zenith column in the sunset portion, and (n)(sub Ave) is the average column over the sunlit disk. Thus, to produce a large sunrise/sunset difference via ion implantation and subsequent release requires efficient (close to total) recycling. We show that the most extensive set of available data reduced to Na column abundance does not show any sunrise enhancement. We argue that the K data do not permit an unambiguous interpretation in favor of sunrise/sunset differences. We further find that if an efficient surface loss process for the alkali is not operating after sunrise, the initial Na and K distribution will relax into the bulk of the solid. Preserved abundance gradients of Na and K in lunar glasses that the Arrhenius coefficients for impact glasses are likely more modest than those for laboratory glasses derived from rock by nonimpact processes, but the effect of the more modest diffusion rates is only to delay the efficient loss of Na by a few Earth days. We argue that implantation can lead to observable regional increases in the observed Na or K column densities only if it occurs at very high latitudes, where diffusion is slow. It is typically lower energy ions which impact at high latitude and these are both more numerous than the high energy ions and possess smaller average penetration depths; thus there are additional reasons to favor a high-latitude locus for any possible prompt return related increases in zenith column. We find that we cannot rule out sputtering as a source process, as the low-energy ions are efficient sputterers. Finally, we argue that the observed Na/K ratio in the atmopshere may be the expression of their different asymptotic rates of loss from the interiors of the regolith grains. If so, this allows us to fix the importance of sputtering and photon stimulated desorption relative to impact vaporization.

Killen, R. M.↗

NASA NTRS1990

Modeling the dust size distribution in comets with dust fragmentation

A hydrodynamic model was developed of a spherically symmetric dusty gas flow in a cometary atmosphere assuming a single fluid, inviscid, perfect gas. The hydrodynamics for gas and dust, which involves the gas drag force (momentum transfer), heat exchange between gas and dust, photodissociation energy for H2O gas, and radiative heating and cooling terms for dust particles, are solved using the Gear method for stiff, coupled differential equations. Calculations were done with a dust size distribution for radii alpha = 0.01 micron to 10 cm with densities variable with the size. A nucleus size of 4.0 km radius with a density of 0.5 g/cu cm and a total dust-to-gas mass ratio chi = 1 was adopted. There are indications from in situ observations that dust particle fragment into smaller ones. Fragmentation of dust particles was incorporated into the model. This is done by adding source and sink terms in the continuity equations for the dust. Lifetimes for the decay of dust particles were assumed as a function of particle size. It is also assumed that dust particles always fragment only into the next smaller size.

Konno, Ichishiro↗

NASA NTRS2020

Effects of electromagnetic wave interference on observations of the Earth radiation budget

This paper investigates conditions necessary to match the irradiance derived by integrating radiances measured by a narrow field of view scanning radiometer with the irradiance measured by a hemispherical radiometer, both placed at a satellite altitude for Earth radiation budget estimates. When all sources are similar and they are spatially distributed randomly, then integrating radiance for the irradiance does not introduce a bias. Although the exact magnitude of the bias in other conditions is unknown, a finite area of the aperture that is much larger than the coherence area of radiation contributing to the Earth radiation budget, and a finite time to take a single measurement that is longer than the coherence time are likely to make the difference of the irradiance integrated from radiances and the irradiance measured by a hemispherical instrument insignificant. This conclusion does not contradict the existence of spatial coherence of light from incoherent sources. Therefore, electromagnetic energy absorbed by Earth is derivable from radiances measured by a scanning radiometer integrated over the Earth-viewing hemisphere and then averaging across all locations on the satellite orbital sphere when combined with solar irradiance measurements. Comparisons made in earlier studies show that the difference is less than 1%. In addition, when surface irradiances computed by a radiative transfer model constrained by top-of-atmosphere irradiances derived from radiance measurements are compared with downward shortwave irradiances taken by combinations of a pyreheliometer and a shaded pyranometer, or pyranometers, and with longwave ir- radiances taken by pyrgeometers, the biases in monthly mean irradiances are less than the uncertainties in the surface observations.

Seiji Kato↗