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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Correlated satellite measurements of low-energy electron precipitation and ground-based observations of a visible auroral arc.

A comparison of low-energy charged-particle intensities measured with the low-altitude satellite Injun 5 and a ground-based observation of an auroral arc at Fort Churchill on December 21, 1968, during late local evening has established that an intense precipitation band of electron intensities provides the primary energy influx for the auroral light. This precipitation event was located poleward of and adjacent to the trapping boundary for more energetic electron (above 45 keV) intensities. Proton and electron intensities similar to those in the plasma sheet in the magnetotail were observed in a substantially less-intense zone positioned equatorward of and adjacent to the trapping boundary. The intense precipitation band of electron intensities poleward of the trapping boundary is interpreted as the signature of direct acceleration of magnetosheath electrons into the earth's atmosphere.

Ackerson, K. L.↗
NASA NTRS1975

Further studies of the new component of cosmic rays at low energies

Recent observations with cosmic ray telescopes aboard the Pioneer 10 space probe have revealed an anomalous spectrum of nitrogen and oxygen nuclei relative to other nuclei such as carbon in the quiet time cosmic radiation below about 40 MeV/nuc. These observations are extended with additional data from Pioneer 10 and considerable new data from an identical telescope aboard Pioneer 11. In addition to the enhancement of nitrogen and oxygen nuclei observed earlier, the intensity of neon is enhanced as well. The spectra of boron, magnesium, and silicon appear to be similar to that of carbon. Data on the isotopic composition, solar modulation, and radial gradient of these nuclei are presented.

Webber, W. R.↗
NASA NTRS1981

Downward shift of the acceleration/injection region during solar flares

Simultaneous observations of impulsive hard X-rays and type III radio bursts associated with two recent solar flares have been analyzed in order to study the characteristic increase in the starting frequency of fast-drift type III bursts during the impulsive phase. The time variation of the starting frequency has been found to be similar to that of approximately 35 keV X-rays, especially during the increasing phase. A similar variation has been observed for the low frequency cutoff of these bursts. The observations are consistent with a systematic downward shift of the electron acceleration/injection region during the impulsive phase of a solar flare.

Kane, S. R.↗
NASA NTRS1992

Auroral X-ray imaging from high- and low-earth orbit

Observations of bremsstrahlung X-rays emitted by energetic electrons impacting the earth's atmosphere can be used for remotely sensing the morphology, intensity, and energy spectra of electron precipitation from the magnetosphere. Two auroral X-ray imagers, developed for future spaceflight, will be discussed. Polar Ionospheric X-ray Imaging Experiment is scheduled for launch on the NASA International Solar-Terrestrial Physics/Global Geospace Science program POLAR satellite in May, 1994. The POLAR orbit, with an apogee and perigee of 9 and 1.8 R(E) (earth radii), respectively, affords the opportunity to image the aurora from high altitude above the north pole continuously for several hours. The Magnetospheric Atmospheric X-ray Imaging Experiment is scheduled for launch aboard the NOAA-I satellite in late 1992. The 800-km polar orbit passes over both the northern and southern auroral zones every 101 minutes. The presentation emphasizes the experimental approaches used to exploit these very different orbits for remote sensing of the earth's auroral zones.

Mckenzie, D. L.↗
NASA NTRS1997

Radiation Near 2f(sub p) and Intensified Emissions Near f(sub p) in the Dayside and Nightside Auroral Region and Polar Cap

This paper reports the discovery in the DE 1 data of propagating radiation near 2f(sub p) (the H component) and relatively intense electromagnetic waves near f(sub p) with fields typically less than or approximately equal to 1 mV/m (the PF or plasma frequency component) on both the dayside and the nightside of Earth. These emissions are observed at auroral and polar cap latitudes for radial distances ranging from 2.5 to 4.5 R(sub E). The H component is unique in that no other 2f(sub p) emissions are known to be generated where the electron gyrofrequency f(sub g) exceeds 2f(sub p). Since existing theories for 2f(sub p) radiation assume f(sub g)/f(sub p) less than 1, new theories will be required to explain the H component. The PF waves near f(sub p) are electromagnetic, but with large ratios E/cB approximately 20. On the basis of cold plasma theory, the wave frequencies and the ratios E/cB, the PF component plausibly consists of zeta-mode and/or whistler mode waves near f(sub p), presumably driven by an electron instability. The H emissions have modest bandwidths of approximately 50% at frequencies ranging from 5 to 20 kHz. Grounds for interpreting the H component as emissions generated near 2f(sub p) are provided by the very good frequency tracking of the PF and H components and typical frequency ratios near 2.0. Strong evidence exists that part of the H component is propagating, electromagnetic radiation, based on propagation effects and spin modulation patterns. However, no magnetic signals have yet been detected for the H component, so that it could be partly electrostatic. Cold plasma theory and the observed wave characteristics favor interpreting the H component as composed of omicron mode and/or zeta mode signals. Combining the DE 1 observations with rocket observations, it is predicted that the much more intense Langmuir-like fields observed in the low altitude auroral zones should also generate observable 2f(sub p) radiation. This prediction should be testable using Polar and future rocket flights. Directions for future research are also described.

Cairns, Iver H.↗
NASA NTRS2010

Climate Benchmark Missions: CLARREO

CLARREO (Climate Absolute Radiance and Refractivity Observatory) is one of the four Tier 1 missions recommended by the recent NRC decadal survey report on Earth Science and Applications from Space (NRC, 2007). The CLARREO mission addresses the need to rigorously observe climate change on decade time scales and to use decadal change observations as the most critical method to determine the accuracy of climate change projections such as those used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). A rigorously known accuracy of both decadal change observations as well as climate projections is critical in order to enable sound policy decisions. The CLARREO mission accomplishes this critical objective through highly accurate and SI traceable decadal change observations sensitive to many of the key uncertainties in climate radiative forcings, responses, and feedbacks that in turn drive uncertainty in current climate model projections. The same uncertainties also lead to uncertainty in attribution of climate change to anthropogenic forcing. The CLARREO breakthrough in decadal climate change observations is to achieve the required levels of accuracy and traceability to SI standards for a set of observations sensitive to a wide range of key decadal change variables. These accuracy levels are determined both by the projected decadal changes as well as by the background natural variability that such signals must be detected against. The accuracy for decadal change traceability to SI standards includes uncertainties of calibration, sampling, and analysis methods. Unlike most other missions, all of the CLARREO requirements are judged not by instantaneous accuracy, but instead by accuracy in large time/space scale average decadal changes. Given the focus on decadal climate change, the NRC Decadal Survey concluded that the single most critical issue for decadal change observations was their lack of accuracy and low confidence in observing the small but critical climate change signals. CLARREO is the recommended attack on this challenge, and builds on the last decade of climate observation advances in the Earth Observing System as well as metrological advances at NIST (National Institute of Standards and Technology) and other standards laboratories.

Wielicki, Bruce A.↗
NASA NTRS1972

Type 3 solar radio bursts

Using low frequency satellite observations, a direct comparison of the different theories is possible of the structure of the interplanetary medium. Measurements were made by satellite electron detectors in the same region of the interplanetary media where rapid drift type 3 solar radio bursts are generated. Results show, on the basis of this comparison, the general inadequacies of current type 3 burst theories and indicate a needed emphasis on formulating a new theory that is consistent with the low frequency observations. Representative observations from the RAE satellite are shown. The brightness temperature, which is a measure of the energy flux, versus frequency was plotted. Two events, a large burst and a large storm are also shown, each recorded at frequencies of 2.8 MHz and 700 KHz. High frequency curves obtained from ground-based observations are given.

Evans, L. G.↗
NASA NTRS1973

Observations of solar cosmic rays at 2 AU

Solid state low-energy telescopic observations on solar and galactic cosmic rays from 2 AU outward by satellites are evaluated. Plots of solar events leading to large injections of particles from the sun show that low energy slower protons arrive first by many hours before the higher energy protons, and that the higher energy particles are falling off more rapidly.

Trainor, J. H.↗
NASA NTRS1974

Satellite observations of type III solar radio bursts at low frequencies

Type III solar radio bursts have been observed from 10 MHz to 10 kHz by satellite experiments above the terrestrial plasmasphere. Solar radio emission in this frequency range results from excitation of the interplanetary plasma by energetic particles propagating outward along open field lines over distances from 5 earth radii to at least 1 AU from the sun. This review summarizes the morphology, characteristics, and analysis of individual as well as storms of bursts. Substantial evidence is available to show that the radio emission is observed at the second harmonic instead of the fundamental of the plasma frequency. This brings the density scale derived by radio observations into better agreement with direct solar wind density measurements at 1 AU and relaxes the requirement for type III propagation along large density-enhanced regions. This density scale with the measured direction of arrival of the radio burst allows the trajectory of the exciter path to be determined from 10 earth radii to 1 AU.

Fainberg, J.↗
NASA NTRS2017

Testing the Universality of the Stellar IMF with Chandra and HST

The stellar initial mass function (IMF), which is often assumed to be universal across unresolved stellar populations, has recently been suggested to be bottom-heavy for massive ellipticals. In these galaxies, the prevalence of gravity-sensitive absorption lines (e.g., Na I and Ca II) in their near-IR spectra implies an excess of low-mass (m < or approx. = 0.5 Stellar Mass) stars over that expected from a canonical IMF observed in low-mass ellipticals. A direct extrapolation of such a bottom-heavy IMF to high stellar masses (m > or approx. = 8 Stellar Mass) would lead to a corresponding deficit of neutron stars and black holes, and therefore of low-mass X-ray binaries (LMXBs), per unit near-IR luminosity in these galaxies. Peacock et al. searched for evidence of this trend and found that the observed number of LMXBs per unit K-band luminosity (N/LK) was nearly constant. We extend this work using new and archival Chandra X-ray Observatory and Hubble Space Telescope observations of seven low-mass ellipticals where N/LK is expected to be the largest and compare these data with a variety of IMF models to test which are consistent with the observed N/LK. We reproduce the result of Peacock et al., strengthening the constraint that the slope of the IMF at m > or approx. = 8 Stellar Mass must be consistent with a Kroupa-like IMF. We construct an IMF model that is a linear combination of a Milky Way-like IMF and a broken power-law IMF, with a steep slope (alpha1 = 3.84) for stars < 0.5 Stellar Mass (as suggested by near-IR indices), and that flattens out (alpha2 = 2.14) for stars > 0.5 Stellar Mass, and discuss its wider ramifications and limitations.

galaxies: elliptical and lenticular↗
NASA NTRS1996

The Astronomical Low-Frequency Array

An array of satellites is proposed to make astronomic observations in the low frequency range of a few tens of MHz down to roughly 100 kHz, a range that cannot be observed through the ionosphere. The array would be in a solar orbit to avoid radio interference from Earth and to simplify trajectory tracking and control.

low-frequency array radio astronomy microsats↗
NASA NTRS1981

Magnetic field-aligned electron distributions in the dayside cusp

Observations of low-energy electron fluxes made over a 6 year period with the photoelectron spectrometer on the AE-C and AE-D satellite are used to investigate electron pitch angles in the low altitude cusp. A 16 point energy spectrum from 2 to 500 eV was obtained at every .25 s, and the location of the cusp was verified by the presence of protons detected by the low-energy electron instrument. Isotropic fluxes of precipitating electrons with Maxwellian energy spectra were observed in the low-altitude cusp, and the presence of low-energy electrons with pitch angles less than 15 deg was determined streaming into the cusp ionosphere. The energies of the streaming electrons sometimes appeared as a peak superimposed on the normal cusp Maxwellian background of isotropic electrons, and it is concluded that the energies and pitch angle distributions of the precipitating electrons may explain the enhancements of auroral emissions and discrete arcs.

Zanetti, L. J.↗
NASA NTRS1976

A comparison of low-cloud satellite wind estimates with analyses based on aircraft observations in a disturbed tropical regime

Low-level, ATS-3 satellite wind estimates are compared with values of wind direction and speed interpolated from analyses based on research aircraft observations of a synoptic tropical wave of moderate intensity on 26 July 1969 during BOMEX. The data were stratified according to whether a satellite estimate was positioned in one of three regions; namely, east or west of the wave trough or north of the disturbance center. When cloud and analysis vector magnitude deviations were computed, regional differences became apparent. These differences are attributed to the physical behavior of the cloud targets tracked under the influence of the surrounding large-scale environment.

Smith, C. L.↗
NASA NTRS1988

IUE observations of the 1987 superoutburst of the dwarf nova Z Cha

Low resolution IUE observations of the dwarf nova Z Cha during superoutburst are presented. These cover most of the development of the outburst and have sufficient time resolution to probe continuum and line behavior on orbital phase. The observed modulation on this phase is very similar to that observed in the related object OY Car. The results imply the presence of a cool spot on the edge of the edge of the accretion disk, which periodically occults the brighter inner disk. Details of the line behavior suggest that the line originated in an extended wind-emitting region. In contrast to archive spectra obtained in normal outburst, the continuum is fainter and redder, indicating that the entire superoutburst disk may be geometrically thicker than during a normal outburst.

Harlaftis, E.↗
NASA NTRS1974

Interplanetary MeV electrons of Jovian origin

Observation of low-energy (0.2- to 8-MeV) electron increases observed in interplanetary space on Pioneer 10 as it approached within 1 AU of Jupiter. These discrete bursts or increases were typically several hundred times the normal quiet-time electron flux and became much more frequent with decreasing distance to Jupiter, the result being the quasi-continuous presence of large fluxes of these electrons in interplanetary space. In view of the likely origin of these electrons at Jupiter and the similarity of these increases to quiet-time electron increases previously observed at earth, the temporal presence of the quiet-time increases has been reexamined. It is found that these increases have a 13-month periodicity, indicating a Jovian origin for the events near the earth as well. It is noted that the integrated flux from quiet-time increase electrons at 1 AU is comparable to the integrated ambient electron flux itself.

Teegarden, B. J.↗
NASA NTRS1974

The 15 cm diameter ion thruster research

The startup reliability of a 15 cm diameter mercury bombardment ion thruster which employs a pulsed high voltage tickler electrode on the main and neutralizer cathodes is examined. Startup of the thruster is achieved 100% of the time on the main cathode and 98.7% of the time on the neutralizer cathode over a 3640 cycle test. The thruster was started from a 20 C initial condition and operated for an hour at a 600 mA beam current. An energy efficiency of 75% and a propellant utilization efficiency of 77% was achieved over the complete cycle. The effect of a single cusp magnetic field thruster length on its performance is discussed. Guidelines are formulated for the shaping of magnetic field lines in thrusters. A model describing double ion production in mercury discharges is presented. The production route is shown to occur through the single ionic ground state. Photographs of the interior of an operating-hollow cathode are presented. A cathode spot is shown to be present if the cathode is free of low work-function surfaces. The spot is observed if a low work-function oxide coating is applied to the cathode insert. Results show that low work-function oxide coatings tend to migrate during thruster operation.

Wilbur, P. J.↗
NASA NTRS1980

Second generation detector for low order global solar oscillations

The first observations of long period low order global solar oscillations grew out of diameter measurements made over an extended period of time. As a result of these investigations, a detailed understanding of the surface properties of the oscillations evolved, allowing development of a second generation detector. This new detector, currently under development directly utilizes various surface properties of the oscillations and does not, therefore, directly involve diameter measurements. The specifications of the detector, its supporting telescope and the observing program are reviewed.

Forbes, F. F.↗
NASA NTRS1990

Mission design for an orbiting volcano observatory

The Mission to Planet Earth initiative will require global observation of land, sea, and atmosphere, and all associated phenomena over the coming years; perhaps for decades. A major phenomenon playing a major part in earth's environment is volcanic activity. Orbital observations, including IR, UV, and visible imaging, may be made to monitor many active sites, and eventually increase our understanding of volcanoes and lead to the predictability of eruptions. This paper presents the orbital design and maneuvering capability of a low cost, volcano observing satellite, flying in low earth orbit. Major science requirements include observing as many as 10 to 20 active sites daily, or every two or three days. Given specific geographic locations of these sites, it is necessary to search the trajectory space for those orbits which maximize overflight opportunities. Also, once the satellite is in orbit, it may be desirable to alter the orbit to fly over targets of opportunity. These are active areas which are not being monitored, but which give indications of erupting, or have in fact erupted. Multiple impulse orbital maneuvering methods have been developed to minimize propellant usage for these orbital changes.

Penzo, Paul A.↗