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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

The interplanetary acceleration of energetic nucleons

Co-rotating proton and electron streams are the dominant type of low-energy (0.1-10 MeV/nucleon) particle event observed at 1 A.U. The radial dependence of these events was studied between 1 and 4.6 A.U. using essentially identical low-energy detector systems on IMP 7, Pioneer 10 and Pioneer 11. It was expected that at a given energy, the intensity of these streams would decrease rapidly with heliocentric distance due to the effects of interplanetary adiabatic deceleration. Instead it was found that from event to event the intensity either remains roughly constant or increases significantly (more than an order of magnitude) between 1 and 3 A.U. It appears that interplanetary acceleration processes are the most plausible explanation. Several possible acceleration models are explored.

Mcdonald, F. B.↗
NASA NTRS1975

Solar gamma rays and other nuclear secondaries

Observations of solar gamma rays and nuclear secondaries associated with flares provide a direct probe into the behavior of energetic solar particles and the conditions under which they are accelerated, stored, and released on the sun. During the August 1972 series of solar events, gamma ray lines at 0.51, 2.23, 4.4, and 6.1 MeV and isotopes of H and He were detected. These experimental results and the present status of their interpretation are reviewed. The constraints that these observations have on general solar flare particle acceleration models are also discussed.

Forrest, D. J.↗
NASA NTRS1976

The interplanetary acceleration of energetic nucleons

Corotating proton and electron streams are the dominant type of low-energy (i.e., 0.1-10 MeV per nucleon) particle event observed at 1 AU. The radial dependence of these events has been studied between 1 and 4 AU using essentially identical low-energy detector systems on IMP-7, Pioneer-10, and Pioneer-11. It had been expected that at a given energy, the intensity of these streams would decrease rapidly with heliocentric distance due to the effects of interplanetary adiabatic deceleration. Instead, it is observed that from event to event, the intensity either remains roughly constant or increases significantly (more than an order of magnitude) between 1 and 4 AU. It appears that interplanetary acceleration processes are the most plausible explanation. Several possible acceleration models are discussed.

Mcdonald, F. B.↗
NASA NTRS1975

Observations of protons not exceeding 1 MeV/nuc and ions during the September 1974 series of flares

Results are presented on observations of energetic particles made during an active solar period in September 1974, concentrating in particular on an ESP (Energetic Storm Particle) event observed in association with an interplanetary shock wave on 21 September. It is shown that the observed variations in the proton to alpha particle ratios and spectral indices can be explained either by pile-up or by acceleration models of ESP events.

Ipavich, F. M.↗
NASA NTRS1975

Time dependences of the 0.51 and 2.2 MeV lines in solar flares

The time dependence of the 0.51 MeV line in solar flares is determined by the following factors: variation with time of the rate of nuclear reactions which produce the positron emitters; mean lives of the positron emitters; slowing-down of the positrons which depends on the ambient density and magnetic field; and annihilation or positronium formation times of the positrons with free or bound electrons. The discussion is limited to the observed intensity-time profile of a 0.35-8 MeV gamma-ray emission and of a 0.51-MeV line calculated for three different ambient densities in the annihilation region. Major conclusions are that (1) MeV electrons and protons of at least 30 MeV/nuc have similar time dependences and hence a common origin in the flare region, which support a two-phase acceleration model in solar flares; and (2) the delayed character of the 0.51-MeV emission is clearly defined, where at a time when the rate of nuclear reactions is zero, there still is considerable 0.51-MeV emission.

Ramaty, R.↗
NASA NTRS1976

The singly averaged differential equations of satellite motion for e greater than or equal to 0 and less than 1

The singly-averaged differential equations of motion of a satellite are developed in terms of parameters valid for all eccentricities less than one. The perturbations included in the acceleration model are due to an aspherical central planet (zonal harmonics up to degree 20 and resonant harmonics up to degree and order 20), atmospheric drag for a time-varying atmosphere, third-body gravity (the sun and moon for an earth satellite), solar radiation pressure with shadowing, and impulsive maneuvers. Analytic averaging is used to remove short-period terms due to the aspherical central planet and third-body gravity. Numerical averaging is used to remove short-period terms due to atmospheric drag and solar radiation pressure.

Dallas, S. S.↗
NASA NTRS1981

Multiple crossings of a very thin plasma sheet in the Earth's magnetotail

High resolution magnetic field, plasma and energetic particle data from the IMP-8 spacecraft were studied for multiple crossings of the Earth's magnetotail plasma sheet when it becomes thin during magnetospheric substorms. Traversals recur on a time scale of several minutes and they are associated with high velocity plasma flows that are usually directed tailward but are occasionally directed earthward for brief intervals. Observations are explained by rapid oscillations of a plasma sheet that is only a few thousand km thick, a dimension comparable to the gyroradius of energetic protons. Differences in the angular distributions of the two energies indicate that the higher energy protons are preferentially located on field lines deeper in the tail lobe. A neutral line acceleration model is supported tailward streaming energetic electrons which are occasionally present at the lobe plasma sheet interface.

Fairfield, D. H.↗
NASA NTRS1980

Observations of a nonthermal ion layer at the plasma sheet boundary during substorm recovery

Measurements of the energy and angular distributions of energetic protons and alpha particles (not less than 30 keV/charge) in the geomagnetic tail are presented. The measurements were made during the recovery phase of a geomagnetic substorm on Apr. 19, 1978, with the Max-Planck-Institut/University of Maryland sensor system on the Isee 1 satellite. The measurements were also correlated with plasma observations made by the LASL/MPE instrument on Isee 1. The data reveal the presence of a thin nonthermal layer of protons and alpha particles at the plasma sheet boundary. The particles have their maximum flux at 60 keV/charge and are streaming highly collimated in the earthward direction. The alpha particle layer is confined within the proton layer. Many aspects of the observations are in agreement with an acceleration model near the neutral line proposed by Jaeger and Speiser (1974)

Moebius, E.↗
NASA NTRS1980

Composition anomalies in solar flares

Flares with anomalies in He-3 and Fe enrichment and unusual abundances of heavy ions are discussed. Enrichment in heavy elements including O, Ne, Mg, Si, S-Ca group, and Fe is found in small flares enriched in He-3 and Fe; the flares enriched in He-3 and all heavy elements through Fe show depletion of the carbon abundance. An extreme case of the carbon abundance depletion with the C/O ratio of 0.01 contrasting with the normal solar flare C/O ratio of 0.5 indicates new constraints on acceleration models for small Fe-rich events.

Mason, G. M.↗
NASA NTRS1981

Effect of choked flow on terminal characteristics of MPD thrusters

A one-dimensional steady real gas MPD accelerator model based on data for various electrode lengths and anode orifice radii is presented. The model relates the electric field to the boundary conditions in a form that agrees with experiment over parametric variations in current and mass flow. The electric field is sensitive to the formulations and assumptions bound into the analysis, and is useful in the modeling of outflow properties. It is shown that the location of the sonic point in the arc chamber shifts upstream for high current operation, and the relation between terminal voltage and current is demonstrated. Experiments using an anode suggested by the theory yield a thrust efficiency 1.5 times that of the unmodified thruster.

King, D. Q.↗
NASA NTRS1981

A nonthermal ion layer with high anisotropies at the plasmasheet boundary during substorm recovery

The energy spectra and anisotropies of protons and alpha particles are investigated at the plasmasheet boundary during the recovery phase of geomagnetic substorms using the Max Planck Institut/University of Maryland sensor system on the ISEE-1 satellite. The observations are found to reveal the presence of a thin nonthermal layer of approximately 60 keV/charge protons and alpha particles at the plasmasheet boundary, the particles streaming highly collimated in earthward direction. It is pointed out that the alpha particle layer is confined within the proton layer. It is thought that the principal features of the layers can be explained in terms of an acceleration model proposed by Speiser (1965) for the environment of a magnetic neutral line.

Moebius, E.↗
NASA NTRS1981

Simultaneous observations of energetic protons close to the bow shock and far upstream

Four upstream energetic proton events (30 keV-75 keV), which were simultaneously observed by the ISEE-1 and ISEE-3 satellites, are investigated. A comparison was made between the absolute flux values about 200 earth radii from the bow shock and the flux values several earth radii in front of the bow shock at two different energies. Close to the bow shock the particle distribution is more or less isotropic and indicates relatively strong scattering of these particles in the upstream wave field. At ISEE-3 between 100 and 200 earth radii upstream from the earth's bow shock, the particles move essentially scatter-free from the general bow shock direction. The proton differential intensity at ISEE-3 is a factor of about 4-15 less than at ISEE-1 at 30 keV. The spectra at ISEE-1 are steeper than the spectra at ISEE-3. Flux ratios and spectra are discussed in terms of a first order Fermi acceleration model with a diffusion coefficient increasing approximately linearly with energy and a free escape boundary at some distance upstream.

Scholer, M.↗
NASA NTRS1981

Temporal development of composition, spectra, and anisotropies during upstream particle events

An analysis is conducted of the temporal development of particle intensity, composition, and anisotropies during diffuse particle events. The observations were made with an ultra-low energy charge analyzer (ULECA) sensor. ULECA basically consists of an electrostatic deflection system and an array of solid state detectors. The simultaneous measurement of energy per charge and total energy makes it possible to determine the charge state of a particle. Spectra are derived by an iterative technique involving the numerical integration of particle spectra with the energy response functions of the individual detectors. The presented data are explained in terms of temporal and spatial structures in the upstream region. The temporal structures during the event onset are consistent with a time-dependent first-order Fermi acceleration model, as discussed by Scholer et al. (1980).

Ipavich, F. M.↗
NASA NTRS1981

Spectral and compositional variations of low energy ions during an energetic storm particle event

Attention is given to variations in the intensity, energy spectra, and composition of low-energy protons, helium, and heavy ions (C, O, and Fe) in the energy range 0.3-20 MeV per nucleon during an energetic storm particle event on September 28-29, 1978. The intensities of low enery (less than or equal to 0.6 MeV per nucleon) particles are found to increase exponentially with time before the arrival of the moving interplanetary shock front. The increase is largest for the particles of lowest energy. The spectral steepening, expressed in terms of differences in the spectral index, increases for particles of increasing mass per charge ratio from a difference of approximately 1 for protons to approximately 3 for iron. As a consequence, the He/O and C/O ratios at equal energy per nucleon are constant, whereas the He/p, Fe/He, and Fe/O ratios decrease by as much as one order of magnitude before passage of the shock. The observations are analyzed in terms of a first-order Fermi acceleration model with a rigidity dependent interplanetary mean free path.

Klecker, B.↗
NASA NTRS1982

X-ray and gamma-ray upper limits for pulsed emission from radio pulsars

Results are given for an HEAO 1 search for pulsed emissions from 11 radio pulsars, in the 15 keV-11 MeV energy range. The upper limits of the Vela pulsar are found to fall below the low-energy extrapolation of the more than 50 MeV pulsed spectrum observed by the COS B satellite, and while consistent with predictions of a polar cap acceleration model, seem barely consistent with a single power-law interpolation between optical intensity and the 50 MeV intensity. High energy X-ray upper limits for seven of the ten other pulsars, which were chosen on the basis of proximity to earth, high rotational energy loss rates and short periods, are found to be only a few percent of their rotational energy losses, assuming a moment of inertia, an emission solid angle, and a pulse duty cycle, that are all similar to the high energy X-ray duty cycle of the Crab pulsar. These upper limits are below the corresponding fraction for the Crab pulsar in the cases of the Vela pulsar, PSR 1929+10 and PSR 1642-03.

Knight, F. K.↗
NASA NTRS1982

Space Shuttle Orbiter onboard rendezvous navigation

Much of the work that the Space Shuttle will perform requires a capability to rendezvous with other orbiting objects. The formulation and design philosophy behind the Space Shuttle Orbiter rendezvous navigation system are the subjects of this paper. The current rendezvous navigation design incorporates a Kalman filter to estimate the relative position and velocity. The filter is augmented with state elements for the estimation of colored measurement noise and acceleration modeling errors. Several measurement types are available to the filter: a manual optical sighting device, an automatic optical tracking instrument, and a rendezvous radar which provides range and range rate measurements as well as the line of sight direction. The filter also includes a technique for detecting highly improbable measurements and excluding them from Kalman processing.

Little, M. J.↗
NASA NTRS1984

The orbits of Comets Halley and Giocobini-Zinner

Ongoing activities to improve the orbits and ephemerides of comets Halley and Giacobini-Zinner are outlined. The nongravitational acceleration model of Marsden et al (1973) is used to represent the motion of these two comets over their observed intervals, and recent orbital updates are presented.

Yeomans, D. K.↗
NASA NTRS1985

Implications of source abundances of ultraheavy cosmic rays

The ratio of cosmic ray source abundance to solar-system abundance was examined for individual elements. Correlations of these ratios with first-ionization potential (FIP) and the expected mass-to-charge ratio (A/Q) of the elements in a million-degree plasma are analyzed. The FIP correlation was examined and it is shown that the correlation is affected by the choice of C2 or C1 chondritic meteorites as the solar-system standard for comparison. An A/Q correlation is suggested as a consequence of the shock acceleration model in the hot interstellar medium. The correlations are presented.

Binns, W. R.↗