9,044 research outputs found
Research in particles and fields
The astrophysical aspects of cosmic and gamma rays and the radiation environment of the Earth and other planets investigated by means of energetic particle detector systems flown on spacecraft and balloons are discussed. The theory of particles and fields in space is also addressed with particular emphasis on models of Saturn's magnetic field
Research in particles and fields
Cosmic rays and astrophysical plasmas, NASA spacecraft experiment activities, and gamma rays are discussed
Research in particles and fields
The astrophysical aspects of cosmic radiation and the radiation and electromagnetic field environment of the Earth and other planets are investigated. Energetic particle and photon detector systems flown on spacecraft and balloons are used. Galactic, solar, interplanetary, and planetary energetic particles and plasmas are also studied with emphasis on precision measurements with high resolution in charge, mass, and energy
Analytic Approximations in the Study of the Solar Modulation of Electrons
Numerical solutions to the transport equation of galactic
cosmic rays in the interplanetary medium have been used to
investigate the applicability of commonly used approximate
analytic solutions for electrons (10 MeV to 10 GeV). We
find that for a given cosmic-ray diffusion coefficient:
(a) the "force-field" approximation is in reasonable agreement
with the numerical solution at energies ≳ 200 MeV, but
deviates significantly at lower energies, depending on the
shape of the interstellar electron spectrum, (b) the
"diffusion-convection" approximation agrees generally with
the numerical solution within a factor of ~ 2 over the
entire energy range
Interplanetary Diffusion Coefficients for Cosmic Rays
Information on the cosmic-ray diffusion coefficient, κ, derived
from near-Earth observations of the solar modulation of galactic
electron fluxes and from the near-Earth power spectra of the
interplanetary magnetic field, has been used to study the
heliocentric radial dependence of κ and to derive limits on
the spatial extent of the solar modulation region.
Representing κ as a separable function of radius r and rigidity,
and assuming κ(r) ∝ r^n, we can place a limit on the power law
exponent, n ≾ 1.2. The distance of the modulation boundary is
a function of n, and, e.g., for n = 0, falls into the range of
6-25 AU
Research in particles and fields
The astrophysical aspects of cosmic rays and gamma rays and of the electromagnetic field environment of the Earth and other planets are investigated. These investigations are carried out by means of energetic particle and photon detector systems flown on spacecraft and balloons
Interstellar Electron Spectrum from the Galactic Non-Thermal Radio Emission
A range of interstellar electron spectra at energies between
100 MeV and 5 GeV has been derived from an analysis of the
observed galactic non-thermal radio spectrum and from consideration
of the existing uncertainties in the other relevant
physical parameters of the galaxy. We find that for energies
larger than ~ 300 MeV the electron spectrum is uncertain to a
factor of 4 due to uncertainties in the galactic magnetic field
strength and the total line-of-sight emission length. The uncertainty
in the electron spectrum increases towards lower
energies, exceeding a factor of 50 near 100 MeV, primarily due
to uncertainties in the galactic parameters affecting interstellar
radio absorption
Space Trajectory Error Analysis Program (STEAP) for halo orbit missions. Volume 2: Programmer's manual
The six month effort was responsible for the development, test, conversion, and documentation of computer software for the mission analysis of missions to halo orbits about libration points in the earth-sun system. The software consisting of two programs called NOMNAL and ERRAN is part of the Space Trajectories Error Analysis Programs. The program NOMNAL targets a transfer trajectory from earth on a given launch date to a specified halo orbit on a required arrival date. Either impulsive or finite thrust insertion maneuvers into halo orbit are permitted by the program. The transfer trajectory is consistent with a realistic launch profile input by the user. The second program ERRAN conducts error analyses of the targeted transfer trajectory. Measurements including range, doppler, star-planet angles, and apparent planet diameter are processed in a Kalman-Schmidt filter to determine the trajectory knowledge uncertainty
Relation of the Radial Gradient of Cosmic-Ray Protons to the Size of the Solar-Modulation Region
The radial intensity-gradient of cosmic-ray protons has been
calculated for a range of values of the distance to the boundary
of a spherically symmetric solar-modulation region. We find
that the radial dependence of the gradients may be described
in terms of two characteristic domains of the modulation region:
(a) an "inner region" where the gradients are relatively small
and constant, and (b), an "outer region"' where the gradients
are large and show a strong radial dependence. The magnitude
of the gradient in the inner region is small for reasonable
values for the physical parameters of the modulation mechanism
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