A note on the compression of the Earth's magnetic field and hypothetically related phenomena.
Features of impact mechanism of electrically neutral stream of ionized particles from Sun upon outer magnetosphere
GEOMAGNETIC STORM↗
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Magnetohydrodynamic Augmented Propulsion Experiment
A fundamental obstacle to routine space access is the specific energy limitations associated with chemical fuels. In the case of vertical take-off, the high thrust needed for vertical liftoff and acceleration to orbit translates into power levels in the 10 GW range. Furthermore, useful payload mass fractions are possible only if the exhaust particle energy (i.e., exhaust velocity) is much greater than that available with traditional chemical propulsion. The electronic binding energy released by the best chemical reactions (e.g., LOX/LH2 for example, is less than 2 eV per product molecule (approx. 1.8 eV per H2O molecule), which translates into particle velocities less than 5 km/s. Useful payload fractions, however, will require exhaust velocities exceeding 15 km/s (i.e., particle energies greater than 20 eV). As an added challenge, the envisioned hypothetical RLV (reusable launch vehicle) should accomplish these amazing performance feats while providing relatively low acceleration levels to orbit (2-3g maximum). From such fundamental considerations, it is painfully obvious that planned and current RLV solutions based on chemical fuels alone represent only a temporary solution and can only result in minor gains, at best. What is truly needed is a revolutionary approach that will dramatically reduce the amount of fuel and size of the launch vehicle. This implies the need for new compact high-power energy sources as well as advanced accelerator technologies for increasing engine exhaust velocity. Electromagnetic acceleration techniques are of immense interest since they can be used to circumvent the thermal limits associated with conventional propulsion systems. This paper describes the Magnetohydrodynamic Augmented Propulsion Experiment (MAPX) being undertaken at NASA Marshall Space Flight Center (MSFC). In this experiment, a 1-MW arc heater is being used as a feeder for a 1-MW magnetohydrodynamic (MHD) accelerator. The purpose of the experiment is to demonstrate that an MHD accelerator can be an effective augmentation system for increasing engine exhaust velocity. More specifically, the experiment is intended to show that electromagnetic effects are effective at producing flow acceleration whereas electrothermal effects do not cause unacceptable heating of the working fluid. The MHD accelerator was designed as an externally diagonalized segmented Faraday channel, which will be inserted into an existing 2-tesla electromagnet. This allows the external power to be connected through two terminals thereby minimizing the complexity and cost associated with powering each segment independently. The design of the accelerator and other components in the flow path has been completed and fabrication activities are underway. This paper provides a full description of MAPX including performance analysis, design, and test plans, and current status.
Litchford, Ron J.↗
Rayleigh, Raman and particulate scattering
Analysis of the visible and near infrared spectra of planetary atmospheres and the multiple scattering of photons within the atmosphere are discussed. Photons detected within the spectral region are solar photons which were scattered by the gas and particles in the planetary atmosphere. An example is given for the incident and emitted fluxes for a hypothetical planet with an effective temperature of 100 K. The absorption spectrum of the planetary atmosphere is discussed in terms of the various scattering processes photons undergo within the atmosphere. Three different physical processes are considered. Rayleigh scattering and Raman scattering by the gas molecules, and scattering by any cloud or dust aerosol particles in the atmosphere. The physics of each of these processes is examined.
Cochran, W. D.↗
Beta decay and the origin of biologial chirality - New experimental results
The hypothetical connection developed by Vester and Ulbricht (1959), between the handedness of beta particles in radioactive decay and the (L) sign of biologial chirality is investigated in a radiolysis experiment. The experiment measured the predicted asymmetry in the formation triplet or 'ortho-' positronium (oPs) in amino acid enantiomers by low energy positrons under conditions of helicity reversal. The positrons were focused on amino acid powder samples. By measuring the time between positron arrival and emission of gamma rays, long-lived oPs were separated from other species. It is found that the asymmetry in leucine (0.8 x 10 to the -4th) is consistent with the theoretical prediction of 10 to the -6th. Neither the experimental limits nor the theoretical estimates are found to rule out a mechanism like that described by Vester and Ulbricht as the cause of the sign of the observed chiral polarization.
Van House, J.↗
Sound production in a moving stream
Jet noise is modeled by particle-attached quadrupoles convected with the velocity of the actual fluid but positioned near a hypothetical instability-free vortex sheet. The strength of each quadrupole is Lighthill's stress tensor per unit mass. The work of Mani (1976) has shown that this type of model agrees well with experiment, and the present work establishes some of the equivalent sources needed for an exact analogy. The instability waves of the shear layer, as they grow into turbulence, are heard as sound that builds up as a precursor of the main turbulence-driven field. The circular compact jet is examined in some detail, and it is found that when the jet is very light it can provide a waveguide in which the effects of source activity persist for some time but eventually leak out as sound. This interaction greatly distorts the free field characteristics of the turbulent sources, so that Reynolds-stress-induced waves have an intensity that scales with the fourth power of jet velocity.
Dowling, A. P.↗
Physics of interplanetary dust capture via impact into organic polymer foams
The physics of hypervelocity impacts into foams is of interest because of the possible application to interplanetary dust particle (IDP) capture by spacecraft. We present a model for the phenomena occurring in such impacts into low-density organic polymer foams. Particles smaller than foam cells behave as if the foam is a series of solid slabs and are fragmented and, at higher velocities, thermally altered. Particles much larger than the foam cells behave as if the foam were a continuum, allowing the use of a continuum mechanics model to describe the effects of drag and ablation. Fragmentation is expected to be a major process, especially for aggregates of small grains. Calculations based on these arguments accurately predict experimental data and, for hypothetical IDPs, indicate that recovery of organic materials will be low for encounter velocities greater than 5 km/s. For an organic particle 100 micrometers in diameter, approx. 35% of the original mass would be collected in an impact at 5 km/s, dropping to approx. 10% at 10 km/s and approx. 0% at 15 km/s. For the same velocities the recovery ratios for troilite (FeS) are approx. 95%, 65%, and 50%, and for olivine (Mg2SiO4) they are approx. 98%, 80%, and 65%, demonstrating that inorganic materials are much more easily collected. The density of the collector material has only a second-order effect, changing the recovered mass by less than 10% of the original mass.
Anderson, William W.↗
The Thermal Expansion of Ring Particles and the Secular Orbital Evolution of Rings Around Planets and Asteroids
The thermal expansion and contraction of ring particles orbiting a planet or asteroid can cause secular orbit evolution. This effect, called here the thermal expansion effect, depends on ring particles entering and exiting the shadow of the body they orbit. A particle cools off in the shadow and heats up again in the sunshine, suffering thermal contraction and expansion. The changing cross-section it presents to solar radiation pressure plus time lags due to thermal inertia lead to a net along-track force. The effect causes outward drift for rocky particles. For the equatorial orbits considered here, the thermal expansion effect is larger than Poynting-Robertson drag in the inner solar system for particles in the size range approx. 0.001 - 0.02 m. This leads to a net increase in the semimajor axis from the two opposing effects at rates ranging from approx. 0.1 R per million years for Mars to approx. 1 R per million years for Mercury, for distances approx. 2R from the body, where R is the body's radius. Asteroid 243 Ida has approx. 10 R per million years, while a hypothetical Near-Earth Asteroid (NEA) can have faster rates of approx. 0.5 R per thousand years, due chiefly to its small radius compared to the planets. The thermal expansion effect weakens greatly at Jupiter and is overwhelmed by Poynting-Robertson for icy particles orbiting Saturn. Meteoroids in eccentric orbits about the Sun also suffer the thermal expansion effect, but with only approx. 0.0003e2 AU change in semimajor axis over a million years for a 2 m meteoroid orbiting between Mercury and Earth.
Ring particles↗
GLAST, the Gamma-ray Large Area Space Telescope
The Gamma-ray Large Area Space Telescope, GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to greater than 300 GeV, with supporting measurements for gamma-ray bursts from 10 keV to 25 MeV. With its upcoming launch in 2008, GLAST will open a new and important window on a wide variety of phenomena, including black holes and active galactic nuclei; the optical-UV extragalactic background light, gamma-ray bursts; the origin of cosmic rays and supernova remnants; and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations and Lorentz invariance violation. In addition to the science opportunities, this talk includes a description of the instruments, the collaboration between particle physicists and astrophysicists, the opportunities for guest observers, and the mission status.
Ritz, Steven↗
GLAST, the Gamma-ray Large Area Space Telescope
The Gamma-ray Large Area Space Telescope, GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to greater than 300 GeV, with supporting measurements for gamma-ray bursts from 10 keV to 25 MeV. With its upcoming launch in 2008, GLAST will open a new and important window on a wide variety of phenomena, including black holes and active galactic nuclei; the optical-UV extragalactic background light, gamma-ray bursts; the origin of cosmic rays and supernova remnants; and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations and Lorentz invariance violation. In addition to the science opportunities, this talk includes a description of the instruments, the collaboration between particle physicists and astrophysicists, the opportunities for guest observers, and the mission status.
Ritz, Steven↗
Particles, environments, and possible ecologies in the Jovian atmosphere
The possible existence of indigenous Jovian organisms is investigated by characterizing the relevant physical environment of Jupiter, discussing the chromophores responsible for the observed coloration of the planet, and analyzing some permissible ecological niches of hypothetical organisms. Values of the eddy diffusion coefficent are estimated separately for the convective troposphere and the more stable mesosphere, and equilibrium condensation is studied for compounds containing Na, Cl, or both. The photoproduction of chromophores and nonequilibrium organic molecules is analyzed, and the motion of hypothetical organisms is examined along with the diffusion of metabolites and the consequent growth of organisms. Four kinds of organisms are considered: primary photosynthetic autotrophs ('sinkers'), larger autotrophs or heterotrophs that actively maintain their pressure level ('floaters'), organisms that seek out others ('hunters'), and organisms that live at almost pyrolytic depths ('scavengers'). It is concluded that ecological niches for sinkers, floaters, and hunters appear to exist in the Jovian atmosphere.
Sagan, C.↗
On Europa's Magnetospheric Interaction: A MHD Simulation of the E4 Flyby
The global three-dimensional interaction of Europa with the Jovian magnetosphere is modeled by using a complete set of ideal magnetohydrodynamic (MHD) equations. The model accounts for exospheric mass loading, ion-neutral charge exchange, recombination, and a possible intrinsic dipole magnetic field of Europa. The single-fluid MHD equations are solved by using a modem, finite volume, higher-order, Godunov-type method on an adoptively refined unstructured grid, which allows detailed modeling of the region near Europa while still resolving both the upstream region and the satellite's wake. The magnetic field and plasma density measured during Galileo's EGA flyby of December 19, 1996, are reproduced reasonably well in the simulation. We find the agreement between the data and our model particularly convincing if we assume that the plasma velocity during the EGA flyby deviated from the nominal corotation direction by approximately 20 deg. Evidence from the Galileo energetic particle detector also supports this assumption. In this case, we can fit the data using a dipole with orientation close to that of an induced dipole arising from the interaction of a hypothetical conducting subsurface layer on Europa with the periodically changing magnetic field of Jupiter. However, the magnitude of the dipole in our model is somewhat smaller (70%) than that suggested by Khurana et al. The total mass loading and ion-neutral charge exchange rates are consistent with the estimates of Europa's atmosphere and ionosphere.
Kabin, K.↗
Evaluating the Performance of Single and Double Moment Microphysics Schemes During a Synoptic-Scale Snowfall Event
Increases in computing resources have allowed for the utilization of high-resolution weather forecast models capable of resolving cloud microphysical and precipitation processes among varying numbers of hydrometeor categories. Several microphysics schemes are currently available within the Weather Research and Forecasting (WRF) model, ranging from single-moment predictions of precipitation content to double-moment predictions that include a prediction of particle number concentrations. Each scheme incorporates several assumptions related to the size distribution, shape, and fall speed relationships of ice crystals in order to simulate cold-cloud processes and resulting precipitation. Field campaign data offer a means of evaluating the assumptions present within each scheme. The Canadian CloudSat/CALIPSO Validation Project (C3VP) represented collaboration among the CloudSat, CALIPSO, and NASA Global Precipitation Measurement mission communities, to observe cold season precipitation processes relevant to forecast model evaluation and the eventual development of satellite retrievals of cloud properties and precipitation rates. During the C3VP campaign, widespread snowfall occurred on 22 January 2007, sampled by aircraft and surface instrumentation that provided particle size distributions, ice water content, and fall speed estimations along with traditional surface measurements of temperature and precipitation. In this study, four single-moment and two double-moment microphysics schemes were utilized to generate hypothetical WRF forecasts of the event, with C3VP data used in evaluation of their varying assumptions. Schemes that incorporate flexibility in size distribution parameters and density assumptions are shown to be preferable to fixed constants, and that a double-moment representation of the snow category may be beneficial when representing the effects of aggregation. These results may guide forecast centers in optimal configurations of their forecast models for winter weather and identify best practices present within these various schemes.
Molthan, Andrew L.↗
GLAST Mission Overview
The Gamma-ray Large Area Space Telescope, GLAST, is a satellite-based observatory under construction to measure the cosmic gamma-ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for gamma-ray bursts from 10 keV to 25 MeV. With its launch in 2007, GLAST will open a new and important window on a wide variety of high energy phenomena, including black holes and active galactic nuclei; gamma-ray bursts; the origin of cosmic rays and supernova remnants; and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations, Lorentz invariance violation, and exotic relics from the Big Bang. In addition to the science opportunities, this talk will include a brief description of the instruments, the collaboration of particle physicists and high energy astrophysicist, the mission status, and the opportunities and support for guest observers.
Ritz, Steve↗
Evolution of Io's volatile inventory
Voyager data are used to make crude estimates of the rate at which Io loses volatiles, by a variety of processes, to the surrounding magnetosphere, for the case of both the current, SO2-dominated atmosphere and hypothetical paleoatmospheres in which such other gases as N2 may have been the dominant constituent. Among the mechanisms making significant contributions to the prodigious rate at which Io is losing volatiles are: the interaction of the magnetospheric plasma with volcanic plume particles and the background atmosphere; the sputtering of ices on the surface, if the nightside atmospheric pressure is low enough; and Jeans' escape of O as a dissociation product of SO2 gas. It is also argued that in the case of paleoatmospheres only the first two alternatives would have been possible and, nevertheless, insufficient to account for N2 loss over the life of the satellite.
Pollack, J. B.↗
Martian sediments and sedimentary rocks
Martian sediments and sedimentary rocks, clastic and nonclastic, should represent a high priority target in any future return-sample mission. The discovery of such materials and their subsequent analysis in terrestrial laboratories, would greatly increase the understanding of the Martian paleoclimate. The formation of Martian clastic sedimentary rocks, under either present, low-pressure, xeric conditions or a postulated, high-pressure, hydric environment, depends upon the existence of a supply of particles, various cementing agents and depositional basins. A very high resolution (mm-cm range) photographic reconnaissance of these areas would produce a quantum jump in the understanding of Martian geological history. Sampling would be confined to more horizontal (recent) surfaces. Exploration techniques are suggested for various hypothetical Martian sedimentary rocks.
Markun, C. D.↗
Dynamical Evolution of Meteoroid Streams, Developments Over the Last 30 Years
As soon as reliable methods for observationally determining the heliocentric orbits of meteoroids and hence the mean orbit of a meteoroid stream in the 1950s and 60s, astronomers strived to investigate the evolution of the orbit under the effects of gravitational perturbations from the planets. At first, the limitations in the capabilities of computers, both in terms of speed and memory, placed severe restrictions on what was possible to do. As a consequence, secular perturbation methods, where the perturbations are averaged over one orbit became the norm. The most popular of these is the Halphen- Goryachev method which was used extensively until the early 1980s. The main disadvantage of these methods lies in the fact that close encounter can be missed, however they remain useful for performing very long-term integrations. Direct integration methods determine the effects of the perturbing forces at many points on an orbit. This give a better picture of the orbital evolution of an individual meteoroid, but many meteoroids have to be integrated in order to obtain a realistic picture of the evolution of a meteoroid stream. The notion of generating a family of hypothetical meteoroids to represent a stream and directly integrate the motion of each was probably first used by Williams Murray & Hughes (1979), to investigate the Quadrantids. Because of computing limitations, only 10 test meteoroids were used. Only two years later, Hughes et. al. (1981) had increased the number of particles 20-fold to 200 while after a further year, Fox Williams and Hughes used 500 000 test meteoroids to model the Geminid stream. With such a number of meteoroids it was possible for the first time to produce a realistic cross-section of the stream on the ecliptic. From that point on there has been a continued increase in the number of meteoroids, the length of time over which integration is carried out and the frequency with which results can be plotted so that it is now possible to produce moving images of the stream. As a consequence, over recent years, emphasis has moved to considering stream formation and the role fragmentation plays in this.
Williams, I. P.↗
The erosion of planetary and satellite atmospheres by energetic atomic particles
Analytic expressions are presented which may be used to compute the sputter-erosion yield from any unimolecular gravitationally bound gas by any atomic charged particle of any energy. A calculation of solar wind proton and alpha particle induced erosion of the CO2 atmosphere of Mars predicts molecular sputtering yields. An expression for the emission yield of energetic molecular fragments produced in primary knock-on events is given in closed form; such fragment emission is of secondary importance for mass loss compared to the molecular yield itself. Erosion by radiation belt protons of a hypothetical thin O2 atmosphere associated with the Jovian satellite Ganymede is considered, and molecular sputtering yields for proton energies are determined.
Haff, P. K.↗
The magnetic pumping of plasmas with sawtooth waveforms
The pumping of plasmas by sawtooth-waveform magnetic induction variations is studied theoretically and by means of computer simulations. A sawtooth is a cycle waveform that is characterized by a slow increase in the magnetic induction followed by a rapid drop in the induction. Two types of sawtooth pumping are analyzed, and the types classified as to whether or not the first adiabatic invariants of the plasma particles are conserved during the rapid drops in the magnetic induction. When the invariants are conserved, the sawtooth waveforms are found to be less efficient than square waves for pumping plasmas. When the adiabatic invariations are not conserved, the pumping efficiency is found to be a slight improvement over square waves. Both types of pumping are applied to a hypothetical tokamak plasma and it is concluded that neither type of sawtooth pumping is practical for heating magnetically confined fusion plasmas.
Borovsky, Joseph E.↗