Toward a self-consistent treatment of wave-particle interactions in the near-Earth environment
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Heliospheric and Magnetospheric Physics↗
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Effective radiation reduction in Space Station and missions beyond the magnetosphere
This paper investigates the efficiency of low- and high-atomic number materials used as protective shields against biologically effective radiation in doses equivalent to those expected in low-earth-orbit and interplanetary manned missions. Results are presented on calculations for single-material shields from polyethylene, water, Be, Al, Fe, and Ta and multilayer shelds made from the combinations of any two or any three of these materials, for both LEO and interplanetary conditions. It is shown that, whereas for protons and Galactic cosmic rays the ordering of shield materials has a negligible effect, for electrons and secondary bremsstrahlung, both the order and the composition are important parameters. It was found that low-atomic-number materials are most effective shields against protons and galactic cosmic rays, and are most effective in decreasing bremsstrahlung production, while high-atomic-number shields are the best attenuators of both primary electrons (if the dose is dominated by primary electrons) and secondary bremsstrahlung (if this is produced).
Jordan, Thomas M.↗
Revisiting the Local Leo Cold Cloud and revised constraints on the Local Hot Bubble
The Local Leo Cold Cloud (LLCC, at a distance of 11–24 pc) was studied in its relation to the Local Hot Bubble (LHB) and the result suggested that much of the observed 1/4 keV emission in that direction originates in front of the cloud. This placed a strong constraint on the distribution of X-ray emission within the LHB and called into question the assumption of a uniform distribution of X-ray emitting plasma within the Local Cavity. However, recent work has quantified the contribution of heliospheric solar wind charge exchange (SWCX) emission to the diffuse X-ray background measured by the ROSAT All-Sky Survey (RASS) at 1/4 keV, and led to the consistency of pressure measurements between the LHB and the local cloud component of the complex of local interstellar clouds (CLICs) surrounding the Sun. In this paper we revisit the LLCC and improve the previous analysis by using higher resolution RASS data, a serendipitous ROSAT pointed observation, a rigorous treatment of the band-averaged X-ray absorption cross section, and models for the heliospheric and magnetospheric SWCX contributions. We find that the foreground emission to the cloud is in excess of the expected heliospheric (interplanetary plus near Earth) SWCX contribution but that it is marginally consistent with the range of possible LHB plasma path lengths between the LLCC and the CLICs given the currently understood plasma emissivity.
79 ASTRONOMY AND ASTROPHYSICS↗
Solar-terrestrial physics.
The work is concerned with solar influences on the earth's upper atmosphere and electromagnetic environment partly through solar ultraviolet and X rays, but particularly through corpuscular radiations. The sun and interplanetary space, the internal structure and magnetic field of the earth, the terrestrial atmosphere and photochemistry, and the dynamics of the upper atmosphere and dynamo action are considered. The formation of the magnetosphere, energetic particles, plasma, and electromagnetic waves in the magnetosphere, solar storms and their extension into interplanetary space, and magnetospheric storms are treated.
Akasofu, S.-I.↗
Radio physics of the outer solar system.
The remote sensing of low frequency nonthermal radio emission is the astronomy of field and particle phenomena. Observations conducted from space lead to information about the composition and dynamic processes occurring in planetary magnetospheres as well as within the interplanetary and interstellar medium. The potential of this technique is demonstrated by considering observations obtained from earth orbit missions.
Stone, R. G.↗
The motion of a proton in the equatorial magnetosphere
In a time-independent model of the magnetosphere including a dipole magnetic field, a convection electric field (deduced from polar orbit observations), and an electric field due to the earth's rotation, the motion of a proton in the equatorial plane is analyzed. By means of the Hamiltonian of the motion, three regimes of motion are identified. A method is then developed for determining for any given observation point which arrival energies correspond to trapped particles and which represent 'open' trajectories.
Stern, D. P.↗
Studies of magnetopause structure
From the International Sun-Earth Explorers (ISEE) 1 magnetopause crossings on November 10, 1977, three-dimensional distribution functions for energetic ions were studied in the magnetosphere, through the magnetopause, and in the magnetosheath (Speiser and Williams, 1982). The particle distributions were particularly examined at and near the times that Russell and Elphic (1978) identified as flux transfer events (FTE). Using a simple, one-dimensional, quasi-static model, particle orbits were followed numerically, from the magnetosphere into the sheath. The inner, trapped, distribution initializes the distribution function. Liouville's theorem allows the inner distribution to be mapped into the sheath following the orbits. This mapping is shown for four mangetosheath ion flows (MIF's) corresponding to four flux transfer events. Results from the studies are discussed. A brief discussion of current sheet particle motion is presented.
Speiser, Theodore W.↗
NASA Center update: Goddard Space Flight Center
The topics covered are presented in viewgraph form and include the following: spacecraft operations, life cycle testing an the Naval Surface Warfare Center (NSWC), and destructive physical analysis at COMSAT laboratories. The subtopics under spacecraft operations are the Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX), the Extreme Ultraviolet Explorer (EUVE), the Upper Atmospheric Research Satellite (UARS), the Compton Gamma Ray Observatory (GRO), the Earth Radiation Budget Satellite (ERBS), and the Hubble Space Telescope (HST). The subtopics under the life cycle testing at NSWC are the following: advanced NiCd cells from Hughes Aircraft Company/Eagle Picher Industries; conventional NiCd cells from Gates Aerospace Batteries; conventional NiCd cells from General Electric; NiCd cells from SAFT; NiH2 celss from Eagle Picher Industries; and data as of 10/26/92.
Rao, Gopalakrishna M.↗
The dynamic cusp at low altitudes: A case study utilizing Viking, DMSP-F7 and Sondrestrom incoherent scatter radar observations
Coincident multi-instrument magnetospheric and ionospheric observations have made it possible to determine the position of the ionospheric footprint of the magnetospheric cusp and to monitor its evolution over time. The data used include charged particle and magnetic field measurements from the Earth-orbiting Viking and DMSP-F7 satellites, electric field measurements from Viking, interplanetary magnetic field and plasma data from IMP-8, and Sondrestrom incoherent scatter radar observations of the ionospheric plasma density, temperature, and convection. Viking detected cusp precipitation poleward of 75.5 deg invariant latitude. The ionospheric response to the observed electron precipitation was simulated using an auroral model. It predicts enhanced plasma density and elevated electron temperature in the upper E- and F- regions. Sondrestrom radar observations are in agreement with the predictions. The radar detected a cusp signature on each of five consecutive antenna elevation scans covering 1.2h local time. The cusp appeared to be about 2 deg invariant latitude wide, and its ionospheric footprint shifted equatorward by nearly 2 deg during this time, possibly influenced by an overall decrease in the interplanetary magnetic field (IMF) B(sub z) component. The radar plasma drift data and the Viking magnetic and electric field data suggest that the cusp was associated with a continuous, rather than a patchy, merging between the IMF and the geomagnetic field.
Watermann, J.↗
The Cassini/Huygens Mission to Saturn
The Cassini/Huygens mission is an international cooperative effort between NASA, the European Space Agency, and the Italian Space Agency to conduct a scientific investigation of the Saturnian system. The spacecraft, which was launched in October of 1997, will use a Venus-Venus-Earth-Jupiter gravity assisted trajectory to arrive at Saturn in July of 2004. The spacecraft, composed of an orbiter and an atmospheric entry probe, will be placed in orbit about Saturn, after which the Huygens probe will be released to enter the atmosphere of Titan, the largest moon of Saturn. The probe data is transmitted during its descent and possible survival on the surface to the orbiter overhead, where it is stored and later relayed to Earth. The orbiter then continues in a four-year mission about Saturn, conducting detailed studies of the atmosphere, the rings, the magnetosphere, Titan, and the icy satellites. The probe carries six instruments to explore the atmosphere and surface of Titan; the orbiter carries twelve instruments for its investigations. This paper characterizes the performance of the Cassini/Huygens spacecraft during its first year and three-quarters of flight, up through the second of the two Venus flybys. The flight system, including the 18 scientific instruments, is described, as well as the detailed overall objectives of the mission.
Mitchell, R.↗
Space Weather Nowcasting of Atmospheric Ionizing Radiation for Aviation Safety
There is a growing concern for the health and safety of commercial aircrew and passengers due to their exposure to ionizing radiation with high linear energy transfer (LET), particularly at high latitudes. The International Commission of Radiobiological Protection (ICRP), the EPA, and the FAA consider the crews of commercial aircraft as radiation workers. During solar energetic particle (SEP) events, radiation exposure can exceed annual limits, and the number of serious health effects is expected to be quite high if precautions are not taken. There is a need for a capability to monitor the real-time, global background radiations levels, from galactic cosmic rays (GCR), at commercial airline altitudes and to provide analytical input for airline operations decisions for altering flight paths and altitudes for the mitigation and reduction of radiation exposure levels during a SEP event. The Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) model is new initiative to provide a global, real-time radiation dosimetry package for archiving and assessing the biologically harmful radiation exposure levels at commercial airline altitudes. The NAIRAS model brings to bear the best available suite of Sun-Earth observations and models for simulating the atmospheric ionizing radiation environment. Observations are utilized from ground (neutron monitors), from the atmosphere (the METO analysis), and from space (NASA/ACE and NOAA/GOES). Atmospheric observations provide the overhead shielding information and the ground- and space-based observations provide boundary conditions on the GCR and SEP energy flux distributions for transport and dosimetry simulations. Dose rates are calculated using the parametric AIR (Atmospheric Ionizing Radiation) model and the physics-based HZETRN (High Charge and Energy Transport) code. Empirical models of the near-Earth radiation environment (GCR/SEP energy flux distributions and geomagnetic cut-off rigidity) are benchmarked against the physics-based CMIT (Coupled Magnetosphere- Ionosphere-Thermosphere) and SEP-trajectory models.
Mertens, Christopher J.↗
Fabrication of Regolith-Derived Radiation Shield Project
Mars and asteroids have little or no atmosphere, and do not possess a magnetosphere that can protect humans, mechanisms and electronics from damaging Galactic Cosmic Radiation (GCR) and solar particle events (SPE) as does the Earth. These types of space radiation present one of the highest risks to a human crew during interplanetary journeys and to onboard electronics. This project aims to evaluate the effectiveness of carbonaceous asteroid materials as a potential radiation shielding material.
Technology Portfolio System↗
Terrestrial kilometric radiation: 1: Spatial structures studies
Observations are presented of lunar occultations of the earth at 250 kHz obtained with the Radio-Astronomy-Explorer-2 satellite which were used to derive two dimensional maps of the location of the sources of terrestrial kilometric radiation (TKR). By examining the two dimensional source distributions as a function of the observer's location (lunar orbit) with respect to the magnetosphere, the average three dimensional location of the emission regions can be estimated. Although TKR events at 250 kHz can often be observed at projected distances corresponding to the 250 kHz electron gyro or plasma level (approximately 2 earth radii), many events are observed much farther from the earth (between 5 and 15 earth radii). Dayside emission apparently in the region of the polar cusp and the magnetosheath and night emission associated with regions of the magnetotail are examined. The nightside emission is suggestive of a mechanism involving plasma sheet electron precipitation in the pre-midnight sector.
Alexander, J. K.↗
Improving Magnetosphere In Situ Observations Using Solar Sails
Past and current magnetosphere missions employ conventional spacecraft formations for in situ observations of the geomagnetic tail. Conventional spacecraft flying in inertially fixed Keplerian orbits are only aligned with the geomagnetic tail once per year, since the geomagnetic tail is always aligned with the Earth-Sun line, and therefore, rotates annually. Solar sails are able to artificially create sunsynchronous orbits such that the orbit apse line remains aligned with the geomagnetic tail line throughout the entire year. This continuous presence in the geomagnetic tail can significantly increase the science phase for magnetosphere missions. In this paper, the problem of solar sail formation design is explored using nonlinear programming to design optimal two-craft, triangle, and tetrahedron solar sail formations, in terms of formation quality and formation stability. The designed formations are directly compared to the formations used in NASA's Magnetospheric Multi-Scale mission.
Sails↗
The main source of radio emission from the magnetosphere of Uranus
Observations of kilometric radiation from Uranus made with the planetary radio astronomy experiment on the Voyager 2 spacecraft are presented and discussed. Similarities between the auroral kilometric radiation from earth and the observed Uranus emission are pointed out. A geometrical beaming model is developed in which a single distributed source is located above the darkside auroral region and emits in the extraordinary mode by the cyclotron maser process. The model can account for nearly all the Uranian kilometric radiation from the high-frequency limit near 850 kHz down to about 150 kHz and for much of it down to the lower limit of 20 kHz.
Gulkis, Samuel↗
Electron Acceleration in the Transition Region Behind the Earth's Bow Shock
Electron acceleration mechanism in transition region behind earth bow shock to account for high energy electron spikes
BOW SHOCK↗
Earth's external magnetic fields at low orbital altitudes
Under our Jun. 1987 proposal, Magnetic Signatures of Near-Earth Distributed Currents, we proposed to render operational a modeling procedure that had been previously developed to compute the magnetic effects of distributed currents flowing in the magnetosphere-ionosphere system. After adaptation of the software to our computing environment we would apply the model to low altitude satellite orbits and would utilize the MAGSAT data suite to guide the analysis. During the first year, basic computer codes to run model systems of Birkeland and ionospheric currents and several graphical output routines were made operational on a VAX 780 in our research facility. Software performance was evaluated using an input matchstick ionospheric current array, field aligned currents were calculated and magnetic perturbations along hypothetical satellite orbits were calculated. The basic operation of the model was verified. Software routines to analyze and display MAGSAT satellite data in terms of deviations with respect to the earth's internal field were also made operational during the first year effort. The complete set of MAGSAT data to be used for evaluation of the models was received at the end of the first year. A detailed annual report in May 1989 described these first year activities completely. That first annual report is included by reference in this final report. This document summarizes our additional activities during the second year of effort and describes the modeling software, its operation, and includes as an attachment the deliverable computer software specified under the contract.
Klumpar, D. M.↗
Terrestrial kilometric radiation. I - Spatial structure studies
Observations of lunar occultations of earth at 250 kHz, obtained with the Radio Astronomy Explorer 2 satellite, have been used to derive two-dimensional maps of the location of the sources of terrestrial kilometric radiation (TKR). By examining the two-dimensional source distributions as a function of the observer's location (lunar orbit) with respect to the magnetosphere, the average three-dimensional location of the emission regions can be estimated. Although TKR events at 250 kHz can often be observed at projected distances corresponding to the 250-kHz electron gyro or plasma level (about 2 earth radii), many events are observed much farther from earth (about 5 to 15 radii). On the dayside, emission was apparently observed in the region of the polar cusp and the magnetosheath at a magnetic latitude of about 70 deg; in the night hemisphere, emission is found to be associated with regions of the magnetotail at latitudes of at least 70 deg. The nightside emission is suggestive of a mechanism involving plasma-sheet electron precipitation in the premidnight sector.
Alexander, J. K.↗