SEARCH · Engineering Papers
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Vibrational-rotational motion effect on electric and magnetic properties of diatomic molecules, calculating magnetic susceptibility and rotational magnetic moment
Two large magnetic field rotations were recorded by the spacecraft Galileo 1 minute before and 2 minutes after its closest approach to the asteroid Gaspra. The timing and the geometry of the field changes suggest a connection with Gaspra, and the events can be interpreted as the result of the draping of the solar wind field around a magnetospheric obstacle. Gaspra's surface field is inferred to be within an order of magnitude of Earth's surface field, and its magnetic moment per unit mass is in the range observed for iron meteorites and highly magnetized chondrites. The location of the magnetic signatures suggests that perturbations are carried by waves in the magnetosonic-whistler mode with wavelengths between electron and ion gyro radii.
The subject grant (NAG 2-501) supported the analysis of magnetic field data from the Pioneer Venus orbiter for the period 10/1/87 to 9/30/94. During that period, 188 papers were contributed to scientific meetings that either analyzed the magnetometer data or used the data as part of the analysis of a scientific problem. Further, 107 papers were published in research journals and books. The magnetic moment of Venus was described. Venus was found to be essentially devoid of any intrinsic magnetic field. There was evidence though for the presence of lightning in the Venus atmosphere. The altitude distribution of impulsive signals in the night atmosphere was mapped and geographic clusters were found, most probably associated with local time ordering. A new means to create flux ropes in the ionosphere was postulated. On the nightside, ionospheric holes, ionospheric clouds, and tail rays were studied. The subsolar ionopause and the magnetic barrier were examined as was the altitude asymmetry of the ionopause, properties of the magnetosheath, and location of the bow shock upstream waves.
Recent USSR studies of the magnetic field and solar wind flow in the vicinity of Mars and Venus confirm earlier U.S. reports of a bow shock wave developed as the solar wind interacts with these planets. Mars 2 and 3 magnetometer experiments report the existence of an intrinsic planetary magnetic field, sufficiently strong to form a magnetopause, deflecting the solar wind around the planet and its ionosphere. This is in contrast to the case for Venus, where it is assumed to be the ionosphere and processes therein which are responsible for the solar wind deflection. An empirical relationship appears to exist between planetary dipole magnetic moments and their angular momentum for the Moon, Mars, Venus, Earth, and Jupiter. Implications for the magnetic fields of Mercury and Saturn are discussed.
It is pointed out that the solar wind is an important contributor to the H and He components of the atmosphere of Mercury. For this reason, and because significant differences exist between the magnetospheres of Mercury and the earth, an investigation was conducted of the magnetospheric processes at Mercury to determine how these processes affect the precipitation of solar wind plasma onto the planetary surface. Attention is given to a review of estimates of the Hermaean magnetic moment, the direct impact of the solar wind on the planetary surface, precipitation along closed dayside magnetic field lines, precipitation along open dayside magnetic field lines, particles precipitating on closed field lines from the plasma sheet, radiogenic and other atmospheric sources, atmospheric loss rates, surface interaction mechanisms, and subsurface residence times and chemical reactions.
The magnetic moment of La(0.9Sr0.1)2CuO4-y was measured as a function of temperature and magnetic field, and the onset of superconductivity was found to occur at a temperature of 35 K. At 2 K, the dc magnetic susceptibility was found to reach 83 percent of perfect diamagnetism. Field studies have shown that the sample is a type-II superconductor and that the temperature dependences of the critical fiedls are anomalous. Its critical fields, kappa, and lambda(eff) are much larger than those for (La0.9Ba0.1)2CuO4-y, and their temperature dependences cannot be explained in terms of BCS theory.
If Mars has a small intrinsic magnetic moment, Mars' magnetosphere could vary on time scales of a few minutes due to reconnection with the solar wind magnetic field. The day-side magnetopause will be one or two reflected-ion Larmor radii from the bow shock. Substorms will have scale-times of about six minutes. Mars' high ionospheric conductance will virtually stop polar cap convection, and create a magnetic 'topological crisis' unless convecting magnetic flux finds a dissipative way to return to the day-side. The strong magnetic shear induced by magnetospheric convection above the ionosphere could be tearing unstable. The magnetic field might diffusively 'percolate' through the tearing layer. This shearing also draws field aligned currents from the ionosphere which could inject few KeV heavy ionospheric ions into the magnetotail.
Measurements were made of the magnetization, differential magnetic susceptibility, and magnetic entropy of powered samples of Dy2Ti2O7. The saturation magnetic moment is 4.7 + or - 0.2 Bohr magnetons per Dy ion, instead of 10 as predicted by Hund's rules. A temperature-independent magnetization is observed in the saturation region. Absolute values of magnetic entropy have been obtained for temperatures from 1.25 to 20 K, in applied fields up to 10.4 tesla. The magnetic entropy approaches a maximum value consistent with a ground-state multiplicity of 2. Low field magnetization and differential susceptibility data show a transition to antiferromagnetism near 1.35 K. A construction of the magnetic specific heat from the zero field entropy shows an anomaly near the same temperature.
Critical measurements relative to interior structure which can be made during a spacecraft mission to Uranus are discussed. Models of atmospheric composition, possible magnetic moment, and gravitational harmonics are described, and it is shown that high quality imaging of the atmospheric rotation and determination of the possible magnetic field rotation will facilitate construction of an accurate model of the interior structure of the planet.
A method of estimating and correcting for the magnetic field of a dual spinning spacecraft has been developed by employing an extension of the dual magnetometer technique of Ness et al. (1971). This new method is useful for those situations in which a magnetometer boom of modest length (7-10 m) is attached to the spinning part of a large spacecraft (800-1000 kg). The purpose of using a dual spinning spacecraft is to accommodate two types of instruments: (1) imaging and similar 'pointed' remote sensing systems on the stationary platform and (2) fields, particles, and other in situ measuring instruments on the spinning portion. Present-day imaging systems are well known to exhibit large magnetic moments, sometimes displaced from the spacecraft center by a significant amount. The new method assumes that the stationary part of the spacecraft possesses a magnetic field which is represented by a combination of a dipole and a quadrupole field.
The qualification model of the lunar roving vehicle (LRV) was tested in the Spacecraft Magnetic Test Facility (SMTF) at the GSFC Magnetic Test Site. Magnetic field measurements were made, both with the vehicle in its as received state and also subsequent to final deperm treatment. These measurements, together with information supplied to GSFC regarding the magnetic moment of the astronaut's extravehicular mobility units (EMU's) were used to calculate 0.5 nanotesla (gamma) contours around the LRV. The results are tabulated. Magnetic field measurements were also made with various items of LRV equipment operational. No significant changes were noted, except during operation of the vehicle wheels.
A steady-state model of Jupiter's electron radiation belt is developed. The model includes injection from the solar wind, radial diffusion, energy degradation by synchrotron radiation, and absorption at Jupiter's surface. A diffusion coefficient of the form D sub RR/R sub J squared = k times R to the m-th power is assumed, and then observed data on synchrotron radiation are used to fit the model. The free parameters determined from this fit are m = 1.95 plus or minus 0.5, k = 1.7 plus or minus 0.5 x 10 to the 9th power per sec, and the magnetic moment of injected particles equals 770 plus or minus 300 MeV/G. The value of m shows quite clearly that the diffusion is not caused by magnetic pumping by a variable solar wind or by a fluctuating convection electric field. The process might be field line exchange driven by atmospheric-ionospheric winds; our diffusion coefficient has roughly the same radial dependence but is considerably smaller in magnitude than the upper bound diffusion coefficients recently suggested for this process by Brice and McDonough (1973) and Jacques and Davis (1972).
Attention is given to the initial results of a model designed to study the modification of the scatter-free, shock drift acceleration of energetic test particles by wave activity in the vicinity of a quasi-perpendicular, fast-mode MHD shock. It is emphasized that the concept of magnetic moment conservation is a valid approximation only in the perpendicular and nearly perpendicular regimes, when the angle theta-Bn between the shock normal and the upstream magnetic field vector is in the range from 70 deg to 90 deg. The present investigation is concerned with one step in a program which is being developed to combine the shock drift and diffusive processes at a shock of arbitrary theta-Bn.
The vector sum of fields produced by a set of magnetic dipoles with different magnetic moments that are both tilted from the planetary spin axis and offset from the planetary center by different amounts can be used to completely represent a planetary magnetic field in the conventional form of spherical harmonic expansion. The scalar equipotential transformation analytically results in 24 equations that may subsequently be solved for the 24 adjustable parameters in dipole systems with the predetermined main dipole. Attention is given to this method's application to the Jovian magnetic field.
The Mariner 10 spacecraft encountered Mercury three times in 1974-1975. The first and third encounters provided detailed observations of a well-developed detached bow shock wave which results from the interaction of the solar wind. The planet possesses a global magnetic field and a modest magnetosphere, which deflects the solar wind. The field is approximately dipolar, with orientation in the same sense as earth, tilted 12 deg from the rotation axis. The magnetic moment corresponds to an undistorted equatorial field intensity of 350 gammas, approximately 1% of earth's. The field, while unequivocally intrinsic to the planet, may be due to remanent magnetization acquired from an extinct dynamo or a primordial magnetic field or due to a presently active dynamo. The latter possibility appears more plausible at present. In any case, the existence of the magnetic field provides very strong evidence of a mature differentiated planetary interior with a large core (core radius about 0.7 Mercury radius) and a record of the history of planetary formation in the magnetization of the crustal rocks.
An extensive literature review of magnetic nozzle research has been performed, examining previous work, as well as a review of fundamental principles. This has allow us to catalog all basic physical mechanisms which we believe underlie the thrust generation process. Energy conversion mechanisms include the approximate conservation of the magnetic moment adiabatic invariant, generalized hall and thermoelectric acceleration, swirl acceleration, thermal energy transformation into directed kinetic energy, and Joule heating. Momentum transfer results from the interaction of the applied magnetic field with currents induced in the plasma plume., while plasma detachment mechanisms include resistive diffusion, recombination and charge exchange collisions, magnetic reconnection, loss of adiabaticity, inertial forces, current closure, and self-field detachment. We have performed a preliminary study of Hall effects on magnetic nozzle jets with weak guiding magnetic fields and weak expansions (p(sub jet) approx. = P(sub background)). The conclusion from this study is that the Hall effect creates an azimuthal rotation of the plasma jet and, more generally, creates helical structures in the induced current, velocity field, and magnetic fields. We have studied plasma jet expansion to near vacuum without a guiding magnetic field, and are presently including a guiding magnetic field using a resistive MHD solver. This research is progressing toward the implementation of a full generalized Ohm's law solver. In our paper, we will summarize the basic principle, as well as the literature survey and briefly review our previous results. Our most recent results at the time of submittal will also be included. Efforts are currently underway to construct an experiment at the University of Michigan Plasmadynamics and Electric Propulsion Laboratory (PEPL) to study magnetic nozzle physics for a RF-thruster. Our computational study will work directly with this experiment to validate the numerical model, in order to study magnetic nozzle physics and optimize magnetic nozzle design. Preliminary results from the PEPL experiment will also be presented.
Two Extended Interaction Klystrons (EIKs) containing strong permanent magnets were modeled magnetically in a representative spacecraft geometry using commercial finite element modeling techniques and were validated against measurements made at varying distances. Initial modeling results for the 63 A-m2 dipole moment magnets showed that magnetic shields would be necessary in order to meet magnetic field requirements for the Surface Water and Ocean Topography (SWOT) spacecraft, which contains components that are susceptible to external DC magnetic fields. JPL and the EIK vendor proposed cold rolled steel and mu-metal as potential shield materials along with proposed thicknesses of 0.5 mm and 1.5 mm. Magnetic shields made from each of these materials were designed and modeled in software, taking highfield saturation into account. Prototype magnetic shields with these parameters were then built, measured with an existing EIK, and compared against modeling results. For single-axis field measurements along the dipole axis, modeling results were within 7 gauss of the measured values at 10 cm from the magnet, and converged to less than 1.5 gauss at distances greater than 14 cm from the magnet. Three-axis field measurements at locations of interest showed that model correlation improved to within 4 gauss at 11 cm and 2 gauss for distances ranging between 15 cm and 36 cm.
Sufficient and unambiguous evidences of the intrinsic martian magnetic field are: (1) the independence of the field polarity in Maritan magnetic tail from interplanetary magnetic fields (IMF) polarity inversion, established with the help of Mars-5 data; and (2) the incongruity between the sign of the radial component of the field measured in Martian tail (Mars-2) and that of the draped model with IMF data measured simultaneously (Mars-3) on February 23-24, 1972. Mar's dipole magnetic moment is within the limits (1.5 to 2.2) x 10 to e 22 G cc. The dipole axis is deflected from that of rotation on the angle I 15 deg. The North magnetic pole is located in the South Hemisphere. In the frame of the precession-dinamo model the magnetic fields of the planets Mars and Earth are similar. The Martian magnetic field is the real obstacle for the solar wind near the planet.