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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Spherical harmonic representation of the main geomagnetic field for world charting and investigations of some fundamental problems of physics and geophysics

Progress in the harmonic analysis of MAGSAT data is reported. Single-day data sets were subdivided into information on the sunrise side of the Earth and information on the sunset side of the Earth. Data for the main and external fields each demonstrate a clear and consistent systematic difference between the sets of data which was determined to be, due to ionospheric currents which differ from the sunset to the sunrise terminator. A toroidal field was analyzed for and determined to be an apparent toroidal field resulting from electric currents concentrated in the two terminators. Progressive elimination of auroral zone data demonstrates that the information presented does not arise from complications due to Birkeland currents.

Barraclough, D. R.↗
NASA NTRS1982

A geomagnetic field spectrum

A spherical harmonic model of the earth's internal magnetic field of degree and order 23 is derived from selected Magsat data, and its power spectrum, computed with terms developed by Mauersberger (1956) and Lowes (1974), is found to exhibit a change of a slope at n = 14 which is interpreted as an indication that the core field dominates at values lower than 13 while the crust field dominates above a value of 15. The representations of the two portions of the spectrum obtained can be used to establish order-of-magnitude inaccuracies due to both crustal fields and the inability to observe core field wavelengths beyond n = 13, at which point they are obscured by the crustal field, in core field models.

Langel, R. A.↗
NASA NTRS1982

Evaluation of high latitude disturbances with Magsat - The importance of the Magsat geomagnetic field model

Studies of Birkeland current systems have been conducted primarily with low altitude satellite magnetometer data whereas electrojet current signatures have been usually analyzed with data from ground-based magnetometer chains. However, the Magsat magnetometer data set allows magnetic disturbances due to both field-aligned and electrojet currents to be examined simultaneously. This is mainly due to Magsat's approximately 400 km altitude, thus providing data closer to the electrojet current system than has been previously available from satellite measurements. Of additional importance are the superior accuracy, both in sensitivity and altitude, of the magnetic field measurements obtained by Magsat and last, but not least, the availability of an accurate magnetic field model of the concurrent epoch (based on the Magsat data set) that allows one to obtain a better baseline than previous models. The aforementioned points are emphasized and both Birkeland and electrojet currents have been analyzed in a case study for November 13, 1979.

Zanetti, L. J.↗
NASA NTRS1983

Storm-time changes of geomagnetic field at MAGSAT altitudes (325-550 Km) and their comparison with changes at ground locations

The values of H, X, Y, Z at MAGSAT altitudes were first expressed as residuals delta H, delta X, delta Y, delta Z after subtracting the model HMD, XMD, YMD, ZMC. The storm-time variations of H showed that delta H (Dusk) was larger (negative) than delta H (Dawn) and occurred earlier, indicating a sort of hysteresis effect. Effects at MAGSAT altitudes were roughly the same (10% accuracy) as at ground, indicating that these effects were mostly of magnetospheric origin. The delta Y component also showed large storm-time changes. The latitudinal distribution of storm-time delta H showed north-south asymmetries varying in nature as the storm progressed. It seems that the central plane of the storm-time magnetospheric ring current undergoes latitudinal meanderings during the course of the storm.

Parada, N. D. J.↗
NASA NTRS1985

Simultaneous excitation of large-scale geomagnetic field fluctuations and plasma density irregularities by powerful radio waves

The physical mechanism of thermal filamentation instability of radio waves whose frequencies can be as low as in the VLF band and as high as in the SHF band are investigated. This instability can excite large-scale magnetic and plasma density fluctuations simultaneously in the ionosphere and magnetosphere. Relevant experiments are reviewed in terms of this instability and other mechanisms.

Lee, M. C.↗
NASA NTRS1987

The origin of polarity asymmetries in the history of the geomagnetic field

The behavior of magnetohydrodynamic stationary modes in the presence of an imposed weak magnetic field originating separately from the dynamo is studied. A rare class of stationary states is found that exhibit high sensitivity to the presence of weak imposed fields. The amplitude of the difference between the total fields of opposite polarity is much larger than the amplitude of the imposed nondynamo fields. It is proposed that Earth's magnetic field operates in such a mode, highly sensitive to the presence of an ambient field. An argument is given to explain why the terrestrial dynamo should choose to operate in one of these rare states. Implications are discussed for the general mechanism of dynamo magnetic field equilibrium in planets.

Levy, E. H.↗
NASA NTRS1989

Simple models of fluid flow at the core surface derived from geomagnetic field models

The fluid flow at the core surface is determined for a given model of temporal magnetic field variation, assuming steady flow and adopting the frozen-flux approximation. Evidence is presented for ageostrophic flow in the form of flow across the geographical equator. A simple pattern of the large-scale toroidal part of the flow is found. The pattern is nearly symmetric about the equator. Changes in the flow pattern are obtained from flow maps covering 5-year intervals beginning in 1915.

Bloxham, Jeremy↗
NASA NTRS1992

Survey Parameters and Availability of Low-level Aeromagnetic Data for Geomagnetic Field Modelling

Since aeromagnetic surveying started immediately after World War II, a considerable area of the earth's surface both onshore (in excess of 25 million sq. km) has been magnetically surveyed. For about the first 15 years or so, fluxgate magnetometers were employed in aeromagnetic surveys, but the introduction of proton free-precession magnetometers resulted in absolute readings being recorded. Proton precession magnetometers have now been replaced to a large extent by the more sensitive optical absorption magnetometers. Some care has to be taken to calibrate aeromagnetic survey systems and this is best done using a calibration range tied to a magnetic observatory so that accuracies of 10nT or better are achieved for the total field values recorded. Survey navigation has always posed a problem for aeromagnetic surveys, especially offshore. Over land, vertically pointed 35 mm cameras were initially used to recover the aircraft track using a combination of aerial photos and topographic maps. Over featureless areas, it was necessary to utilize existing electronic positioning systems such as Loran C or set up special navigation systems. The advent of the satellite-based Global Positioning Systems (GPS) has to a larger extent solved the navigational problem because there is now almost continuous worldwide coverage to 10 m accuracy in the differential mode. The resultant aeromagnetic data is normally compiled into contour maps in which the diurnal variation and aircraft heading effects are removed. The resultant digital data are normally made publicly available both in gridded and profile form along with the published contour maps. Most aeromagnetic coverage has been obtained in the developed western countries, but elsewhere a considerable amount of surveying has been carried out; as an example, some 80 percent of Africa has been surveyed mostly as a result of aid programs. The data is usually held by the national geological survey or equivalent organizations, but in a number of cases the data (e.g., for the Magnetic Anomaly Map of North America) is also held by the World Data Centres.

Hood, Peter↗
NASA NTRS1993

Geomagnetic field models incorporating frozen-flux constraints

An algorithm is developed for constructing plausible field models satisfying the frozen-flux hypothesis of Roberts and Scott (1965), which supposes that, for short time intervals, diffusion can be neglected. The algorithm is based on a new parameterization of the field in terms of its radial component B(r) at the core-mantle boundary (CMB). The model consists of values of B(r) at a finite set of points on the CMB, together with a rule for interpolating the values to other points. The parameterization of the B(r) is used to construct field models satisfying the frozen-flux hypothesis for the epochs 1945.5 and 1980.

Constable, Catherine G.↗
NASA NTRS1994

Separation of lithospheric, external, and core components of the south polar geomagnetic field at satellite altitudes

We present a new approach to producing scalar Magsat magnetic anomaly maps based on correlation coefficient filtering and the use of almost all of the available orbits. Our method differs from earlier techniques with respect to the following: (1) Passes are selected based on their variance properties rather than planetary indices such as Kp. (2) The core field model is least squares fit to individual passes and subsequently removed instead of substracting the model directly. This technique replaces band pass filtering or polynomial trend removal methods. (3) Each selected pass is sorted geographically and by local time, placed into one of four different altitude bands, and correlation coefficient filtered with the two adjacent passes. The filtering is the second step toward isolating the static lithospheric signal from the more dynamic external field signals. (4) Least squares collocation is used to grid the correlated passes; subsequently, the dawn and dusk maps are also correlation filtered providing another step toward removal of external fields. (5) The four resultant total field maps are continued to a common altitude and again correlation filtered for the static lithospheric anomalies. (6) The filtered results are then averaged together to provide a new total field map of the lithosphere south of 40 deg S latitude. Our total field map differs from previous efforts over the crustal blocks of West Antarctica. We obtained a positive anomaly over Edward VII Peninsula, extending into the Byrd subglacial basin and obtained a negative anomaly over the Ellsworth Mountains and parts of the Byrd subglacial basin. Also, a positive anomaly extending from the Ross Sea to offshore Wilkes Land is present in our map; however, this feature is absent in other maps. Positive anomalies marking the Weddell Sea in previous efforts are not present in our map. Prominent external field anomalies in the quadrant offshore of Wilkes Land are present in all previous efforts; however, these signatures are reduced in our total field map. This map significantly advances efforts for the identification and interpretation of magnetic anomalies of the south polar lithosphere.

Alsdorf, Douglas E.↗
NASA NTRS1995

SAMPEX studies of anomalous cosmic rays using the geomagnetic field

We report new measurements of the composition and energy spectra of anomalous cosmic rays (ACRs) made with the MAST instrument of SAMPEX. The 82 deg orbit on SAMPEX allows MAST to survey the magnetic latitude distribution of energetic particles with greater than 15 MeV/nuc. Because ACRs are singly-charged, they have a much greater magnetic rigidity than solar energetic particles or galactic cosmic rays with the same energy/nuc, and can be observed to much lower latitude. This allows SAMPEX to employ the Earth's field as a magnetic filter to obtain a 'pure' sample of ACR nuclei, uncontaminated by solar particles or galactic cosmic rays. We report new measurements of the composition and energy spectra of 'anomalous' nuclei from He to Fe observed by this 'double spectrometer' approach. In particular, the energy spectrum of ACR oxygen is observed to extend to approximately 100 MeV/nucleon, which has implications for the ACR acceleration mechanism.

Mewaldt, R. A.↗
NASA NTRS2000

Advances in Modeling the Generation of the Geomagnetic Field by the Using of Massively Parallel Computers and Profound Optimization

At the Earth's surface, the magnetic field that is observed is similar to that that would be generated by a simple bar magnet running through the Earth's axis. This idea (permanent magnetism) was commonly believed a century ago. Because the temperature of the core is so high, permanent magnetism is not possible. Therefore, the magnetic field should decay, over tens of thousands of years. Since it does not, the field must be regenerating. Since the turn of the century, the idea that the core is molten iron which by moving generates a magnetic field arose. The set of equations to describe this are extremely non-linear and complex. Only in the last five to ten years have computers been able to solve these equations.

Clune, Thomas↗
NASA NTRS1985

Variation of tidal winds in the ionosphere inferred from geomagnetic SQ field

The geomagnetic Sq field is mainly generated by the dynamo action of tidal winds in the ionosphere, and therefore some information can be derived from the variation of the Sq field. The geomagnetic Sq field was analyzed during March 1 to 18, 1980, when the geomagnetic activity was exceptionally low, and the equivalent Sq currents calculated every 2 hours by using the spherical harmonics method. Then additional Sq currents were extracted by subtracting the currents averaged through all days in the period from the original currents at each UT. The change of the instantaneous Sq current system by the above-mentioned method is discussed.

Takeda, M.↗
NASA NTRS2018

The International Space Station Space Radiation Environment: Avionics Systems Performance in Low-Earth Orbit Single Event Effects (SEE) Environments

Single event effects (SEE) are those errors, anomalies, or failures in microelectronic devices caused by the passage of a single energetic charged particle through the device. Spacecraft SEE environments consist primarily of energetic charged particles; both primary particles originating in the natural environment and secondary particles (including secondary neutrons) produced by nuclear reactions of primary particles with spacecraft materials. The energetic charged particle components (electrons, protons, and atomic nuclei) of the spacecraft SEE environment include galactic cosmic rays (GCR), and planetary radiation belt charged particles, as well as solar energetic particle event (SPE) charged particles. The International Space Station (ISS) orbital altitude and inclination (~350 km to ~420 km at 51.6o inclination) results in a spacecraft SEE environment that varies dramatically with the location in Earth?s geomagnetic field. Geomagnetic GCR shielding diminishes with distance from the geomagnetic equator. Near + 51.6o latitude the ISS GCR environment has a high degree of similarity to the interplanetary GCR environment in cis-Lunar space.SEE environments supporting ISS avionics systems design, development, test, and verification are documented in SSP-30512, Space Station Ionizing Radiation Design Environment. Comparisons of overall ISS avionics systems in-flight performance with pre-flight verification report predictions have been previously reported and meet or exceed expectations in all cases.In this paper we report the results of more detailed investigations of the effects of geographic location, altitude, solar cycle, and shielding mass effects on the in-flight SEE performance of the ISS command and data handling system during the past 17 years. In addition, we report on the preflight testing and in-flight performance of the commercial-off-the-shelf lap top computers used on ISS. Finally, we present an assessment of ISS as an avionics SEE test and flight demonstration platform for exploration hardware destined for the cis-lunar or other inner solar system environments.

International Space Station↗