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NASA NTRS1976

Extraterrestrial magnetic fields - Achievements and opportunities

The major scientific achievements associated with the measurement of magnetic fields in space over the past decade and a half are reviewed. Aspects of space technology relevant to magnetic-field observations are discussed: magnetometers and how they operate, problems arising from spacecraft-generated magnetic fields and appropriate countermeasures and on-board processing of magnetometer data. The solar wind and interplanetary magnetic field, the earth's magnetic field in space, the interaction of the solar wind with the planets, planetary magnetic fields, and the permanent magnetic fields of the moon are discussed. A fairly complete bibliography lists original contributions as well as more recent publications and review articles.

Smith, E. J.↗

NASA NTRS1976

Attitude transfer assembly design for MAGSAT

A description is given of a design for an instrument system that will monitor the orientation of a boom-mounted vector magnetometer relative to the main spacecraft body. The attitude of the magnetometer is measured with respect to X and Z axes lateral to the boom length and also a twist axis around the boom center line. These measurements are made in a noncontact optical approach employing a three-axis autocollimator system mounted on the main body of the spacecraft with only passive elements (reflectors) located at the end of the 20-foot boom.

Collyer, P. W.↗

NASA NTRS1977

A high accuracy all-angle gyroscope readout using quantized flux

Means are described to use SQUID magnetometer flux counting and the London moment of a spherical superconducting gyroscope to read out the gyroscope spin axis direction to an accuracy of at least 23 bits per quadrant. The system is discussed in analogy to optical fringe counting as applied to distance measurement. Several methods of applying both analog and digital SQUID magnetometers to the readout problem are given, as well as limitations on each. Described are two methods of increasing the flux available for measurement: magnetizing the gyroscope with a trapped field, and optimizing readout circuit inductances. Finally, the same principle on which the gyroscope readout is based is applied to a description of a high accuracy, flux counting, digital angle encoder.

Anderson, J. T.↗

NASA NTRS1976

The Jovian magnetosphere and magnetopause

The characteristics of the planet Jupiter's inner magnetosphere are examined, taking into account the Pioneer 10 and 11 magnetometer data. Data on the reliability of spherical harmonic expansions are presented in a table. The properties of the Jovian magnetosheath and magnetopause are described. Bow shock and magnetopause crossings were securely identified in plasma data and were usually identified in plasma data and were usually identifiable in the magnetometer data. Explanations for the large number of observed crossings are discussed. It is pointed out that in the case of the outer magnetosphere the observed field strength is nearly an order of magnitude larger than would be expected from Jupiter's dipole moment. The distinguishing characteristics of the magnetic field in the middle magnetosphere are also considered.

Davis, L., Jr.↗

NASA NTRS1976

Survey of the Pioneer 10 and 11 Jupiter mission

After a description of the Pioneer 10 and 11 spacecraft, the following scientific experiments are discussed: Helium Vector Magnetometer, Fluxgate Magnetometer, Plasma Analyzer, Geiger Tube Telescope, Cosmic Ray Telescope, Trapped Radiation Detector, Ultraviolet Photometer, Imaging Photopolarimeter, Infrared Radiometer, Asteroid-Meteoroid Detector, and Meteoroid detector. Also reviewed are the mission profile and status.

Wolfe, J. H.↗

NASA NTRS1976

Magnetic evidence concerning a lunar core

Two different methods were used to determine the lunar electromagnetic response: (1) comparison of Apollo 12 and Explorer 35 magnetometer data; and (2) observation of the dipole field configuration by orbiting Apollo 15 and 16 subsatellites. The methods give significantly different results. The subsatellite observations require the existence of a core, while the Apollo 12 and Explorer magnetometer measurements allow, but do not require, the existence of a core. Despite this, an upper limit of 580 km has been computed for the radius of the core.

Goldstein, B. E.↗

NASA NTRS1977

A new source of lunar electromagnetic induction - Forcing by the diamagnetic cavity

Analysis of the power spectral densities (PSD's) of eight 50-hour time series from Apollo 12 lunar surface magnetometer (LSM) and isochronous Explorer 35 Ames magnetometer data points to the existence of a new source of electromagnetic induction in the interior of the moon which is independent of the transverse electric mode. This source is hypothesized to arise from extension of the cavity diamagnetic field into the moon in analogy with the fringing field of a solenoid.

Sonett, C. P.↗

NASA NTRS1977

Magnetic field experiment for Voyagers 1 and 2

The magnetic field experiments of the Voyager program involve studies of the planetary fields of Jupiter, Saturn, possibly Uranus, and several satellites; the solar wind and satellite interactions with the planetary fields, as well as large- and micro-scale features of the interplanetary magnetic field will also be investigated. Dual low field and high field magnetometer systems with dynamic ranges of + or - 0.5 G and + or - 20 G respectively provide high reliability for the missions and permit the separation of the spacecraft and ambient fields. Quantization uncertainty, rms noise levels and data compaction schemes of the magnetometer systems are also mentioned.

Behannon, K. W.↗

NASA NTRS1977

Geologic-magnetic correlations on the moon - Apollo subsatellite results

Comparison of the magnetic-field measurements of the Apollo subsatellite magnetometers with USGS geologic maps suggests that the ancient lunar field may have been greater during the Imbrian Period than the earlier Pre-Nectarian and Nectarian periods. Further, the field seems to have varied in direction. These data are consistent with a model in which the ancient lunar magnetizing field arises from a core dynamo which does not form until the Imbrian Period. Impacts during this period then result in magnetized crater melt and ejecta blankets. It is emphasized, however, that the area sampled by the subsatellite magnetometers is but a small fraction of the lunar surface. These results must be confirmed with studies of independent regions of the lunar surface before they can be considered conclusive.

Russell, C. T.↗

NASA NTRS1979

Satellite to study earth's magnetic field

The Magnetic Field Satellite (Magsat) designed to measure the near earth magnetic field and crustal anomalies is briefly described. A scalar magnetometer to measure the magnitude of the earth's crustal magnetic field and a vector magnetometer to measure magnetic field direction as well as magnitude are included. The mission and its objectives are summarized along with the data collection and processing system.

Source record↗

NASA NTRS1978

Biomagnetic instrumentation and measurement

The instruments and techniques of biomagnetic measurement have progressed greatly in the past 15 years and are now of a quality appropriate to clinical applications. The paper reports on recent developments in the design and application of SQUID (Superconducting Quantum Interference Device) magnetometers to biomagnetic measurement. The discussion covers biomagnetic field levels, magnetocardiography, magnetic susceptibility plethysmography, ambient noise and sensor types, principles of operation of a SQUID magnetometer, and laboratory techniques. Of the many promising applications of noninvasive biomagnetic measurement, magnetocardiography is the most advanced and the most likely to find clinical application in the near future.

Iufer, E. J.↗

NASA NTRS1981

Improved LEEM ranges over four decades

Low-energy electron magnetometer is suitable for terrestrial and aerial applications. Electron beam strikes tantalum collector plates in device, amplifying current and converting it to frequency. Current difference increases with beam deflection, providing measure of local field strength. LEEM operation requires no liquid helium unlike superconducting quantum interference device. LEEM sensitivity compares favorably with that of optical absorption magnetometers, and microsecond response range makes analyzing fast magnetic transients and signatures possible.

Singh, J. J.↗

NASA NTRS1980

Space applications of superconductivity - Low frequency superconducting sensors

Although this paper deals with several low-frequency instruments and devices, most of the discussion relates to SQUID (Superconducting QUantum Interference Device) magnetometers and gradiometers, since these are perceived as the instruments with the greatest potential for space applications. The discussion covers SQUID for magnetic field measurements; present state of the art of SQUID technology; ultimate potential performance; applications to magnetic measurements in space; SQUID galvanometers, voltage and current sensors, and wide-band amplifiers; magnetic shielding, and superconducting dc transformer. SQUIDS are superior to all other magnetic sensors in sensitivity, frequency response, range, and linearity. It is suggested that SQUID instruments, both magnetometers and gradiometers, would be valuable in studies of the dynamics of interplanetary and planetary fields. SQUID gradiometers are useful for detection and mapping of magnetic anomalies at short to moderate ranges.

Zimmerman, J. E.↗

NASA NTRS1979

Electrical conductivity anomalies associated with circular lunar maria

A strong anisotropy is observed in magnetic field fluctuations measured by the Lunokhod 2 magnetometer located on the eastern edge of Mare Serenitatis. This anisotropy can be explained by a regional anomaly in the subsurface electrical conductivity distribution associated with the mare similar to the proposed conductivity anomaly associated with Mare Imbrium. The Serenitatis magnetic field anisotropy is compared to the field fluctuation measured by the Apollo 16 magnetometer 1100 km to the south, and this comparison indicates that the subsurface conductivity distribution can be modeled by a nonconducting layer in the lunar lithosphere which is 150 km thick beneath the highlands and 300 km thick beneath Serenitatis. The decrease in electrical conductivity of the upper mantle beneath the mare may result from lower temperatures due to transport of thermal energy and radioactive heat sources to the surface during mare flooding. This proposed anomaly, along with that proposed for Mare Imbrium, strengthens the possibility of regional anomalies in electrical conductivity associated with all circular lunar maria.

Dyal, P.↗

NASA NTRS1980

Simultaneous observations of field-aligned currents and plasma drift velocities by Atmosphere Explorer C

The three-axis flux gate magnetometer on board the Atmosphere Explorer C (AE-C) has provided an additional magnetic field data set to the already broad spectrum of AE-C measurement. The results of an investigation into the feasibility of using the magnetometer for scientific purposes are described. It is shown that within the limitations inherent in the device and in the data reduction technique used, meaningful results can be obtained when the spacecraft is in the spinning mode. From a comparison between the field-aligned current signatures and the simultaneously observed ion convection velocity, it proved possible to locate regions of ionospheric conductivity gradients.

Bythrow, P. F.↗

NASA NTRS1980

The suprathermal electron contributions to high-latitude Birkeland currents

The paper extends the search for return current carriers to the thermal energy range for electrons, using simultaneous observations on Isis 2 by a magnetometer, retarding potential analyzer, and soft particle spectrometer. Each instrument is described along with data available. Simple magnetic models are used to illustrate how magnetic perturbations may be interpreted as currents remote from the satellite or local to it and that the choice of model cannot be uniquely established by magnetometer measurements alone.

Maier, E. J.↗

NASA NTRS1976

Geomagnetic field mapping from a satellite: Spatial power spectra of the geomagnetic field at various satellite altitudes relative to natural noise sources and instrument noise

The spectra for the field are presented together with power spectra of the natural magnetospheric and ionosheric noise and a power spectrum of instrumental noise for a typical fluxgate magnetometer. The source of these data is described. The implications of these data relative to desirable instrument frequency resonse, stability and resolution specification as well as the implications relative to desirable spacecraft position and orientation accuracy specifications and desirable environmental (temperature, magnetic noise) specifications are discussed. Implications of these power spectra relative to choice of a suitable magnetometer and relative to desirable methods of data processing are considered. Finally, implications for desirable orbit and mission duration are discussed.

Mcleod, M. G.↗

NASA NTRS1981

Application of microprocessors in an upper atmosphere instrument package

A servo-driven magnetometer table measuring offset from magnetic north has been developed by NASA to calculate payload azimuth required to point at a celestial target. Used as an aid to the study of gamma-ray phenomena, the high-altitude balloon-borne instrument determines a geocentric reference system, and calculates a set of pointing directions with respect to the system. Principal components include the magnetometer, stepping motor, microcomputer, and gray code shaft encoder. The single-chip microcomputer is used to control the orientation of the system, and consists of a central processing unit, program memory, data memory and input/output ports. Principal advantages include a low power requirement, consuming 6 watts, as compared to 30 watts consumed by the previous system.

Lim, T. S.↗