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At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

On the applicability of integrated circuit technology to general aviation orientation estimation

The criteria of the significant value of the panel instruments used in general aviation were examined and kinematic equations were added for comparison. An instrument survey was performed to establish the present state of the art in linear and angular accelerometers, pressure transducers, and magnetometers. A very preliminary evaluation was done of the computers available for data evaluation and estimator mechanization. The mathematical model of a light twin aircraft employed in the evaluation was documented, the results of the sensor survey and the results of the design studies were presented.

Debra, D. B.↗
NASA NTRS1977

Magnetic field experiment for Voyagers 1 and 2

The magnetic field experiment to be carried on the Voyager 1 and 2 missions consists of dual low field (LFM) and high field magnetometer (HFM) systems. The dual systems provide greater reliability and, in the case of the LFM's, permit the separation of spacecraft magnetic fields from the ambient fields. Additional reliability is achieved through electronics redundancy. The wide dynamic ranges of plus or minus 0.5G for the LFM's and plus or minus 20G for the HFM's, low quantization uncertainty of plus or minus 0.002 gamma in the most sensitive (plus or minus 8 gamma) LFM range, low sensor RMS noise level of 0.006 gamma, and use of data compaction schemes to optimize the experiment information rate all combine to permit the study of a broad spectrum of phenomena during the mission. Planetary fields at Jupiter, Saturn, and possibly Uranus; satellites of these planets; solar wind and satellite interactions with the planetary fields; and the large-scale structure and microscale characteristics of the interplanetary magnetic field are studied. The interstellar field may also be measured.

Behannon, K. W.↗
NASA NTRS1977

On the origin of the Bangui magnetic anomaly, central African empire

A large magnetic anomaly was recognized in satellite magnetometer data over the Central African Empire in central Africa. They named this anomaly the Bangui magnetic anomaly due to its location near the capital city of Bangui, C.A.E. Because large crustal magnetic anomalies are uncommon, the origin of this anomaly has provoked some interest. The area of the anomaly was visited to make ground magnetic measurements, geologic observations, and in-situ magnetic susceptibility measurements. Some rock samples were also collected and chemically analyzed. The results of these investigations are presented.

Marsh, B. D.↗
NASA NTRS1977

Magsat: A satellite for measuring near earth magnetic fields

Magsat, designed for making measurements of the geomagnetic vector field, is evaluated. For accurate vector measurements the attitude of the fluxgate magnetometer will be determined to about 15 arc-seconds. Expected measurement accuracy will be 6 (gamma) in each component and 3 in magnitude. The Magsat data will be applied to solid earth studies including modeling of the Earth's main magnetic field, delineation of regional magnetic anomalies of crustal origin, and interpretation of those anomalies in terms of geologic and geophysical models. An opportunity will be presented to the scientific community to participate in data use investigations.

Langel, R. A.↗
NASA NTRS1976

Jupiter's magnetic field and magnetosphere

The Jovian magnetosphere is described on the basis of observations made by vector helium magnetometers aboard Pioneers 10 and 11. The results obtained from the two encounters are combined without emphasizing details peculiar to either of them. It is shown that near the planet, Jupiter's field is that of an eccentric tilted dipole with some admixture of higher-order terms; in this respect, it is similar to the earth's field, although it is 10 times as strong and has the opposite polarity. The magnetic field measurements reveal the existence of 3 distinct regions within the magnetosphere: outer magnetosphere, inner magnetosphere, and middle magnetosphere. The properties of these three regions are discussed, with observations being explained in terms of plausible physical causes. The observations are compared with several large-scale models of the entire magnetosphere. These observations do not favor models based on the continual outflow or convection of plasma from the Jovian magnetosphere in the vicinity of the equator.

Smith, E. J.↗
NASA NTRS1976

On the occurrence of magnetopause crossings at 6.6 RE

The vector magnetometer data from the ATS-1 spacecraft in synchronous orbit for the period of December 1966 to December 1968 were scanned. Magnetopause crossings were identified by sudden changes in field magnitude accompanied by directional changes and increased noise levels. There was little difficulty in identifying magnetopause traversals near noon at synchronous orbit within 6.6 earth radii. Magnetopause traversals were observed on 5 of the 545 days, ranging in duration from 1 min to over 3 hr. Extrapolating the magnetopause crossing statistics to lower radial distances linearly on a semilog plot suggests that the noon magnetopause is flatter at disturbed times than at quiet times.

Russell, C. T.↗
NASA NTRS1976

Variations in plasma characteristics near D sheets in the solar wind

A strong interplanetary shock was detected by the Pioneer 8 magnetometer, plasma probe, and wave instrument at 0048 UT, on June 11, 1968. During the rest of this day the interplanetary medium was highly disturbed as seven well-defined current layers or D sheets, as well as a number of other localized interaction regions, swept past the spacecraft. The local plasma characteristics that were best correlated with passage of the D sheets appeared to involve changes in the suprathermal electron population. Changes in the 400-Hz wave levels were also detected near the discontinuities during periods when the local ion plasma frequency was near 400 Hz, but the limited measurement capability of the Pioneer 8 wave instrument does not allow an unambiguous identification of the wave-particle interactions associated with these measurements.

Scarf, F. L.↗
NASA NTRS1976

Field-aligned currents in the Jovian magnetosphere - Pioneer 10 and 11

Field-aligned currents, which are known to play an important role in the dynamics of the earth's magnetosphere, would also be expected to flow in the Jovian magnetosphere during magnetically active periods. Such currents are difficult to observe largely because of their limited spatial extent and intermittent nature, but on the Pioneer 11 inbound pass to Jupiter on day 336, 1800 GRT, near the L shell of Ganymede, the helium vector magnetometer recorded a structured perturbation with the characteristic signature of a field-aligned current. No analogous structure was found on a similar Pioneer 10 inbound pass (day 337, 1200 GRT). The perturbation could have been caused by turbulence with the wake of Ganymede through which the spacecraft was moving or the perturbation could represent the first observation of a Jovian substorm. The observations are discussed in terms of both models, and difficulties are examined.

Kivelson, M. G.↗
NASA NTRS1976

On tenuous plasmas, fireballs, and boundary layers in the earth's magnetotail

The plasma instrumentation (the Lepedea) and the magnetometer aboard IMP 8 performed correlative measurements of magnetic fields and plasmas within the geomagnetic tail at geocentric radial distances of about 23-46 R-E during March-October 1974. The hot tenuous plasmas within the plasma sheet were found to be in a state of almost continuous flow and were threaded with northward, or closed geomagnetic lines. The satellite encountered a region of acceleration in the magnetotail, the 'fireball' which exhibits strong jetting of plasmas in excess of 1000 km/s, proton temperatures of about 10 to the 7th K, disordered magnetic fields, southward magnetic fields during tailward jetting of plasmas, and northward magnetic fields for fast plasma flows toward earth. In addition, the magnetosheath plasmas within the boundary layers which are contiguous to the plasma sheet display evidence of plasma heating, great changes in bulk flow velocities, and acceleration of energetic electrons with an energy of greater than 45 keV.

Frank, L. A.↗
NASA NTRS1976

A statistical study of Pc 1 magnetic pulsations at synchronous orbit

The statistical properties of Pc 1 magnetic pulsations at synchronous orbit are examined by using measurements obtained with the UCLA flux-gate magnetometer on board ATS 1. In 1967, 121 intervals of Pc 1 activity occurred. These events typically had amplitudes of 1-7 gamma and periods of 2-5 sec. Most events lasted less than 30 min and occurred in the afternoon sector. Pc 1 waves were more probable during the main phase of a geomagnetic storm, within 1 hour of a substorm expansion. While they do not have the signature of IPDP (intervals of pulsations of diminishing periods) events at ATS, simultaneous ground records show the occurrence of rising frequency tones characteristic of IPDP events in seven out of ten cases. The wave frequency ranged principally from 0.1 to 0.2 of the local proton gyrofrequency, similar to observations of electron cyclotron waves. The observed Pc 1 activity is consistent with the generation by cyclotron resonance of 30-keV protons in a 30/cu cm plasma.

Bossen, M.↗
NASA NTRS1977

Observation of a structured auroral field-aligned current system

A rocketborne experiment package was launched over a structured auroral arc from Poker Flat, Alaska, at 0722 UT on February 25, 1972. The results of the flight vector-magnetometer data have been detailed by Casserly and Cloutier (1975), who report the detection of a pair of oppositely directed Birkeland current sheets associated with the auroral band. This association has now been extensively investigated, and it has been shown that some observed structures in the arc due to the presence of a fold are also evident in the Birkeland current system. In particular, the field-aligned current to the east of the fold is at a higher geomagnetic latitude than the current to the west of the fold. Variations in other model current parameters are also shown to be well correlated with changes in the visual arc system.

Casserly, R. T., Jr.↗
NASA NTRS1977

A high accuracy gyroscope readout test facility for the relativity gyroscope experiment

An apparatus is under construction for ground-based testing of a gyroscope system to be used in a satellite test of general relativity. The immediate goal is a readout capable of measuring the direction of the gyroscope spin axis to an angular resolution of one arcsecond over a limited range. A combination of SQUID magnetometers and persistent current loops are used to measure the London moment of the spinning superconducting rotor levitated electrostatically. To obtain a trapped flux signal in the gyroscope sufficiently smaller than the London moment signal, the apparatus makes use of a new magnetic field shielding technique for obtaining large superconductor shielded regions below 0.1 millionth of a Gauss.

Cabrera, B.↗
NASA NTRS1977

The storm-time equatorial electrojet

A Petrel rocket carrying a double cell rubidium magnetometer was launched from the Thumba Equatorial Rocket Launching Station during the early main phase of a magnetic storm. No ionospheric currents associated with the storm were observed, and the large field depression at the flight time must therefore be attributed to currents at higher altitudes. The equatorial enhancement of ionospheric magnetic storm currents, predicted on the basis of theory and earlier ground data, was not observed.

Burrows, K.↗
NASA NTRS1976

Shear dampers for deflections of micro-inch magnitudes

The rotation of the TV camera on the Mariner Jupiter/Saturn 1977 (MJS77) spacecraft will excite the long magnetometer and heavy RTG booms which are slightly damped perturbances that have long settling times. To ensure clear TV pictures additional damping was required over micro-inch displacements and at low frequencies. The solution incorporated elastomeric shear dampers at the base of these booms which possessed high loss tangent values in the expected frequency and temperature ranges. Presented are the shear damper design, results of full scale horizontal boom tests and relative effects of damper sizing and temperature. Boom instrumentation and excitation used for the full scale tests are also discussed.

Otth, D.↗
NASA NTRS1977

A statistical study of Pc 3 magnetic pulsations at synchronous orbit, ATS 6

Results are reported for a study designed to determine statistically the nature and variation of the polarization parameters of Pc3 magnetic pulsations at synchronous orbit. Data obtained with a triaxial flux gate magnetometer on the geosynchronous satellite ATS 6 are subjected to routine power spectral and polarization analyses, and the events examined are identified as peaks in the spectra. Coherence analysis of spectral matrices for these events indicates that Pc3 are very common at synchronous orbit and are primarily a local morning phenomenon with an occurrence peak around 1000 LT; that the pulsations occur at all frequencies in the Pc3 band, with the most common frequency at about 0.35 Hz; that the Pc3 at synchronous orbit are most often linear and generally transverse, but some have significant compressional components; and that based on azimuth angle, there are two distinct classes of Pc3 (azimuthal and radial) with different characteristics. These statistical results are compared with model predictions and ground-based observations.

Arthur, C. W.↗
NASA NTRS1977

The remanent magnetic field of the moon

Measurements of the moon's remanent magnetic field near the Apollo landing sites and from lunar orbit with the Apollo subsatellites are reviewed. Contour maps are presented for the intensity of the radial, eastward, and northward components of the remanent field as measured with Apollo subsatellite magnetometers at altitudes of 10 to 170 km. Attempts to fit the subsatellite measurements to various models are discussed along with indirect measurements of the remanent field. It is shown that scale sizes of field sources range from 1 to at least 100 km, that the magnetic fields on the far side are stronger and more variable than those on the near side, and that the lunar remanent field apparently exhibits a significant latitude dependence. The origin of the field responsible for the remanent magnetization is considered.

Coleman, P. J., Jr.↗
NASA NTRS1977

The magnetopause at 5.2 R/E/ in August 1972 - Magnetopause motion

The paper analyzes magnetic field records from ATS 5 and Explorer 45 satellites, provided with triaxial flux gate magnetometer, during the close approach of the magnetopause to the earth. Attention is directed to a discussion of the observing arrangements, a detailed comparison of the two sets of observations, and an interpretation of the magnetopause motion and of magnetic pulsations. The pulsations appear not to be due to surface waves propagating in the magnetopause.

Cahill, L. J., Jr.↗
NASA NTRS1977

The magnetopause at 5.2 R/E/ on August 4, 1972 - Magnetopause shape and structure

The relatively large magnitude magnetopause field observed in several crossings associated with the ATS 5 and Explorer 45 satellites on August 4, 1972, is used to examine the structure of the magnetopause. The discussion covers magnetopause normals and their intepretation with respect to the shape of the magnetopause and to waves propagating in the magnetopause; magnetopause structure in terms of the field changes observed during magnetopause passages and of the associated magnetopause electric currents interred from the observations; and comparison of the observations with theoretical properties of open and close magnetopause models. Features necessary for comparison of magnetometer observations with pertinent theories are highlighted.

Kaufmann, R. L.↗