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All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

PC 4 - PC 1 magnetic pulsations at synchronous orbit and their relation to pulsations on the ground

Three types of Pc 4 pulsations with periods in the range 40-200 s have been identified in the ATS 6 satellite data. Two types are not observed on the ground. Both of these are accompanied by Pc 1-2 activity that is seen simultaneously both at the satellite and on the ground. One of these two types occurs during substorms and coincides with the development of the IPDP subtype of Pc 1-2. The other is observed in the magnetosphere during slow, smooth changes of the background magnetic field during the recovery phase of storms. Puslation amplitude for these two types is from 5 to several tens of nanoTeslas. The third type of Pc 4 pulsation has significantly smaller amplitudes in the magnetosphere and can be observed on the ground with amplitudes usually greater than in the magnetosphere. The properties of the first two types of long-period pulsations suggest that the mechanism for their generation is the drift-dissipative instability of the ring current plasma.

Maltseva, N.↗
NASA NTRS2008

Magnetic Field Observations of Partial Ring Current during Storm Recovery Phase

We present results of an extensive survey of the magnetic field observations in the inner magnetosphere using 30 years of magnetospheric magnetic field data from Polar, Cluster, ISEE, and AMPTE/CCE missions. The purpose of this study is to understand the magnetic field evolution during the recovery phase of geomagnetic storms, and its implication to the ring current recovery and loss mechanisms of ring current particles. It is now commonly believed that a strong partial ring current is formed during the storm main phase due to the enhanced earthward convection of energetic ions from nightside plasma sheet. But the presence of a strong partial ring current throughout the recovery phase remains controversial. The magnetic field generated by the ring current inflates the inner magnetosphere and causes magnetic field depressions in the equatorial magnetosphere. During the storm recovery phase, we find that the distribution of the equatorial magnetic field depression exhibits similar local time dependence as the ring current distribution obtained from the combined dataset in the earlier study. It shows that a strong partial ring current is a permanent feature throughout the recovery phase. In the early recovery phase, the partial ring current peaks near the dusk terminator as indicated by the peak of the magnetic field depression. As the recovery phase progresses, the partial ring current decays most quickly near the dusk and results in a dusk-to-midnight moving of the peak of the partial ring current. Thus the loss mechanisms work most effectively near the dusk. The magnetic field depression increases the gyroradius of ring current protons to a scale greater or comparable to the thickness of the magnetopause, which increases the chance of ion drift loss near the dusk magnetopause at larger L-shell (L greater than 5). But the drift loss mechanism alone cannot explain the loss of ring current ions especially in the smaller L-shell (L less than 5). The precipitation loss due to wave-particle interaction is most likely the dominant loss mechanism in the small L-shell as it works most effectively at the same local time.

Le, G.↗
NASA NTRS2007

Magnetic Field Observations of Partial Ring Current during Storm Recovery Phase

We present results of an extensive survey of the magnetic field observations in the inner magnetosphere using 30 years of magnetospheric magnetic field data from Polar, Cluster, ISEE, and AMPTE/CCE missions. The purpose of this study is to understand the magnetic field evolution during the recovery phase of geomagnetic storms, and its implication to the ring current recovery and loss mechanisms of ring current particles. Our previous work on global ring current distribution [Le et al., 2004] has shown that a significant partial ring current is always present at all Dst levels (regardless of storm phases) even for quiet time ring current. The total current carried by the partial ring current is much stronger than (during stormtime) or at least comparable to (during quiet time) the symmetric ring current. It is now commonly believed that a strong partial ring current is formed during the storm main phase due to the enhanced earthward convection of energetic ions from nightside plasma sheet. But the presence of a strong partial ring current throughout the recovery phase remains controversial. The magnetic field generated by the ring current inflates the inner magnetosphere and causes magnetic field depressions in the equatorial magnetosphere. During the storm recovery phase, we find that the distribution of the equatorial magnetic field depression exhibits similar local time dependence as the ring current distribution obtained from the combined dataset in the earlier study. It shows that a strong partial ring current is a permanent feature throughout the recovery phase. In the early recovery phase, the partial ring current peaks near the dusk terminator as indicated by the peak of the magnetic field depression. As the recovery phase progresses, the partial ring current decays most quickly near the dusk and results in a dusk-to-midnight moving of the peak of the partial ring current. Thus the loss mechanisms work most effectively near the dusk. The magnetic field depression increases the gyroradius of ring current protons to a scale greater or comparable to the thickness of the magnetopause, which increases the chance of ion drift loss near the dusk magnetopause at larger L-shell (L>5). But the drift loss mechanism alone cannot explain the loss of ring current ions especially in the smaller L-shell (L<5). The precipitation loss due to wave-particle interaction is most likely the dominant loss mechanism in the small L-shell as it works most effectively at the same local time.

Le, Guan↗
NASA NTRS1981

The rigidity dependence of cosmic ray solar modulation

Continuous particle flux measurements above rigidity thresholds of 1.2, 2.2, 5.5 and 11 GV were made by using the thresholds of two Cerenkov detectors aboard the ISEE-3 spacecraft. The ISEE-3 was launched in August 1978, near the beginning of the current solar cycle's heavy modulation phase, and the data presented represent the first direct measurement made at these energies with such a long time base. The measured long term modulation rigidity spectrum is compared with other data and with the spectrum of Forbush decreases, and it is found that the agreement between electron and positively charged particle results must be considered a constraint on cosmic ray modulation models involving the mechanism of gradient and curvature drift in the interplanetary magnetic field.

Evenson, P.↗
NASA NTRS2010

Large-Scale Aspects and Temporal Evolution of Pulsating Aurora

Pulsating aurora is a common phenomenon generally believed to occur mainly in the aftermath of a, substorm, where dim long-period pulsating patches appear. The study determines the temporal and spatial evolution of pulsating events using two THEN IIIS ASI stations, at Gillam (66.18 mlat, 332.78 mlon, magnetic midnight at 0634 UT) and Fort Smith, (67.38 mlat, 306.64 mlon, magnetic midnight at, 0806 UT) along roughly the same invariant latitude. Parameters have been calculated from a database of 74 pulsating aurora events from 119 days of good optical data within the period from September 2007 through March 2008 as identified with the Gillam camera. It is shown that the source region of pulsating aurora drifts or expands eastward, away from magnetic midnight, for pre-midnight onsets and that the spatial evolution is more complicated for post midnight onsets, which has implications for the source mechanism. The most probable duration of a pulsating aurora event is roughly 1.5 hours while the distribution of possible event durations includes many long (several hours) events. This may suggest that pulsating aurora is not strictly a substorm recovery phase phenomenon but rather a persistent, long-lived phenomenon that may be temporarily disrupted by auroral substorms. Observations from the Gillam station show that in fact, pulsating aurora is quite common with the occurrence rate increasing to around 60% for morning hours, with 6910 of pulsating aurora onsets occurring after substorm breakup.

Jones, S. L.↗
NASA NTRS1976

Simultaneous Pc 1 observations by the synchronous satellite ATS-1 and ground stations - Implications concerning IPDP generation mechanisms

Results are presented for an experimental study designed to examine the properties of Pc 1 activity observed simultaneously at ATS 1 and two Canadian ground stations. The Pc 1 activity is found to follow substorm expansion phase onsets and to occur most frequently at dusk. Dynamic spectra waves at both ground stations are that of IPDP (Intervals of Pulsations Diminishing by Period) type Pc 1. A previously proposed mechanism to explain IPDP generation, which required a rapid increase in the equatorial magnetic field to produce IPDP, is inconsistent with the dynamic spectra and magnetic field observations. Either purely azimuthal or a combination of azimuthal and radial inward drift of energetic resonant protons is an equally plausible mechanism to explain IPDP generation.

Bossen, M.↗
NASA NTRS1993

Spacecraft signal sources portable test system

There is a frequent need to measure the frequency stability and phase noise levels of very high performance signal sources that are required for certain spacecraft missions. These measurements need to be done at different locations as the spacecraft subsystems progress through the various stages of development, assembly, test, and integration. Allan Deviation and Phase Noise of high performance sources are generally measured by comparing the unit under test to a reference standard. Five basic requirements are associated with making these kind of measurements: (1) the reference standard performance needs to be equal or better than the unit under test; (2) the measurement system needs to accommodate odd, nonstandard measurement frequencies that can range from 4 MHz to 35 GHz; (3) warm-up frequency drift and aging can corrupt a measurement and must be dealt with; (4) test equipment generated noise must be understood and prevented from limiting the measurements; (5) test equipment noise performance must be verifiable in the field as needed. A portable measurement system that was built by JPL and used in the field is described. The methods of addressing the above requirements are outlined and some measurement noise floor values are given. This test set was recently used to measure state of the art crystal oscillator frequency standards on the TOPEX and MARS OBSERVER spacecraft during several stages of acceptance tests.

Kirk, Albert↗
NASA NTRS1972

A space maintainability experiment aboard the Ben Franklin submersible during the 30-day Gulf Stream drift mission.

In the summer of 1969, a deep submersible drifted for 30 days below the surface of the Gulf Stream, while operated by a six man crew. The main purpose of the mission was oceanographic research. The crew's activities and completely self-contained environment resembled those of a space station such as Skylab. Because of these similarities aspects of onboard vehicle maintenance during the actual conduct of a scientific mission were investigated. The maintainability study was accomplished in six distinct phases. Two useful plots of manpower distribution were developed. A maintenance action summary is presented in a table.

Kappler, J. R.↗
NASA NTRS1973

High latitude proton precipitation and light-ion density profiles during the magnetic storm initial phase

Measurements of precipitating protons and light ion densities by experiments on OGO-4 indicate that widespread proton precipitation occurs in predawn hours during the magnetic storm initial phase from the latitude of the high-latitude ion trough, or plasmapause , up to Lambda 75 deg. A softening of the proton spectrum is apparent as the plasmapause is approached. The separation of the low-latitude precipitation boundaries for 7.3 kev and 23.8 kev protons is approximately 1 deg, compared with a 3.6 deg separation which has been computed using the formulas of Gendrin and Eather and Carovillano. Consideration of probable proton drift morphology leads to the conclusion that protons ase injected in predawn hours, with widespread precipitation occurring in the region outside the plasmapause. Protons less energetic than approximately 7 kev drift eastward, while the more energetic protons drift westward, producing the observed dawn-dusk asymmetry for the lower-energy protons.

Burch, J. L.↗
NASA NTRS1974

Optimizing signal-to-error ratio in standing wave ultrasonic measurements

Standing wave ultrasonic techniques for the measurement of very small changes in acoustic attenuation and phase velocity are discussed. Enhanced sensitivity to these small changes was achieved by making the specimen part of a composite ultrasonic resonator. It was found that a point of maximum sensitivity on the response of such an ultrasonic resonator need not coincide with a point of maximum signal-to-error ratio. A model is presented and analyzed which takes into account error due to long term (low frequency) noise effects such as gain drifts and dc level shifts. This model yields a quantitative value for the signal-to-error ratio in which the signal is defined as the ideal change in the monitored response and the error as the difference between the experimentally measured change and the signal. The specific frequency dependent forms for the ultrasonic response and the sensitivity enhancement factor were used to predict the operating point on a mechanical resonance corresponding to maximum signal-to-error ratio.

Brown, J. J.↗
NASA NTRS1974

Theoretical researches into planetary atmospheres and their influence upon surface features

The interface between certain geological and atmospheric phenomena on Mars was studied by examining those geological features which are associated with the presence of water in the liquid or solid phases. Several classes of Martian surface features thought to have had their origins in flow processes were studied in order to determine the role ice may have played in their creations. Preliminary studies concerning the behavior of Martian ice shelves were conducted, with the conclusion that flow rates of Martian and earth ice sheets are similar. Withdrawal of subsurface ice was found to be among the explanations for the origins of the chaotic terrains and drifted blocks.

Goody, R.↗
NASA NTRS1990

Optimization of the effective GPS data rate

Ohio University's Avionics Engineering Center is performing research directed towards the integration of the NAVSTAR Global Positioning System (GPS) and the Inertial Navigation System (INS) for attitude and heading determination. The integration of GPS/INS offers synergistic benefits. INS gyro drift error can be compensated by the long-term stability of GPS by means of an in-flight data monitoring algorithm. Using GPS data as a reference is more advantageous than implementing an additional INS since GPS offers a dissimilar redundancy to the attitude and heading determination configuration. In converse, the short-term stability of the INS can be used to correct or substitute for faulty GPS data due to tracking loop phase lag or data gaps because of satellite shielding. The optimization of the effective GPS data rate is essential for the proper execution of an integrated GPS/INS in-flight algorithm. GPS attitude and heading information must be consistently available during INS outages. Present research efforts involve the development of an in-flight algorithm that maximizes the potential of integrated GPS/INS. This algorithm determines the acceptable limits of phase lag that the GPS tracking loop introduces to the flight control system (FCS) during the transmission of information. Once these calculated limits are exceeded, INS data are used to insure the continuous availability of attitude and heading information to the flight control system.

Mcintyre, David S.↗
NASA NTRS1989

Simultaneous observations of neutral winds and electric fields at spaced locations in the dawn auroral oval

Results are presented on simultaneous observations of neutral winds and electric fields at spaced locations in the dawn auroral oval, carried out during a chemical release experiment on March 21, 1987. The observed plasma drifts and electron densities indicated the presence of a significant coupling between plasma and neutrals at the altitude of the F region but little coupling in the lower E region. The wind variations in the height range between 95 and 130 km were suggestive of the variations and amplitudes expected if the flow was dominated by the semidiurnal tide. However, a comparison of the flow with the model developed by Forbes (1982) showed that the phase differs by 4-5 hours from the predictions. Moreover, the measured divergence and vorticity in the flow are much larger than those predicted by the model, indicating that higher-order modes than those treated by Forbes may contribute significantly to the high-latitude thermospheric flow.

Larsen, M. F.↗
NASA NTRS1993

Ion Measurements During Pioneer Venus Reentry: Implications for Solar Cycle Variation of Ion Composition and Dynamics

During the final, low solar activity phase of the Pioneer Venus mission, the Orbiter Ion Mass Spectrometer measurements found all ion species, in the midnight-dusk sector, reduced in concentration relative to that observed at solar maximum. Molecular ion species comprised a greater part of the total ion concentration as O(+) and H(+) had the greatest depletions. The nightside ionospheric states were strikingly similar to the isolated solar maximum "disappearing" ionospheres. Both are very dynamic states characterized by a rapidly drifting plasma and 30-100 eV superthermal O(+) ions.

Grebowsky, J. M.↗
NASA NTRS1992

Formation of the stable auroral arc that intensifies at substorm onset

Observational evidence that the auroral arc that intensifies at substorm onset is formed on magnetic field lines that map to within about 1 to 2 Re of synchronous orbit, where plasma pressures are about 1 to 10 nPa during the substorm growth phase, is discussed. It is proposed that the arc is formed by a perpendicular magnetospheric-current divergence that results from a strong dawn-to-dusk directed pressure gradient in the vicinity of magnetic midnight. It is estimated that the current divergence is sufficiently strong that a greater than 1 kV field-aligned potential drop is required to maintain ionospheric-current continuity. It is suggested that the azimuthal pressure gradient results from proton drifts in the vicinity of synchronous orbit that are directed nearly parallel to the cross-tail electric field.

Lyons, L. R.↗
NASA NTRS1975

The MVM imaging system and its spacecraft interactions

The present work describes the main considerations and steps taken in determining the functional design of the imaging system of the Mariner Venus/Mercury (MVM) spacecraft and gives examples of some of the interactions between the spacecraft and the imaging instrument during the design and testing phases. Stringent cost and scheduling constraints dictated the use of the previous Mariner 9 dual-camera TV system. The TV parameters laid the groundwork for the imaging definition. Based on the flyby distances from Venus and Mercury and the goal of surface resolution better than 500 meters per sample pair, calculation was performed on focal length, format size, planetary coverage, and data rates. Some problems encountered in initial mechanical operation and as a result of spacecraft drift during the mission are also discussed.

Vescelus, F. E.↗
NASA NTRS1993

Ion measurements during Pioneer Venus reentry: Implications for solar cycle variation of ion composition and dynamics

During the final, low solar activity phase of the Pioneer Venus (PV) mission, the Orbiter Ion Mass Spectrometer (OIMS) measurements found all ion species, in the midnight-dusk sector, reduced in concentration relative to that observed at solar maximum. Molecular ion species comprised a greater part of the total ion concentration as O(+) and H(+) had the greatest depletions. The nightside ionospheric states were strikingly similar to the isolated solar maximum 'disappearing' ionospheres. Both are very dynamic states characterized by a rapidly drifting plasma and 30-100 eV superthermal O(+) ions.

Grebowsky, J. M.↗
NASA NTRS1987

The electromagnetic ion cyclotron beam anisotropy instability

Electromagnetic instabilities driven by an anisotropic, relatively cool ion beam are studied for the case in which both the beam and the instabilities propagate parallel or antiparallel to a uniform magnetic field. At modest beam-core relative drift speeds, sufficiently large perpendicular-to-parallel beam temperature ratios and sufficiently large plasma beta, the mode of fastest growth rate is the ion cyclotron beam anisotropy instability. Because the right-hand polarized waves observed upstream of slow shocks in the earth's magnetotail can lead to the appropriate beam anisotropy, the ion cyclotron instability may be present and account for the left-hand polarized magnetic waves observed there. Also, because of its relatively low phase speed, the ion cyclotron beam anisotropy instability may provide the scattering necessary for ion Fermi acceleration at slow shocks of sufficiently high plasma beta.

Peter Gary, S.↗