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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 397 records · Page 22
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NASA NTRS1979

Siple station experiments on wave-particle interactions in the magnetosphere

Natural and controlled whistler-mode signals have been used to study nonlinear mechanisms of wave growth and wave-wave interactions (WWI) in the magnetosphere; three general classes of WWI (triggering, suppression, and entrainment) are identified and interpreted in terms of a model based on cyclotron resonance interaction. This model is also used to estimate the wave field intensity associated with different types of WWI. A new type of triggered emission, the band-limited impulse (BLI) is interpreted in terms of the switching of phase-bunched currents. In addition, an experiment to find a threshold for the excitation of the coherent wave instability is discussed, and observed VLF wave-induced transient bursts of X-rays, light and E-region ionization enhancements are considered with regard to a step function wave interacting with all resonant electrons in a given energy range.

Helliwell, R. A.↗
NASA NTRS1980

Side-band mutual interactions in the magnetosphere

Sideband mutual interactions between VLF waves in the magnetosphere are investigated. Results of an experimental program involving the generation of sidebands by means of frequency shift keying are presented which indicate that the energetic electrons in the magnetosphere can interact only with sidebands generated by signals with short modulation periods. Using the value of the memory time during which electrons interact with the waves implied by the above result, it is estimated that the length of the electron interaction region in the magnetosphere is between 4000 and 2000 km. Sideband interactions are found to be similar to those between constant-frequency signals, exhibiting suppression and energy coupling. Results from a second sideband transmitting program show that for most cases the coherence bandwidth of sidebands is about 50 Hz. Sideband mutual interactions are then explained by the overlap of the ranges of the parallel velocity of the electrons which the sidebands organize, and the wave intensity in the interaction region is estimated to be 2.5-10 milli-gamma, in agreement with satellite measurements.

Chang, D. C. D.↗
NASA NTRS1980

Polar 5 - An electron accelerator experiment within an aurora. I - Instrumentation and geophysical conditions

A mother-daughter rocket was launched over two auroral structures, which included a 10 keV electron accelerator and a series of diagnostic instruments for monitoring optical and wave effects generated through beam-atmospheric interactions and production of secondary electrons. The instrumentation, the ground and rocket background measurements obtained, and some of the beam effects on various geophysical parameters are presented. Attention is given to the rocket geometry, capacitance probe, particle counters, photometers, and the bremsstrahlung X-ray detector. Observations on the plasma environment, auroral particle precipitation, d.c. electric field, optical emissions, and auroral background HF and VLF emissions are also discussed.

Maehlum, B. N.↗
NASA NTRS1980

Waves In Space Plasmas (WISP)

Topics included in the WISP science objectives are: (1) VLF wave injection experiments; (2) traveling ionospheric disturbances and atmospheric gravity waves; (3) ionospheric bubbles; and (4) plasma wave physics. Flow charts of the WISP investigation organization, the project life cycle and the instrumentation are given.

Fredericks, R. W.↗
NASA NTRS1981

Electrical coupling between the lower atmosphere and the ionosphere

The evidence for interactions between the ionosphere and troposphere is reviewed as a first step in establishing the role of electrical coupling between two regions. Upward processes appear to include the transfer of energy through gravity waves, or through the transmittance of VLF radio waves induced by lightning. In each case, the excitation of the upper atmosphere by tropospheric sources can stimulate feedback processes returning to the troposphere. Downward coupling involves changes in the global and local electrical structure of the atmosphere, and is often induced by solar activity. These effects are more direct and may possibly bypass the stratosphere. The responses in the atmospheric circuit to local changes are nearly instantaneous, and therefore are looked on with promise for possible influences on weather systems. Emerging experimental evidence indicates that atmospheric electric fields, especially at high latitudes and in the upper atmosphere, are responsive to solar and geomagnetic phenomena. Corpuscular radiations are known to strongly enhance the local atmospheric electrical conductivity and ionizations at stratospheric and mesospheric altitudes. Theories postulate that the electric field perturbations regulated by solar activity may be responsibile for the observed statistical correlations between solar activity and thunderstorms.

Goldberg, R. A.↗
NASA NTRS1981

Precise time and frequency intercomparison between NPL, India and PTB, Federal Republic of Germany via satellite symphonie-1

A time and frequency intercomparison experiment conducted using Earth stations in New Delhi, India and Raisting, FRG is described. The NPL clock was placed at New Delhi Earth Station and the Raisting Clock was calibrated with PTB/Primary standard via LORAN-C and travelling clocks. The random uncertainity of time comparisons, represented by two sample Allan Variance sigma (30 seconds), was less than 10 nanoseconds. The relative frequency difference between the NPL and Raisting Clocks, SNPL, RAIS, as measured over the 44 days period was found to be -15.7 x 10 to the -13th power. The relative frequency difference between PTB Primary Standard and Raisting Clock, SPTB, RAIS, during this period, was measured to be -22.8 x 10 to the -13th power. The relative frequency difference between NPL clock and PTB Primary Standard, SNPL, PTB, thus, is +7.1 x 10 to the -13th power. The clock rate (UTC, India) of +7.1 + or - 0.5 x 10 to the -13th power, agrees well with that obtained via VLF phase measurements over one year period and with USNO travelling clock time comparisons made in September, 1980.

Mathur, B. S.↗
NASA NTRS1978

Electrodynamic tether

Areas of scientific investigation which are suitable for study with an Electrodynamic Tether are considered and recommendations for an evolutionary development program which ties together many of the studies are presented. The essential component of an Electrodynamic Tether System is an insulated, conducting tether. A voltage monitor and a current controller then provide a means of performing the majority of the measurements and experiments involved in the scientific investigations. The scientific areas of study which were identified include: potential difference measurements between widely spaced (10-100 km) regions in the ionosphere; plasma disturbance generation and propagation; wave injection studies in the VLF to ULF (micropulsation) region; and the current-voltage characteristic of a spherical satellite.

Williamson, P. R.↗
NASA NTRS1981

Shuttle Orbiter tethered subsatellite for exploring and tapping space plasmas

Consideration is given to the possibilities for studies in space plasma physics offered by a subsatellite mechanically tethered above the Space Shuttle Orbiter by a long conducting wire. The proposed experiment, designated the Shuttle Electrodynamic Tether Systems (SETS) is based on the concept of collecting electrons at the subsatellite and ejecting them from the Orbiter, made possible by the emf generated by the motion of the tether across geomagnetic field lines. The power generated in this manner can be used both for practical purposes within the Orbiter and for the creation of large-amplitude plasma and electromagnetic waves within the surrounding plasma. For a conducting spherical subsatellite 30 m in diameter with a 10-km tether drawing 1 A, calculations show that emfs on the order of 1000-2000 V and energy dissipation of as much as 10,000 W can be obtained, accompanied by the generation of two regions of net electric charge in the ionosphere. Scientific studies considered for SETS include the measurement of MHD waves artificially generated in the ionosphere, the investigation of current-driven plasma instabilities, VLF wave generation and the simulation of electrodynamics associated with the motion of celestial bodies through plasma.

Banks, P. M.↗
NASA NTRS1981

Jikiken /EXOS-B/ observation of Siple transmissions

Preliminary results of observations by the Japanese magnetospheric satellite Jikiken (EXOS-B) of Siple transmissions and VLF emissions triggered by the Siple signals are reviewed. The experiments discussed were carried out in July, August, and September of 1979 and in December 1979 and January 1980. Only four events concentrated within the period from August 14 to 18 were found in which triggered emissions were associated with Siple transmissions. The electron distributions observed on the equatorial crossing passes, when Siple triggered emissions were detected, suggest that the cyclotron resonance condition is satisfied for Siple signals and electrons of energy around 1 keV or less, provided the interaction region is inside the plasmapause. It is noted that if these emissions were generated outside the plasmapause, electron energies much higher than 10 keV would be necessary for the cyclotron interaction, which were above the range of the measurements. For the high latitude passes of August 14 and 17, the electron fluxes were found to be very small.

Kimura, I.↗
NASA NTRS1980

Ionospheric disturbance overview

A program of research and exploratory development was undertaken to assess the potential impact of Satellite Power System operation on the ionosphere. The program relies on the utilization of ground-based ionospheric heating facilities in order to simulate the ionospheric heating that will come from the Satellite Power System. Thus far, the experimental program directed toward assessing telecommunications impacts has received the most attention, and little impact was observed on VLF, LF, and MF operations.

Rush, C. M.↗
NASA NTRS1981

Waves in Space Plasmas Program

The Waves in Space Plasmas (WISP) program is a joint international effort involving instrumentation to be designed and fabricated by funding from NASA and the National Research Council of Canada. The instrumentation, with a tentatively planned payload for 1986, can be used to perturb the plasma with radio waves to solve problems in ionospheric, atmospheric, magnetospheric, and plasma physics. Among the ionospheric and plasma phenomena to be investigated using WISP instrumentation are VLF wave-particle interactions; ELF/VLF propagation; traveling ionospheric disturbances and gravity wave coupling; equatorial plasma bubble phenomena; plasma wave physics such as mode-coupling, dispersion, and instabilities; and plasma physics of the antenna-plasma interactions.

Fredricks, R. W.↗
NASA NTRS1982

Current status of IMS plasma wave research

The present investigation is concerned with a review of the status of magnetospheric plasma wave science as a result of the International Magnetospheric Study (IMS). The presence of an international effort has supported the development and completion of the numerous magnetospheric science spacecraft launched during the IMS, including GEOS, ISEE, and EXOS B. Ground-based VLF observations are considered along with coordinated ground-based and satellite observations. During the IMS, plasma wave research using satellite data has covered a wide range of subjects. Attention is given to magnetospheric electrostatic emissions, magnetospheric electromagnetic plasma waves, continuum radiation, auroral kilometric radiation, auroral zone plasma waves, plasma waves in the magnetosheath and near the mangetopause, and plasma waves at the bow shock.

Anderson, R. R.↗
NASA NTRS1982

Spacelab-1: An early space station for science and technology

The scientific capabilities of the Spacelab manned pallet are reviewed, together with the implications of an expansion of the research effectiveness with a free-flying platform. The premier Spacelab flight will carry out earth observations with a metric camera and SAR, atmospheric studies will be performed with imaging spectrometers, and space plasma physics will be examined by injecting particle beams or VLF waves into the near-Shuttle environment. Radiance and spectrum data will be gathered of the sun and UV and X ray information will be recorded from the stars. Experimentation will also be carried out for on-board crystal growth, metallurgy, and glassy material production, as well as the response of biological systems to zero-g conditions and hard space radiation. The telemetry, time, crewmember participation, and on-board controls required for Spacelab operations are outlined. Missions for a space platform for studying the atmosphere/space interface are described.

Knott, K.↗
NASA NTRS1983

Quiet-time electron precipitation at L = 4 in the South Atlantic anomaly

A Superarcas sounding rocket was launched from Siple Station, Antarctica in January 1978, during a prolonged geomagnetically quiet period with very low VLF activity. The observed electron flux is the first direct measurement in the high latitude mesosphere of the quiet-time precipitating electrons in the South Atlantic anomaly. The integrated flux agrees resonably well with satellite measurements and predictions. The calculated energy spectrum of the precipitating electrons is much softer than typical measured quiet-time trapped spectra reported from satellite measurements after extended periods of low magnetic activity.

Benbrook, J. R.↗
NASA NTRS1982

The NASA Space Environment Simulation Laboratory

The NASA Space Environment Simulation Laboratory (SESL) features a chamber for studying specific space plasma physics phenomena. The test chamber, an upright domed cylinder having a 17 m diam and a 27 m height for an inner working volume, is lined with magnetic field generator coils. The chamber pressure is nominally 1/1,000,000th torr. Equipment positioning is carried out by remote control from outside guided by a closed circuit television system. Plasma is generated in the chamber by means of a 30 cm Kaufman thruster which produces ion densities of 100,000-1,000,000/cu cm. The ion bulk flow energy is in the range of 20-50 eV and a charge exchange with the ambient gas produces a cold isotropic ion component. Langmuir probes provide measurements of the electron temperature and density, and the composition and pressure are monitored by mass spectrometry and ion gages. Experiments have been performed on electron beam-plasma interactions, VLF antenna impedance measurements, and high voltage plasma sheaths which may be encountered by spacecraft.

Jost, R. J.↗
NASA NTRS1982

Studies of beam plasma interactions in a space simulation chamber using prototype Space Shuttle instruments

In March, 1981, electron beam experiments were conducted in a large space simulation chamber using equipment destined to be flown aboard NASA's Office of Space Science-1 pallet (OSS-1). Two major flight experiments were involved. They include the Vehicle Charging and Potential (VCAP) experiment and the Plasma Diagnostics Package (PDP). Apparatus connected with VCAP included a Fast Pulse Electron Gun (FPEG), and a Charge and Current Probe (CCP). A preliminary view is provided of the results obtained when the electron emissions were held steady over relatively long periods of time such that steady state conditions could be obtained with respect to the electron beam interaction with the neutral gases and plasma of the vacuum chamber. Of particular interest was the plasma instability feature known as the Beam Plasma Discharge. For the present experiments the FPEG was used in a dc mode with a range of currents of 2 to 80 mA at a beam energy of 970 eV. Attention is given to the emissions of VLF and HF noise associated with the dc beam.

Banks, P. M.↗
NASA NTRS1983

Narrow spectral peaks in electrons precipitating from the slot region

Narrow L-dependent peaks commonly occur in the energy spectra of electrons precipitating from the inner radiation belt at L approximately equal to 1.5-1.85, and the cause of the peaks has been attributed to cyclotron resonance interactions with waves generated by VLF transmitters. In the slot region, L-dependent peaks have also been reported at L approximately equal to 2-3.5, but these have been predominately wider and consistent with their origin being cyclotron resonance interactions involving naturally occurring hiss. The infrequent occurrence of narrow peaks in electrons precipitating at L greater than or approximately equal to 2 is investigated. From coordinated wave and plasma density measurements it is found that if the narrow peaks are formed by first-order cyclotron resonant interactions occurring close to the magnetic equator between narrow band waves and the trapped electron population, then the equatorial plasma density gradients are unusually steep. This finding is consistent with the evidence previously obtained by other techniques for structured plasma density profiles in that L shell region of space.

Imhof, W. L.↗
NASA NTRS1983

Electron beam experiments aboard the Space Shuttle

A 100 W, 0.1A electron gun was used in DC and pulsed modes in a series of vehicle charging and wave stimulation observations on a space shuttle. The results show that strong wave-electron scattering is present in most gun operations. It was possible to stimulate intense plasma waves in the ELF, VLF and HF frequency bands.

Banks, P. M.↗