Engineering topics

Kurth, W. S.

Publications and source records attributed to Kurth, W. S..

At least 127 records · Page 7

NASA NTRS1986

Measurements of plasma parameters in the vicinity of the Space Shuttle

A Langmuir probe flown as part of the Plasma Diagnostics Package aboard the third Space Shuttle flight was used to determine electron densities, temperatures, and plasma potential in the vicinity of the Shuttle Orbiter. Measurements taken both in the cargo bay and 10 m above the cargo bay on the Remote Manipulator System arm are consistent with small satellite and laboratory results, in that reduced densities and elevated temperatures are observed in the Shuttle wake. The primary difference in the Shuttle measurements is one of magnitude; i.e., orders-of-magnitude density decreases and factor-of-five temperature enhancements. Analysis of data taken in (Delta N)/N turbulence can be as high as a few percent, and the most intense turbulence seems to occur near regions with a steep gradient in plasma pressure.

Murphy, G.↗

NASA NTRS1986

First plasma wave observations of Uranus

Plasma wave data collected by instrumentation on Voyager 2 as it passed Uranus magnetosphere are discussed. Radio signals at 31.1 and 56.2 kHz were detected 5 days from closest approach and were buried in a burst of electrostatic noise as the spacecraft crossed the bow shock 10 hr before closest approach. The noise arose from electrons escaping the bow shock into the solar wind. Electric field intensities downstream of the shock were reduced, a situation similar to those observed around Saturn and Jupiter. Whistler-mode hiss and chorus emissions were prominent within the magnetosphere at less than 8 Uranus radii, a region where particle detectors registered intense energetic electron fluxes. Also, micron-sized particle impacts at a rate of 30-50 impacts/sec occurred when passing through the ring plane. The duration of the micro-impact phase was sufficient to estimate the ring thickness as about 4000 km.

Gurnett, D. A.↗

NASA NTRS1986

Whistler-mode radiation from the Spacelab 2 electron beam

During the Spacelab 2 mission the Plasma Diagnostics Package (PDP) performed a fly-around of the Shuttle at distances of up to 300 meters while an electron beam was being ejected from the Shuttle. A magnetic conjunction of the Shuttle and the PDP while the electron gun was operating in a steady (DC) mode is discussed. During this conjunction, the PDP detected a clear funnel-shaped emission that is believed to be caused by whistler-mode emission from the beam. Ray-path calculations show that the shape of the funnel can be accounted for by whistler-mode waves propagating near the resonance cone. Because the beam and waves are propagating in the same direction, the radiation must be produced by a Landau interaction with the beam. Other types of waves generated by the beam are also described.

Gurnett, D. A.↗

NASA NTRS1986

Plasma waves and continuum radiation in planetary magnetospheres

Voyager data on whistler mode waves and electron cyclotron harmonic emissions are analyzed to understand the interaction of the waves with the dynamics of the electrons. The occurrence and characteristics of Jovian whistler mode chorus and the interactions with the plasma in and near the Io torus are emphasized. Bernstein waves, especially those near the upper hybrid or plasma frequency are discussed to provide insight into an important plasma diagnostic tool and to compare the relevant portions of the electron distribution function at Earth, Jupiter, and Saturn. The nonthermal continuum radiation common to the magnetospheres of Earth, Jupiter, and Saturn is considered. Because of the very low frequency of these radio waves and their close association with upper hybrid resonance emissions, continuum radiation is often associated more closely with the plasma wave spectrum of a planetary magnetosphere than with the planet's radio spectrum.

Kurth, W. S.↗

NASA NTRS1986

Plasma waves and continuum radiation in planetary magnetospheres

Observations of whistler and Bernstein waves at the earth, Jupiter, and Saturn are discussed, as well as nonthermal continuum radiation which is common to the magnetospheres of these planets. Whistler mode waves and electron cyclotron harmonic emissions are examined in detail, with the purpose of understanding the interaction of these waves with the dynamics of the plasma electrons. Emphasis is placed on the occurrence and characteristics of the Jovian whistler mode chorus and the interactions with the plasma in and near the Io torus.

Kurth, W. S.↗

NASA NTRS1986

Recent observations of the very low frequency interplanetary radio emission

Observations of radio emissions in the frequency range of 2 to 3 kHz have been made in the distant heliosphere by the Voyager 1 and 2 plasma wave instruments. Based primarily on wideband observations made periodically throughout the cruise phases of the missions the radio emission, first observed in 1982, appears to have been present almost continuously since 1983. The spectrum is complex, usually showing two peaks, one near 2 and another near 3 kHz. Occasionally, only one of the peaks is observed. A possible source for the radio emissions is the terminal shock in the outer heliosphere.

Kurth, W. S.↗

NASA NTRS1985

Particle acceleration in Saturn's outer magnetosphere - In memoriam Alois Schardt

Fluctuations in field strength and particle flux observed during the outbound pass of Voyager 2 through the Saturnian magnetosphere are discussed. The observations of injections of energetic electrons and ions, associated plasma wave activity, and magnetic field perturbations are described. These data imply the existence of an acceleration or heating site some distance from the Voyager 2. A correlation between impulsive injections of 0.35-2 MeV electrons, increase in the hot ion flux of 28-215 KeV, a dip in magnetic field magnitude, and a signal from the plasma wave instrument in the 562 Hz channel was detected. An explanation of these observations is provided.

Schardt, A. W.↗

NASA NTRS1985

Effects of chemical releases by the STS 3 orbiter on the ionosphere

The Plasma Diagnostics Package, flown aboard STS-3 as part of the first Shuttle payload (OSS-1), recorded the effects of various chemical releases from the Orbiter. Changes in the plasma environment was observed during flash evaporator system releases, water dumps and maneuvering thruster operations. During flash evaporator operations, broadband Orbiter-generated electrostatic noise was enhanced and plasma density irregularities were observed to increase by 3 to 30 times with a spectrum which rose steeply and peaked below 6 Hz. In the case of water dumps, background electrostatic noise was enhanced at frequencies below about 3 kHz and suppressed at frequencies above 2 kHz. Thruster activity also stimulated electrostatic noise with a spectrum which peaked at approximately 0.5 kHz. In addition, ions with energies up to 1 keV were seen during some thruster events.

Pickett, J. S.↗

NASA NTRS1985

High time resolution plasma wave and magnetic field observations of the Jovian bow shock

High time resolution (60 ms) Voyager magnetometer and plasma wave measurements of a strong (fast Mach number 16), quasi-perpendicular Jovian bow shock reveal an abrupt change in the plasma wave spectrum at the leading edge of the shock foot. Upstream electron plasma waves terminate at the leading edge, and are replaced by a lower-frequency broadband spectrum of ion-acoustic-like waves, which terminates at the main shock ramp. The clear association with the foot region of the lower frequency component suggests that it is generated by reflected ions. If the upstream plasma waves are generated by an escaping electron heat flux, their termination at the leading edge suggests that electrons are heated by the low-frequency waves in the shock foot.

Moses, S. L.↗

NASA NTRS1985

A summary of whistlers observed by Voyager 1 at Jupiter

We summarize the Voyager 1 observations of whistlers at Jupiter in order to provide a basis for further analyses of the density profile of the Io plasma torus as well as to support studies of atmospheric lightning at Jupiter. All the whistlers detected by Voyager 1 fell into three general regions in the torus at radial distances ranging beteen 5 and 6 R sub J. An analysis of the broadband wave amplitudes measured by the Voyayer 1 plasma wave instrument and estimates of the peak whistler amplitudes imply the grouping of whistlers was due to variations in the sensitivity of the receiver to whistlers and not to variations in the source or propagation paths of the whistlers. The whistler dispersions are presented in statistical form for each of the three groups of events and analyzed in view of the structure of the Io plasma torus as determined by plasma probe measurements. The results of these analyses give source locations for the whistlers at the foot of the magnetic field lines threading the torus in both hemispheres and over a range of longitudes.

Kurth, W. S.↗

NASA NTRS1985

Voyager observations of lower hybrid noise in the Io plasma torus and anomalous plasma heating rates

A study of Voyager 1 electric field measurements obtained by the plasma wave instrument in the Io plasma torus has been carried out. A survey of the data has revealed the presence of persistent peaks in electric field spectra in the frequency range 100-600 Hz consistent with their identification as lower hybrid noise for a heavy-ion plasma of sulfur and oxygen. Typical wave intensities are 0.1 mV/m, and the spectra also show significant Doppler broadening, Delta omega/omega approximately 1. A theoretical analysis of lower hybrid wave generation by a bump-on-tail ring distribution of ions is given. The model is appropriate for plasmas with a superthermal pickup ion population present. A general methodology is used to demonstrate that the maximum plasma heating rate possible through anomalous wave-particle heat exchange is less than approximately 10 to the -14th ergs per cu cm per s. Although insufficient to meet the power requirement of the EUV-emitting warm torus, the heating rate is large enough to maintain a low-density (0.01-0.1 percent) superthermal electron population of keV electrons, which may lead to a small but significant anomalous ionization effect.

Barbosa, D. D.↗

NASA NTRS1984

A new radio emission at 3 kHz in the outer heliosphere

Evidence of a radio source in the outer heliosphere based on observations made by the plasma wave receivers on Voyagers 1 and 2 at heliocentric radial distances ranging from 13 to 20 AU is given. The radio emission is observed in the frequency range 2 to 3 kHz, and is above the local electron plasma frequency whenever supporting plasma density data are available. The maximum spectral density of the emission is 10 to the minus 14 th power V sq/m/Hz. The bandwidth of the radio noise is 1 kHz. One possible source for the emission is radiation at the second harmonic of the plasma frequency at the heliopause.

Kurth, W. S.↗

NASA NTRS1984

Detection of a radio emission at 3 kHz in the outer heliosphere

A radio source in the outer heliosphere has been detected by the plasma wave receivers on Voyagers 1 and 2. The radio emission is observed in the frequency range 2-3 kHz, and is above the local solar wind electron plasma frequency whenever supporting plasma density data are available. The maximum spectral density of the emission recorded is about 10 to the -14th V-squared/m-squared/Hz. The bandwidth of the radio noise is about 1 kHz. Possible sources include continuum radiation from Jupiter's distant magnetotail and radiation at the second harmonic of the plasma frequency at the heliopause. If the latter interpretation is correct, these data represent the first remote observations of the heliopause.

Kurth, W. S.↗

NASA NTRS1984

Analysis of chorus emissions at Jupiter

The emissions in the chorus frequency band which were detected on the Voyager 1 inbound pass between about ten and six Jupiter radii are surveyed. An overview of the plasma and wave observations during the inbound pass is presented and the spatial regions in which chorus band signals were observed are discussed. A series of wide-band frequency-time frames which characterize the onset of two observed intervals of chorus band activity is displayed. A detailed examination is made of the spectra for rising chorus which sweeps upward in frequency from 0.2 to 0.5 times the electron cyclotron frequency f(c). Two temporally successive wide-band frames in which several types of chorus band emissions were observed are discussed. The spatial morphology of chorus is discussed in terms of the electron energies which resonate with whistler mode waves. A recent theory of chorus generation is reviewed along with theories and a model explaining the narrow-band emissions above f(c)/2.

Coroniti, F. V.↗

NASA NTRS1984

Interpretation of STS-3/plasma diagnostics package results in terms of large space structure plasma interactions

The Plasma Diagnostics Package, which was flown aboard STS-3 recorded various chemical releases from the Orbiter. Changes in the plasma environment were observed to occur during Flash Evaporator System (FES) releases, water dumps and maneuvering thruster operations. During flash evaporator operations, broadband Orbiter-generated electro-static noise is enhanced and plasma density irregularity (delta n/N) is observed to increase by as much as 4 times and is strongly peaked below 6 Hz. In the case of water dumps, background electrostatic noise is enhanced or suppressed depending on frequency and Delta N/N is also seen to increase by as much as 4 times. Various changes in the plasma environment are effected by primary and vernier thruster operations. In addition, thruster activity stimulates electrostatic noise with a spectrum which is most intense at frequencies below 10 kHz.

Kurth, W. S.↗

NASA NTRS1984

Chorus-related electrostatic bursts at Jupiter and Saturn

Analyses of the wideband plasma wave data obtained by Voyagers 1 and 2 at Jupiter and Saturn have revealed electrostatic bursts similar to those recently discovered at earth in association with whistler-mode chorus. In all three magnetospheres the bursts are characterized by sporadic emissions near or slightly below the electron plasma frequency with bandwidths ranging from 10 percent to more than 50 percent of the center frequency. The events found at Jupiter occur in the middle magnetosphere during both the dayside as well as the early morning passes. At Saturn, the bursts occurred in the outer regions of the magnetosphere during the dayside pass. In each of the events analyzed, evidence exists for modulation of the electrostatic bursts by a low frequency wave, presumably chorus. One of the observations gained at Jupiter includes the detection of a low-frequency band at the proper frequency for chorus. Detailed waveform analysis confirms that this band does, indeed, modulate the electrostatic bursts. Based on the present understanding of the terrestrial observations it is believed that the electrostatic bursts are generated by an electron beam trapped in Landau resonance with the chorus. Previously announced in STAR as N83-37042

Reinleitner, L. A.↗

NASA NTRS1984

Saturn as a radio source

Magnetospheric radio emissions, Saturn electrostatic discharges, inferred source locations, and emission theories are addressed.

Kaiser, M.L.↗

NASA NTRS1983

Effects of chemical releases by the STS-3 Orbiter on the ionosphere

Pickett, J. S.↗