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Stone, N. H.

Publications and source records attributed to Stone, N. H..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

On the interpretation of measured ion streams in the wake of the Shuttle Orbiter in terms of plasma expansion processes

Measurements of the flow vector and current density of ion streams between 11 and 18 m downstream in the near wake of the Shuttle Orbiter during the Spacelab 2 mission are compared with a one-dimensional, time-dependent plasma expansion model for wake filling. The model is based on the self-consistent plasma model of Singh et al. (1987) modified to simulate the one-dimensional expansion of counter-streaming plasmas. The results show good agreement between the model and the experimental results, suggesting that the measured streams can be interpreted in terms of collisionless plasma expansion.

Singh, N.↗
NASA NTRS1989

Insight into theory-experiment comparisons of wake measurements in the plasmasphere

Calculated results from a modified one-dimensional time-dependent plasma expansion model are compared with wake measurements of low-energy H(+) ions made in the plasmasphere which consists of 77-90 percent H(+) and 23-10 percent He(+). The variation of the theoretical-to-experimental results with the H(+) ionic Mach number in the range 0.5-1.2 is shown. It is found that the theoretical model used overestimates the particle flux in the wake by factors of 2 to 6. Possible causes for these differences are examined.

Samir, U.↗
NASA NTRS1988

On the expansion of ionospheric plasma into the near-wake of the Space Shuttle Orbiter

During the Spacelab 2 mission, while the Plasma Diagnostics Package was attached to the Remote Manipulator System, differential ion vector measurements were obtained in the near wake at a distance of 4-5 Shuttle radii. The Orbiter's wake was found to fill in at a much faster rate than can be explained by simple thermal motion. The measurements strongly suggest that filling of the Orbiter's wake is produced by the process of 'collisionless plasma expansion into a vacuum' and that, for oblique angles of the magnetic field and velocity vectors, the near wake plasma depletion a few radii downstream is not sensitive to the body scale size.

Stone, N. H.↗
NASA NTRS1987

Intercomparison among plasma wake models for plasmaspheric and ionospheric conditions

The angular distributions of ions in the wake of a body moving through a space plasma computed from three different models are compared in order to investigate wake current depletion ratios under conditions simulating the topside ionosphere and plasmasphere. Results demonstrate the importance of taking into account the thermal flux at low Mach numbers and the angular acceptance of ion detectors in making theory-experiment comparisons. For all models considered, gradients in the angular variations of the fluxes are shown to be steeper near the wake-ambient interface than closer to the maximum rarefaction region.

Samir, U.↗
NASA NTRS1987

The emissions of broadband electrostatic noise in the near vicinity of the Shuttle Orbiter

Measurements of the Space Shuttle environment from the STS-3 and Spacelab 2 missions indicate the presence of oblique ion streams and broadband electrostatic noise. A two-dimensional theoretical model is applied to study a possible causal relationship between the ion streams and the broadband noise, especially in terms of the ion acoustic wave and ion-ion wave modes. This model predicts the generation of waves with frequencies ranging from the ion cyclotron frequency up to values greater than the ion plasma frequency, with the maximum growth rate occurring in the 10-kHz range. These results are consistent with the observational data from the STS-3 mission. The model also shows that these two wave modes can coexist only when the wave vectors of the two wave modes are nearly perpendicular. The parametric dependence of the wave instabilities on the plasma parameters and the inclination of the wave propagation vector is also studied.

Hwang, K. S.↗
NASA NTRS1987

Effect of object potentials on the wake of a flowing plasma

The structure of the electric potential and ion density of the ion front in the near wake created by the flow of synthetic plasma past a conducting plate was investigated experimentally and numerically, with particular attention given to the effect of plate potential on the structure of the ion front. Results were obtained for a molecular nitrogen plasma with ambient electron densities of about 100,000/cu cm, ion temperatures of about 0.025 eV, electron temperatures of about 0.3 eV, and plasma flow velocities of about 10,000 m/s. Two-dimensional simulations of the laboratory experiments were performed by using a multiple waterbag technique. The calculated and experimental results show that wake closure is well described by the acceleration of ions in the plasma steady-state electric field. However, the ion-front motion is strongly affected by the imposed potential of the object creating the wake.

Katz, I.↗
NASA NTRS1987

A possible explanation of the electron temperature enhancement in the wake of a satellite

A numerical simulation was performed in an attempt to explain the enhancement of electron temperature in the wake of an ionospheric satellite in terms of counterstreaming plasma expansions. The simulation was conducted using full kinetic treatments (Vlasov-Poisson code) for both the plasma electrons and ions. The calculations indicated that at a distance of a few Debye lengths from the surface of the body the wake/ambient electron-temperature ratio reaches a value of about 2. This result is in good agreement with some in situ and laboratory experimental results.

Singh, Nagendra↗
NASA NTRS1986

The plasma dynamics of hypersonic spacecraft: Applications of laboratory simulations and active in situ experiments

Attempts to gain an understanding of spacecraft plasma dynamics via experimental investigation of the interaction between artificially synthesized, collisionless, flowing plasmas and laboratory test bodies date back to the early 1960's. In the past 25 years, a number of researchers have succeeded in simulating certain limited aspects of the complex spacecraft-space plasma interaction reasonably well. Theoretical treatments have also provided limited models of the phenomena. Several active experiments were recently conducted from the space shuttle that specifically attempted to observe the Orbiter-ionospheric interaction. These experiments have contributed greatly to an appreciation for the complexity of spacecraft-space plasma interaction but, so far, have answered few questions. Therefore, even though the plasma dynamics of hypersonic spacecraft is fundamental to space technology, it remains largely an open issue. A brief overview is provided of the primary results from previous ground-based experimental investigations and the preliminary results of investigations conducted on the STS-3 and Spacelab 2 missions. In addition, several, as yet unexplained, aspects of the spacecraft-space plasma interaction are suggested for future research.

Stone, N. H.↗
NASA NTRS1986

Observations of low-energy ions in the wake of a magnetospheric satellite

Measurements of low-energy ions made by the retarding ion mass spectrometer (RIMS) onboard the Dynamics Explorer 1 (DE 1) satellite are used to study some aspects of 'body-plasma interactions' in the terrestrial plasmasphere. Preliminary results are presented, yielding the degree of H+ and He+ ion depletion in the wake of the satellite in terms of specific and average ion Mach numbers, average ion mass, body size normalized to ionic Debye length, and body potential normalized to ion thermal energy. Some results from the RIMS measurements are compared with relevant results from the Explorer 31 and the Atmosphere Explorer C ionospheric satellites. Wake depletion is found to vary approximately linearly for small bodies (R-sub-Di less than about 12) and exponentially for large bodies (R-sub-Di greater than 50).

Samir, U.↗
NASA NTRS1986

Further observations of Space Shuttle plasma-electrodynamic effects from OSS-1/STS-3

Recent analyses of ion measurements obtained from the Differential Ion Flux Probe (DIFP) on the deployed Plasma Diagnostics Package (PDP) during the OSS-1/STS-3 mission have provided an additional insight into the plasma-electrodynamics of the Space Shuttle Orbiter: (1) Measured ion flow directions and energies suggest that the disturbance created in the ionospheric plasma by the Shuttle Orbiter may be confined to an interaction region that extends on the order of 10 m in the forward direction and has a boundary thickness of about 2 m. (2) A correlation between the DIFP and pressure gauge measurements indicates a direct, local proportionality between the neutral gas and ion densities. (3) Preliminary results from a theoretical model of the possible interaction between measured secondary, high inclination ion streams and the ambient plasma indicate the generation of broad-band electrostatic noise such as that observed by wave instruments on the PDP.

Stone, N. H.↗
NASA NTRS1986

More on the expansion of a collisionless plasma into the wake of a body

Recent laboratory measurements of plasma expansion in a plasma wake experiment (Wright et al., 1985) are compared with analytical expressions which approximate the plasma expansion model of Crow et al. (1975). Good quantitative agreement is found between the data and theory for the velocity and position of the ion expansion front. These results provide an important insight into the behavior of the expansion early in its development.

Wright, K. H., Jr.↗
NASA NTRS1986

On plasma disturbances caused by the motion of the Space Shuttle and small satellites - A comparison of in situ observations

Recent results regarding the interactions between a body and its environmental space plasma, made by charged particle probes mounted in the bay of the Space Shuttle Orbiter Columbia (STS 3 mission), are compared with earlier results, obtained from small ionospheric satellites, in an attempt to widen our scope of knowledge and understanding regarding such interactions. The objective is to work toward a unified model of body-space plasma interactions in the solar system covering a variety of plasma and body conditions. The comparisons focus mainly on (1) the (wake/ram) current ratio; (2) the generation of charged particle density fluctuations (indicative of plasma turbulence) around the body; and (3) the increase in electron temperature ahead and in the wake of the satellite. The main results of the comparison are that (1) the (wake/ram) current ratio (or current depletion in the wake) for the Orbiter is 1 to 2 orders of magnitude larger than the ratio for small ionospheric satellites; and (2) fluctuations in density (or turbulence) are observed for both 'large body' (Shuttle Orbiter) and 'smaller body' (standard ionospheric satellites). However, the cause of the turbulence may not be the same for both cases; (3) the results for the electronic temperature enhancement due to the Shuttle Orbiter are in contrast with measurements from smaller ionospheric satellites. A path to follow in future Shuttle experiments is suggested and caution that care be taken in interpreting local particle and field measurements.

Samir, U.↗
NASA NTRS1986

Ion acceleration - A phenomenon characteristic of the 'expansion of plasma into a vacuum'

The physics of the complex process by which plasma expands across a strong density gradient is briefly discussed with particular emphasis on the resulting ion acceleration. The results from a laboratory experiment that addresses the steady-state expansion of a collisionless, streaming plasma into the wake of a body are presented. The experimental results are in good qualitative agreement with theoretical predictions, thereby demonstrating the equivalence of expansion with distance in the flow direction to time in the one-dimensional theory. On this basis, the potential application of the plasma process in space plasma physics is mentioned.

Samir, Uri↗
NASA NTRS1985

Instrument for differential on flux vector measurements on Spacelab 2

The DIF (differential ion flux) probe used on the Spacelab-2 mission as part of the PDP (plasma diagnostic package) as well as the DIF design, operational characteristics and data reduction procedures required to obtain plasma properties are described. The basic principles, the sensor head design, and the electronics design are discussed. Plasma properties such as ion drift energy and temperature, ion flow direction, and ion flux density are explained, and in addition, calibration procedures and calibration data on detection of multiple ion streams and detection of ion streams superimposed on an isotropic plasma are analyzed. Finally, the mounting and role of the DIF probe on the PDP are briefly reviewed. Schematics of the instrument and of its control logic are included.

Stone, N. H.↗
NASA NTRS1985

Electrodynamic Interactions

It is apparent that the electrodynamic tether offers new potential for unique scientific experiments which should enhance the understanding of space plasma physics and in particular certain classes of solar system plasma phenomena, and that these science studies will also address a number of key engineering concerns which may open up new power and thrust generation technology that could be a significant factor in future space operations.

Stone, N. H.↗
NASA NTRS1985

Report of the Electrodynamic Interactions Panel

A wide range of opportunities is provided by the electrodynamic tether to more fully understand the generation of waves in plasmas, the behavior of field aligned currents, the behavior of large body-space plasma interactions, and for process simulation, using the electrodynamic tether to study processes and phenomena relevant to solar system and astrophysics plasma physics. The electrodynamic tether offers a means of study and experimentation in space which will provide a rich yield in new scientific results and will enhance the understanding of space plasma physics. It also has promising technological applications (e.g., the generation of electrical power and thrust) which may be highly significant to future space operations.

Stone, N. H.↗