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NASA NTRS1978

Charge exchange lifetimes for ring current ions

In view of the importance of charge exchange decay as a loss mechanism for magnetospheric ions, the paper summarizes the latest and best measurements of the physical quantities involved in the calculation of the charge exchange lifetime of the mirroring ions. The normalized atomic hydrogen distribution is presented as a function of radial distance on the basis of the Chamberlain model for a range of exobase temperatures and for various combinations of satellite particles. Cross section measurements for various ions in the energy range 1 keV to 200 keV are summarized in the form of normalized charge exchange lifetimes. The equatorial lifetimes can be determined for any of these ions at a specific energy and L-value.

Smith, P. H.↗

NASA NTRS1979

Glossary of terms and table of conversion factors used in design of chemical propulsion systems

The glossary presented is based entirely on terms used in the monographs on Chemical Propulsion. Significant terms relating to material properties and to material fabrication are presented. The terms are arranged in alphabetical order, with multiple word terms appearing in the normal sequence of usage; for example, ablative cooling appears as such, not as cooling, ablative, and lip seal appears as such, not as seal, lip. Conversion Factors for converting U.S. customary units to the International System of Units are presented in alphabetical order of the physical quantity (e.g., density, heat flux, specific impulse) involved.

Keller, R. B., Jr.↗

NASA NTRS1980

Space applications of superconductivity - Resonators for high stability oscillators and other applications

The potential applications of superconductivity in space are examined. It is shown that superconducting oscillators have achieved better frequency stability that any other device for averaging times of 10 s to 1000 s. Such a high stability results from the use of solid niobium resonators having Q factors greater that 10 to the 10th. Oscillators of this type have direct applications as clocks and spectrally pure sources. In addition, they may also be used for accurate measurements of many physical quantities and to perform a variety of experiments on fundamental constants, relativity, and gravity waves.

Stein, S. R.↗

NASA NTRS1983

Optical Temperature Sensor Has Digital Output

New instrument measures temperature reliabily and accurately. Device uses Fabry-Perot multiple-beam sensor. Both temperature sensor and optical lines are free of all electrical and electromagnetic effects and interference. Variation in spacer is made sensitive to other physical quantities, such as pressure. Sensing element itself is quite small, enhancing use in confined areas.

James, K.↗

NASA NTRS1980

Simulation of spacecraft charging environments by monoenergetic beams

To simulate the distributed spectra of plasmas in space, the differential current density spectrum of the plasma was divided into a number of energy bands and the beam energy and current were calculated for each band to provide a piecewise reproduction of the distributed spectrum. Beam energies and current densities were chosen to match the velocity moments of the plasma distribution function. The velocity moments are averages related to physical quantities such as particle density, flux, pressure, and energy flux, and have been used extensively to characterize the measured properties of plasmas in space. Combinations of one, two, and three beams were found to match two to six velocity moments of Maxwellian distributions. A computational model was used to compare the charging of a spacecraft by plasmas with distributed spectra and by monoenergetic beams.

Halverson, W.↗

NASA NTRS1983

Steady flow approximations to the helium r-process

A steady flow approximation to the r-process is presented and used for numerical experiments with physical quantities to determine the sensitivity of the process to variations in those quantities. The effect of neutron capture cross sections along the capture path and of recently available improved beta decay rates on the r-process are discussed. The peaks in the observed r-process yield curve near mass numbers 80 and 130 are roughly characterized by a neutron number density of 10 to the 20th per cu/cm; the mean beta decay rates are about 10/s, and the freezing time is comparable to or less than 0.1 s. The peak near mass number 195 is roughly characterized by a neutron number density of 10 to the 21st/cm, the mean beta decay rates are about 100/s, and the freezing time is comparable to or less than 0.01 s. The flow path of the steady state r-process is sensitively dependent upon the neutron capture cross sections in the flow network and on the values of the beta decay rates.

Cameron, A. G. W.↗

NASA NTRS1983

Solar flare X-ray spectra from the P78-1 spacecraft

Results from the high resolution solar X-ray spectrometer experiments on the P78-1 spacecraft are discussed. These results concern physical quantities such as electron temperature and density, turbulence, mass motions, and state of ionization equilibrium, characteristic of the thermal soft X-ray emitting flare plasma, and the time behavior of these quantities during flares. In addition, a brief description of the instruments is given, the plasma diagnostics used in interpreting the spectra are summarized, and the origin of the thermal soft X-ray emitting plasma is discussed in light of the P78-1 results, earlier data, and numerical simulations of magnetic flux tubes heated to solar flare temperatures.

Doschek, G. A.↗

NASA NTRS1984

A reevaluation of the 20-micron magnitude system

The 20-micron infrared magnitude system is reexamined by observing primary infrared standards and seven A V stars. The purpose is to determine whether Alpha Lyr has colors consistent with the average of A0 stars and to determine the relative magnitude of the primary standards to that of Alpha Lyr. The data presented are consistent with the interpretation that the spectrum of Alpha Lyr is a blackbody and that it is a viable flux standard at 10 and 20 microns. The absolute flux density scale, the physical quantity of interest, is found to be consistent with an extrapolation of the Alpha Lyr spectrum from the near infrared on the basis of the comparison of stars to Mars and asteroids. Adoption of a 0.0 magnitude for Alpha Lyr requires that the magnitudes given by Morrison and Simon (1973) and by Simon et al. (1972) be revised downward by 0.14 mag.

Tokunaga, A. T.↗

NASA NTRS1985

An Unusual Application of NASTRAN Contour Plotting Capability

A procedure is presented for obtaining contour plots of any physical quantity defined on a number of points of the surface of a structure. Rigid Format 1 of HEAT approach in Cosmic NASTRAN is ALTERED to enable use of contour plotting capability for scalar quantities. The ALTERED DMAP sequence is given. Examples include temperature distribution on the face of a cooled laser mirror and the angle of incidence or a radome surface.

Mittal, S.↗

NASA NTRS1984

On the psychophysics of workload - Why bother with subjective measures?

Psychophysical functions describe the relationship between variations in the amplitude of a defined physical quantity and the psychological perception of these changes. Examples are brightness, loudness, and pain. The regularities of these relationships have been formulated into psychophysical laws. The measurement methodology of psychophysical scaling has been refined by the Harvard group led by Stevens (1957 and 1966), who proposed a power function as a general form for such laws. It is argued here that a similar scaling approach can be adapted to the measurement of workload and task demands based upon subjective estimates. The rationale is that these estimates, like other psychophysical judgments, reflect the individual's perception of the amount of processing resources that the subject invests to meet the demand imposed by a task. This approach was successfully applied to the assessment of 21 experimental conditions given to a group of 60 subjects. The paper discusses the main results of this effort and their implications to theory and application in human performance.

Gopher, D.↗

NASA NTRS1985

Analytic structure of cosmic radio jets - A preliminary investigation

The structure of the steady radio jet is discussed by analyzing the relativistic Euler equation in the case where surfaces of constant angular momentum coincide with surfaces of constant angular velocities. A closed analytic expression for the potential and other physical quantities is derived in a general stationary background geometry. The effect of the angular momentum component and the radial momentum component on the structure of the jet is studied in detail for Schwarzschild geometry. The jets are found to be pressure-confined and angular momentum-supported. The possibility of obtaining arbitrarily well-collimated jets very near to a black hole is discussed.

Chakrabarti, S. K.↗

NASA NTRS1985

Electron-impact vibrational excitation rates in the flow field of aeroassisted orbital transfer vehicles

This paper examines the vibrational excitation rate processes expected in the flow field of aeroassisted orbital transfer vehicles (AOTVs). An analysis of the multiple-quantum vibrational excitation processes by electron impact is made to predict the vibrational excitation cross sections, rate coefficients, and relaxation times which control vibrational temperature. The expression for the rate of electron-vibration energy transfer is derived by solving the system of master equations which account for the multiple-level transitions. The vibrational excitation coefficients, which are the prerequisite physical quantities in solving the obtained vibrational equation, are calculated based on the theoretically predicted cross sections. These cross sections are obtained from quantum mechanical calculations, based on the concept that vibrational excitation of molecules by electron impact occurs through formation of an intermediate negative ion state. Finally, the modified Landau-Teller-type rate equation, which is suitable for the numerical calculations for the AOTV flow fields, is suggested.

Lee, J.-H.↗

NASA NTRS1985

DE 1 RIMS operational characteristics

The Retarding Ion Mass Spectrometer (RIMS) on the Dynamics Explorer 1 spacecraft observes both the thermal and superthermal (50 eV) ions of the ionosphere and inner magnetosphere. It is capable of measuring the detailed species distribution function of these ions in many cases. It was equipped with an integral electrometer to permit in-flight calibration of the detector sensitivities and variations thereof. A guide to understanding the RIMS data set is given. The reduction process from count rates to physical quantities is discussed in some detail. The procedure used to establish in-flight calibration is described, and results of a comparison with densities from plasma wave measurements are provided. Finally, a discussion is provided of various anomalies in the data set, including changes of channeltron efficiency with time, spin modulation of the axial sensor heads, apparent potential differences between the sensor heads, and failures of the radial head retarding potential sweep and of the -Z axial head aperture plane bias. Studies of the RIMS data set should be conducted only with a thorough awareness of the material presented here, or in collaboration with one of the scientists actively involved with RIMS data analysis.

Olsen, R. C.↗

NASA NTRS1986

Instrumentation in wind tunnels

Requirements in designing instrumentation systems and measurements of various physical quantities in wind tunnels are surveyed. Emphasis is given to sensors used for measuring pressure, temperature, and angle, and the measurements of air turbulence and boundary layers. Instrumentation in wind tunnels require accuracy, fast response, diversity and operational simplicity. Measurements of force, pressure, attitude angle, free flow, pressure distribution, and temperature are illustrated by a table, and a block diagram. The LDV (laser Doppler velocimeter) method for measuring air turbulence and flow velocity and measurement of skin friction and flow fields using laser holograms are discussed. The future potential of these techniques is studied.

Takashima, K.↗

NASA NTRS1986

Generalization and extension of the law of acoustic energy conservation in a nonuniform flow

An exact conservation equation is derived which generalizes the familiar acoustic energy equations. The new relation is valid for arbitrary disturbances to a viscous, compressible flow. It is suggested by a development of the acoustic energy equation by means of a regular perturbation expansion of the general energy equation of fluid mechanics. A perturbation energy density and flux are defined and identified as the exact physical quantities whose leading order perturbation representations are the usual acoustic energy density and flux. The conservation equation governing the perturbation energy quantities is shown to yield previously known results for several special cases.

Myers, M. K.↗

NASA NTRS1985

Optical characteristics of lightning and thunderstorm currents

Researchers determined that lightning can be used to determine the diurnal variations of thunderstorms, i.e., storms that produce audible thunder, and that these variations are also in good agreement with diurnal variations in rainfall and convective activity. Measurements of the Maxwell current density, J sub m, under active thunderstorms show that this physical quantity is quasi-steady between lightning discharges and that lightning does not produce large changes in J sub m. Maps of J sub m show contours of iso-current density that are consistent with the locations of radar echos and the locations of where lightning has altered the cloud charge distribution.

Krider, E. P.↗

NASA NTRS1986

Magnetic helicity as a constraint on coronal dissipation

The Taylor hypothesis has provided a model for the relaxed magnetic configurations of not only laboratory plasmas, but also of astrophysical plasmas. However, energy dissipation is possible only for systems which depart from a strict Taylor state, and hence a parameter describing that departure must be introduced, when the Taylor hypothesis is used to estimate the dissipation. An application of the Taylor hypothesis to the problem of coronal heating provides an insight into this difficult problem. When particular sorts of footpoint motions put energy and helicity in the corona, the conservation of helicity puts a constraint on how much of the energy can be dissipated. However, on considering a random distribution of footpoint motions, this constraint gets washed away, and the Taylor hypothesis is probably not going to play any significant role in the actual calculation of relevant physical quantities in the coronal heating problem.

Choudhuri, Arnab Rai↗

NASA NTRS1986

An exact energy corollary for homentropic flow

An exact conservation equation is developed which generalizes the familiar acoustic energy equation. The new relation is valid for arbitrary homentropic disturbances to a homentropic steady flow. It is suggested by a derivation of the acoustic energy equation by means of a regular perturbation expansion of the general energy equation for an ideal compressible fluid. A perturbation energy density and flux are defined and are identified as the exact physical quantities whose leading order representations are the usual acoustic energy density and flux.

Myers, M. K.↗