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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 613 records · Page 34
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NASA NTRS1976

Galilean satellites - Observations of mutual occultations and eclipses in 1973

Seven Galilean satellite mutual events, two occultations and two eclipses of Europa and three eclipses of Io, were observed at three wavelengths (0.35, 0.50, 0.91 micrometers) with a time resolution of 0.1 sec. Preliminary model fits to the light curves are presented. Model satellites with different albedo distributions (uniform disk, bright solar caps, bright quadrant) are used in generating model occultation and eclipse curves to demonstrate the sensitivity of observed light curves to the brightness distribution on the surface of the occulted or eclipsed satellite. At the present the observations yield no conclusive information of the limb-darkening of Io. The best data for Europa indicate that the satellite is limb-darkened at both 0.50 and 0.91 micrometers.

Wasserman, L. H.↗
NASA NTRS1976

Solar wind structure at large heliocentric distances - An interpretation of Pioneer 10 observations

Examination of hourly values of the solar wind speed observed by the Pioneer 10 spacecraft beyond a heliocentric distance of 4 AU reveals (1) a prevalent 'sawtoothlike' speed-time profile, most speed fluctuations displaying a rapid rise and a much slower decline, and (2) the nearly universal appearance of abrupt (on the 1-hour time resolution of these data) changes in the speed on the rising portions of the speed fluctuations. These previously unreported characteristics, as well as the rate of decay of stream amplitudes derived earlier by Collard and Wolfe, are in general agreement with the predictions of stream propagation models that neglect any conversion of kinetic energy to thermal energy outside of shock fronts. Thus the Pioneer 10 observations give the first confirmation of the general concept of solar wind stream evolution employed in these models, i.e., that solar wind speed inhomogeneities appear to steepen to form shock waves and that the 'wave amplitudes' decay slowly as the shock waves propagate outward from the sun.

Hundhausen, A. J.↗
NASA NTRS1976

Solar radiation measurement - Techniques and instrumentation

A general survey is presented of solar radiation measurement, techniques, and instrumentation. The importance of determining the total and spectral irradiance of the sun is examined in the context of the energy crisis and utilization of solar energy. The survey includes the extraterrestrial solar fluxes, their possible variations, problems relating to energy received by collecting surfaces on the ground, major types of instrumentation, and the radiation scales to which the measurements are referred. The type of insolation data available is reviewed. Alternate techniques of deriving insolation data with high space-time resolution are discussed with reference to solar energy conversion requirements. Energy received on the ground can be computed from known values of the extraterrestrial solar spectrum and of the spectral absorption parameters of the atmosphere. Another technique is based on measurements made by meteorological satellites of the cloud-cover and of the solar energy reflected and scattered back to space by the earth-atmosphere system.

Thekaekara, M. P.↗
NASA NTRS1976

CO/d-3 Delta sub i to X-1 Sigma +/ fluorescence from photodissociation of CO2 by 923 A photons

Measurements of vacuum ultraviolet fluorescence from the photodissociation of CO2 by photons from a N IV line emission source at a wavelength of 923 A have revealed a second CO band system in addition to the expected emission bands. Spectra with time resolution were obtained and the fluorescence lifetime and the dependence of fluorescence intensity on CO2 pressure were measured. An analysis of this data has permitted the second band system to be identified as originating from CO(d-3 Delta sub i to X-1 Sigma +) transitions.

Phillips, E.↗
NASA NTRS1977

Uranus occults SAO158687

Experience gained in obtaining atmospheric parameters, oblatenesses, and diameters of Jupiter and Mars from recent stellar occultations by these planets is used to predict what can be learned from the March 1977 occultation of the star SAO158687 by Uranus. The spectra of this star and Uranus are compared to indicate the relative instrument intensities of the two objects, the four passbands where the relative intensities are most nearly equal are listed, and expected photon fluxes from the star are computed on the assumption that it has UBVRI colors appropriate for a K5 main-sequence object. It is shown that low photon noise errors can be achieved by choosing appropriate passbands for observation, and the rms error expected for the Uranus temperature profiles obtained from the occultation light curves is calculated. It is suggested that observers of this occultation should record their data digitally for optimum time resolution.

Elliot, J. L.↗
NASA NTRS1977

The detection and analysis of point processes in biological signals

A pragmatic approach to the detection and analysis of discrete events in biomedical signals is taken. Examples from both clinical and basic research are provided. Introductory sections discuss not only discrete events which are easily extracted from recordings by conventional threshold detectors but also events embedded in other information carrying signals. The primary considerations are factors governing event-time resolution and the effects limits to this resolution have on the subsequent analysis of the underlying process. The analysis portion describes tests for qualifying the records as stationary point processes and procedures for providing meaningful information about the biological signals under investigation. All of these procedures are designed to be implemented on laboratory computers of modest computational capacity.

Anderson, D. J.↗
NASA NTRS1977

Analysis of the occultation of Epsilon Geminorum by Mars

High-time-resolution photoelectric measurements of the occultation of Epsilon Gem by Mars were obtained with the 36-in. telescope at Goddard Space Flight Center. Temperature profiles as a function of number density have been determined by inverting the immersion and emersion light curves on the assumption of a pure CO2 atmosphere. For number densities between 10 to the 13th and 10 to the 15th power per cu cm, the temperature varies in a wavelike fashion about a mean value near 150 K. These temperature profiles agree well with those derived from airborne observations by Elliot et al. (1977), indicating that the atmospheric features producing the excursions in the temperature profiles extend for at least 100 km along the Martian limb.

Wasserman, L. H.↗
NASA NTRS1977

The Mechanics of Atmospheric Systems Derived Through Vertical and Horizontal Analysis of Parametric Data

For 36 hours during April 1975, an atmospheric variability experiment was conducted. This research effort supported an observational program in which rawinsonde data, radar data, and satellite data were collected from a network of 42 stations east of the Rocky Mountains at intervals of 3 hours. This program presents data with a high degree of time resolution over a spatially and temporally extensive network. Reduction of the experiment data is intended primarily as a documentation of the checking and processing of the data and should be useful to prospective users. Various flow diagrams of the data processing procedures are described, and a complete summary of the formulas used in the data processing is provided. A wind computation scheme designed to extract as much detailed wind information as possible from the unique experiment data set is discussed. The accuracy of the thermodynamic and wind data were estimated. Errors in the thermodynamic and wind data are given.

Turner, R. E.↗
NASA NTRS1977

Pulse profile and refined orbital elements for SMC X-1

Results of a reanalysis of SAS-3 data for SMC X-1, including greatly improved orbital elements, are presented. These elements, when combined with newly available data for the optical companion, Sk 160, yield improved estimates for the masses of SMC X-1 and Sk 160. A significant rate of change of intrinsic pulse period is detected during the course of the four-day observation which is consistent with the average value that was previously deduced from observations separated by 5 years. The X-ray pulse profile, averaged over one orbital cycle and with approximately 15-ms time resolution, is also presented. The pulse profile is found to be constant to within statistics, as a function of orbital phase. The implications of the small observed eccentricities of SMC X-1 and other binary X-ray pulsar systems are discussed.

Primini, F.↗
NASA NTRS1977

Occultation of Epsilon Geminorum by Mars. II - The structure and extinction of the Martian upper atmosphere

The occultation of Epsilon Geminorum by Mars on April 8, 1976, was observed at three wavelengths and 4-ms time resolution with the 91-cm telescope aboard NASA's G. P. Kuiper Airborne Observatory. Temperature, pressure, and number-density profiles of the Martian atmosphere were obtained for both the immersion and emersion events. Within the altitude range 50-80 km above the mean surface, the mean temperature is about 145 K, and the profiles exhibit wavelike structures with a peak-to-peak amplitude of 35 K and a vertical scale of about 20 km. The ratio of the refractivity of the atmosphere at 4500 A and 7500 A is consistent with the atmospheric composition measured by Viking 1. From the 'central flash' - a bright feature in the light curve midway between immersion and emersion - an optical depth at 4500 A of 3.3 + or - 1.7 per km atm (about 0.23 per equivalent Martian air mass) is found for the atmosphere about 25 km above the mean surface near the south polar region. This large value and its weak wavelength dependence rule out Rayleigh scattering as the principal cause of the observed extinction.

Elliot, J. L.↗
NASA NTRS1978

Frequency analysis of 4- to 6-keV electrons associated with an auroral arc

The high time resolution (HTR) experiment considered consists of four sections, including electrostatic deflection plates, electron multiplier, preamplifier-integrator, and frequency analyzer. Electrons in the energy range from 4 to 6 keV electrons are selected by the deflection system, after which they are detected, multiplied, and passed to the charge sensitive preamplifier. The charge pulses are amplified and integrated, and the resulting voltage pulse series is fed to the frequency analyzer. The experiment is essentially a flux detector, so that estimates of the input flux can be made from the mean value of the output spectrum. The results obtained with the HTR in a rocket flight on March 14, 1974, are discussed. The lack of modulation noticed in the high-frequency range indicates that there is insufficient wave energy available in the vicinity of the rocket to produce a wave-particle interaction which the HTR is able to observe. This finding is consistent with the stabilization of the plasma by the low flux of energetic electrons.

Murphree, J. S.↗
NASA NTRS1978

A precision measurement of the X-ray polarization of the Crab Nebula without pulsar contamination

The linear X-ray polarization of the Crab Nebula has been precisely measured at 2.6 keV and 5.2 keV with the OSO 8 graphite crystal polarimeters. The 1.4 ms time resolution of these instruments permitted the removal of any contribution to the polarization from the pulsar. The nebular polarization is 19.2% plus or minus 1.0% at a position angle of 156.4 plus or minus 1.4 deg at 2.6 keV. At 5.2 keV the corresponding results are 19.5% plus or minus 2.8% at 152.6 plus or minus 4.0 deg.

Weisskopf, M. C.↗
NASA NTRS1978

A voltage to frequency converter for astronomical photometry

A voltage to frequency converter (VFC) for general use with photomultipliers is described. For high light levels, when the dead-time corrections for a photon counter would be excessive, the VFC maintains a linear response and allows the recording of data at high time resolution. Results of laboratory tests are given for the signal-to-noise characteristics, linearity, stability, and transient response of the VFC when used in conjunction with EMI 9658 and RCA C31034 photomultipliers.

Dunham, E.↗
NASA NTRS1978

An experiment to study energetic particle fluxes in and beyond the earth's outer magnetosphere

This experiment is designed to take advantage of the ISEE Mother/Daughter dual spacecraft system to study energetic particle phenomena in the earth's outer magnetosphere and beyond. Large geometric factor fixed voltage electrostatic analyzers and passively cooled semiconductor detector telescopes provide high time resolution coverage of the energy range from 1.5 to 300 keV for both ions and electrons. Essentially identical instrumentation is placed on the two spacecraft to separate temporal from spatial effects in the observed particle phenomena.

Anderson, K. A.↗
NASA NTRS1978

Measurement and analysis of magnetic field variation during a class 2b flare

A digital analysis of high-time-resolution videomagnetograms taken during a class 2b flare that occurred at 60 deg east is reported. The data were obtained at the Big Bear Observatory and calibrated by a Mt. Wilson magnetogram. Changes of weak magnetic fields (less than 100 G) with an amplitude of 30% to 100% have been detected over 55% of the optical flare region, apparently taking place at the initial phase of the flare. Statistical considerations suggest a real flare association with most of these changes. H-alpha observations show that large changes took place over the footpoints of heavily inclined structures like penumbral fibrils, while smaller changes took place over the plage region. An apparent polarity reversal was found at the feet of erupted fibrils. Based on force-free field calculations these changes can be reasonably explained as a transformation of the current-carrying fields to potential fields which produced large changes in the field-line inclination and rotation.

Tanaka, K.↗
NASA NTRS1978

Observations of auroral fading before breakup

The onset of auroral breakup was studied by means of a variety of instruments with time resolution of some tens of seconds. Rapid sequences of all-sky photographs and fast meridian scans by photometers show that breakup is usually preceded by moderate brightening which is followed by fading of the auroral brightness lasting one or two min, all occurring before the actual breakup. Data from the International Magnetospheric Study magnetometer network might indicate a correlated response by the local auroral and ionospheric currents. Riometer recordings show a slow decrease in ionospheric radio wave absorption over a period of about 10 min prior to breakup. The observations are discussed with reference to the trigger mechanism for the expansion phase of a magnetospheric substorm.

Pellinen, R. J.↗
NASA NTRS1978

Imp 6 measurements in the distant polar cusp during substorms

High time-resolution data from the magnetic field, plasma, energetic particle, and VLF wave experiments performed aboard Imp 6 in a study of the distant dayside cusp during substorms are described. The cusp was studied when its location was slightly equatorward of its normal location and the geomagnetic dipole was tilted in the appropriate direction. The data support both reconnection and diffusion as methods of particle entry to the magnetosphere. The evidence (1) indicates an acceleration process to explain enhancements of 400 to 600-km/sec protons above their magnetosheath intensities, and (2) suggests convection of field lines over the polar cap as a means of explaining the lack of low-energy protons near the low-latitude boundary of the cusp. Magnetic field fluctuations, a perturbation vector, ion cyclotron waves, and an abrupt change in the intensity of both whistler waves and electrostatic waves are characterized.

Fairfield, D. H.↗
NASA NTRS1978

Rapid space/time variations in mesospheric ozone

A 5 meter telescope was used to observe variations in the narrow emission line which is present in the nightime emission spectrum of ozone. The line was measured for several nights on two different transitions of the ozone molecule at 110.8 GHz and 142.2 GHz. Individual spectra with a time resolution of 5 minutes were taken. The narrow emission line showed considerable variation in intensity indicating that the ozone layer from which its arises has a rather detailed structure. Analysis of the line profile shows that the emission is coming from an ozone layer in the 55-75 km region of the mesosphere. This layer has a column density of 2 x 10 to the 16th power molecules/sq cm in a vertical path through the region.

Buhl, D.↗