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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 469 records · Page 26
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NASA NTRS1976

Spectrophotometry of comet Kohoutek (1973f) during pre-perihelion period

Scans of the head of comet Kohoutek obtained during the pre-perihelion period with a photoelectric spectrum scanner are discussed. The mean relative flux distributions and the continuum energy distribution of the head of comet Kohoutek are given and normalized to 479 nm. The emission features of CN, C3, Ch, and the principal Swan band sequences of C2 and Na are identified and discussed. The adopted monochromatic values relative to 479 nm are given and plotted along with the energy distribution of the sun.

Babu, G. S. D.↗
NASA NTRS1976

High photovoltages in ferroelectric ceramics

The short-circuit currents and photo-emfs were measured for various ceramics including barium titanate, lead metaniobate, and lead titanate. It is suggested that the emfs and currents arise from the presence of photoconductor-insulator sandwiches in the presence of space-charge-produced internal fields. Results are in agreement with the proposed theory and indicate that the ferroelectric ceramics are not only producers of high-voltage photoelectricity but a photo-battery, the polarity and magnitude of which can be switched by application of an electrical signal.

Brody, P. S.↗
NASA NTRS1976

Absorption dips at low X-ray energies in Cygnus X-1

Absorbing material in Cygnus X-1 jitters near the line joining the two stars, out of the orbital plane is described. Three looks with the Copernicus satellite at Cygnus X-1 have produced four examples of absorption dips (decreases in the 2 to 7 keV flux from Cygnus X-1 with an increase of spectral hardness consistent with photoelectric absorption).

Murdin, P. G.↗
NASA NTRS1975

A calibration of detectors and gratings between 100 and 600 Angstroms

Calibration and efficiency measurements of magnetic electron multipliers, diffraction gratings, and photocathodes over the wavelength range 100 to 600 A are reported. For some of the measurements it was found necessary to use the synchrotron radiation from a storage ring. Measurements of grating efficiencies, the polarization produced by diffraction gratings, and the photoelectric yields of various photocathodes are included.

Samson, J. A. R.↗
NASA NTRS1976

Photometry of R Coronae Borealis

Visual and photoelectric observations of R Coronae Borealis are presented, including a number of observations surrounding the 1974 minimum. The recent visual history of the variable is examined and the discrete cloud obscuration model is considered.

Dawson, D. W.↗
NASA NTRS1976

The NASA-NMSU automated meteor observatory

A new observatory for meteor research which provides data for study of meteor heights, velocities, orbits, and meteoroid abundances is described. The observing equipment is automated to take advantage of the long periods of favorable observing weather common to the region. Four K-24 cameras, electrically operated, provide the triangulation observations, and four Maksutov f/1.3 cameras with blazed transmission grating provide spectral coverage. The patrol cameras have operated for a year and a half, and approximately 6,000 frames have been exposed by 9 March 1975. Meteor trails appear on 260 of these frames. Sixty-eight trails are of meteors photographed from two locations and thus allow trajectory and orbit determinations for 34 meteors. Photoelectric sensors initiate the 2-second spectrograph exposures, and electrical controls open and close the observatory at present times.

Harvey, G. A.↗
NASA NTRS1975

de Sitter's theory 'melts' Europa's polar cap

In photoelectric observations of a series of occultations of the Jovian satellite Europa by the Jovian satellite Io it was observed that increasingly larger fractions of the north polar region of the former were covered at mid-event with each successive occultation. One of the possible explanations of the observed phenomena involves the existence of a bright north polar cap for Europa. The reported investigation shows that a second explanation may be more plausible. This explanation is related to the possibility that at mid-event the projected minimum distance between the centers of the satellites was smaller than predicted by Sampson's theory.

Aksnes, K.↗
NASA NTRS1975

The effect of atmospheric haze on images of the earth's surface

The adding method to solve the equation of radiative transfer has been applied to a sunlit haze above a reflecting surface. The method was modified to include the effect of inhomogeneities on the underlying surface whose dimensions are less than the mean free path of the photons in the haze. Numerical examples of surface-feature contrast degradation due to haze are presented. This analysis renders it feasible to determine the optical thickness of hazes from haze-degraded images of the ground and also provides a technique to restore ground-image contrast, which has been obscured by haze, in photoelectrically scanned images.

Odell, A. P.↗
NASA NTRS1975

Photon-counting detector arrays based on microchannel array plates

The recent development of the channel electron multiplier (CEM) and its miniaturization into the microchannel array plate (MCP) offers the possibility of fully combining the advantages of the photographic and photoelectric detection systems. The MCP has an image-intensifying capability and the potential of being developed to yield signal outputs superior to those of conventional photomultipliers. In particular, the MCP has a photon-counting capability with a negligible dark-count rate. Furthermore, the MCP can operate stably and efficiently at extreme-ultraviolet and soft X-ray wavelengths in a windowless configuration or can be integrated with a photo-cathode in a sealed tube for use at ultraviolet and visible wavelengths. The operation of one- and two-dimensional photon-counting detector arrays based on the MCP at extreme-ultraviolet wavelengths is described, and the design of sealed arrays for use at ultraviolet and visible wavelengths is briefly discussed.

Timothy, J. G.↗
NASA NTRS1975

Digital image centering. I

A series of parallax plates have been measured on a PDS microdensitometer to assess the possibility of using the PDS for precision relative astrometry and to investigate centering algorithms that might be used to analyze digital images obtained with the Large Space Telescope. The basic repeatability of the PDS is found to be plus or minus 0.6 micron, with the potential for reaching plus or minus 0.2 micron. A very efficient centering algorithm has been developed which fits the marginal density distributions of the image with a Gaussian profile and a sloping background. The accuracy is comparable with the best results obtained with a photoelectric image bisector.

Van Altena, W. F.↗
NASA NTRS1976

Minor planets and related objects. XIX - Shape and pole orientation of /39/ Laetitia

Results are reported for analyses of UBV photoelectric photometric data and light curves of the asteroid Laetitia. The pole orientation is determined using a technique for reducing the scatter in the magnitude-phase relation. No significant variations in color are found over the surface, and the light curves are found to indicate topographic elements (peaks, scarps, or depressions) approximately 10 km in radius. It is shown that the light-curve amplitudes as well as the wide scatter in observed magnitude and phase relation can be explained by a triaxial ellipsoidal figure with a dimensional ratio of about 15:9:5. It is concluded that the size, shape, and composition of this asteroid are highly suggestive of a major collisional fragment from a substantially more massive differentiated parent body.

Sather, R. E.↗
NASA NTRS1976

Mass loss in red giants and supergiants

The circumstellar envelopes surrounding 13 late-type giants and supergiants have been studied using a homogeneous collection of high-resolution, photoelectric scans of strong optical resonance lines. Various properties of the envelopes, including the mass loss rate, dilution factor, hydrogen density, and degree of ionization, have been determined quantitatively.

Sanner, F.↗
NASA NTRS1976

Secular acceleration of Phobos and Q of Mars

Reductions of Mariner 9 TV data of Phobos and Deimos tend to corroborate the existence of a secular acceleration of Phobos commensurate with two recently reported values based on a reprocessing of earth-based data. These values of secular acceleration have been used together with Mariner 9 data on the physical size of Phobos and earth-based photoelectric observations which infer a carbonaceous composition for Phobos to place upper and lower bounds of 50 and 150, respectively, on the tidal dissipation function of Mars. The corresponding upper and lower bounds on the tidal lag angle are 0.19 and 0.57 deg.

Smith, J. C.↗
NASA NTRS1976

Spectrophotometry and UBVRI photometry of Eros

Spectrophotometric and broad-band photoelectric observations of Eros are reported. No existing meteorite spectrum matches the asteroid data directly. Assemblages of iron or stony-iron with ordinary-chondrite material generate the best match for the reflectivity curve of Eros. Variability was found in the 0.6 micron band and V-R and V-I colors.

Wisniewski, W. Z.↗
NASA NTRS1976

The diameter and thermal inertia of 433 Eros

Radiometry of Eros at 10 and 20 micrometers demonstrates that the thermal conductivity of the upper centimeter of the surface is approximately as low as that of the moon, suggesting that the asteroid has a regolith of highly porous rocky material. When combined with photoelectric photometry, these infrared measurements yield an effective diameter of Eros at maximum light of 22 plus or minus 2 km and a geometric albedo of 0.18 plus or minus 0.03.

Morrison, D.↗
NASA NTRS1976

Three-color photometry of HDE 226868 - The optical counterpart of Cygnus X-1

Results of UBV photoelectric observations of HDE 226868 (Cyg X-1) obtained on fifty nights during 1974 are presented. These observations show a light curve with the following characteristics: (1) two unequal light maxima and minima during the 5.6-day orbital period which exhibit a peak-to-peak magnitude change of about 0.07 mag in all colors; (2) a small phase-dependent color variation which results in a reddening in both color indices of about 0.003 mag at times of light minima; (3) erratic light variability on a general time scale of days with an amplitude of plus or minus 0.01 to 0.02 mag and no apparent color dependence.

Lester, D. F.↗
NASA NTRS1976

Martian atmospheric water vapor observations - 1972-74 apparition

Results are reported for 469 photoelectric spectral scans of the Doppler-shifted Martian water lines (at 8197.704 and 8176.975 A), which were obtained during the 1972-74 apparition with an echelle-coude scanner mounted on a 107-in. telescope. These observations covered almost an entire Martian year and were made in three ways: pole to pole on the central meridian, parallel to the equator at various latitudes, and parallel to the terminator at various positions between the limb and the terminator. Previous observations of Martian water vapor are reviewed, and the data-reduction procedures used in the present study are described in detail. The major conclusions are: (1) both seasonal and diurnal variations seem to be controlled by insolation rather than by local topography relative to the 6.1-mb surface; (2) there was a slight negative correlation with elevation, but this improved during seasons of greater water content; (3) the planetwide abundance is low during both equinoctical periods; (4) the maximum abundance occurs at about 40 deg latitude in each hemisphere after solstice; and (5) during the 'drier' seasons near the equinoxes, the atmospheric water vapor content changes by a factor of 2 to 3 over a diurnal cycle with the maximum near local noon.

Barker, E. S.↗
NASA NTRS1976

A real-time optical data processing device

A novel liquid-crystal electro-optical device useful as a real-time input device in coherent optical data processing is described. The device is a special adaptation of an ac photoactivated liquid-crystal light valve, and utilizes a hybrid field effect (45 deg twisted nematic effect in OFF state and pure optical birefringence of the liquid crystal in ON state). A thin-film sandwich exerts photoelectric control over the optical birefringence of a thin liquid-crystal layer. Liquid-crystal layer thickness is successfully reduced without image degradation. The device offers high resolution (better than 100 lines/mm), contrast (better than 100/1), high speed (10 msec ON, 15 msec OFF), high input sensitivity, low power input, low fabrication cost, and can be operated at below 10 V rms. Preliminary measurements on device performance in level slicing, filtering, contrast reversal, and edge enhancement are under way.

Jacobson, A.↗