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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 505 records · Page 28
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NASA NTRS1977

Recombination lasing in a magnetoplasmadynamic arcjet

The plasmadynamic recombination laser concept is verified experimentally in a high power quasi-steady MPD arcjet operating at 4 kA and 12 g/sec of argon. Measurements of the spatial variation of electron temperature, electron density, and population densities in the arc exhaust flow confirm that inverted populations of the 4p to 4s Ar II transitions are established by collisional-radiative recombination of the Ar III ion. Using an optical cavity aligned transversely to the flow, recombination lasing of four such transitions, 5145, 4880, 4764 and 4727 A, is observed spectro-photographically and photoelectrically over the entire 1-msec discharge.

Campbell, E. M.↗
NASA NTRS1976

Gamma-ray astronomy: Nuclear transition region

This monograph reviews the major theoretical and experimental efforts made during the past 12 years in gamma-ray astronomy over the energy range from 10 keV to about 100 MeV, where nuclear-transition lines are expected. Early attempts to detect celestial gamma rays are recounted, mechanisms of gamma-ray line and continuum production are examined, and formulas giving the various possible differential gamma-ray spectral shapes are provided. Predicted fluxes are discussed for solar gamma rays as well as for gamma emission from supernova remnants, supernovae, neutron stars, flare stars, the galactic core and disk, black holes, and diffuse sources. Gamma-ray interactions with matter are analyzed, particularly the photoelectric effect, Compton scattering from free electrons, and pair production in nuclear fields. Significant results are summarized for observations of gamma rays from the sun as well as from point and extended sources within and beyond the Galaxy, including diffuse fluxes and transient gamma-ray bursts. Factors pertaining to the design of gamma-ray astronomy experiments are considered, especially detector background limitations, gamma-ray production within instruments, and present-day detection methods.

Chupp, E. L.↗
NASA NTRS1977

Facular line profiles and facular models

Profiles for lines near 5250 A have been calculated from facular models and compared with observed profiles. The observations are from photographic and photoelectric spectra. The atomic parameters are determined by comparison of calculated profiles with those observed for the quiet sun. The effects of finite spatial resolution and a magnetic field are required to obtain agreement with observed facular line profiles. The empirical magnetic field deduced by matching observed and calculated profiles is reasonably consistent with that in the facular models. The main purpose of this paper is to show that by including the effects of scattered photospheric light and a strong magnetic field, reasonable agreement can be achieved between observed and calculated facular line profiles. Results are also presented for the wing of the Ca II K line, showing line profiles and effective filtergram contrasts for several facular models. It is concluded that observations made with weak Fraunhofer lines are not very useful for discrimination among facular models, particularly without simultaneous magnetic-field measurements. The K line may offer a better discriminator. The facular model presently favored has a magnetic field strength of about 1500 gauss at the surface of the photosphere.

Chapman, G. A.↗
NASA NTRS1977

The solar boron abundance

Positive evidence for the presence of boron in the sun is reported, and the chemical abundance of boron in the photosphere is derived from photoelectric measurements of the solar spectrum near 2500 A obtained with a rocketborne high-resolution spectrometer. Short sections of the spectrum in the vicinities of the B I lines at 2496.772 and 2497.723 A are plotted. The photospheric boron abundance is determined primarily by analyzing the solar-center spectrum near the first of the two lines in the framework of several single-component photospheric models. The logarithmic boron abundance obtained is 2.6, with an estimated uncertainty of plus or minus 0.3 dex, on the scale where that of hydrogen is 12.0. This value is shown to be in excellent agreement with that predicted for a nucleosynthesis model in which Li, Be, and B are produced by cosmic-ray spallation.

Kohl, J. L.↗
NASA NTRS1977

Observations of the phase variation of Venus CO2 equivalent widths

Equivalent widths determined from photoelectric scans of Venus CO2 absorption lines measured at phase angles of 5.1 to 170 deg are presented. The data-reduction procedure is described in detail, and phase curves are plotted for three model atmospheres in which CO2 is homogeneously mixed with Mie-scattering particles or inhomogeneously mixed with Henyey-Greenstein particles. All three data sets are found to indicate that the equivalent-width maximum occurs at a phase angle much lower than 100 deg. It is concluded that two scattering layers are not required on Venus to explain the shape of the observed phase curve and that the mixing ratio of scattering particles to CO2 increases with depth at high altitudes.

Barker, E. S.↗
NASA NTRS1977

Optical detection of blade flutter

The paper examines the capabilities of photoelectric scanning (PES) and stroboscopic imagery (SI) as optical monitoring tools for detection of the onset of flutter in the fan blades of an aircraft gas turbine engine. Both optical techniques give visual data in real time as well as video-tape records. PES is shown to be an ideal flutter monitor, since a single cathode ray tube displays the behavior of all the blades in a stage simultaneously. Operation of the SI system continuously while searching for a flutter condition imposes severe demands on the flash tube and affects its reliability, thus limiting its use as a flutter monitor. A better method of operation is to search for flutter with the PES and limit the use of SI to those times when the PES indicates interesting blade activity.

Nieberding, W. C.↗
NASA NTRS1977

Extreme ultraviolet spectrograph ATM experiment S082B

The extreme-ultraviolet double-dispersion photographic spectrograph for the Apollo Telescope Mount (ATM) experiment S082B on Skylab is described. Novel features were the use of a predisperser grating with a ruling whose spacing varied approximately linearly with distance for the purpose of increasing the instrument speed by reducing the astigmatism and a photoelectric servosystem to stabilize to 1 sec of arc the solar image at various near-limb positions. The 970-3940-A range was covered in two sections with effective resolving power of approximately 30,000 from 1100 A to 1970 A. The spatial resolution was 2 x 60 solar sec of arc. During the Skylab mission 6400 exposures were made with the instrument pointed by an astronaut at selected and recorded solar positions.

Bartoe, J.-D. F.↗
NASA NTRS1977

Preliminary photometry in the nuclear region of NGC 6624

Results are presented for initial observations near the center of NGC 6624. Photoelectrically calibrated photographic photometry is used to discuss the characteristics of the nucleus and individual stars in its vicinity. The data in their present form are not conclusive, but could imply the presence of a closely bound group of stars near the cluster center. It is proposed that one or more of these stars may be binary systems similar to the model recently suggested for Cyg X-2. However, a massive object near the center cannot be ruled out.

Harvel, C. A.↗
NASA NTRS1977

Recombination lasing in a magnetoplasmadynamic arcjet

The plasmadynamic recombination laser concept is verified experimentally in a high-power quasisteady MPD arcjet operating at 4 kA and 12 g/sec of argon. Measurements of the spatial variation of electron temperature, electron density, and population densities in the arc exhaust flow confirm that inverted populations of the 4p to 4s ArII transitions are established by collisional-radiative recombination of the ArIII ion. Using an optical cavity aligned transversely to the flow, recombination lasing of four such transitions, 5145, 4880, 4764, and 4727 A, is observed spectrophotographically and photoelectrically over the entire 1-msec discharge.

Campbell, E. M.↗
NASA NTRS1977

Three-dimensional determination of the center of the Watts datum relative to the lunar center of mass

The location of the origin of the Watts datum for the marginal zone of the moon is determined using results of 2770 photoelectric occultation observations obtained over an 18-yr period in combination with 1787 laser time-delay measurements carried out over a five-year period. The lunar ephemeris employed is an experimental one developed from a much shorter span of laser observations. The final solution is obtained by adopting LURE2 parameters and correcting 19 lunar orbital, solar orbital, and coordinate-system parameters. The offsets for the center of the Watts datum are found to be approximately +6.8 km for x1, -2.5 km for x2, and +0.06 km for x3 with respect to the lunar principal axes of inertia.

Mulholland, J. D.↗
NASA NTRS1977

Trajectories and orbits from the NASA-NMSU Meteor Observatory. II

Trajectory data and orbital elements for 12 double-station meteors photographed by the NASA-NMSU Meteor Observatory during the winter of 1975-1976 are presented. Three of these are members of the Quadrantid stream. Photoelectric timing of meteors, uncertainties in the derived orbital elements, and monitoring of the night sky with a two-channel photometer are discussed.

Harvey, G. A.↗
NASA NTRS1977

Uranus - Limb and polar brightening at 7300 A

Pinhole photoelectric area-scanning photometry of the Uranus disk demonstrates directly the existence of both limb and polar brightening in the 7300 A CH4 band. Polar brightening, which appears to be present also at continuum wavelengths, is interpreted as being caused by scattering in a thin aerosol haze located over the polar region.

Franz, O. G.↗
NASA NTRS1977

Observed departures from LTE ionization equilibrium in late-type giants

Photoelectric scans of the Ca I line at 6572 A and the forbidden Ca II transition at 7323 A are studied in the K giant alpha Tau, the M supergiant alpha Ori, and the M giants beta And, alpha Cet, mu Gem, and beta Peg. The relative strengths of these lines are shown to be indicative of the ratio of the relative number densities of the neutral and ionized species in the photosphere. The analysis indicates an overionization relative to LTE in qualitative agreement with the theoretical calculations of Auman and Woodrow for the K and M giants. The M supergiant alpha Ori exhibits a large overionization relative to LTE.

Ramsey, L. W.↗
NASA NTRS1977

UBV photometry of small and distant asteroids

Photoelectric magnitudes and colors on the ultraviolet (UBV) system are presented for 65 minor planets, including four Mars crossers, six Trojans, and main-belt objects down to 6 km in diameter. The Trojans all have very similar colors not characteristic of the main-belt population. A paucity of S-type asteroids at the smallest diameters, predicted from trends seen at larger sizes, is not observed. The newly available color data for small objects ranging from 1.0 to 5.2 astronomic units in heliocentric distance show the main belt to be a transition zone between predominantly silicate and carbonaceous compositions.

Zellner, B.↗
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 Lyman alpha coronagraph

The rocket-borne Lyman alpha coronagraph (RLAC) is to be used in the absence of a natural solar eclipse to determine coronal temperatures from measurements of the line width of Lyman-alpha and to determine neutral hydrogen densities of coronal material from the absolute intensity. The coronagraph consists of a 75-cm Fastie-Ebert scanning spectrometer with an AMR 641 photoelectric detection system, an off-axis parabolic primary mirror, and an occulting system. A special optical arrangement achieves rejection of radiation from the solar disk.

Kohl, J. L.↗
NASA NTRS1977

A search for interstellar NaH in diffuse clouds

The paper reports on a search for the (8, 0) R(0) line of the A-X transition of NaH at 3990.88 A toward Zeta Oph and Sigma Sco, which was performed using a spectroscopic photoelectric imaging Fabry-Perot interferometer at the coude focus of a 2.2-m telescope. One-sigma upper limits on the NaH equivalent width are derived (0.26 mA for Zeta Oph and 0.69 mA for Sigma Sco), and two-sigma upper limits on the NaH column densities are obtained which imply that the formation rate for NaH cannot be large. It is noted that the latter upper limits are only about one order of magnitude higher than the most optimistic expectation of the NaH column density for formation of this molecule on grains.

Snow, T. P., Jr.↗
NASA NTRS1977

Extended observations of Vela X-1 by OSO-8

The Goddard Space Flight Center Cosmic X-Ray Experiment aboard OSO-8 viewed the X-ray binary pulsar, Vela X-1, on three occasions from late 1975 through late 1976. The X-ray spectrum is well represented by a power law modified by photoelectric absorption, a high energy cutoff, and a line feature at approximately 6.8 keV. When combined with other observations, our measurements show that the pulse period is not decreasing monotonically. The three eclipses observed all indicate a significant eclipse flux.

Becker, R. H.↗