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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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NASA NTRS1975

Far-infrared observations of W51 with high spatial resolution

Observations of the core of W51 have been made from the NASA C-141 Airborne Infrared Observatory at 55 microns with 17-, 35-, and 85-arc sec apertures and at 100 microns with a 35-arc sec aperture. These observations suggest the presence of a small less than about 20 arc sec source at 55 microns surrounded by a much broader diffuse background. In the center of the source the optical depth at 55 and 100 microns is on the order of 0.1-0.2.

Harvey, P. M.↗

NASA NTRS1975

Marking LANDSAT images with small mirror reflectors

Uniquely identifiable artificial landmarks were generated in LANDSAT imagery by making use of specular solar reflection from small, easily transportable mirrors. The results are impressive in well-registered color composite enlargements, where the mirror returns appear as bright white spots. The signatures are unique enough that returns can be readily located in the computer compatible tape records either manually or by machine search. As embodied in experiments to date, the system is entirely passive. Mirrors must be carefully positioned prior to each satellite pass, but the required angle calculations are simple enough to be made on a hand calculator and the required input data are easily available. Possible applications of the technique include providing site identification and geodetic control in remote regions of the earth, enhancement of small targets such as offshore oil derricks, providing atmospheric transmission data coincident with other LANDSAT experiments, and providing a nearly perfect optical point source for overall system checkout.

Evans, W. E.↗

NASA NTRS1977

Characterization of gigahertz (GHz) bandwidth photomultipliers

The average impulse response, root-mean-square times jitter as a function of signal level, single photoelectron distribution, and multiphotoelectron dark-count distribution have been measured for two static crossed-field and five electrostatic photomultipliers. The optical signal source for the first three of these tests was a 30 picosecond mode-locked laser pulse at 0.53 micron. The static crossed-field detectors had 2-photoelectron resolution, less than 200 ps rise times, and rms time jitters of 30 ps at the single photoelectron level. The electrostatic photomultipliers had rise times from 1 to 2.5 nanoseconds, and rms time jitters from 160 to 650 ps at the same signal level. The two static crossed-field photomultipliers had ion-feedback-generated dark pulses to the 50-photoelectron level, whereas one electrostatic photomultiplier had dark pulses to the 30-photoelectron level.

Abshire, J. B.↗

NASA NTRS1977

Systems for measuring response statistics of gigahertz bandwidth photomultipliers

New systems have been developed for measuring the average impulse response, the pulse-height spectrum, the transit-time statistics as a function of signal level, and the dark-count spectrum of gigahertz bandwidth photomultipliers. Measurements showed that the 0.53 microns pulse used as an optical test source had a 30 picoseconds and less than 70 ps pulse width. Calibration data showed the system resolution to be less than 20 ps for root mean square transit-time measurements. Test data for a static crossed-field photomultiplier showed 2-photoelectron resolution and less than 30-ps time jitter over the 1- to 100-photoelectron range.

Abshire, J. B.↗

NASA NTRS1977

High resolution X-ray optics for astronomical and laboratory sources

In recent years X-ray telescopes have been used successfully for high resolution observations of astronomical objects, in particular the solar corona. At the present time X-ray microscopes are being developed for diagnostics of laser and electron beam induced fusion plasmas. This paper describes both types of imaging systems using as examples the AS&E X-ray telescope on Skylab and a 10X microscope being built for Los Alamos Scientific Laboratories. The designs, manufacturing tolerances, fabrication, testing, and performance are discussed. Steps for further development in both imaging areas are identified.

Silk, J. K.↗

NASA NTRS1979

High power phase locked laser oscillators

The feasibility of mechanizing an adaptive array of independent laser oscillators for generation of a high power coherent output was experimentally investigated. Tests were structured to evaluate component/system requirements for delivery of energy to a low-earth orbit satellite. Initial experiments addressed the control issues of phase locking unstable resonators at low power levels. A successful phase lock demonstration formed the basis for the design and fabrication of the high power, water-cooled, control mirror subsequently installed in the NASA LeRC high power laser. Tests were performed to characterize the operational limits of the laser system and included quantitative assessment of the frequency stability, noise sources, and optical properties of the beam.

Hayes, C. L.↗

NASA NTRS1978

Study, optimization, and design of a laser heat engine

Laser heat engine concepts, proposed for satellite applications, are analyzed to determine which engine concept best meets the requirements of high efficiency (50 percent or better), continuous operation in space using near-term technology. The analysis of laser heat engines includes the thermodynamic cycles, engine design, laser power sources, collector/concentrator optics, receiving windows, absorbers, working fluids, electricity generation, and heat rejection. Specific engine concepts, optimized according to thermal efficiency, are rated by their technological availability and scaling to higher powers. A near-term experimental demonstration of the laser heat engine concept appears feasible utilizing an Otto cycle powered by CO2 laser radiation coupled into the engine through a diamond window. Higher cycle temperatures, higher efficiencies, and scalability to larger sizes appear to be achievable from a laser heat engine design based on the Brayton cycle and powered by a CO laser.

Taussig, R. T.↗

NASA NTRS1979

Simultaneous detection and intensity estimation of an optical image

A statistical model for simultaneous detection and single parameter estimation of a stochastic signal against background noise is obtained. Two strategies, Bayes and maximum likelihood, are discussed. The detection of an optical point source imaged on a photosensitive surface and the estimation of its intensity based on such strategies are examined. An almost optimum estimate is also proposed and its statistical properties are studied.

Wang, L.↗

NASA NTRS1979

Infrared and optical measurements of the ionized gas in K3-50

Results are reported for optical, near-IR, and mid-IR spectrophotometry of the compact H II region K3-50A. The emission-line observations imply an electron density of about 100,000 per cu cm; the consistency of density measurements in the optical, IR, and radio sources suggests that the optical counterpart of K3-50A is a reflection nebula. Previous measurements of the anomalous extinction law in K3-50A are confirmed, this law is extended out to B-alpha at 4 microns, and a 9-micron optical depth of about 2.5 is obtained. Elemental abundances are derived from measurements of emission lines of several dominant ions of the same element and found to be in close agreement (50%) with mean cosmic abundances. Individual ionic ratios are compared with model H II region calculations to determine the nature of the ionizing radiation. It is concluded that if nongray UV dust absorption does not modify the spectrum appreciably, the radiation temperature can be associated with a stellar surface temperature of about 37,000 K, corresponding to an O6 supergiant.

Lester, D. F.↗

NASA NTRS1980

Observations of interstellar H2O emission at 183 gigahertz

Observations of the 183-GHz rotational transition of water vapor in interstellar molecular clouds are reported. The observations were made with a portable double-sideband superheterodyne radiometer used with the 91-cm Cassegrain telescope on board the Kuiper Airborne Observatory. An emission feature was detected in the direction of the Kleinmann-Low nebula in Orion with a peak antenna temperature of 15 K, a local standard of rest velocity of 8 km/sec, and a width of 15 km/sec. A plateau component of the emission profile is attributed to the 1-arcmin region characteristic of plateau emission from other observed molecules, with emission enhanced over that expected for thermal excitation, while the spike component observed is consistent with an optically thick source of the size of the molecular ridge in Orion at a temperature of 50 K and a column density greater than or equal to 3 x 10 to the 17th/sq cm, implying that H2O is one of the more abundant species in the Orion Molecular Cloud. Emission at 183 GHz was not detected in Sgr A, Sgr B2, W3, W43, W49, W51, DR 21, NGC 1333, NGC 7027, GL 2591 or the Rho Oph cloud; it may have been detected in M 17.

Waters, J. W.↗

NASA NTRS1980

The distance and spectrum of the Apollo gamma-ray burst

The gamma-ray spectrometer on Apollo 16 obtained spectral information with good energy resolution from more than 2500 burst photons in the energy range 0.06-5.16 MeV. The spectrum from 1 keV to 2 MeV, observed at X-ray energies by the Apollo X-ray spectrometer, is fitted by a thermal bremsstrahlung spectrum with kT = 500 keV. The success of the fit implies that the source is optically thin, and it follows that it must be closer than 50 pc. Absence of spectral variability suggests that the burst results from isothermal changes in emission measure.

Gilman, D.↗

NASA NTRS1983

X-ray observations of 20 3CR radio galaxies and their environs

X-ray observations of 20 3CR radio galaxies using the Imaging Proportional Counter on the Einstein Observatory are reported. Fourteen of the 18 galaxies, plus two sources without optical identification, are detected with soft X-ray luminosities (Lx) ranging from 10 to the 40.9th to 10 to the 44.4th ergs/s. In four of the galaxies there is evidence for extended X-ray structure. Lx is statistically correlated with the radio power of the core, the lobe radio power (especially below 1 GHz), and the steepness of the lobe radio spectrum at high frequencies. The complex interrelations between X-ray luminosities and radio core, radio lobe, optical nuclei, and galaxy clustering are examined; and it is found that a cluster origin of the X-rays provides the best explanation of these effects. Constraints on synchrotron and inverse Compton production of X-rays in radio lobes and on mechanisms of lobe confinement are also discussed.

Feigelson, E. D.↗

NASA NTRS1984

Variability of the ultraviolet spectrum of BL Lacertae objects

Attention is given to repeated observations of the two nearby BL Lac objects, Mrk 421 and PKS 0521-36, comparing the temporal behavior of their continuum in the 1300-3000 A range with that observed in intrinsically bright BL Lac objects and in Seyfert galaxies. Also discussed are the emission lines in the UV and optical spectrum of PKS 0521-36. It is suggested that the difference in variability pattern between BL Lac objects and Seyfert galaxies may be due to differences in the properties of the nonthermal continuum related to differences in accretion regimes, although it is more probably due to the presence of different continuum components in Seyfert galaxies. In BL Lac objects, the UV spectrum is likely to be synchrotron radiation from an optically thin source.

Ulrich, M. H.↗

NASA NTRS1984

Testing relativity with solar system dynamics

A major breakthrough is described in the accuracy of Solar System dynamical tests of relativistic gravity. The breakthrough was achieved by factoring in ranging data from Viking Landers 1 and 2 from the surface of Mars. Other key data sources included optical transit circle observations, lunar laser ranging, planetary radar, and spacecraft (Mariner 9 to Mars and Mariner 10 to Mercury). The Solar System model which is used to fit the data and the process by which such fits are performed are explained and results are discussed. The results are fully consistent with the predictions of General Relativity.

Hellings, R. W.↗

NASA NTRS1986

Saturn: A unique magnetosphere/ionosphere/ring interaction

Latitudinal variations in images of Saturn's disk, upper atmospheric temperatures, and ionospheric electron density anomalies found in magnetic conjugacy with features in Saturn's ring plane are discussed. It is suggested that latitudinal variations are the result of a variable influx of water, transported along magnetic field lines from sources in Saturn's ring plane. Two such sources with optical counterparts in the inner B ring can be readily attributed to an electromagnetic erosion process that transports water in the form of high charge to mass ratio particles (ions or submicron grains with 1 electron charge) along magnetic field lines from the ring plane to Saturn's atmosphere. Another is attributed to erosion of the icy satellite Enceladus and the associated E ring.

Converney, J. E. P.↗

NASA NTRS1986

The synchrotron-self-Compton process in spherical geometries. II - Application to active galactic nuclei

Observational implications and constraints on spherical nonthermal synchrotron self-Compton models with applications to AGNs are discussed. The Compton optical depth of the source and the synchrotron optical depth are considered, and plausible electron distributions are discussed. The alpha(0x), alpha(rx), and alpha(0r) system of comparing the fluxes in different energy bands is related to the nonthermal models, and sample spectra are presented that show the spectral features the models can produce. The models are applied to radio-quiet AGNs. It is shown that the infrared and X-ray continua of the AGNs can be produced by nonthermal processes.

Band, D. L.↗

NASA NTRS1986

Saturn - A unique magnetosphere/ionosphere/ring interaction

Latitudinal variations in images of Saturn's disc, upper atmospheric temperatures, and ionospheric electron density anomalies are found in magnetic conjugacy with - i.e., magnetically linked to - features in Saturn's ring plane. It is suggested that these latitudinal variations are the result of a variable influx of water, transported along magnetic field lines from sources in Saturn's ring plane. Two such sources with optical counterparts in the inner B ring can be readily attributed to an electromagnetic erosion process that transports water in the form of high charge to mass ratio particles (ions or submicron grains with 1 electron charge) along magnetic field lines from the ring plane to Saturn's atmosphere. Another is attributed to erosion of the icy satellite Enceladus and the associated E ring.

Connerney, J. E. P.↗

NASA NTRS1987

MODIS - A global ocean facility for the Earth Observing System

A Moderate Resolution Imaging Spectrometer (MODIS) is being planned as a NASA furnished facility for the Earth Observing System (Eos). This sensor will be the primary source of optical global ocean data for a ten-year period following the Eos launch in the mid-1990's. During this period, the MODIS will survey the Earth's surface continuously once every three days in over 100 spectral bands ranging from 0.4 to 14.2 micrometers at a spatial resolution of 1 kilometer. The system is to be divided into two units, MODIS-T which consists of 64 visible and near-infrared channels and which is capable of tilting to avoid specular reflectance from the ocean surface, and MODIS-N with 31-40 spectral channels including ocean color, ocean temperature and atmospheric characterization bands. The total system is anticipated to be a powerful tool for studying global ocean productivity, dynamics and long-term trends.

Barnes, W. L.↗