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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The application of laser Rayleigh scattering to gas density measurements in hypersonic helium flows

Measurements of the mean static free-stream gas density have been made in two Langley Research Center helium facilities, the 3-inch leg of the high-Reynolds-number helium complex and the 22-inch hypersonic helium tunnel. Rayleigh scattering of a CW argon ion laser beam at 514.5 nm provided the basic physical mechanism. The behavior of the scattered signal was linear, confirmed by a preliminary laboratory study. That study also revealed the need to introduce baffles to reduce stray light. A relatively simple optical system and associated photon-counting electronics were utilized to obtain data for densities from 10 to the 23rd to 10 to the 25th per cu m. The major purpose, to confirm the applicability of this technique in the hypersonic helium flow, was accomplished.

Hoppe, J. C.↗
NASA NTRS1979

Optical counterpart of 2A0311-227

Spectrophotometric observations of the optical counterpart of the X-ray source 2A0311-227 are reported. A 1.3-m telescope associated with a photon-counting spectral scanner was used for observations in the range 4000 to 5800 A. Strong emission features are noted for H I, He II at 4686 A and the C III-N III blend at 4640-4650 A. Analyses of radial velocities show the star to be a spectroscopic binary with a period of 81.04 + or - 0.01 min, while blue and yellow light curves reveal variations in stellar color. Similarities between this binary and AM Herculis are noted and a model of a 1.2-solar mass white dwarf with a 0.2-solar mass companion at a separation of 0.7 solar radii is suggested.

Williams, G.↗
NASA NTRS1979

Faint-object spectrograph for Space Telescope

The paper presents the Faint Object Spectrograph (FOS) for the Space Telescope to provide a digitized spectra of faint astronomical objects over the 115 to 700 nm wavelength range at resolving powers of 1000 and 100. A variety of concave gratings and prisms is employed to form nearly stigmatic spectra on one of the two Digicon photon counting detectors which are optimized for two different but overlapping ranges. The scientific goals associated with quasars, active galaxies, and objects within our solar system are discussed, and the FOS optical design features, including detectors, electronics, signal processing, power supplies, and data handling are examined. The FOS structural system, mechanism, and controls are described, along with the predicted performance capabilities in the spectral and spectropolarimetry modes. Finally, system performance parameters, including spatial resolution, time resolution, noise, and efficiency are discussed.

Harms, r. J.↗
NASA NTRS1980

Rocket instrument for far-UV spectrophotometry of faint astronomical objects

A sensitive sounding rocket instrument for moderate (about 10-A) resolution far-UV (1160-1750-A) spectrophotometry of faint astronomical objects has been developed. The instrument employes a photon-counting microchannel plate imaging detector and a concave grating spectrograph behind a 40-cm Dall-Kirkham telescope. A unique remote-control pointing system, incorporating an SIT vidicon aspect camera, two star trackers, and a tone-encoded command telemetry link, permits the telescope to be oriented to within 5 arc sec of any target for which suitable guide stars can be found. The design, construction, calibration, and flight performance of the instrument are discussed.

Hartig, G. F.↗
NASA NTRS1979

Multi-anode microchannel arrays

The Multi-Anode Microchannel Arrays (MAMA's) are a family of photoelectric, photon-counting array detectors being developed for use in instruments on both ground-based and space-borne telescopes. These detectors combine high sensitivity and photometric stability with a high-resolution imaging capability. MAMA detectors can be operated in a windowless configuration at extreme-ultraviolet and soft X-ray wavelengths or in a sealed configuration at ultraviolet and visible wavelengths. Prototype MAMA detectors with up to 512 x 512 pixels are now being tested in the laboratory and telescope operation of a simple (10 x 10)-pixel visible-light detector has been initiated. The construction and modes-of-operation of the MAMA detectors are briefly described and performance data are presented.

Timothy, J. G.↗
NASA NTRS1980

New position-sensitive hard X-ray spectrometer

The design and features of a new prototype Lixiscope (Low intensity X-ray imaging scope) is described. It is shown that in addition to good spatial and temporal resolution in the 20 keV to 200 keV region, it is capable of single-photon counting, imaging as well as good energy resolution. It is concluded that the device is well suited for future low-flux applications in astronomy, medicine, and industry.

Yin, L. I.↗
NASA NTRS1982

Improved Lixiscope

Improved lixiscope utilizes fast-decay scintillators and multiple or curved microchannels to achieve high energy and spatial resolution as well as single-photon counting. New unit, with higher energy resolution, is intended for X-ray astronomy, although it could be applied terrestrially wherever a sensitive portable radiation spectrometer is required for 20-to-200-keV range.

Yin, L. I.↗
NASA NTRS1981

Laser radar

A laser radar system to measure the altitude distribution of atmospheric sodium in the 80 to 100 km altitude region was constructed. The system consists of a high power pulsed dye laser, large aperture receiving telescope, and photon counting and signal processing equipment. The receiving system development, and the construction and development of the dye laser are discussed. Spatial and temporal filtering of the data to enhance the resolution of the sodium lidar profiles is described as well as computer model studies of the sodium density response to gravity wave perturbations.

Source record↗
NASA NTRS1980

A lower limit on the magnitude of the companion to HDE 226868 /Cygnus X-1/

High-precision digital spectra of the HDE 226868/Cygnus X-1 system have been obtained at a variety of orbital phases, using a Digicon photon counting array at the coude focus of the Lick Shane reflector. The spectra have been cross-correlated to search for evidence for the existence of a luminous stellar companion to HDE 226868, as has been suggested by several models where the secondary star is not a black hole. We find no evidence for such a star and place a lower limit on the difference between HDE 226868 and its companion of 4 magnitudes. This limit rules out all of the models for the Cygnus X-1 system calculated by Avni and Bahcall which include main-sequence stars as secondaries rather than black holes. A merit function generally useful for cross-correlation of digital spectra is described.

Shafter, A. W.↗
NASA NTRS1980

A dual charge-coupled device /CCD/, astronomical spectrometer and direct imaging camera. I - Optical and detector systems

The MASCOT (MIT Astronomical Spectrometer/Camera for Optical Telescopes), an instrument capable of simultaneously performing both direct imaging and spectrometry of faint objects, is examined. An optical layout is given of the instrument which uses two CCD's mounted on the same temperature regulated detector block. Two sources of noise on the signal are discussed: (1) the CCD readout noise, which results in a constant uncertainty in the number of electrons collected from each pixel; and (2) the photon counting noise. The sensitivity of the device is limited by the sky brightness, the overall quantum efficiency, the resolution, and the readout noise of the CCD. Therefore, total system efficiency is calculated at about 15%.

Meyer, S. S.↗
NASA NTRS1981

The Johns Hopkins Ultraviolet Telescope for Shuttle astronomy

The Hopkins Ultraviolet Telescope (HUT) is a 90-cm f/2 prime focus telescope and spectrometer with a photon-counting microchannel plate detector designed to obtain moderate resolution (wavelength interval, approximately 4 A) spectrophotometry of faint (visual magnitude, less than approximately 17) objects in the far-ultraviolet spectral region (approximately 900-1700 A). The HUT will be mounted on the Spacelab Instrument Pointing System and will be operated by a Payload Specialist using a field acquisition TV system to assist in locating targets. The initial flight of the HUT, expected in 1984 or 1985, will be devoted primarily to the study of quasars and active galactic nuclei, emphasizing the 900-1200 A spectral region which is inaccessible with other existing or currently planned orbiting instruments.

Davidson, A. F.↗
NASA NTRS1981

A spectroscopic study of the high excitation nebula NGC 6302

The wonderfully intricate irregular gaseous nebula NGC 6302 shows a great range of excitation from the S I to Fe VII forbidden lines. Data obtained with the International Ultraviolet Explorer (IUE) covering the spectral range of wavelengths 1200-3203 and with the image-photon counting system at the Anglo-Australian telescope emphasizing the region of wavelengths 3200-4880 are used for a new determination of the chemical composition of this object. No simple theoretical model can represent the observed intensities. Helium and nitrogen are enhanced in abundance, as noted by previous observers, but the enrichment of nitrogen is a whole order of magnitude. Carbon and oxygen are decreased in abundance, neon and heavier elements show a 'normal' abundance pattern, but calcium and possibly silicon are depleted; presumably they are concentrated in grains.

Aller, L. H.↗
NASA NTRS1982

MAGELLAN: High resolution spectroscopy at FUV and EUV wavelengths

The aim of ESA's MAGELLAN mission is to provide high resolution spectra of celestial sources down to sixteenth magnitude over the extreme ultraviolet wavelength range (between 50 and 140 nm). This range extends from studies of interstellar matter in the disc and halo of this and other galaxies, to stellar envelopes, hot and evolved stars, clusters, intergalactic matter, nuclei of galaxies, quasars, and, finally, planets and satellites. The instrument has a nonconventional optical design using only one reflecting surface; a high groove density concave grating collects the star light, diffracts it and focuses its spectrum into a bidimensional windowless detector operated in a photon counting mode. The slitless configuration provides the spectra of all the sources (point like and extended) in the field of view of the grating. This field of view is limited by a grid collimator to reduce the diffuse background, the stray light and the probability of overlapping spectra in crowded fields.

Grewing, M.↗
NASA NTRS1980

Performance of a near-optimum receiver for optical antipodal signals

The well known photon-counting, heterodyning and homodyning optical receivers (operating over a free-space channel) do not achieve the performance of the optimum quantum receiver, which attains significantly lower error-probabilities than the above receiver structures. A demonstration and analysis are given of a binary antipodal optical receiver that exponentially approaches the performance of the optimum quantum receiver. A general mathematical model is developed, and subsequently used to evaluate the effects of external interference and internal error-sources on receiver performance.

Vilnrotter, V. A.↗
NASA NTRS1982

Rocket-borne instrument with a high-resolution microchannel plate detector for planetary UV spectroscopy

A telescope-spectrograph employing a photon-counting microchannel plate (MCP)-CODACON detector has been built, tested, and flown on a sounding rocket. The detector uses a curved-channel MCP proximity focused onto a coded anode array of 1024 channels spaced 25.4-mm center to center. High quantum efficiency is obtained by depositing a cesium iodide photocathode on the front surface of the MCP. The instrument has obtained an ultraviolet spectrum of Jupiter with a spectral resolution of 8 A, which is higher than that of any previously reported observation in this wavelength range.

Mcclintock, W. E.↗
NASA NTRS1982

Recent progress with multi-anode microchannel array detector systems

The construction and modes of operation of Multi-Anode Microchannel Arrays (MAMA's) are briefly reviewed. The MAMA detectors, which are a family of photoelectric, photon-counting array detectors being developed specifically for use in instruments on ground-based and space-borne telescopes, combine the high sensitivity and photometric stability of a conventional channel electron multiplier with a high-resolution imaging capability. The MAMA detectors feature low applied potential (less than 3 kV), high gain (greater than 10 to the 6th electrons/pulse), an absolute event timing accuracy of 100 ns or better, a very long count lifetime (greater than 2.5 x 10 to the 11th counts/sq mm), and a power consumption of less than 30 W for a complete system

Timothy, J. G.↗
NASA NTRS1984

Efficient Coding for Optical Communication

Possibility of using photon counting, rather than conventional linear amplification, for optical communications discussed. Study suggests combination of pulse-position modulation and Reed-Solomon coding gives signaling efficiency of 3 to 4 bits/photon.

Mceliece, R. J.↗