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At least 847 records · Page 47

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NASA NTRS1989

Design and performance analysis of the CLAES Ne/CO2 cryostat

The design of the dual-stage Ne/CO2 cryostat, constructed for the Cryogenic Limb Array Etalon Spectrometer (CLAES) for the cooling, to their respective required operation temperatures, of the focal plane (to less than 15 K), spectrometer (to less than 30 K), telescope (to less than 150 K), and baffles (to less than 180 K) is described, and the cryostat's performance is analyzed. The results of this study show that the current cryostat will meet all sensor cooling requirements. The cryostat weighs 2276 lbs, of which 988 lbs are charged to the neon and 484 lbs are charged to the CO2. Schematic diagrams of the CLAES cooler/sensor and of the external plumbing are presented together with the test data.

Naes, L. G.↗

NASA NTRS1990

Wavelengths and intensities of a platinum/neon hollow cathode lamp in the region 1100-4000 A

The spectrum of a platinum hollow cathode lamp containing neon carrier gas was recorded photographically and photoelectrically with a 10.7 m normal-incidence vacuum spectrograph. Wavelengths and intensities were determined for about 3000 lines in the region 1100-4000 A. The uncertainty of the measured wavelengths is estimated to be + or - 0.0020 A. Ritz-type wavelengths are given for about 550 classified lines of Pt II with uncertainites varying from + or - 0.0004 A to + or - 0.0025 A. The uncertainty of the relative intensities is estimated to be about 20 percent.

Reader, Joseph↗

NASA NTRS1989

Diamondlike carbon protective coatings for optical windows

Diamondlike carbon (DLC) films were deposited on infrared transmitting optical windows and were evaluated as protective coatings for these windows exposed to particle and rain erosion. The DLC films were deposited on zinc selenide (ZnSe) and zinc sulfide (ZnS) by three different ion beam methods: (1) sputter deposition from a carbon target using an 8-cm argon ion source; (2) direct deposition by a 30-cm hollow cathode ion source with hydrocarbon gas in argon; and (3) dual beam direct deposition by the 30-cm hollow cathode ion source and an 8-cm argon ion source. In an attempt to improve the adherence of the DLC films on ZnSc and ZnS, ion beam cleaning, ion implantation with helium and neon ions, or sputter deposition of a thin, ion beam intermediate coating was employed prior to deposition of the DLC film. The protection that the DLC films afforded the windows from particle and rain erosion was evaluated, along with the hydrogen content, adherence, intrinsic stress, and infrared transmittance of the films. Because of the elevated stress levels in the ion beam sputtered DLC films and in those ion beam deposited with butane, films thicker than 0.1 micron and with good adherence on ZnS and ZnSe could not be generated. An intermediate coating of germanium successfully allowed the DLC films to remain adherent to the optical windows and caused only negligible reduction in the specular transmittance of the ZnS and ZnSe at 10 microns.

Swec, Diane M.↗

NASA NTRS1990

Degradation of the lunar vacuum by a moon base

Several industrial processes requiring high and ultra-high vacuum similar to the lunar vacuum are outlined. The effects of a 20-person lunar base and a 250-person industrial facility on this vacuum are discussed. It is shown that exhaust from transport spacecraft and leakage from the habitat will be comparable to the daytime gas pressure for the 20-person base, and will degrade the vacuum to the range of 2 x 10 to the -9th torr for the use of 250-person facility. This will result in replacing the mostly nonreactive gases hydrogen, helium, and neon with more reactive gases containing carbon and oxygen. This vacuum is still good enough to perform many important vacuum processes such as plasma-deposition of amorphous silicon for solar cells, but processes such as molecular beam epitaxy or locating an intersecting beam accelerator on the moon will require additional vacuum pumping.

Landis, Geoffrey↗

NASA NTRS1990

The nu-process

As the core of a massive star collapses to form a neutron star, the flux of neutrinos in the overlying shells of heavy elements becomes so great that, despite the small cross section, substantial nuclear transmutation is induced. Neutrinos excite heavy elements and even helium to particle unbound levels. The evaporation of a single neutron or proton, and the back reaction of these nucleons on other species present, significantly alters the outcome of traditional nucleosynthesis calculations leading to a new process: nu-nucleosynthesis. Modifications to traditional hydrostatic and explosive varieties of helium, carbon, neon, oxygen, and silicon burning are considered. The results show that a large number of rare isotopes, including many of the odd-Z nuclei from boron through copper, owe much of their present abundance in nature to this process.

Woosley, S. E.↗

NASA NTRS1991

Mixed-Gas Sorption Joule-Thomson Refrigerator

Proposed mixed-gas sorption Joule-Thomson refrigerator provides cooling down to temperature of 70 K. Includes only one stage and no mechanical compressor. Simpler, operates without vibrating, and consumes less power in producing same amount of cooling. Same sorption principle of operation applicable in compressor that chemisorbs oxygen or hydrogen from mixture with helium, neon, and/or other nonreactive gases.

Jones, Jack A.↗

NASA NTRS1990

Ultraviolet spectroscopy of planetary nebulae: Cosmological implications

Optical spectrophotometry of PW Vulpeculae (Nova Vul 1984 no. 1) is combined with ultraviolet data to estimate electron temperatures, densities, and abundances in the ejecta of this slow classical nova. The reddening, distance, and evolution of the ultraviolet spectrum are also discussed. Abundances are nearly solar, with the exception of Nitrogen, which is substantially higher. Although Neon has been reported to be enhanced in several novae, it does not seem to be the case for PW Vul. Photoionization model calculations are presented of the ejecta that give a reasonable match of the observed emission spectrum. A strong featureless continuum shows that very hot, presumably shock heated, gas plays a major role in determining the energetics of this nova. Emission from this hot gas is responsible for the ionization of the nebular gas. A calculation of the masses of both the hot coronal gas and the cooler nebular gas shows that the former may account for most of the mass of the ejecta.

Ferland, Gary J.↗

NASA NTRS1990

Optical measurement of propeller blade deflections in a spin facility

A nonintrusive optical system for measuring propeller blade deflections has been used in the NASA Lewis dynamic spin facility. Deflection of points at the leading and trailing edges of a blade section can be obtained with a narrow light beam from a low power helium-neon laser. A system used to measure these deflections at three spanwise locations is described. Modifications required to operate the lasers in a near-vacuum environment are also discussed.

Ramsey, John K.↗

NASA NTRS1990

The impact of IUE on studies of the nova outburst: 1986 to 1990

Developments in understanding the nova outbursts that have occurred since the IUE (International Ultraviolet Explorer) meetings in 1986 and 1988 are outlined. Those developments that have occurred as a direct result of studies with the IUE satellite are emphasized. These involve the four outbursts that occurred in the large Magellanic cloud, the numerous recurrent novae outbursts, and a number of archival studies. As a direct result of IUE studies done since 1986, it is shown that fast novae become super Eddington at maximum, that many novae decline at the same rate, and that neon novae may be more numerous than previously thought. In addition, it is shown that there are differences in the ourburst characteristics between recurrent novae with giant secondaries and those with compact secondaries.

Starrfield, Sumner G.↗

NASA NTRS1991

The Interstellar Gas Experiment (IGE)

The Interstellar Gas Experiment (IGE) exposed thin metallic foils in order to collect neutral particles from the interstellar gas. These particles were entrapped in the foils along with precipitating magnetospheric and ambient atmospheric particles. Seven of these foils collected particles arriving from seven different directions as seen from the spacecraft for the entire duration of the Long Duration Exposure Facility (LDEF) mission. The authors' mass spectroscopy analysis of the noble gas component of these interstellar particles detected isotopes of helium and neon. These preliminary measurements suggest that the various isotopes are occurring in approximately the expected amounts and that their distribution in direction of arrival is close to what models predict. The analysis to subtract the background fluxes of magnetospheric and atmospheric particles is still in progress. The hope of this experiment is to investigate the noble gas isotopic ratios of this interstellar sample of matter which originated outside the solar system.

Lind, Don↗

NASA NTRS1991

Radiation sensitive area detection device and method

A radiation sensitive area detection device for use in conjunction with an X ray, ultraviolet or other radiation source is provided which comprises a phosphor containing film which releases a stored diffraction pattern image in response to incoming light or other electromagnetic wave. A light source such as a helium-neon laser, an optical fiber capable of directing light from the laser source onto the phosphor film and also capable of channelling the fluoresced light from the phosphor film to an integrating sphere which directs the light to a signal processing means including a light receiving means such as a photomultiplier tube. The signal processing means allows translation of the fluoresced light in order to detect the original pattern caused by the diffraction of the radiation by the original sample. The optical fiber is retained directly in front of the phosphor screen by a thin metal holder which moves up and down across the phosphor screen and which features a replaceable pinhole which allows easy adjustment of the resolution of the light projected onto the phosphor film. The device produces near real time images with high spatial resolution and without the distortion that accompanies prior art devices employing photomultiplier tubes. A method is also provided for carrying out radiation area detection using the device of the invention.

Carter, Daniel C.↗

NASA NTRS1990

Optical measurement of unducted fan blade deflections

A nonintrusive optical method for measuring unducted fan (or propeller) blade deflections is described and evaluated. The measurement does not depend on blade surface reflectivity. Deflection of a point at the leading edge and a point at the trailing edge in a plane nearly perpendicular to the pitch axis is obtained with a single light beam generated by a low-power, helium-neon laser. Quantitative analyses are performed from taped signals on a digital computer. Averaging techniques are employed to reduce random errors. Measured static deflections from a series of high-speed wind tunnel tests of a counterrotating unducted fan model are compared with available, predicted deflections, which are also used to evaluate systematic errors.

Kurkov, A. P.↗

NASA NTRS1989

A high resolution electro-optical displacement measurement system

An improved electrooptical system has been developed to sense wind tunnel model position. The original system using 25.6 mm, 1024-element linear photodiode arrays (PDAs) is being successfully used at a NASA wind tunnel but has a limited range. A new two-channel system using 61.44 mm, 4096-element PDAs has been developed to double the range of vertical and pitch measurement and increase the resolution by 60 percent. The PDAs are illuminated by expanding the beam of a single low power helium neon laser into a collimated sheet of light. An object placed in front of the two parallel PDAs produces a shadow on the array apertures which determines the object's position or size. The system has an overall precision of 12.7 microns and + or - 0.015 degrees in linear and angular measurements.

Schott, Timothy D.↗

NASA NTRS1991

PW Vulpeculae - A nova with nearly solar abundances

Optical spectrophotometry of PW Vulpeculae is combined with ultraviolet data to estimate electron temperatures, densities, and abundances in the ejecta of this slow classical nova. The reddening, the distance, and the evolution of the ultraviolet spectrum are discussed. Abundances are nearly solar, with the exception of nitrogen, which is substantially higher. Although neon has been reported to be enhanced in several novae, it does not seem to be the case for PW Vul. Photoionization model calculations of the ejecta that give a reasonable match of the observed emission spectrum are presented. A strong featureless continuum shows that very hot, presumably shock-heated, gas plays a major role in determining the energetics of this nova. Emission from this hot gas is responsible for the ionization of the nebular gas. A calculation of the masses of both the hot coronal gas and the cooler nebular gas shows that the former may account for most of the mass of the ejecta.

Saizar, Pedro↗

NASA NTRS1991

Abundance variations in solar active regions

The diversity in the published values of coronal abundances is unsettling, especially as the range of results seems to be beyond the quoted uncertainties. Measurements of the relative abundance of iron and neon derived from soft X-ray spectra of active regions are presented. From a data base of over 200 spectra taken by the Solar Maximum Mission Flat Crystal Spectrometer, it is found that the relative abundance can vary by as much as a factor of about 7 and can change on timescales of less than 1 h.

Strong, K. T.↗

NASA NTRS1991

A collection of diverse micrometeorites recovered from 100 tonnes of Antarctic blue ice

A new type of meteoritic material, intermediate in size between meteorites and interplanetary dust particles (IDPs), is described. Melting and filtering of about 100 tons of blue ice near Cap Prudhomme, Antarctica, yielded 7500 or more irregular, friable particles and about 1500 melted spherules, about 100 microns in size, both showing a 'chondritic' composition suggestive of an extraterrestrial origin. Analyzed irregular particles appear to be unmelted and have similarities with the fine-grained matrix of primitive carbonaceous chondrites, but are extremely diverse in composition. Isotopic analysis of trapped neon confirms an extraterrestrial origin for 16 of 47 irregular particles and 2 of 19 spherules studied and strongly suggests that they were exposed in space as micrometeoroids. These large Antarctic micrometeorites constitute a new family, or at least a new population, of solar system objects, in a mass range corresponding to the bulk of extraterrestrial material accreted by the earth today.

Maurette, M.↗

NASA NTRS1991

The role of matrix material and CCl4 (electron acceptor) on the ionization mechanisms of matrix-isolated naphthalene

The formation mechanisms and optical properties of polycyclic aromatic hydrocarbons (PAH) isolated in argon and neon matrices were studied in a systematic manner in an attempt to provide spectroscopic data on PAH ions under conditions relevant to astrophysical applications. The results obtained indicate the strong influence of the matrix material on the competing radiative (fluorescence and phosphorescence) and nonradiative (internal conversion and intersystem crossing) relaxation processes of the trapped molecule.

Salama, F.↗

NASA NTRS1992

Tables Of Gaussian-Type Orbital Basis Functions

NASA technical memorandum contains tables of estimated Hartree-Fock wave functions for atoms lithium through neon and potassium through krypton. Sets contain optimized Gaussian-type orbital exponents and coefficients, and near Hartree-Fock quality. Orbital exponents optimized by minimizing restricted Hartree-Fock energy via scaled Newton-Raphson scheme in which Hessian evaluated numerically by use of analytically determined gradients.

Partridge, Harry↗