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At least 271 records · Page 15

Two normal incidence collimators designed for the calibration of the extreme ultraviolet explorer

Two Dall-Kirkham, normal incidence collimators have been designed to calibrate the imaging properties of the Extreme Ultraviolet Explorer over the wavelength region from 114 to 2000 A. The mirrors of the short-wavelength, 25-cm diameter collimator are superpolished Zerodur which have been multilayer coated for optimal reflectivity at 114 A. The mirrors of the long-wavelength, 41.25-cm diameter collimator are gold coated Zerodur for high reflectance above 300 A. The design, performance, and future use of these collimators in the extreme ultra-violet is discussed.

Jelinsky, Sharon R.↗

EIT: Solar corona synoptic observations from SOHO with an Extreme-ultraviolet Imaging Telescope

The Extreme-ultraviolet Imaging Telescope (EIT) of SOHO (solar and heliospheric observatory) will provide full disk images in emission lines formed at temperatures that map solar structures ranging from the chromospheric network to the hot magnetically confined plasma in the corona. Images in four narrow bandpasses will be obtained using normal incidence multilayered optics deposited on quadrants of a Ritchey-Chretien telescope. The EIT is capable of providing a uniform one arc second resolution over its entire 50 by 50 arc min field of view. Data from the EIT will be extremely valuable for identifying and interpreting the spatial and temperature fine structures of the solar atmosphere. Temporal analysis will provide information on the stability of these structures and identify dynamical processes. EIT images, issued daily, will provide the global corona context for aid in unifying the investigations and in forming the observing plans for SOHO coronal instruments.

Delaboudiniere, J. P.↗

Flat field response of the microchannel plate detectors used on the Extreme Ultraviolet Explorer

The results of the extreme ultraviolet (EUV) flat field calibrations of two of the flight detectors to be flown on the Extreme Ultraviolet Explorer Satellite (EUVE) are presented. Images of about 40 million detected events binned 512 by 512 are sufficient to show microchannel plate fixed pattern noise such as hexagonal microchannel multifiber bundle interfaces, 'dead' spots, edge distortion, and differential nonlinearity. Differences due to photocathode material and dependencies on EUV wavelength are also described. Over large spatial scales, the detector response is flat to better than 10 percent of the mean response, but, at spatial scales less than 1 mm, the variations from the mean can be as large as 20 percent.

Vallerga, J. V.↗

Scanning X-Ray Or Extreme-Ultraviolet Monochromator

Wavelength of peak transmission of proposed high-throughput, narrow-band-pass x-ray or extreme-ultraviolet monochromator continuously adjustable. Essential filtering and reflecting components designed according to principles described in "Compact X-Ray and Extreme-Ultraviolet Monochromator" (MFS-28499). However, angle of incidence varied to change wavelength of Bragg reflection.

Hoover, Richard↗

The extreme ultraviolet explorer

The Extreme Ultraviolet Explorer (EUVE) mission, currently scheduled for launch in September 1991, is described. The primary purpose of the mission is to survey the celestial sphere for astronomical sources of Extreme Ultraviolet (EUV) radiation. The survey will be accomplished with the use of three EUV telescopes, each sensitive to a different segment of the EUV band. A fourth telescope will perform a high sensitivity search of a limited sample of the sky in the shortest wavelength bands. The all sky survey will be carried out in the first six months of the mission and will be made in four bands, or colors. The second phase of the mission, conducted entirely by guest observers selected by NASA, will be devoted to spectroscopic observations of EUV sources. The performance of the instrument components is described. An end to end model of the mission, from a stellar source to the resulting scientific data, was constructed. Hypothetical data from astronomical sources processed through this model are shown.

Bowyer, Stuart↗

Flexible diaphragm-extreme temperature usage

A diaphragm suitable for extreme temperature usage, such as encountered in critical aerospace applications, is fabricated by a unique method, and of a unique combination of materials. The materials include multilayered lay-ups of diaphragm materials sandwiched between layers of bleeder fabrics. After being formed in the desired shape on a mold, they are vacuum sealed and then cured under pressure, in a heated autoclave. A bond capable of withstanding extreme temperatures are produced.

Lerma, Guillermo↗

Extreme ultraviolet transmission of a synthetic diamond thin film

Measurements are presented of a thin film of synthetic diamond at various wavelengths in the extreme ultraviolet. The synthetic diamond combines the transmission properties of carbon with the strength, density, and ruggedness of a natural diamond. The Extreme Ultraviolet Transmission (EUV) of a film of the synthetic diamond has shown the existence of a thin surface layer of silicon, probably in the form of silicon carbide, which is not a contaminant layer.

Vallerga, John V.↗

Extreme Ultraviolet Explorer (EUVE): Emergency support

The Extreme Ultraviolet Explorer (EUVE) will conduct a survey of the entire celestial sphere in the extreme ultraviolet (UV) spectrum, 100 to 1000 angstrom units. This survey will be accomplished using four grazing incidence telescopes mounted on a spinning spacecraft whose spin axis is along the Sun line. Data is taken only when the spacecraft is in the Earth's shadow. The EUVE will be placed in a near circular orbit by a Delta expendable launch vehicle. The design orbit is circular at an altitude of 550 km by 28.5 degrees for a period of 96 minutes. The EUVE will be flown on a standardized Explorer Platform (EP) which will be reused for followup Explorer missions. Coverage will be provided by the Deep Space Network (DSN) for EUVE emergencies that would prevent communications via the normal channels of the Tracking and Data Relay Satellite System (TDRSS). Emergency support will be provided by the 26-meter subnet. Data is presented in tabular form for DSN support, frequency assignments, telemetry, and command.

Zayas, H.↗

A preliminary design and analysis of an advanced heat-rejection system for an extreme altitude advanced variable cycle diesel engine installed in a high-altitude advanced research platform

Satellite surveillance in such areas as the Antarctic indicates that from time to time concentration of ozone grows and shrinks. An effort to obtain useful atmospheric data for determining the causes of ozone depletion would require a flight capable of reaching altitudes of at least 100,000 ft and flying subsonically during the sampling portion of the mission. A study of a heat rejection system for an advanced variable cycle diesel (AVCD) engine was conducted. The engine was installed in an extreme altitude, high altitude advanced research platform. Results indicate that the waste heat from an AVCD engine propulsion system can be rejected at the maximum cruise altitude of 120,000 ft. Fifteen performance points, reflecting the behavior of the engine as the vehicle proceeded through the mission, were used to characterize the heat exchanger operation. That portion of the study is described in a appendix titled, 'A Detailed Study of the Heat Rejection System for an Extreme Altitude Atmospheric Sampling Aircraft,' by a consultant, Mr. James Bourne, Lytron, Incorporated.

Johnston, Richard P.↗

Dome cities for extreme environments

Extreme environments whether they be the frigid nights of the polar regions, the burning sands of the desert, or the harsh environment of space pose interesting challenges to the architect, the engineer, and the constructor in their efforts to create habitats for mankind. In space, the goals are to provide radiation protection while also providing an aesthetic living environment for long duration missions. Because of the need to provide both radiation protection and options for expansion of base facilities, a unique structural system which separates the radiation protection systems from the pressure envelope of the habitats was created. The system uses cable networks in a tensioned structural system, which supports the lunar regolith used for shielding above the facilities. The system is modular, easily expandable, and simple to construct. Additional innovations include the use of rock melting perpetrators for piles and anchoring deadmen, and various sized craters to provide side shielding. The reflective properties of the fabric used in the membrane are utilized to provide diffuse illumination. The use of craters along with the suspended shielding allows the dome to be utilized in fashions similar to those proposed by various designers unaware of the Moon's hostile radiation environment. Additional topics addressed deal with construction techniques for large domes, i.e., on the order of 100's to 1000's of meters, thermal control, the integration of tertiary water treatment schemes with architectural design, human factors, and its implications for the design of habitats for long term use in extreme environments.

Leonard, Raymond S.↗

The Extreme Ultraviolet Explorer Mission

The Extreme Ultraviolet Explorer (EUVE) mission, currently scheduled from launch in September 1991, is described. The primary purpose of the mission is to survey the celestial sphere for astronomical sources of extreme ultraviolet (EUV) radiation with the use of three EUV telescope, each sensitive to a different segment of the EUV band. A fourth telescope is planned to perform a high-sensitivity search of a limited sample of the sky in the shortest wavelength bands. The all-sky survey is planned to be carried out in the first six months of the mission in four bands, or colors, 70-180 A, 170-250 A, 400-600 A, and 500-700 A. The second phase of the mission is devoted to spectroscopic observations of EUV sources. A high-efficiency grazing-incidence spectrometer using variable line-space gratings is planned to provide spectral data with about 1-A resolution. An end-to-end model of the mission, from a stellar source to the resulting scientific data, is presented. Hypothetical data from astronomical sources were processed through this model and are shown.

Bowyer, S.↗

Mesosiderite clasts with the most extreme positive europium anomalies among solar system rocks

Pigeonite-plagioclase gabbros that occur as clasts in mesosiderites (brecciated stony-iron meteorites) show extreme fractionations of the rare-earth elements (REEs) with larger positive europium anomalies than any previously known for igneous rocks from the earth, moon, or meteorite parent bodies and greater depletions of light REEs relative to heavy REEs than known for comparable cumulate gabbros. The REE pattern for merrillite in one of these clasts is depleted in light REEs and has a large positive europium anomaly as a result of metamorphic equilibration with the silicates. The extreme REE ratios exhibited by the mesosiderite clasts demonstrate that multistage igneous processes must have occurred on some asteroids in the early solar system. Melting of the crust by large-scale impacts or electrical induction from an early T-Tauri-phase sun may be responsible for these processes.

Mittlefehldt, David W.↗

Vibration Test With Extremal Dual Control

Report discusses use of extremal dual control to prevent overtesting. In extremal dual control, electronic test-control subsystem automatically reduces excitation supplied to shaker subsystem to keep force applied by shaker below preset force limit and to keep acceleration of shaker below preset acceleration limit.

Scharton, Terry D.↗

Extreme Ultraviolet Explorer. Long look at the next window

The Extreme Ultraviolet Explorer (EUVE) will map the entire sky to determine the existence, direction, brightness, and temperature of thousands of objects that are sources of so-called extreme ultraviolet (EUV) radiation. The EUV spectral region is located between the x-ray and ultraviolet regions of the electromagnetic spectrum. From the sky survey by EUVE, astronomers will determine the nature of sources of EUV light in our galaxy, and infer the distribution of interstellar gas for hundreds of light years around the solar system. It is from this gas and the accompanying dust in space that new stars and solar systems are born and to which evolving and dying stars return much of their material in an endless cosmic cycle of birth, death, and rebirth. Besides surveying the sky, astronomers will make detailed studies of selected objects with EUVE to determine their physical properties and chemical compositions. Also, they will learn about the conditions that prevail and the processes at work in stars, planets, and other sources of EUV radiation, maybe even quasars. The EUVE mission and instruments are described. The objects that EUVE will likely find are described.

Maran, Stephen P.↗

Fiberoptic characteristics for extreme operating environments

Fiberoptics could offer several major benefits for cryogenic liquid-fueled rocket engines, including lightning immunity, weight reduction, and the possibility of implementing a number of new measurements for engine condition monitoring. The technical feasibility of using fiberoptics in the severe environments posed by cryogenic liquid-fueled rocket engines was determined. The issues of importance and subsequent requirements for this use of fiberoptics were compiled. These included temperature ranges, moisture embrittlement succeptability, and the ability to withstand extreme shock and vibration levels. Different types of optical fibers were evaluated and several types of optical fibers' ability to withstand use in cryogenic liquid-fueled rocket engines was demonstrated through environmental testing of samples. This testing included: cold-bend testing, moisture embrittlement testing, temperature cycling, temperature extremes testing, vibration testing, and shock testing. Three of five fiber samples withstood the tests to a level proving feasibility, and two of these remained intact in all six of the tests. A fiberoptic bundle was also tested, and completed testing without breakage. Preliminary cabling and harnessing for fiber protection was also demonstrated. According to cable manufacturers, the successful -300 F cold bend, vibration, and shock tests are the first instance of any major fiberoptic cable testing below roughly -55 F. This program has demonstrated the basic technical feasibility of implementing optical fibers on cryogenic liquid-fueled rocket engines, and a development plan is included highlighting requirements and issues for such an implementation.

Delcher, R. C.↗

Far and extreme ultraviolet astronomy with ORFEUS

ORFEUS (Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer) is a 1 m normal incidence telescope for spectroscopic investigations of cosmic sources in the far and extreme ultraviolet spectral range. The instrument will be integrated into the freeflyer platform ASTRO-SPAS. ORFEUS-SPAS is scheduled with STS ENDEAVOUR in September 1992. We describe the telescope with its two spectrometer and their capabilities i.e., spectral range, resolution and overall sensitivity. The main classes of objects to be observed with the instrument are discussed and two examples of simulated spectra for the white dwarf HZ43 and an O9-star in LMC are shown.

Kraemer, G.↗

Case studies of extreme climatic events in the Amazon basin

The present exploration of climate-anomaly mechanisms, on the basis of surface-climatological and hydrological series, as well as upper-air and satellite observations, gives attention to the March-April rainy season peak in northern Amazonia. While the moderately wet year 1986 exhibited a far-southerly location of the Atlantic near-equatorial trough, and an embedded intertropical convergence zone (ITCZ), the extremely dry El Nino year 1983 featured a more northerly ITCZ. Major mechanisms of extreme rainfall events are synthesized on the basis of these analyses.

Marengo, Jose A.↗

Thin film filter lifetesting results in the extreme ultraviolet

We present the results of the thin film filter lifetesting program conducted as part of the NASA Extreme Ultraviolet Explorer (EUVE) satellite mission. This lifetesting program is designed to monitor changes in the transmission and mechanical properties of the EUVE filters over the lifetime of the mission (fabrication, assembly, launch and operation). Witness test filters were fabricated from thin film foils identical to those used in the flight filters. The witness filters have been examined and calibrated periodically over the past seven years. The filters have been examined for evidence of pinholing, mechanical degradation, and oxidation. Absolute transmissions of the flight and witness filters have been measured in the extreme ultraviolet (EUV) over six orders of magnitude at numerous wavelengths using the Berkeley EUV Calibration Facility.

Vedder, P. W.↗