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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 1,441 records · Page 80
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NASA NTRS1984

An extreme ultraviolet spectrometer experiment for the Shuttle Get Away Special Program

An extreme ultraviolet (EUV) spectrometer experiment operated successfully during the STS-7 mission in an experiment to measure the global and diurnal variation of the EUV airglow. The spectrometer is an F 3.5 Wadsworth mount with mechanical collimator, a 75 x 75 mm grating, and a bare microchannel plate detector providing a spectral resolution of 7 X FWHM. Read-out of the signal is through discrete channels or resistive anode techniques. The experiment includes a microcomputer, 20 Mbit tape recorder, and a 28V, 40 Ahr silver-zinc battery. It is the first GAS payload to use an opening door. The spectrometer's 0.1 x 4.2 deg field of view is pointed vertically out of the shuttle bay. During the STS-7 flight data were acquired continuously for a period of 5 hours and 37 minutes, providing spectra of the 570 A to 850 A wavelength region of the airglow. Five diurnal cycles of the 584 A emission of neutral helium and the 834 A emission of ionized atomic oxygen were recorded. The experiment also recorded ion events and pressure pulses associated with thruster firings. The experiment is to fly again on Mission 41-F.

Conway, R. R.↗
NASA NTRS1983

The extreme LMC supergiant HD 38489 - An optical and ultraviolet study

Near-IR, optical, and UV observations covering the 1200-7000 A range are combined in the present study of the extremely luminous B star HD 38489 = S134, which is found to be an evolved B star of 80-90 solar masses and 70 solar radii, with a T(eff) of 25,000 K. Its mass loss, at 0.00001 solar masses/year, is comparable to that of galactic stars, and additional similarities are noted to stars of the Hubble-Sandage class and to the 6-20 range is suggested, and a model envelope is derived.

Shore, S. N.↗
NASA NTRS1983

Solar irradiance variations. II - Analysis of the extreme ultraviolet measurements onboard the Atmosphere Explorer E satellite

Five of the extreme ultraviolet channels (L-alpha, L-beta, He I, He II, Fe XV) measuring irradiance fluctuations on board the AE-E satellite between 1977 and 1980 have been studied in detail. It is shown that the daily variations correspond very closely to the daily variations in solar radio emission (F10.7), but that the UV data are afflicted with serious and to date unrecognized calibration changes during the period of operation of the instruments. In order to correct for these changes, a statistical analysis is carried out, and a set of corrections to the raw data is suggested. The resulting, now uniform, data are then compared with rocket measurements (L-alpha) and data acquired onboard the AE-C satellite (L-beta). Finally the remaining discrepancies are discussed. After concluding that they are below the overall level of uncertainties, a first-order 10-year run of EUV irradiances derived from F10.7 data is proposed. This estimate includes the ratio of irradiance levels between the maxima of solar cycles 20 and 21 and the intervening minimum.

Oster, L.↗
NASA NTRS1983

A spectroscopic method for calibration of solar extreme ultraviolet instrumentation

A method of calibrating solar extreme ultraviolet spectrographs in space using coronal emission lines of known relative intensity is presented and demonstrated. This approach is useful for recalibrating orbiting instruments that may be subject to degradation during extended periods of operation. The calibration results are insensitive to the physical distribution of emitting plasma in any likely solar coronal source. It is suggested that this technique may be useful for calibration of spectrographs used in the study of laboratory plasmas.

Neupert, W. M.↗
NASA NTRS1984

A study of extreme carbon stars. I - Silicon carbide emission features

10-micron spectra of many extreme carbon stars reveal a prominent emission feature near 11 microns. This is compared with laboratory spectra of SiC grains. Two distinct types of features are found, perhaps indicative of different mechanisms of grain formation in different stars. Estimates are made of probable column densities and total masses of SiC in the circumstellar shells.

Cohen, M.↗
NASA NTRS1984

Microchannel plate EUV detectors for the Extreme Ultraviolet Explorer

The design and operating characteristics of the prototype imaging microchannel plate (MCP) detector for the Extreme Ultraviolet Explorer (EUVE) Satellite are discussed. It is shown that this detector has achieved high position resolution performance (greater than 512 x 512 pixels) and has low (less than one percent) image distortion. In addition, the channel plate scheme used has tight pulse height distributions (less than 40 percent FWHM) for UV radiation and displays low (less than 0.2 cnt/sq cm-s) dark background counting rates. Work that has been done on EUV filters in relation to the envisaged filter and photocathode complement is also described.

Siegmund, O. H. W.↗
NASA NTRS1984

Attitude Control System for the Extreme Ultraviolet Explorer Satellite

The requirements, design, and expected performance of the Attitude Control Subsystem for the spin-stabilized Extreme Ultraviolet Explorer Satellite are presented. In the sky-mapping phase, closed-loop magnetic control keeps the spin axis pointed toward the sun. In the spectroscopy phase, the attitude control loop is closed via the ground. The satellite's attitude and spin rate are determined using periodically downlinked star data. An attitude control algorithm generates commands to be uplinked to the satellite for spin axis precession and spin rate control. Computer simulations of the satellite dynamic response, pointing error, and stability during spin axis precession are presented, and parameters that affect the pointing performance are evaluated.

Wong, E. C.↗
NASA NTRS1984

Two new extremely hot pulsating white dwarfs

High speed photometry of the extremely hot, nearly degenerate stars PG 1707 + 427 and PG 2131 + 066 reveals that they are low-amplitude pulsating variables. Power spectral analysis shows both to be multiperiodic, with dominant periods of 7.5 and 6.4-6.9 minutes, respectively. Together with the known pulsators PG 1159 - 035 and the central star of the planetary nebula Kohoutek 1-16, these objects define a new pulsational instability strip at the hot edge of the H-R diagram. The variations of these objects closely resemble those of the much cooler pulsating ZZ Ceti DA white dwarfs; both groups are probably nonradial g-mode pulsators. Evolutionary contraction of the PG 1159 - 035 variables may lead to period changes that would be detectable in as little as 1 year. The optical and IUE spectra of the PG 1159 - 035 variables are characterized by absorption lines of C IV and other CNO ions, indicating radiative levitation of species heavier than helium. He II is also present in the spectra, but the hydrogen Balmer lines are absent. Effective temperatures near 100,000 K are required, and the He II 4686 A profiles indicate log g greater than 6. These helium-rich pulsators form the hottest known subgroup of the DO white dwarfs.

Bond, H. E.↗
NASA NTRS1984

Absolute measurement of the extreme UV solar flux

A windowless rare-gas ionization chamber has been developed to measure the absolute value of the solar extreme UV flux in the 50-575-A region. Successful results were obtained on a solar-pointing sounding rocket. The ionization chamber, operated in total absorption, is an inherently stable absolute detector of ionizing UV radiation and was designed to be independent of effects from secondary ionization and gas effusion. The net error of the measurement is + or - 7.3 percent, which is primarily due to residual outgassing in the instrument, other errors such as multiple ionization, photoelectron collection, and extrapolation to the zero atmospheric optical depth being small in comparison. For the day of the flight, Aug. 10, 1982, the solar irradiance (50-575 A), normalized to unit solar distance, was found to be 5.71 + or - 0.42 x 10 to the 10th photons per sq cm sec.

Carlson, R. W.↗
NASA NTRS1984

Reheating the intergalactic medium under extremal conditions

Sherman (1982) commenced the investigation of a hypothetical closure density intergalactic medium (IGM) in the recombination epoch and found present acceptable temperatures in the range from 160,000 to 4,200,000 K for IGM heating. The present investigation has the objective to complete these calculations by finding extreme bounds on the reheating epoch which preceded recombination. The final results are presented in a table. Three models have been generated. The presented models suggest that a closure density IGM is constrained to be heated by a source in the range from 10 to the -31st to 10 to the -27th ergs per s per cu cm. The heating had to originate no earlier than z approximately 28.

Sherman, R. D.↗
NASA NTRS1985

Research in extreme ultraviolet and far ultraviolet astronomy

The Far Ultraviolet imager (FUVI) was flown on the Aries class sounding rocket 24.015, producing outstanding results. The diffuse extreme ultraviolet (EUV) background spectrometer which is under construction is described. It will be launched on the Black Brant sounding rocket flight number 27.086. Ongoing design studies of a high resolution spectrometer are discussed. This instrument incorporates a one meter normal incidence mirror and will be suitable for an advanced Spartan mission.

Bowyer, C. S.↗
NASA NTRS1984

Microbial ecology of extreme environments: Antarctic yeasts and growth in substrate-limited habitats

An extreme environment is by definition one with a depauperate biota. While the Ross Desert is by no means homogeneous, the most exposed and arid habitats, soils in the unglaciated high valleys, do indeed contain a very sparse biota of low diversity. So sparse that the natives could easily be outnumbered by airborne exogenous microbes. Native biota must be capable of overwintering as well as growing in the high valley summer. Tourists may undergo a few divisions before contributing their enzymes and, ultimately, elements to the soil - or may die before landing. The simplest way to demonstrate the indigenicity of a particular microbe is therefore to establish unique distribution; occurrence only in the habitat in question precludes foreign origin.

Vishniac, H. S.↗
NASA NTRS1985

Extraction of aerodynamic parameters for aircraft at extreme flight conditions

The maximum likelihood estimator has been used to extract stability and control derivatives from flight data for many years. Most of the literature on aircraft estimation concentrates on new developments and applications, assuming familiarity with basic concepts. This paper briefly discusses the maximum likelihood estimator and the aircraft equations of motion that the estimator uses. The current strength and limitations associated with obtaining flight-determined aerodynamic coefficients in extreme flight conditions is assessed. The importance of the careful combining of wind tunnel results (or calculations) and flight results and the thorough evaluation of the mathematical model is emphasized. The basic concepts of minimization and estimation are examined for a simple computed aircraft example, and the cost functions that are to be minimized during estimation are defined and discussed. Graphic representations of the cost functions are given to help illustrate the minimization process. Finally, the basic concepts are generalized, and estimation of stability and control derivatives from flight data is discussed.

Iliff, K. W.↗
NASA NTRS1985

Research in extreme ultraviolet and far ultraviolet astronomy

Instruments designed to explore different aspects of far and extreme ultraviolet cosmic radiation were studied. The far ultraviolet imager (FUVI) was flown on the Aries sounding rocket. Its unique large format 75mm detector mapped out the far ultraviolet background radiation with a resolution of only a few arc minutes. Analysis of this data indicates to what extent the FUVI background is extra galactic in origin. A power spectrum of the spatial fluctuations will have direct consequences for galactic evolution.

Labov, S. E.↗
NASA NTRS1984

Extreme UV measurements of a varied line-space Hitachi reflection grating - Efficiency and scattering

The first extreme UV measurements of a grating mechanically ruled with smooth variations in the grating constant are presented. The grating characteristics are summarized and a schematic of the testing apparatus is shown and described. The procedure for obtaining the absolute grating efficiency is given. The results for that efficiency as a function of wavelengths of 68, 170, 256, 304, 584, and 1216 A are reported and discussed. Efficiency measurements were also made as a function of position across the ruled width at 256 A and 87 deg incident angle, and the results are discussed. Scattering measurements performed via computer acquisition of diffracted image profiles are reported.

Edelstein, J.↗
NASA NTRS1985

Boron and silicon - Filters for the extreme ultraviolet

Thin films of boron and silicon have been developed using electron beam deposition. The transmissions of these filters were measured from soft X-ray wavelengths to the far ultraviolet and at optical wavelengths. The boron filter transmission peaks near 66 A and the silicon filter peaks near 136 A as expected on theoretical grounds, but the extreme ultraviolet bandpass is narrower than expected. The peak transmission of these filters does not change with time, but the width of the silicon filter bandpass is reduced slightly as the filter ages.

Labov, S.↗
NASA NTRS1984

Normal incidence multilayer mirrors for extreme ultraviolet astronomy

Sputtered multilayer coatings allow the use of normal incidence optics in the extreme ultraviolet (EUV) region below 500 A. Multilayer mirrors can be tailored to provide images at strong EUV lines in the sun and stars, in many cases making more efficient use of the telescope aperture than grazing incidence optics. Alternatively, the bandpass can be broadened at the expense of peak effective area, by varying the multilayer structure over the mirror surface. Such mirrors can also serve as optical elements in spectrographs for investigation of specific emission and absorption line complexes, and are self-filtering in that they reject nearby geocoronal and cosmic resonance line backgrounds. Current efforts at the Lockheed Palo Alto Research Laboratory in the design, fabrication, and testing of EUV multilayer mirrors are discussed. This program includes the design and fabrication of normal incidence EUV multilayer mirrors, and the deposition of multilayers on lacquer-coated substrates.

Stern, R. A.↗
NASA NTRS1985

A study of the extreme ultraviolet spectrum of O2 by electron impact

The electron impact emission cross sections for O2 at 200 eV have been measured in the laboratory. Included in the study are all emission features in the extreme ultraviolet from 40 to 131 nm at a resolution of 0.5 nm. The features are entirely from the dissociation products (O I, O II, O III). Additionally, the excitation functions from 0 to 400 eV have been measured for characteristic O I multiplets at 98.9 and 102.6 nm and for O II multiplets at 53.9 and 83.3 nm. It is found that O I multiplets are formed near the dissociation limit whereas the O II multiplets have a threshold about 10 eV above the dissociation limit. The total VUV emission cross section of O2 is determined from 40 to 200 nm and the effects of autoionization to the measured emission spectrum are indicated.

Ajello, J. M.↗