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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1951

X-Ray Diffraction Study of the Internal Structure of Supercooled Water

A Bragg X-ray spectrometer equipped with a volume-sensitive Geiger counter and Soller slits and employing filtered molybdenum Ka radiation was used to obtain a set of diffracted intensity curves as a Punction of angle for supercooled water. Diffracted intensity curves in the temperature region of 21 to -16 C were obtained. The minimum between the two main diffraction peaks deepened continuously with lowering temperature, indicating a gradual change in the internal structure of the water. No discontinuity in this trend was noted at the melting point. The internal structure of supercooled water was concluded to become progressively more ice-like as the temperature is lowered.

Dorsch, Robert G.↗
NASA NTRS1981

A possible technique for cometary studies with high angular and spectral resolution

The echelle spectrographs, designed for and used at the Cassegrain stations of the KPNO and CTIO 4-meter telescopes, are capable of cometary spectroscopy with seeing-limited angular resolution along the slit and with spectral resolving power (lambda/delta lambda) ranging from 10 to the 4th power to 10 to the 5th power. Various gratings, cameras and detectors can be used in combination for specific studies in the 3000A to 10,000A range.

Gull, T. R.↗
NASA NTRS1981

Narrow passband imagery of comets

During an emission-line survey of the Milky Way, Comet West was accidently imaged through four different narrow passbands with a wide-field, image-intensified camera. Three passbands recorded very similar head plus tail structure. The fourth passband shows an additional large, diffuse component around the head. It was serendipitous that such was recorded as the filters, being selected for studies of emission nebulae, are not particularly suited for studies of comets. However the imagery, plus subsequent studies, suggests that much can be learned about the structure of comets using narrow passband imagery simultaneously with long slit spectroscopy.

Gull, T. R.↗
NASA NTRS1981

Photographic observations of comets at Lowell Observatory

Observations of Halley's comet at Lowell Observatory cover a period from November 10, 1909 to May 17, 1911: 334 direct photographs were taken, 118 objective prism spectra, and 32 slit spectrograms of the nucleus, many of them including 5 arc minutes of the surrounding coma. Just one morning's observations are illustrated as an example of utilizing every possible resource available at the Observatory at the time. Observational improvements developed since then are described and some suggestions for the coming return of Halley's comet are made.

Giclas, H. L.↗
NASA NTRS1980

Advanced Gas Turbine (AGT) powertrain system initial development report

The powertrain consists of a single shaft regenerated gas turbine engine utilizing ceramic hot section components, coupled to a slit differential gearbox with an available variable stator torque converter and an available Ford intergral overdrive four-speed automatic transmission. Predicted fuel economy using gasoline fuel over the combined federal driving cycle (CFDC) is 15.3 km/1, which represents a 59% improvement over the spark-ignition-powered baseline vehicle. Using DF2 fuel, CFDC mileage estimates are 17.43 km/1. Zero to 96.6 km/hr acceleration time is 11.9 seconds with a four-second accleration distance of 21.0 m. The ceramic radial turbine rotor is discussed along with the control system for the powertrain.

Source record↗
NASA NTRS1982

Determination of the efficiency of a proportional counter for detecting X-rays

A parallel beam of X-rays (approximately monoenergetic) passing through a rectangular slit and scattering from two flat mirrors comprise the X-ray test. The two mirrors are arranged in a periscope geometry so that the final reflected beam is parallel to the incident beam but displaced laterally by given amount. One of the detectors used to intercept the reflected X-rays is a one dimensional gas-filled proportional counter which is sensitive to the position (in 1 dimension) at which the X-rays are incident within its detecting "window". The total length of the anode wire of the proportional counter is 120 mm and this length can be divided electronically into a maximum of 1,024 parts. Hence, the output of an experimental run would be the number of incident X-rays that registered on each of the 1,024 channels. Each channel would represent an X-ray at a different spatial location and, hence, at a different scattering angle. In order to look at a wider range of scattering angles, the detector is placed on an optical table which can be rotated.

Williams, A. C.↗
NASA NTRS1981

Very wide field camera

The study of galactic and faint extragalactic extended sources and peculiar ultraviolet objects by a very wide field of view camera, operated in the ultraviolet photometric and spectrometric modes is discussed. The photometric mode is direct photography through filters for observation of the following sources: (1) large scale distribution of ultraviolet radiation in the Milky Way; (2) diffusion of the galactic light above the galactic plane and in front of the large absorbing clouds; (3) the optical emission of the interstellar matter; (4) stars, and starlike objects with diameters less than 3 arc minutes. In the spectrometric mode (nebular spectrograph) the light from the center of the photometric field is concentrated on a slit covering 10 degrees by 10 arc minutes on the sky.

Courtes, G.↗
NASA NTRS1981

Autonomous attitude determination from star data for a dual-spin planetary spacecraft

A batch mode process which identifies three reference stars within a rotor-mounted star scanner's field-of-view based on the criteria of intensity and geometry was established. The sequential mode which continuously tracks the reference stars provides star transit times and estimates of rotor's spin rate. A least-square estimator was formulated which sequentially determines the spacecraft attitude from sucessive star crossings by minimizing the error in the star and scanner slit normal orthogonality. This spacecraft attitude also provides intermittent updates for the gyro propagated inertial attitude of the despun science platform. Simulation results are presented, showing successful star identification and attitude convergence in the presence of nutation and star transit time uncertainty.

Wong, E. C.↗
NASA NTRS1982

Fast generation of three-dimensional computational boundary-conforming periodic grids of C-type

A fast computer program, GRID3C, was developed to generate multilevel three dimensional, C type, periodic, boundary conforming grids for the calculation of realistic turbomachinery and propeller flow fields. The technique is based on two analytic functions that conformally map a cascade of semi-infinite slits to a cascade of doubly infinite strips on different Riemann sheets. Up to four consecutively refined three dimensional grids are automatically generated and permanently stored on four different computer tapes. Grid nonorthogonality is introduced by a separate coordinate shearing and stretching performed in each of three coordinate directions. The grids are easily clustered closer to the blade surface, the trailing and leading edges and the hub or shroud regions by changing appropriate input parameters. Hub and duct (or outer free boundary) have different axisymmetric shapes. A vortex sheet of arbitrary thickness emanating smoothly from the blade trailing edge is generated automatically by GRID3C. Blade cross sectional shape, chord length, twist angle, sweep angle, and dihedral angle can vary in an arbitrary smooth fashion in the spanwise direction.

Dulikravich, D. S.↗
NASA NTRS1982

The Faint Object Camera

The Faint Object Camera fully exploits the spatial resolution capability of the Space Telescope on the very faintest detectable objects over a broad wavelength range. A full complement of filters, objective prisms and polarizers, a choice of coronograhic masks, and a variety of scan formats extend the scientific versatility of the direct imaging mode. In addition, the Faint Object Camera provides the unique facility of long-slit spectroscopy to Space Telescope observers.

Macchetto, F.↗
NASA NTRS1981

Quiescent prominence spectrophotometry - Sodium D1,2, helium D3, and calcium /plus/ lambda 8498

The reported observations were carried out by means of a 25 cm coronagraph/coude spectrograph with a Si vidicon Optical Multichannel Analyzer (OMA) detector. The results of the investigation are presented in a number of tables, and the main conclusions concerning the studies are discussed. The relative behavior of prominence Na D line emission shows that the employed observing techniques yield reliable measures of prominence line strengths, not degraded to any substantial extent, in particular, by possible slit-filling effects. This conclusion is limited principally by the assumption that systematic vertical velocity fields in the prominences are not greater than 1.5 km/s. The Na D line profiles are well fitted by a one-component (i.e., homogeneous) line-forming region, thus reinforcing previous conclusions regarding the source of the enhanced wing emission.

Landman, D. A.↗
NASA NTRS1982

Echelle spectrographs at grazing incidence

It is shown that by using the conical diffraction mount, existing echelle gratings can be used at grazing incidence to achieve high spectral resolution in the extreme UV and soft X rays. Design considerations for grazing incidence echelle spectrographs are examined, and two sample designs are discussed. The first, for use in the extreme UV, has a primary mirror and an entrance slit to the spectrograph. The system has a resolution of 10,000, operates at any wavelength longward of 100 A, and covers 30% of the spectrum at a single setting. The X-ray spectrograph uses objective gratings to obtain spectral resolution of 28,000 over any factor of 2 in. wavelength. It operates to wavelengths as short as 4 A.

Cash, W.↗
NASA NTRS1982

Doppler wavelength shifts of ultraviolet spectral lines in solar active regions

Doppler shifts are measured for solar UV emission lines formed in the lower transition region of active regions. Doppler shifts in different regions at the same solar location, variations of Doppler shift with position of an active region on the disk, and variations of Doppler shift with time at the same solar location in the same active region were studied. Observations were made with the NRL slit spectrograph on Skylab. Excluding flare and flare-related phenomena, only redshifts are found whose magnitudes correspond to downflow velocities between about 4 and 17 km/s. Shifts are largest for lines formed between about 50,000 and 100,000 K, and are distinctly less for lines formed above 100,000 K. The shifts persist out to the limb, but not above it. There is no obvious change in redshift for lines measured at the same solar location over time intervals of about 20 minutes.

Feldman, U.↗
NASA NTRS1982

An efficient low- and moderate-resolution spectrograph for the Hale telescope

A new low-to-moderate resolution spectrograph has been designed and built for the Cassegrain focus of the Hale 5.08-meter telescope. To maximize efficiency, resolution, and wavelength coverage the light is divided into two spectra regions by a dichroic filter behind the entrance slit, after which there are two completely separate spectrographs. The blue spectrograph operates from 3200 A to 5200 A while the red one goes from 5200 A to 10,000 A. The red detector is an 800 x 800 TI CCD while the blue detector is a 320 x 512 RCA CCD or a Shectrograph image pulse-counting system. A Boksenberg IPCS can also be mounted on the blue camera. The overall efficiency of the Cassegrain telescope, spectrographs, and CCD's combined, ranges from 5 percent to 13 percent between 3600 A and 8200 A. The spectrograph is usable from 3200 A to 10,400 A.

Oke, J. B.↗
NASA NTRS1982

Measurements of the limb darkening of faculae near the solar limb

Measurements are presented of the contrast at 525 nm of solar faculae. The measurements were obtained using an extreme limb photometer (ELP) in 1975 and 1979 at the San Fernando Observatory. The mean contrast of active regions was determined from the limb inward to 54 arcsec, averaged over an annulus determined using the slits of the ELP. It is found that the contrast of faculae increases with heliocentric angle theta, from mu approximately 0.25 to mu approximately 0.065, where mu is the cosine of theta. The average value of the mean contrast of facular regions is 2.1%, with a possible upper limit of approximately 5% at mu approximately 0.1, determined from regions with the greatest filling factor. When corrected for a filling factor of 10-15%, this mean contrast implies a contrast for individual faculae of 30-50%.

Chapman, G. A.↗
NASA NTRS1984

Collecting Light From Point Images

Light from sources at varying positions brought to fixed opening. In telescope field divided into 10 strips, 10 pairs of optical fibers moved laterally and longitudinally to any required position in their assigned strips. Fixed ends of fibers arrayed in line at spectrograph entrance slit. Concept developed to enhance efficiency of spectrographs on astronomical telescopes.

Goss, W. C.↗
NASA NTRS1984

Lensless Image Scanner

Image scanner uses moving and stationary parallel slits to produce pictures of visible, infrared, X-ray microwave, or acoustic sources. No lenses or mirrors required. Single detector views all parts of image simultaneously rather than raster making relatively-short exposure times possible. Potential applications of system include medical x-ray imaging.

Schindler, R. A.↗