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Results for “two-dimensional mirrors”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Global auroral imaging instrumentation for the Dynamics Explorer Mission

The instrumentation for obtaining global images of the auroral oval from the high-altitude spacecraft of the Dynamics Explorer Mission is described. It is noted that the three spin-scan auroral imaging photometers are expected to be able to effectively view the dim emissions from earth in the presence of strong stray light sources near their fields-of-view along the sunlit portion of the spacecraft orbit. A special optical design that includes an off-axis parabolic mirror as the focusing element and super-reflecting mirror surfaces is used to minimize the effects of stray light. The rotation of the spacecraft and an instrument scanning mirror provide the two-dimensional array of pixels making up an image frame. It is pointed out that the full width of the fields-of-view of the photometers corresponding to a single pixel is 0.29 deg and that the angular dimensions of a typical full frame are 30 deg x 30 deg and span 14,400 pixels.

Frank, L. A.↗
NASA NTRS1986

Optical arrays for future astronomical telescopes in space

NASA's Marshall Space Flight Center is currently evaluating several advanced optical space telescope concepts for the achievement of both higher sensitivity and greater angular resolution than the Hubble Space Telescope; their designs encompass one- and two-dimensional coherent arrays of mirrors in both focal and afocal configurations. Attention is given to those arrays that appear capable of fabrication and orbital deployment by the year 2005, and to the tradeoff involved between synthetic aperture concepts that furnish high angular resolution and those that yield sensitivity for faint, extended source imaging.

Bunner, Alan N.↗
NASA NTRS1980

Design of nonimaging concentrators as second stages in tandem with image-forming first-stage concentrators

The paper discusses the paraboloidal mirror as a tracking solar concentrator, fitting a nonimaging second stage to the paraboloidal mirror, other image-forming systems as first stages, and tracking systems in two-dimensional geometry. Because of inherent aberrations, the paraboloidal mirror cannot achieve the thermodynamic limit. It is shown how paraboloidal mirrors of short focal ratio and similar systems can have their flux concentration enhanced to near the thermodynamic limit by the addition of nonimaging compound elliptical concentrators.

Winston, R.↗
NASA NTRS1988

Optical modeling of a space relay experiment

The optical modeling of laser beam propagation between two points on the earth's surface is discussed with reference to a space relay experiment using relay mirrors on one or more satellites. A two-dimensional laser beam propagation code is applied, and several novel modules are developed to realistically model the environment of the experiment. These are the Kolmogorov atmosphere, a deformable mirror, a segmented aperture, and wind shear. The model allows the calculation of the beam-Strehl ratio and efficiency of the energy transfer for an arbitrary input beam distribution.

Scholl, Marija S.↗
NASA NTRS1988

Monolithic two-dimensional surface-emitting arrays of GaAs/AlGaAs diode lasers

Monolithic two-dimensional arrays of GaAs/AlGaAs diode lasers with light emission normal to the surface have been obtained by fabricating edge-emitting quantum-well lasers coupled with external mirrors that deflect the radiation from the laser facets by 90 degrees. Linear arrays of GaAs/AlGaAs devices in which one of the laser facets was cleaved while the other facet and an adjacent 45 degree deflector were formed by ion-beam-assisted etching (IBAE) have been reported. For the arrays reported in this section, IBAE was used to form all of the laser facets and the deflecting mirrors. A mass transport process of the type employed to fabricate two-dimensional arrays of GaInAsP/InP lasers coupled with deflecting mirrors is not known for AlGaAs.

Source record↗
NASA NTRS1984

Imaging spectrometer concepts for next-generation planetary missions

In recent years there has been an increasing interest in the imaging spectrometer concept, in which imaging is accomplished in multiple, contiguous spectral bands at typical intervals of 5 to 20 nm. There are two implementations of this concept under consideration for upcoming planetary missions. One is the scanning, or 'whisk-broom' approach, in which each picture element (pixel) of the scene is spectrally dispersed onto a linear array of detectors; the spatial information is provided by a scan mirror in combination with the vehicle motion. The second approach is the 'push-broom' imager, in which a line of pixels from the scene is spectrally dispersed onto a two-dimensional (area-array) detector. In this approach, the scan mirror is eliminated, but the optics and focal plane are more complex. This paper discusses the application of these emerging instrument concepts to the planetary program. Key issues are the trade-off between the two types of imaging spectrometer, the available data rate from a typical planetary mission, and the focal-plane cooling requirements. Specific straw-man conceptual designs for the Mars Geoscience/Climatology Orbiter (MGCO) and the Mariner Mark II Comet Rendezvous/Asteroid Flyby (CRAF) missions are discussed.

Herring, M.↗
NASA NTRS1974

Apparatus for scanning the surface of a cylindrical body

A laser scanning system for providing a two-dimensional display of a cylindrical surface, such as to display striae of a fired bullet is described. The cylinder is scanned along its axis by vibrating one mirror in the laser beam path, and is scanned in a direction normal to its axis by vibrating a second mirror in a direction normal to the first or by rotating the bullet. Scan control signals are adjusted in phase to produce a synchronized display of a video signal obtained from detection of scattered light from the surface thus scanned by a laser beam.

Nakich, R. B.↗
NASA NTRS1986

Soft X-ray photoemission with the SSX-100 spectrometer

Photoemission and SEXAFS experiments were conducted using a double crystal monochromator at the Stanford Synchrotron Radiation Laboratory. Photoelectrons were detected using a Surface Science Laboratories SSX-100 electron analyzer, which employs a magnetic/electrostatic lens, hemispherical geometry, and a two-dimensional position-sensitive detector. In the kinetic energy range of interest (1000-2000 eV), a significant improvement in count rate was observed over a single channel cylindrical mirror analyzer system. Ten second scans of the KLL silicon Auger peak manifold were recorded at a large number of photon energies for subsequent determination of SEXAFS spectra.

Hecht, M. H.↗
NASA NTRS1989

Strength distribution of reinforcing fibers in a Nicalon fiber/chemically vapor infiltrated silicon carbide matrix composite

The strength distribution of fibers within a two-dimensional laminate ceramic/ceramic composite consisting of an eight harness satin weave of Nicalon continuous fiber within a chemically vapor infiltrated SiC matrix was determined from analysis of the fracture mirrors of the fibers. Comparison of the fiber strengths and the Weibull moduli with those for Nicalon fibers prior to incorporation into composites suggests that possible fiber damage may occur either during the weaving or during another stage of the composite manufacture. Observations also indicate that it is the higher-strength fibers which experience the greatest extent of fiber pullout and thus make a larger contribution to the overall composite toughness than do the weaker fibers.

Eckel, Andrew J.↗
NASA NTRS1979

Airframe noise component interaction studies

Acoustic wind tunnel tests were conducted to examine the noise-generating processes of an airframe during approach flight. The airframe model was a two-dimensional wing section, to which highlift leading and trailing edge devices and landing gear could be added. Far field conventional microphones were utilized to determine component spectrum levels. An acoustic mirror directional microphone was utilized to examine noise source distributions on airframe components extended separately and in combination. Measured quantities are compared with predictions inferred from aircraft flyover data. Aeroacoustic mechanisms for each airframe component are identified. Component interaction effects on total radiated noise generally were small (within about 2 dB). However, some interactions significantly redistributed the local noise source strengths by changing local flow velocities and turbulence levels. Possibilities for noise reduction exist if trailing edge flaps could be modified to decrease their noise radiation caused by incident turbulent flow.

Fink, M. R.↗
NASA NTRS1987

Ion distributions in a two-dimensional reconnection field geometry

ISEE observations have shown trapped ion distributions in the magnetosphere along with streaming ion distributions in the magnetosheath. The more energetic ion beams are further away from the magnetopause than lower-energy ion beams. Predictions made with a simple two-dimensional reconnection model which contains a neutral line and an azimuthal electric field were compared with the experimental data of Sept., 1978. The model explains trapped particles in the magnetosphere due to nonadiabatic mirroring in the magnetosheath and streaming ions in the magnetosheath due to energization at the magnetopause. The model also shows the higher-energy ions extending further into the magnetosheath and farther away from the magnetopause than the lower-energy ions. This suggests the ion data of Sept., 1978 are consistent with a reconnection geometry.

Curran, D. B.↗
NASA NTRS1987

Coronagraph for astronomical imaging and spectrophotometry

A coronagraph designed to minimize scattered light in astronomical observations caused by the structure of the primary mirror, secondary mirror, and secondary support structure of a Cassegrainian telescope is described. Direct (1:1) and reducing (2.7:1) imaging of astronomical fields are possible. High-quality images are produced. The coronagraph can be used with either a two-dimensional charge-coupled device or photographic film camera. The addition of transmission dispersing optics converts the coronagraph into a low-resolution spectrograph. The instrument is modular and portable for transport to different observatories.

Vilas, Faith↗
NASA NTRS1990

Three-dimensional analytical model for the spatial variation of the foreshock electron distribution function - Systematics and comparisons with ISEE observations

A model which is consistent with the solar wind and shock surface boundary conditions for the foreshock electron distribution in the absence of wave-particle effects is formulated for an arbitrary location behind the magnetic tangent to the earth's bow shock. Variations of the gyrophase-averaged velocity distribution are compared and contrasted with in situ ISEE observations. It is found that magnetic mirroring of solar wind electrons is the most important process by which nonmonotonic reduced electron distributions in the foreshock are produced. Leakage of particles from the magnetosheath is shown to be relatively unimportant in determining reduced distributions that are nonmonotonic. The two-dimensional distribution function off the magnetic field direction is the crucial contribution in producing reduced distributions which have beams. The time scale for modification of the electron velocity distribution in velocity space can be significantly influenced by steady state spatial gradients in the background imposed by the curved shock geometry.

Fitzenreiter, R. J.↗
NASA NTRS1975

Drift-free magnetic geometries in adiabatic motion

There exist magnetic fields in which particles bouncing between mirror points experience no net first-order guiding center drift. In such fields, even though the instantaneous gradient and curvature drifts are not zero, their total effect integrated over any bounce period vanishes, so that particles merely wobble back and forth around fixed field lines. A class of two-dimensional drift-free fields, somewhat resembling the configuration found in the geomagnetic tail, is described; several proofs of the drift-free property are given, including some that suggest that the property of vanishing net drift might extend to nonadiabatic orbits. A general criterion for identifying drift-free fields is developed, and a case of motion in a nearly drift-free field is also investigated. The theory is applied to the plasma sheet in the earth's magnetotail, and observational evidence is presented suggesting that the magnetic field there indeed approaches a drift-free configuration.

Stern, D. P.↗
NASA NTRS1977

A moderate-resolution, wide-band, astronomical echelle spectrograph

An echelle spectrograph is described which is specifically designed for use on a 52-in. f/7.6 telescope as an instrument optimally suited for studying spectra of the faint optical counterparts to X-ray stars at moderate spectral resolution. The spectrograph is also able to accomodate a two-dimensional photon-tagging panoramic image detector so that high-time-resolution studies of the spectra of variable stars can be carried out. The equations for echelle spectrographs are summarized, and some features of the present instrument are discussed. These include its prism cross-disperser, small elliptical flat mirror, and unusually high efficiency. An iron-argon calibration spectrum obtained by pressing the film against the output fiber optics of a three-stage electrostatically focused image intensifier, a spectrum of P Cygni taken by placing the film directly in the image plane of the spectrograph, and a photon-counted image of a small section of an echellogram produced during an observation of the Ring nebula in Lyra are provided to illustrate the performance of the instrument.

Bardas, D.↗
NASA NTRS1973

Two-component, self-aligning laser vector velocimeter

A newly developed laser Doppler velocimeter is described. The basic optical component of the instrument is a two-dimensional ultrasonic Bragg cell. It is shown that use of this Bragg cell simplifies the optics usually required for the more conventional velocimeters, allows measurement of two-vector components of velocity, requires no adjustment of alignment mirrors, and enables both velocity component signals to be detected with a single detector. Some results from experiments using this velocimeter in an atmospheric application are described.

Farmer, W. M.↗
NASA NTRS1979

Airframe noise component interaction studies

Acoustic wind tunnel tests were conducted of a two-dimensional wing section with removable high-lift leading and trailing edge devices and a removeable two-wheel landing gear with open cavity. An array of far field conventional microphones and an acoustic mirror directional microphone were utilized to determine far field spectrum levels and noise source distribution. Data were obtained for the wing with components deployed separately and in various combinations. The basic wing model had 0.305 m (1.00 ft) chord, which is roughly 1/10 scale for a one-hundred passenger transport airplane. Most of the data were obtained at 70.7 and 100 m/sec (232 and 328 ft/sec) airspeeds, which bracket the range of practical approach speeds for such aircraft. Data were obtained at frequence to 40 kHz so that, when scaled to s typical full-airframe, the frequency region which strongly influences preceived noise level would be included.

Fink, M. R.↗
NASA NTRS1986

Improved Skin Friction Interferometer

An improved system for measuring aerodynamic skin friction which uses a dual-laser-beam oil-film interferometer was developed. Improvements in the optical hardware provided equal signal characteristics for each beam and reduced the cost and complexity of the system by replacing polarization rotation by a mirrored prism for separation of the two signals. An automated, objective, data-reduction procedure was implemented to eliminate tedious manual manipulation of the interferometry data records. The present system was intended for use in two-dimensional, incompressible flows over a smooth, level surface without pressure gradient, but the improvements discussed are not limited to this application.

Westphal, R. V.↗