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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Modulation of centimetric waves by long gravity waves - Progress report on field and laboratory results

Results are presented from laboratory and field experiments on the modulation of short waves by long waves. The field study employed a wave follower capable of tracking ocean waves with frequencies less than 1.0 Hz and heights less than 2.0 m. A high-response laser-optical system was used to detect upwind-downwind and cross-wind slopes of short waves. The laboratory study was conducted with wind over periodic long waves. The laboratory findings are discussed and compared with laboratory radar measurements and also short wave measurements obtained in the field. It is found that long waves significantly modulate the short wave dispersion by their orbital velocity, and that demodulation is necessary if the data collected by remote sensors are to be compared to surface penetrating devices. The modulation level is weak for wavelengths in the range 2.76-3.30 cm. Other relevant results are also presented.

Shemdin, O. H.↗
NASA NTRS1980

An investigation of the modulation of capillary and short gravity waves in the open ocean

A preliminary investigation of the modulation of capillary and gravity waves by long ocean waves is described. A pressure transducer is used to obtain water surface displacements, and a high-response laser-optical system is used to detect short-wave slopes. Analytical techniques are developed to account for the orbital motion of long waves. The local mean squared wave slope is found to be maximum leeward of the long-wave crests. For the long waves studied here and for short waves from 1 cm to 1 m, the longer a short-wave component is, the more leeward its maximum tends to occur. Also, the shortest waves tend to modulate least. The modulation of short waves is found to be strong enough to be an important component of the synthetic aperture radar image formation mechanism for long ocean waves.

Evans, D. D.↗
NASA NTRS1981

Position measurements for heavy ion beams using a sodium iodide scintillator

A 50 cm diameter, 1.7 cm thick disc of NaI scintillator has been mounted to permit edge viewing by four photomultipliers. Energetic heavy ions passing through the scintillator at different positions cause a variation in the division of light among the photomultipliers. A performance close to the expected limit for 670 MeV/n neon has been achieved. Calculations of expected response using an optical model agree well with the measurements.

Buffington, A.↗
NASA NTRS1984

Conceptual design of a hybrid Ge:Ga detector array

For potential applications in space infrared astronomy missions such as the Space Infrared Telescope Facility and the Large Deployable Reflector, integrated arrays of long-wavelength detectors are desired. The results of a feasibility study which developed a design for applying integrated array techniques to a long-wavelength (gallium-doped germanium) material to achieve spectral coverage between 30 and 200 microns are presented. An approach which builds up a two-dimensional array by stacking linear detector modules is presented. The spectral response of the Ge:Ga detectors is extended to 200 microns by application of uniaxial stress to the stack of modules. The detectors are assembled with 1 mm spacing between the elements. Multiplexed readout of each module is accomplished with integration sampling of a metal-oxide-semiconductor (MOS) switch chip. Aspects of the overall design, including the anticipated level of particle effects on the array in the space environment, a transparent electrode design for 200 microns response, estimates of optical crosstalk, and mechanical stress design calculations are included.

Parry, C. M.↗
NASA NTRS1985

Cosmic-ray backgrounds in infrared bolometers

Model calculations for the production of cosmic ray events in IR detectors by energy impulses due to fast charged particles' ionization trails are presently compared to the pulse-amplitude spectrum observed from a balloon at an altitude of 38 km. The results are pertinent to the current understanding of cosmic ray backgrounds found in all high sensitivity bolometer applications. The observed signal transients are in all details consistent with the modeling of known cosmic charged particle flux characteristics and with the detector response. Generally, the optics design should minimize detector/substrate cross section.

Nolt, I. G.↗
NASA NTRS1985

Ultraviolet observations of low-excitation Herbig-Haro objects

The Herbig-Haro (HH) objects rank among the faintest objects (v approx. 17) observed with the I.U.E. Expectations that the low-excitation shock-excited HHs should be dominated by H two-photon (2q) UV emission were borne out in the first observation of HH 43 and 47 obtained in 1982. The UV continuous energy distributions in the SWP spectra of these objects were found to peak near 1500 Angstroms as predicted by the 2q hypothesis. In addition, emission lines in the Lyman band of H sub 2, excited by Lyman alpha fluorescence, were detected in HH 43. It is not clear if the molecular gas is coextensive with the atomic gas responsible for the optical emission, or if the molecular gas is immediately adjacent to the region of optical emission. The two-photon energy distribution and H sub 2 fluorescent emission were previously discussed.

Schwartz, R. D.↗
NASA NTRS1985

Thermal stress cycling of GaAs solar cells

A thermal cycling experiment was performed on GaAs solar cells to establish the electrical and structural integrity of these cells under the temperature conditions of a simulated low-Earth orbit of 3-year duration. Thirty single junction GaAs cells were obtained and tests were performed to establish the beginning-of-life characteristics of these cells. The tests consisted of cell I-V power output curves, from which were obtained short-circuit current, open circuit voltage, fill factor, and cell efficiency, and optical micrographs, spectral response, and ion microprobe mass analysis (IMMA) depth profiles on both the front surfaces and the front metallic contacts of the cells. Following 5,000 thermal cycles, the performance of the cells was reexamined in addition to any factors which might contribute to performance degradation. It is established that, after 5,000 thermal cycles, the cells retain their power output with no loss of structural integrity or change in physical appearance.

Janousek, B. K.↗
NASA NTRS1985

The X-ray spectroscopy of active galactic nuclei

The scientific goals of X-ray spectroscopy of active galactic nuclei are discussed. The underlying energy source, the regions responsible for the optical emission lines, the different types of active galaxies, and cosmology are considered. The requirements for an X-ray mission of broad band width, large collecting area, modest spatial resolution and good spectral resolution are outlined. It is concluded that the ESA XMM mission meets these requirements.

Mushotzky, R.↗
NASA NTRS1986

Inversion methods for satellite studies of the Earth Radiation Budget - Development of algorithms for the ERBE mission

The Earth Radiation Budget Experiment carries a three-channel scanning radiometer and a set of nadir-looking wide and medium field-of-view instruments for measuring the radiation emitted from earth and the solar radiation reflected from earth. This paper describes the algorithms which are used to compute the radiant exitances at a reference level ('top of the atmosphere') from these measurements. Methods used to analyze data from previous radiation budget experiments are reviewed, and the rationale for the present algorithms is developed. The scanner data are converted to radiances by use of spectral factors, which account for imperfect spectral response of the optics. These radiances are converted to radiant exitances at the reference level by use of directional models, which account for anisotropy of the radiation as it leaves the earth. The spectral factors and directional models are selected on the basis of the scene, which is identified on the basis of the location and the long-wave and shortwave radiances. These individual results are averaged over 2.5 x 2.5 deg regions. Data from the wide and medium field-of-view instruments are analyzed by use of the traditional shape factor method and also by use of a numerical filter, which permits resolution enhancement along the orbit track.

Smith, G. L.↗
NASA NTRS1987

Long-life 3-axis satellite attitude sensing, phase 1

The purpose was to investigate the feasibility of new, moderate-cost, high reliability navigation sensors for high-altitude satellites, using stellar sources to obviate the use of gyroscopic devices. The primary investigation focused on the need for developing a star tracker model to replace an old star tracker which is still needed for current probe and satellite programs. One innovative element of the proposed star tracker was the design, development, and testing of technology components related to a phase scrambler plate. The purpose of the phase scrambler plate is to convert the impulse response of the optical system from a point image to a uniformly bright, square, angularly large, in-focus image of the star source. A collimated star source was built and tested. A breadboard star tracker with an 8 x 8 degree field of view was designed and built. It was tested in normal quad-cell mode (without the phase scrambler plate) and with the phase scrambler plate. Although the phase scrambler plate was crudely made, the performance of the star tracker breadboard was greatly improved using the phase scrambler plate, instead of system defocus. If further developed, the phase scrambler plate may be added as a low-cost retroconversion to any objective lens to greatly improve quad-cell or CCD array tracking; applications include star trackers, laser metrology, laser machining optics, and surveying instrumentation.

Arild, Tor↗
NASA NTRS1995

Second Annual Research Center for Optical Physics (RCOP) Forum

The Research Center for Optical Physics (RCOP) held its Second Annual Forum on September 23-24, 1994. The forum consisted of two days of technical sessions with invited talks, submitted talks, and a student poster session. Participants in the technical sessions included students and researchers from CCNY/CUNY, Fisk University, Georgia Institute of Technology, Hampton University, University of Maryland, the Univeristy of Michigan, NASA Langley Research Center, North Caroline A and T University, Steven's Institute of Technology, and NAWC-Warminster. Topics included chaotic lasers, pumped optical filters, nonlinear responses in polythiophene and thiophene based thin films, crystal growth and spectroscopy, laser-induced photochromic centers, raman scattering in phorphyrin, superradiance, doped fluoride crystals, luminescence of terbium in silicate glass, and radiative and nonradiative transitions in rare-earth ions.

Allario, Frank↗
NASA NTRS1995

Analysis of an astrometric Fizeau interferometer for GAIA

The concepts related to the operation and design of the global astrometric interferometer for astrophysics (GAIA) bring together solutions chosen for the astrometry satellite and interferometric techniques. Like the Hipparcos satellite, GAIA is a continuously scanning instrument for which the integration time on any observed object is limited by the field of view of the detector. If a final astrometric accuracy of 10 microarcsec is aimed at, a field of 1 deg in diameter is needed. A design is presented for the proposed 2.6 m baseline Fizeau interferometer with two 40 cm apertures and overall dimensions compatible with the size of the Ariane 5 payload shroud. It has a 0.9 deg diffraction limited field of view. The response of the optical system to small perturbations on each optical element is given in terms of the fringe visibility, which is shown to be dependent on the sub-aperture spot separation. The robustness of the design to thermal, mechanical and manufacturing errors is discussed. The unavoidable distortion present in wide field optical systems is analyzed in terms of displacement of the interference fringes.

Loiseau, Sacha↗
NASA NTRS1996

Infrared Spectroscopy of Pa-beta and [Fe II] Emission in NGC 4151

We present spatially resolved 1.24-1.30 micron spectroscopy with a resolution of 240 km/s of the Seyfert 1.5 galaxy NGC 4151. Broad Pa-beta, narrow Pa-beta, and narrow [Fe II] (lambda = 1.2567 micron) emission lines are identified in the spectrum. Additionally, a spatially unresolved narrow component probably due to [S ix] (lambda = 1.25235 micron) is observed on the nucleus. The narrow Pa-beta and [Fe II] lines are observed to be extended over a scale of 5 sec. The spatial variation of the velocity centers of the Pa-beta and [Fe II] lines show remarkable similarity, and additionally show similarities to the velocity structure previously observed in ground based spectroscopy of [O III] emission in NGC 4151. This leads to the conclusion that the [Fe II] emission arises in clouds in the Seyfert narrow line region that are physically correlated with those narrow line clouds responsible for the optical emission. The [Fe II] emission line, however, is significantly wider than the Pa-beta emission line along the full spatial extent of the observed emission. This result suggests that despite the correlation between the bulk kinematics of Pa-beta and [Fe II], there is an additional process, perhaps fast shocks from a wind in the Seyfert nucleus, contributing to the [Fe II] emission.

Knop, R. A.↗
NASA NTRS1998

Coulomb Crystallization of Charged Microspheres Levitated in a Gas Discharge Plasma

The technical topic of the project was the experimental observation of Coulomb crystallization of charged microspheres levitated in a gas discharge plasma. This suspension, sometimes termed a dusty plasma, is closely analogous to a colloidal suspension, except that it has a much faster time response, is more optically thin, and has no buoyancy forces to suspend the particles. The particles are levitated by electric fields. Through their collective Coulomb repulsions, the particles arrange themselves in a lattice with a crystalline symmetry, which undergoes an order-disorder phase transition analogous to melting when the effective temperature of the system is increased. Due to gravitational sedimentation, the particles form a thin layer in the laboratory, so that the experimental system is nearly 2D, whereas in future microgravity experiments they are expected to fill a larger volume and behave like a 3D solid or liquid. The particles are imaged using a video camera by illuminating them with a sheet of laser light. Because the suspension is optically thin, this imaging method will work as well in a 3D microgravity experiment as it does in a 2D laboratory system.

Goree, John↗
NASA NTRS1996

3C 279 Multiwavelength Monitoring: The Ground-Based Campaign - 2

The optically violently variable quasar 3C 279 was monitored simultaneously from radio to gamma-ray frequencies in 1992 December - 1993 January. We report a detailed study of the ground-based results from radio to optical wavelengths. These data show that 3C 279 has a typical blazar spectrum, slightly rising at radio frequency and then progressively steeper above a first turnover frequency between 37 and 90 GHz. In the millimeter wavelength region, a simple power law is not an adequate description of the spectrum. We suggest that the millimeter "shoulder" corresponds to an additional emission component, self-absorbed between 150 and 375 GHz, possibly associated with the detachment of a new Very Long Base Interferometry (VLBI) knot and with the start of radio flare. A flux increase of 20% over 20 days was observed at 37 and 90 GHz, while contemporaneously the R-band flux doubled in about two weeks. The lack of strong variability in contemporaneous X-ray light curves (possible X-ray variations are less than 30%) implies no direct (i.e., zero lag) correlation between the optical and X-ray fluxes. If X-rays are produced by inverse-Compton scattering of relativistic electrons on some seed photons, the above results exclude that the observed optical photons are the seeds and/or that the relativistic electrons radiating via synchrotron in the optical band are responsible for the scattering to X-ray energies. We suggest that the X-rays are instead produced through the inverse-Compton process by electrons of lower energy, which radiate via synchrotron in the radio to millimeter wave bands and which scatter either on the synchrotron photons themselves or on external photons.

Grandi, P.↗
NASA NTRS2003

Gas Scintillation Proportional Counters for High-Energy X-ray Astronomy

A focal plane array of high-pressure gas scintillation proportional counters (GSPC) for a balloon-borne hard-x-ray telescope is under development at the Marshall Space Flight Center. These detectors have an active area of approx. 20 sq cm, and are filled with a high pressure (10(exp 6) Pa) xenon-helium mixture. Imaging is via crossed-grid position-sensitive phototubes sensitive in the UV region. The performance of the GSPC is well matched to that of the telescopes x-ray optics which have response to 75 keV and a focal spot size of approx. 500 microns. The detector s energy resolution, 4% FWHM at 60 keV, is adequate for resolving the broad spectral lines of astrophysical importance and for accurate continuum measurements. Full details of the instrument and its performance will be provided.

Gubarev, Mikhail↗
NASA NTRS2004

Performance of Gas Scintillation Proportional Counter Array for High-Energy X-Ray Observatory

A focal plane array of high-pressure gas scintillation proportional counters (GSPC) for a High Energy X-Ray Observatory (HERO) is developed at the Marshall Space Flight Center. The array is consisted from eight GSPCs and is a part of balloon born payload scheduled to flight in May 2004. These detectors have an active area of approximately 20 square centimeters, and are filled with a high pressure (10(exp 6) Pa) xenon-helium mixture. Imaging is via crossed-grid position-sensitive phototubes sensitive in the UV region. The performance of the GSPC is well matched to that of the telescopes x-ray optics which have response to 75 keV and a focal spot size of approximately 500 microns. The detector's energy resolution, 4% FWHM at 60 keV, is adequate for resolving the broad spectral lines of astrophysical importance and for accurate continuum measurements. Results of the on-earth detector calibration will be presented and in-flight detector performance will be provided, as available.

Gubarev, Mikhail↗
NASA NTRS2004

Infrared Avionics Signal Distribution Using WDM

Supporting analog RF signal transmission over optical fibers, this project demonstrates a successful application of wavelength division multiplexing (WDM) to the avionics environment. We characterize the simultaneous transmission of four RF signals (channels) over a single optical fiber. At different points along a fiber optic backbone, these four analog channels are sequentially multiplexed and demultiplexed to more closely emulate the conditions in existing onboard aircraft. We present data from measurements of optical power, transmission response (loss and gain), reflection response, group delay that defines phase distortion, signal-to-noise ratio (SNR), and dynamic range that defines nonlinear distortion. The data indicate that WDM is very suitable for avionics applications.

Atiquzzaman, Mohammed↗