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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Microelectromechanical Systems (MEMS) Broadband Light Source Developed

A miniature, low-power broadband light source has been developed for aerospace applications, including calibrating spectrometers and powering miniature optical sensors. The initial motivation for this research was based on flight tests of a Fabry-Perot fiberoptic temperature sensor system used to detect aircraft engine exhaust gas temperature. Although the feasibility of the sensor system was proven, the commercial light source optically powering the device was identified as a critical component requiring improvement. Problems with the light source included a long stabilization time (approximately 1 hr), a large amount of heat generation, and a large input electrical power (6.5 W). Thus, we developed a new light source to enable the use of broadband optical sensors in aerospace applications. Semiconductor chip-based light sources, such as lasers and light-emitting diodes, have a relatively narrow range of emission wavelengths in comparison to incandescent sources. Incandescent light sources emit broadband radiation from visible to infrared wavelengths; the intensity at each wavelength is determined by the filament temperature and the materials chosen for the filament and the lamp window. However, present commercial incandescent light sources are large in size and inefficient, requiring several watts of electrical power to obtain the desired optical power, and they emit a large percentage of the input power as heat that must be dissipated. The miniature light source, developed jointly by the NASA Glenn Research Center, the Jet Propulsion Laboratory, and the Lighting Innovations Institute, requires one-fifth the electrical input power of some commercial light sources, while providing similar output light power that is easily coupled to an optical fiber. Furthermore, it is small, rugged, and lightweight. Microfabrication technology was used to reduce the size, weight, power consumption, and potential cost-parameters critical to future aerospace applications. This chip-based light source has the potential for monolithic fabrication with on-chip drive electronics. Other uses for these light sources are in systems for vehicle navigation, remote sensing applications such as monitoring bridges for stress, calibration sources for spectrometers, light sources for space sensors, display lighting, addressable arrays, and industrial plant monitoring. Two methods for filament fabrication are being developed: wet-chemical etching and laser ablation. Both yield a 25-mm-thick tungsten spiral filament. The proof-of-concept filament shown was fabricated with the wet etch method. Then it was tested by heating it in a vacuum chamber using about 1.25 W of electrical power; it generated bright, blackbody radiation at approximately 2650 K. The filament was packaged in Glenn's clean-room facilities. This design uses three chips vacuum-sealed with glass tape. The bottom chip consists of a reflective film deposited on silicon, the middle chip contains a tungsten filament bonded to silicon, and the top layer is a transparent window. Lifetime testing on the package will begin shortly. The emitted optical power is expected to be approximately 1.0 W with the spectral peak at 1.1 mm.

Tuma, Margaret L.↗
NASA NTRS1983

Nuclear cascades in Saturn's rings - Cosmic ray albedo neutron decay and origins of trapped protons in the inner magnetosphere

The nearly equatorial trajectory of the Pioneer 11 spacecraft through Saturn's high energy proton radiation belts and under the main A-B-C rings provided a unique opportunity to study the radial dependence of the greater than 30 MeV proton intensities in the belts in terms of models for secondary nucleon production by cosmic ray interactions in the rings, in situ proton injection in the radiation belts by neutron beta decay, magnetospheric diffusion, and absorption by planetary rings and satellites. Maximum trapped proton intensities measured by Pioneer 11 in the radiation belts are compared with calculated intensities and found consistent with trapping times of roughly 40 years and a radial diffusion coefficient of about 10 to the -15th L to the 9th R sub s squared/s. Differential energy spectra proportional to E to the -2 estimated from integral measurements of trapped photons with E greater than 100 MeV are consistent with the beta decay model, but an inferred turndown of the spectra toward lower energies and reported integral proton anisotropies of a specified form both indicate the need for more realistic calculations of the neutron source from the rings and the radiation belt loss processes.

Cooper, J. F.↗
NASA NTRS1976

Soft X-rays from Her X-1 during the off phase

Weak 0.28-keV radiation was observed from Her X-1 5 days before turn-on in the 35 day cycle. The observations were made from an Aerobee rocket. The 0.28-keV intensity is about 1/25 that observed during the on phase. Some evidence for X-rays above 1 keV is also present, and it is possible that the spectrum is different only in intensity from the spectrum in the on phase. The radiation may be X-rays from the vicinity of the neutron star, scattered by ionized material in the inner accretion disk, or may be thermal radiation from the inner accretion disk, or both.

Fritz, G.↗
NASA NTRS1994

The effect of comet Shoemaker-Levy 9 on Jupiter's synchrotron radiation

Solid material from comet Shoemaker-Levy 9 is expected to modify Jupiter's decimetric radio emission. Electrons passing through dust grains suffer a degradation in their energy, while larger sized material absorbs all electrons impinging on it. If there is enough dust and/or larger sized material in the magnetosphere, the effect on the energetic electrons can be observed via their synchrotron radiation, emitted at microwave frequencies. The planet's radio emission is expected to decrease, and the presence of dust induces a hardening in the radio spectrum. We expect the intensity to decrease immediately after cometary material enters the radiation belts; the radio emission continues to drop for many months as electrons diffuse inwards through a dusty magnetosphere. Radio observations of the planet during and after the cometary impact thus yield information on the amount of cometary material (optical depth of the dust and macroscopic material), impacts between cometary material and Jupiter's ring, and the diffusion process of energetic electrons through the magnetosphere.

De Pater, Imke↗
NASA NTRS1971

Improved source of infrared radiation for spectroscopy

Radiation from a crimped V-groove in the electrically heated metallic element of a high-resolution infrared spectrometer is more intense than that from plane areas adjacent to the element. Radiation from the vee and the flat was compared by alternately focusing on the entrance slit of a spectrograph.

Burkhard, D. G.↗
NASA NTRS1983

Si III line ratios in the sun

New atomic data for Si III have been used to predict level populations and emission-line intensity ratios for electron densities and temperatures appropriate to the solar transition region. The electron impact collision rates used here are substantially larger than those previously published owing to delineation of the complex resonance structures in the low-energy collision strengths. This together with small changes in the spontaneous radiative rates produces significant changes in the calculated intensity ratios. Generally good agreement is found with observations obtained using the Naval Research Laboratory slit spectrograph aboard Skylab, electron densities from three Si III ratios and from other methods normally agreeing to 0.2 dex or better for a wide variety of solar features. For a fourth ratio, incorporating lines with a wide wavelength separation, the agreement is less satisfactory, possibly owing to uncertainties in the observational data.

Dufton, P. L.↗
NASA NTRS1994

The highly ionized regions of NGC 6302 and NGC 6537

We present (Ne V) 24.32 micrometer and 3426 A emission-line fluxes for NGC 6302 and NGC 6537. These fluxes along with those of (Ne V) 14.3 micrometer allow us to determine the physical conditions within the highly ionized regions of these nebulae. The electron densities found via the (Ne V) line ratios are similar to those found in studies of the low-ionization regions. However, the electron temperatures determined from the (Ne V) line ratios are much greater than those in the low-ionization regions. However, the electron temperatures determined from the (Ne V) line ratios are much greater than those in the low-ionization regions. We use photoionization models to show that these high derived electron temperatures are inconsistent with the assumption that the nebular ionization is produced solely by radiation from the central star. Much of the intense (Ne V) 3426 A emission from these objects must arise from highly ionized shocked material; a conclusion which is in accord with other evidence. The fact that the (Ne V) infrared lines are less affected by the shock means that we can estimate the relative volumes of the shocked and radiatively excited portions of these nebulae. In the most likely scenario, the volume of the highly ionized shocked region is less than 10% that of the highly ionized region formed by photoionization. We note that under such conditions, infrared emission lines are more useful than optical or UV emission lines for abundance studies because they are less affected by shocks. With appropiate corrections to the optical and UV emission-line fluxes, these nebulae can still be described by photoionization models.

Rowlands, N.↗
NASA NTRS1974

The earth as a radio source: The non-thermal continuum

A weak nonthermal continuum, radiated by the earth from energetic electrons in the outer radiation zone, is studied. It is shown that the frequency spectrum of the continuum radiation consists of two components, a trapped component, which is permanently trapped within the magnetosphere at frequencies below the solar wind plasma frequency, and an escaping component which propagates freely away from the earth at frequencies above the solar wind plasma frequency. Direction finding measurements and measurements of the spatial distribution of intensity for both components indicated that the continuum radiation is generated (1) in a broad region which extends through the morning and early afternoon immediately beyond the plasmapause boundary, and (2) over a broad range of latitudes, including the magnetic equator. Possible mechanisms by which this radiation is generated, including gyro-synchrotron radiation from energetic electrons in the outer radiation zone, are discussed.

Gurnett, D. A.↗
NASA NTRS1990

Radiation of partially ionized atomic hydrogen

A nonlinear collisional-radiative model for determination of production of electrons, positive and negative ions, excited atoms, and spectral and continuum line intensities in stationary partially ionized atomic hydrogen is presented. Transport of radiation is included by coupling the rate equations for production of the electrons, ions, and excited atoms with the radiation escape factors, which are not constant but depend on plasma conditions. It is found that the contribution of the negative ion emission to the total continuum emission can be important. Comparison of the calculated total continuum emission coefficient, including the negative ion emission, is in good agreement with experimental results.

Soon, W. H.↗
NASA NTRS2014

Analytical-HZETRN Model for Rapid Assessment of Active Magnetic Radiation Shielding

The use of active radiation shielding designs has the potential to reduce the radiation exposure received by astronauts on deep-space missions at a significantly lower mass penalty than designs utilizing only passive shielding. Unfortunately, the determination of the radiation exposure inside these shielded environments often involves lengthy and computationally intensive Monte Carlo analysis. In order to evaluate the large trade space of design parameters associated with a magnetic radiation shield design, an analytical model was developed for the determination of flux inside a solenoid magnetic field due to the Galactic Cosmic Radiation (GCR) radiation environment. This analytical model was then coupled with NASA's radiation transport code, HZETRN, to account for the effects of passive/structural shielding mass. The resulting model can rapidly obtain results for a given configuration and can therefore be used to analyze an entire trade space of potential variables in less time than is required for even a single Monte Carlo run. Analyzing this trade space for a solenoid magnetic shield design indicates that active shield bending powers greater than 15 Tm and passive/structural shielding thicknesses greater than 40 g/cm2 have a limited impact on reducing dose equivalent values. Also, it is shown that higher magnetic field strengths are more effective than thicker magnetic fields at reducing dose equivalent.

Washburn, S. A.↗
NASA NTRS1983

Laboratory simulation of Venusian lightning

Evidence of lightning activity in the Venusian atmosphere has been obtained from the Venera 9, 11, and 12 spacecraft, and from the Pioneer Venus Orbiter (PVO). However, a search for optical pulses expected from Venusian lightning using the star sensor on the PVO did not detect any signals. It has been suggested that the star sensor did not detect lightning because Venusian lightning does not radiate in the 500- to 900-nm spectral region detected by the star sensor. In this paper, spectra obtained from a laboratory simulation of Venusian lightning are discussed. Both the laboratory spectrum and the results of a theoretical calculation of line intensities show that Venusian lightning can be expected to radiate strongly in the 600- to 900-nm spectral region. Hence, the failure of the star sensor to detect lightning must be caused by the low flashing rate or by the low intensity of Venusian lightning.

Borucki, W. J.↗
NASA NTRS1972

Performance of silicon solar cell assemblies

Solar cell assembly current-voltage characteristics, thermal-optical properties, and power performance were determined. Solar cell cover glass thermal radiation, optical properties, confidence limits, and temperature intensity effects on maximum power were discussed.

Ross, R. G., Jr.↗
NASA NTRS1972

Quantum-mechanical treatment of an electron undergoing synchrotron radiation.

The problem of an electron moving perpendicular to an intense magnetic field is approached from the framework of quantum mechanics. A numerical solution to the related rate equations describing the probabilities of occupation of the electron's energy states is put forth along with the expected errors involved. The quantum-mechanical approach is found to predict a significant amount of energy broadening with time for an initially monoenergetic electron beam entering a region of an intense magnetic field as long as the product of initial energy and magnetic field is of order 50 MG BeV or larger.

White, D.↗