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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

A Study of Photon-Dominated Regions in Reflection Nebulae

The goals of this research were to determine the physical conditions of the Photon-Dominated Regions (PDRS) surrounding the cooler stars (B0-A0) of several reflection nebulae and to test theoretical "low-density" PDR models. In contrast to the substantial investigation on "high-density" PDRS, " low-density" PDRs have been adequately modelled, but have not been adequately tested. At the start of this project, we had reduced Kuiper Airborne Observatory spectra of several far-infrared (FIR) fine structure lines on eight reflection nebulae that cover a range in cooler stellar spectral types (A0-B0). We analyzed these data in the context of "los-density" PDR models asking the question: Do the physical conditions in these reflection nebulae change with stellar spectral type as predicted?

Meixner, Margaret↗
NASA NTRS1998

A Study of Photon-Dominated Regions in Reflection Nebulae

The goals of this research were to determine the physical conditions of the Photon-Dominated Regions (PDRS) surrounding the cooler stars (BO-AO) of several reflection nebulae and to test theoretical "low-density" PDR models. In contrast to the substantial investigation on "high-density" PDRS, "low-density" PDRs have been adequately modelled, but have not been adequately tested. At the start of this project, we had reduced Kuiper Airborne Observatory spectra of several far-infrared (FIR) fine structure lines on eight reflection nebulae that cover a range in cooler stellar spectral types (AO-BO). We analyzed these data in the context of "low-density" PDR models asking the question: Do the physical conditions in these reflection nebulae change with stellar spectral type as predicted? A brief description of the findings as well as a short list of names and dates of anticipated publications are presented.

Meixner, Margaret↗
NASA NTRS2001

Development of Numerical Models for Performance Predictions of Single-Photon Avalanche Photodetectors (SPAP) for the 2-Micron Regime

Field dependent drift velocity results are presented for electron transport in bulk Indium Arsenide (InAs) material based on a Monte Carlo model, which includes an analytical treatment of band-to-band impact ionization. Avalanche multiplication and related excess noise factor (F) are computed as a function of device length and applied voltage. A decrease in F with increases in device length is obtained. The results suggest an inherent utility for InAs-based single-photon avalanche detectors, particularly around the 2 microns region of interest for atmospheric remote sensing applications. The dark current response was also evaluated. The role of the various components has been analyzed. For shorter devices, the tunneling component is shown to dominate at low temperatures. Finally, possible structures for enhanced photodetection are proposed for future research.

Joshi, Ravindra P.↗
NASA NTRS2003

X-ray single Photon Spectrometers

The research at Yale on superconducting tunnel junctions (STJs) focussed on x-ray detectors, using a 5.9 keV x-ray source. All the Yale tests were carried out at 0.21 K, in a two-stage helium 3 dewar. Careful attention was given to grounding and shielding. All current waveforms were digitially recorded and analyzed subsequently on computer. The imaging device geometry was studied. This allows imaging along the length of the tantalum (Ta) absorber, which is 600 nm thick to provide good x-ray absorption. The quasiparticles produced by single photon absorption rapidly cool to the Ta gap, E(sub g_Ta) = 1.4 meV, and then diffuse. They are trapped in the A1 traps at the two ends (E(sub g_A1) = 0.4 meV), to give two charges that tunnel out of the A1 traps, Q(sub 1) and Q(sub 2). The total charge is Q = Q(sub 1) + Q(sub 2). This lateral trapping is what allows imaging.

Prober, Daniel↗
NASA NTRS2003

"DUST BUSTER" - A Single Photon Ionization TOF MS for Cometary Dusts

It is hard to predict the properties and composition of dust that will be returned by STARDUST from WED- 2. The most interesting but challenging case would be grains, pg to fg in weight, each carrying its own isotopic signature characteristic of its source zones in a variety of stars. How do we extract the maximum amount of science from such grains? Clearly, the best that can be accomplished is to measure every atom in each grain.Academia Sinica and Argonne National Laboratory (ANL) have entered into a collaboration to develop a SPI TOF MS instrument for analysis of stardust grains. A new instrument will be built at Academia Sinica based on the new TOF mass spectrometer design developed, built and operating at ANL. The instrument is intended for SPI TOF MS analysis of elements from Ca to Cu plus Li after first using SIMS to measure H, C, N, 0, Si, and S. There are still technical challenges facing the technique. We will need to improve submicrometer sample handling, avoid the effects of space charge, and increase the Mamie range of the detector. The most difficult obstacle to overcome may be the fact that the flux density of present high repetition rate, WV lasers is below the level needed to ensure full ionization (saturation) in the source region, which must be several mm in size to achieve the high useful yield needed for analysis of small stardust grains. A potential breakthrough effort is to exploit the novel free electron laser being pioneered at ANL. In principle, this FEL can reach ionization saturation and is tunable up to photon energies of 25 eV, which is higher than the ionization potential of any element.

Chen, C.-Y.↗
NASA NTRS2002

NASA's Photon-Counting SLR2000 Satellite Laser Ranging System: Progress and Applications

NASA's new unmanned SLR2000 system is designed to track, with millimeter precision and using single photon returns, a constellation of roughly 24 retroreflector-equipped satellites, which range in altitude from about 300 km to 20,000 km. Totally autonomous operation and a common engineering configuration are expected to greatly reduce station operations costs relative to NASA's current manned systems. The system has also been designed with a goal of significantly lowering replication costs. All of the prototype components and subsystems have been completed and tested and have substantially met the original specifications. The prototype system is presently undergoing final integration and testing in a dedicated shelter with an azimuth tracking dome synchronized to the optical tracking mount. The facility also features a number of security features such as security cameras and sensors designed to detect power or thermal control problems or entry by unauthorized personnel. Field tests are in progress. The present paper provides an overview of the various subsystems and test results to date. The meteorological subsystem, which has operated successfully in the field for almost three years, consists of several sensors which measure: (1) pressure, temperature, and relative humidity; (2) wind speed and direction; (3) ground visibility and precipitation; and (4) local cloud cover as a function of station azimuth and elevation (day and night). A "pseudo-operator" software program interprets the sensor readings and modifies satellite tracking priorities based on local meteorological conditions.

Degnan, John J.↗
NASA NTRS2004

Characteristic Matrices for Spherical Shell Photonic Systems

We establish a parallel between the transfer matrix used in the study of plane-parallel photonic structures and the matrix characterizing transfer of partial waves in concentric spheres. We derive explicit expressions for the elements of the transfer matrix for concentric spherical layers, and from those expressions derive the scattering coefficients of a multilayered sphere. The transfer matrices are 4x4 block diagonal with only four independent elements. Matrix elements for the case of TM waves are related to those for the case of TE waves through simple interchange and multiplicative constants. In analogy with plane parallel layers, the transfer matrix for concentric multilayers is simply the product of the transfer matrices of the individual layers.

Fuller, Kirk A.↗
NASA NTRS2004

Photon Dynamics in Coherently Coupled Optical Resonators

The temporal response of coupled resonators is investigated using a linear systems analysis and coupled mode theory. Damped Rabi oscillations, slow and fast light, and coherent photon transfer techniques are demonstrated in these systems.

Smith, David D.↗
NASA NTRS2004

Photon Counting Detectors for the 1.0 - 2.0 Micron Wavelength Range

We describe results on the development of greater than 200 micron diameter, single-element photon-counting detectors for the 1-2 micron wavelength range. The technical goals include quantum efficiency in the range 10-70%; detector diameter greater than 200 microns; dark count rate below 100 kilo counts-per-second (cps), and maximum count rate above 10 Mcps.

Krainak, Michael A.↗
NASA NTRS2005

The Highest-Energy Photons Seen by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory

During its nine-year lifetime, the Energetic Gamma Ray Experiment Telescope (EGBET) on the Compton Gamma Ray Observatory (CGRO) detected 1506 cosmic photons with measured energy E>10 GeV. Of this number, 187 are found within a 1 deg of sources that are listed in the Third EGRET Catalog and were included in determining the detection likelihood, flux, and spectra of those sources. In particular, five detected EGRET pulsars are found to have events above 10 GeV, and together they account for 37 events. A pulsar not included in the Third EGRET Catalog has 2 events, both with the same phase and in one peak of the lower-energy gamma-ray light-curve. Most of the remaining 1319 events appear to be diffuse Galactic and extragalactic radiation based on the similarity of the their spatial and energy distributions with the diffuse model and in the E>100, MeV emission. No significant time clustering which would suggest a burst was detected.

Thompson, D. J.↗
NASA NTRS2004

Solar Variability and the Near-Earth Environment: Mining Enhanced Low Dose Rate Sensitivity Data From the Microelectronics and Photonics Test Bed Space Experiment

This effort is a detailed analysis of existing microelectronics and photonics test bed satellite data from one experiment, the bipolar test board, looking to improve our understanding of the enhanced low dose rate sensitivity (ELDRS) phenomenon. Over the past several years, extensive total dose irradiations of bipolar devices have demonstrated that many of these devices exhibited ELDRS. In sensitive bipolar transistors, ELDRS produced enhanced degradation of base current, resulting in enhanced gain degradation at dose rates <0.1 rd(Si)/s compared to similar transistors irradiated at dose rates >1 rd(Si)/s. This Technical Publication provides updated information about the test devices, the in-flight experiment, and both flight-and ground-based observations. Flight data are presented for the past 5 yr of the mission. These data are compared to ground-based data taken on devices from the same date code lots. Information about temperature fluctuations, power shutdowns, and other variables encountered during the space flight are documented.

Turflinger, T.↗
NASA NTRS2004

Displacement Damage Effects in Solar Cells: Mining Damage From the Microelectronics and Photonics Test Bed Space Experiment

The objective is to develop an improved space solar cell radiation response analysis capability and to produce a computer modeling tool which implements the analysis. This was accomplished through analysis of solar cell flight data taken on the Microelectronics and Photonics Test Bed experiment. This effort specifically addresses issues related to rapid technological change in the area of solar cells for space applications in order to enhance system performance, decrease risk, and reduce cost for future missions.

Hardage, Donna↗
NASA NTRS2005

The Role of Space Experiments in the Radiation Qualification of Electronic and Photonic Devices and Systems

Space experiments are occasionally launched to study the effects of radiation on electronic and photonic devices. This begs the following questions: Are space experiments necessary? Do the costs justify the benefits? How does one judge success of space experiment? What have we learned from past space experiments? How does one design a space experiment? This viewgraph presentation provides information on the usefulness of space and ground tests for simulating radiation damage to spacecraft components.

Buchner, S.↗
NASA NTRS2002

Optical communication noise rejection using corelated photons

This paper describes a completely new way to perform noise rejection using photons correlated through quantum entanglement to improve an optical communications link in the presence of uncorrelated noise. In particular, a detailed analysis is made of the case where a classical link would be saturated by an intense background, such as when a satellite is in front of the sun, and identifies where the quantum correlating system has superior performance.

signal to noise enhancement↗