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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Polycapillary X-Ray Optics for X-Ray Astronomy

High-energy x-ray spectrometry from astronomical sources is difficult due to low flux rates and high background. Polycapillary x-ray optics can be used to increase the signal-to-noise ratio by focusing photons onto a small energy dispersive detector. Two optics, both designed for x-ray astronomy, have been built and tested as collimating optics with a microfocus x-ray source for x-ray energies up to 70 keV and as focusing optics with parallel x-rays up to 50 keV. Results from these tests show that polycapillary x-ray optics have transmission efficiencies ranging from 5% to 40% and signal gains ranging from 5 to over 100 for energies up to 50 keV. Furthermore the results show that these optics have potential for use up to 100 keV. The experimental results as well as simulations for the measured and for optimized optics will be discussed.

Russell, C. H.↗
NASA NTRS2016

A Day in the Life of the Laser Communications Relay Demonstration (LCRD) Project.

This presentation provides an overview of the planned concept of operations for the Laser Communications Relay Demonstration Project (LCRD), a joint project among NASA's Goddard Space Flight Center (GSFC), the Jet Propulsion Laboratory, California Institute of Technology (JPL), and the Massachusetts Institute of Technology Lincoln Laboratory (MITLL). LCRD will provide at least two years of bi-directional optical communications at user data rates of up to 1.244 Gbps in an operational environment. The project lays the ground work for establishing communications architecture and protocols, and developing the communications hardware and support infrastructure, concluding in a demonstration of optical communications potential to meet NASAs growing need for higher data rates for future science and exploration missions. A pair of flight optical communications terminals will reside on a single commercial communications satellite in geostationary orbit; the two ground optical communications terminals will be located in Southern California and Hawaii. This paper summarizes the current LCRD architecture and key systems for the demonstration, focusing on what it will take to operate an optical communications relay that can support space-to-space, space-to-air, and space-to-ground optical links.

Optical↗
NASA NTRS2016

A Day in the Life of the Laser Communications Relay Demonstration Project

This paper provides an overview of the planned concept of operations for the Laser Communications Relay Demonstration Project (LCRD), a joint project among NASA's Goddard Space Flight Center (GSFC), the Jet Propulsion Laboratory, California Institute of Technology (JPL), and the Massachusetts Institute of Technology Lincoln Laboratory (MIT/LL). LCRD will provide at least two years of bi-directional optical communications at user data rates of up to 1.244 Gbps in an operational environment. The project lays the groundwork for establishing communications architecture and protocols, and developing the communications hardware and support infrastructure, concluding in a demonstration of optical communications' potential to meet NASA's growing need for higher data rates for future science and exploration missions. A pair of flight optical communications terminals will reside on a single commercial communications satellite in geostationary orbit; the two ground optical communications terminals will be located in Southern California and Hawaii. This paper summarizes the current LCRD architecture and key systems for the demonstration, focusing on what it will take to operate an optical communications relay that can support space-to-space, space-to-air, and space-to-ground optical links.

Communications↗
NASA NTRS1994

Geometrical evidence for dark matter: X-ray constraints on the mass of the elliptical galaxy NGC 720

We describe (1) a new test for dark matter and alternate theories of gravitation based on the relative geometries of the X-ray and optical surface brightness distributions and an assumed form for the potential, of the optical light, (2) a technique to measure the shapes of the total gravitating matter and dark matter of an ellipsoidal system which is insensitive to the precise value of the temperature of the gas and to modest temperature gradients, and (3) a new method to determine the ratio of dark mass to stellar mass that is dependent on the functional forms for the visible star, gas and dark matter distributions, but independent of the distance to the galaxy or the gas temperature. We apply these techniques to X-ray data from the ROSAT Position Sensitive Proportional Counter (PSPC) of the optically flattened elliptical galaxy NGC 720; the optical isophotes have ellipticity epsilon approximately 0.40 extending out to approximately 120 sec. The X-ray isophotes are significantly elongated, epsilon = 0.20-0.30 for semimajor axis a approximately 100 sec. The major axes of the optical and X-ray isophotes are misaligned by approximately 30 deg +/- 15 deg. Spectral analysis of the X-ray data reveals no evidence of temperature gradients or anisotropies and demonstrates that a single-temperature plasma (T approximately 0.6 keV) having subsolar heavy element abundances and a two-temperature model having solar abundances describe the spectrum equally well. Considering only the relative geometries of the X-ray and optical surface brightness distributions and an assumed functional form for the potential of the optical light, we conclude that matter distributed like the optical light cannot produce the observed ellipticities of the X-ray isophotes, independent of the gas pressure, the gas temperature, and the value of the stellar mass; this comparison assumes a state of quasi-hydrostatic equilibrium so that the three-dimensional surfaces of the gas emissivity trace the three-dimensional isopotential surfaces -- we discuss the viability of this assumption for NGC 720. Milgrom's Modification of Newtonian Dynamics (MOND) cannot dispel this manifestation of dark matter. Hence, geometrical considerations require, without mention of pressure or temperature, the presence of an extended, massive dark matter halo in NGC 720. Employing essentially the technique of Buote & Canizares (1992; Buote 1992) we use the shape of the X-ray surface brightness to constrain the shape of the total gravitating matter. The total matter is modeled as either an oblate or prolate spheriod of constant shape and orientation having either a Ferrers (rho approximately r(exp -n)) or Hernquist density. Assuming the X-ray gas is in hydrostatic equilibrium, we construct a model X-ray gas distribution for various temperature profiles. We determine the ellipticity of the total gravitating matter to be epsilon approximately 0.50-0.70. Using the single-temperature model we estimate a total mass approximately (0.41-1.4) x 10(exp 12) h(sub 80) solar mass interior to the ellipsoid of semimajor axis 43.6 h(sub 80) kpc. Ferrers densities as steep as r(exp -3) do not fit the data, but the r(exp -2) and Hernquist models yield excellent fits. We estimate the mass distributions of the stars and the gas and fit the dark matter directly. For a given gas equation of state and functional forms for the visible stars, gas, and dark matter, these models yield a distance-independent and temperature-independent measurement of the ratio of dark mass to stellar mass M(sub DM)/M(sub stars). We estimate a minimum M(sub DM)/M(sub stars) greater than or equal to 4 which corresponds to a total mass slightly greater than that derived from the single-temperature models for distance D = 20h(sub 80) Mpc.

Buote, David A.↗
NASA NTRS2007

Chemical-Sensing Cables Detect Potential Threats

Intelligent Optical Systems Inc. (IOS) completed Phase I and II Small Business Innovation Research (SBIR) contracts with NASA's Langley Research Center to develop moisture- and pH-sensitive sensors to detect corrosion or pre-corrosive conditions, warning of potentially dangerous conditions before significant structural damage occurs. This new type of sensor uses a specially manufactured optical fiber whose entire length is chemically sensitive, changing color in response to contact with its target, and demonstrated to detect potentially corrosive moisture incursions to within 2 cm. After completing the work with NASA, the company received a Defense Advanced Research Projects Agency (DARPA) Phase III SBIR to develop the sensors further for detecting chemical warfare agents, for which they proved just as successful. The company then worked with the U.S. Department of Defense (DoD) to fine tune the sensors for detecting potential threats, such as toxic industrial compounds and nerve agents. In addition to the work with government agencies, Intelligent Optical Systems has sold the chemically sensitive fiber optic cables to major automotive and aerospace companies, who are finding a variety of uses for the devices. Marketed under the brand name Distributed Intrinsic Chemical Agent Sensing and Transmission (DICAST), these unique continuous-cable fiber optic chemical sensors can serve in a variety of applications: Corrosive-condition monitoring, aiding experimentation with nontraditional power sources, as an economical means of detecting chemical release in large facilities, as an inexpensive "alarm" systems to alert the user to a change in the chemical environment anywhere along the cable, or in distance-resolved optical time domain reflectometry systems to provide detailed profiles of chemical concentration versus length.

Source record↗
NASA NTRS1988

An optical heterodyne densitometer

Researchers are developing an optical heterodyne densitometer with the potential to measure optical density over an unprecedented dynamic range with high accuracy and sensitivity. This device uses a Mach-Zender interferometer configuration with heterodyne detection to make direct comparisons between optical and RF attenuators. Researchers expect to attain measurements of filter transmittance down to 10 to the minus 12th power with better than 1 percent uncertainty. In addition, they intend to extend the technique to the problem of measuring low levels of light scattering from reflective and transmissive optics.

Migdall, A. L.↗
NASA NTRS1992

Faraday anomalous dispersion optical tuners

Common methods for frequency stabilizing diode lasers systems employ gratings, etalons, optical electric double feedback, atomic resonance, and a Faraday cell with low magnetic field. Our method, the Faraday Anomalous Dispersion Optical Transmitter (FADOT) laser locking, is much simpler than other schemes. The FADOT uses commercial laser diodes with no antireflection coatings, an atomic Faraday cell with a single polarizer, and an output coupler to form a compound cavity. This method is vibration insensitive, thermal expansion effects are minimal, and the system has a frequency pull in range of 443.2 GHz (9A). Our technique is based on the Faraday anomalous dispersion optical filter. This method has potential applications in optical communication, remote sensing, and pumping laser excited optical filters. We present the first theoretical model for the FADOT and compare the calculations to our experimental results.

Wanninger, P.↗
NASA NTRS1992

Automated in situ observations of upper ocean biogeochemistry, bio-optics, and physics and their potential use for global studies

The processes controlling the flux of carbon in the upper ocean have dynamic ranges in space and time of at least nine orders of magnitude. These processes depend on a broad suite of inter-related biogeochemical, bio-optical, and physical variables. These variables should be sampled on scales matching the relevant phenomena. Traditional ship-based sampling, while critical for detailed and more comprehensive observations, can span only limited portions of these ranges because of logistical and financial constraints. Further, remote observations from satellite platforms enable broad horizontal coverage which is restricted to the upper few meters of the ocean. For these main reasons, automated subsurface measurement systems are important for the fulfillment of research goals related to the regional and global estimation and modeling of time varying biogeochemical fluxes. Within the past few years, new sensors and systems capable of autonomously measuring several of the critical variables have been developed. The platforms for deploying these systems now include moorings and drifters and it is likely that autonomous underwater vehicles (AUV's) will become available for use in the future. Each of these platforms satisfies particular sampling needs and can be used to complement both shipboard and satellite observations. In the present review, (1) sampling considerations will be summarized, (2) examples of data obtained from some of the existing automated in situ sampling systems will be highlighted, (3) future sensors and systems will be discussed, (4) data management issues for present and future automated systems will be considered, and (5) the status of near real-time data telemetry will be outlined. Finally, we wish to make it clear at the outset that the perspectives presented here are those of the authors and are not intended to represent those of the United States JGOFS program, the International JGOFS program, NOAA's C&GC program, or other global ocean programs.

Dickey, Tommy D.↗
NASA NTRS1981

Optical-model abrasion cross sections for high-energy heavy ions

Within the context of eikonal scattering theory, a generalized optical model potential approximation to the nucleus-nucleus multiple scattering series is used in an abrasion-ablation collision model to predict abrasion cross sections for relativistic projectile heavy ions. Unlike the optical limit of Glauber theory, which cannot be used for very light nuclei, the abrasion formalism is valid for any projectile target combination at any incident kinetic energy for which eikonal scattering theory can be utilized. Results are compared with experimental results and predictions from Glauber theory.

Townsend, L. W.↗
NASA NTRS2006

Optically Thin Liquid Water Clouds: Their Importance and Our Challenge

Many of the clouds important to the Earth's energy balance, from the tropics to the Arctic, are optically thin and contain liquid water. Longwave and shortwave radiative fluxes are very sensitive to small perturbations of the cloud liquid water path (LWP) when the liquid water path is small (i.e., < g/sq m) and, thus, the radiative properties of these clouds must be well understood to capture them correctly in climate models. We review the importance of these thin clouds to the Earth's energy balance, and explain the difficulties in observing them. In particular, because these clouds are optically thin, potentially mixed-phase, and often (i.e., have large 3-D variability), it is challenging to retrieve their microphysical properties accurately. We describe a retrieval algorithm intercomparison that was conducted to evaluate the issues involved. The intercomparison included eighteen different algorithms to evaluate their retrieved LWP, optical depth, and effective radii. Surprisingly, evaluation of the simplest case, a single-layer overcast cloud, revealed that huge discrepancies exist among the various techniques, even among different algorithms that are in the same general classification. This suggests that, despite considerable advances that have occurred in the field, much more work must be done, and we discuss potential avenues for future work.

Turner, D. D.↗
NASA NTRS1976

Two improved coherent optical feedback systems for optical information processing

Coherent optical feedback systems are Fabry-Perot interferometers modified to perform optical information processing. Two new systems based on plane parallel and confocal Fabry-Perot interferometers are introduced. The plane parallel system can be used for contrast control, intensity level selection, and image thresholding. The confocal system can be used for image restoration and solving partial differential equations. These devices are simpler and less expensive than previous systems. Experimental results are presented to demonstrate their potential for optical information processing.

Lee, S. H.↗
NASA NTRS1993

Calculating potential fields using microchannel spatial light modulators

We describe and present experimental results of the optical calculation of potential field maps suitable for mobile robot navigation. The optical computation employs two write modes of a microchannel spatial light modulator (MSLM). In one mode, written patterns expand spatially, and this characteristic is used to create an extended two dimensional function representing the influence of the goal in a robot's workspace. Distinct obstacle patterns are written in a second, non-expanding, mode. A model of the mechanisms determining MSLM write mode characteristics is developed and used to derive the optical calculation time for full potential field maps. Field calculations at a few hertz are possible with current technology, and calculation time vs. map size scales favorably in comparison to digital electronic computation.

Reid, Max B.↗
NASA NTRS1972

A computer code for predicting gamma production cross sections by neutron inelastic scattering from light nuclei

Gamma-ray production cross section by the inelastic scattering of neutrons from light nuclei are considered. The applicability of optical model potential is discussed. Based on experimental data, a cascade approach is developed to calculate the inelastic gamma production cross sections. In the case of O-16 using computer code LINGAP in conjunction with ABACUS-2; results are compared with reported values.

George, M. C.↗
NASA NTRS1971

Biochronometry; Proceedings of the Symposium, Friday Harbor, Wash., September 4-6, 1969.

Topics discussed include circadian activity rhythms in birds and man, variation of circadian rhythms in monkeys, resetting of circadian eclosion rhythm in fruitflies, the effectiveness of mathematical models of circadian rhythms, the influence of ac electric fields on circadian rhythms in man, the relation between changes in the metabolic rate and circadian periodicity of the resistance of pocket mice to ionizing radiation, the relation between circadian organization and the photoperiodic time measurement in moths, the circadian rhythm of optic nerve potentials in the isolated eye of the sea hare, phasing of circadian temperature rhythms in the pocket mouse by specific spectral regions, the phase-shifting effect of light on circadian rhymicity in the fruifly, hormonal control of circadian rhythms in the fruitfly, metabolically controlled temperature compensation in the circadian rhythm of algae, and circadian rhythms in the chloroplasts of algae. Individual items are abstracted in this issue.

Menaker, M.↗