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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 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Data acquisition and analysis of range-finding systems for spacing construction

For space missions of future, completely autonomous robotic machines will be required to free astronauts from routine chores of equipment maintenance, servicing of faulty systems, etc. and to extend human capabilities in hazardous environments full of cosmic and other harmful radiations. In places of high radiation and uncontrollable ambient illuminations, T.V. camera based vision systems cannot work effectively. However, a vision system utilizing directly measured range information with a time of flight laser rangefinder, can successfully operate under these environments. Such a system will be independent of proper illumination conditions and the interfering effects of intense radiation of all kinds will be eliminated by the tuned input of the laser instrument. Processing the range data according to certain decision, stochastic estimation and heuristic schemes, the laser based vision system will recognize known objects and thus provide sufficient information to the robot's control system which can develop strategies for various objectives.

Shen, C. N.↗
NASA NTRS1986

Laser microprobe characterization of C species in Interplanetary Dust Particles (IDP)

Preliminary results of a study whose aim is the characterization of carbon (C) species in microvolumes of materials by means of laser ionization mass spectrometry (LIMS) are presented. The LIMS instrument employs a pulsed UV laser to produce nearly instantaneous vaporization and ionization of materials, followed by acceleration and time-of-flight analysis of the ions produced. LIMS provides a survey technique with nearly simultaneous acquisition of mass spectra covering the entire elemental range. The main limitation of the LIMS technique at present is its limited ability to perform quantitative analysis, due in part to insufficient knowledge of the mechanism of laser-solid interaction. However, considerable effort is now being directed at making LIMS a more quantitative technique. A variety of different C samples, both natural and man made were analyzed to establish the ability of LIMS to differentiate among the various C phases. The results of preliminary analyses performed on meteoritical and interplanetary dust samples are also presented. The C standards selected for the LIMS characterization range from essentially amorphous soot to diamond, which exhibits the highest degree of ordering.

Dibrozolo, F. R.↗
NASA NTRS1987

Tunable diode laser measurements of absolute linestrengths in the HNO3 band near 5.8 microns

Absolute line strengths of selected lines in the nu 2 band of HNO3 have been measured using a tunable diode laser spectrometer operating in a sweep integration mode. The direct measurement technique has been employed to obtain line intensities at 296 K for 22 isolated lines in the 1720-1725/cm region. The reported line strengths have estimated uncertainties of 4 percent, a significant portion of this uncertainty arising from spectral interference from hot band transitions. From these line-strength measurements, an integrated band intensity of 1375/sq cm per atm at 296 K is inferred.

May, Randy D.↗
NASA NTRS1989

Solar power for the lunar night

Providing power over the 354 hour lunar night provides a considerable challenge to solar power concepts for a moonbase. Concepts are reviewed for providing night power for a solar powered moonbase. The categories of solutions considered are electrical storage, physical storage, transmitted power, and innovative concepts. Electrical storage is the most well-developed option. Less developed electrical storage options are capacitors and superconducting inductors. Physical storage options include storage of potential energy and storage of energy in flywheels. Thermal storage has potentially high energy/weight, but problems of conduction and radiation losses during the night need to be addressed. Transmitted power considers use of microwave or laser beams to transmit power either from orbit or directly from the Earth. Finally, innovative concepts proposed include reflecting light from orbital mirrors, locating the moonbase at a lunar pole, converting reflected Earthlight, or moving the moonbase to follow the sun.

Landis, Geoffrey A.↗
NASA NTRS1989

Thermocapillary migration of liquid droplets in a temperature gradient in a density matched system

An experimental investigation of thermocapillary flow in droplets of a vegetable oil (partially hydrogenated soybean oil) immersed in silicone oil was conducted in a test cell with a heated top wall and a cooled bottom wall. The liquids are nearly immiscible and have equal densities at a temperature below the room temperature, thus providing a simulation of low-gravity conditions by reducing the buoyancy forces. The interfacial tension between the two oils was measured in the temperature range 20 to 50 C using a capillary tube and (d sigma)/(d T) was determined to be negative. Droplets ranging in sizes from 3 mm to 1 cm diameter were injected into the silicone oil. The vertical temperature profile in the bulk liquid (silicone oil) produces temperature variations along the interface which induce variations in the interfacial tension. The flow inside the droplet driven by the resulting interfacial shear stresses was observed using a laser light-sheet flow visualization technique. The flow direction is consistent with the sign of (d sigma)/(d T). The observed maximum surface velocities are compared to the theoretical predictions of Young et al. (1959).

Rashidnia, N.↗
NASA NTRS1989

HERMIES-3: A step toward autonomous mobility, manipulation, and perception

HERMIES-III is an autonomous robot comprised of a seven degree-of-freedom (DOF) manipulator designed for human scale tasks, a laser range finder, a sonar array, an omni-directional wheel-driven chassis, multiple cameras, and a dual computer system containing a 16-node hypercube expandable to 128 nodes. The current experimental program involves performance of human-scale tasks (e.g., valve manipulation, use of tools), integration of a dexterous manipulator and platform motion in geometrically complex environments, and effective use of multiple cooperating robots (HERMIES-IIB and HERMIES-III). The environment in which the robots operate has been designed to include multiple valves, pipes, meters, obstacles on the floor, valves occluded from view, and multiple paths of differing navigation complexity. The ongoing research program supports the development of autonomous capability for HERMIES-IIB and III to perform complex navigation and manipulation under time constraints, while dealing with imprecise sensory information.

Weisbin, C. R.↗
NASA NTRS1989

Spatially resolved organic analysis of the Allende meteorite

The distribution of polycyclic aromatic hydrocarbons (PAHs) in the Allende meteorite has been probed with two-step laser desorption/laser multiphoton ionization mass spectrometry. This method allows direct in situ analysis with a spatial resolution of 1 sq mm or better of selected organic molecules. Spectra from freshly fractured interior surfaces of the meteorite show that PAH concentrations are locally high compared to the average concentrations found by wet chemical analysis of pulverized samples. The data suggest that the PAHs are primarily associated with the fine-grained matrix, where the organic polymer occurs. In addition, highly substituted PAH skeletons were observed. Interiors of individual chondrules were devoid of PAHs at the detection limit (about 0.05 ppm).

Zenobi, Renato↗
NASA NTRS1989

Slot clock recovery in optical PPM communication systems with avalanche photodiode photodetectors

Slot timing recovery in a direct-detection optical PPM communication system can be achieved by processing the photodetector output waveform with a nonlinear device whose output forms the input to a phase-locked loop. The choice of a simple transition detector as the nonlinearity is shown to give satisfactory synchronization performance. The rms phase error of the recovered slot clock and the effect of slot timing jitter on the bit error probability were directly measured. The experimental system consisted of an AlGaAs laser diode (wavelength = 834 nm) and a silicon avalanche photodiode photodetector. The system used Q = 4 PPM signaling and operated at a source data rate of 25 Mbits/s. The mathematical model developed to compute the rms phase error of the recovered clock is shown to be in good agreement with results of actual measurements of phase errors. The use of the recovered slot clock in the receiver resulted in no significant degradation in receiver sensitivity compared to a system with perfect slot timing. The system achieved a bit error probability of 10 to the -6th at a received optical signal energy of 55 detected photons per information bit.

Davidson, Frederic M.↗
NASA NTRS1989

Solar power for the lunar night

Providing power over the 354 hour lunar night provides a considerable challenge to solar power concepts for a moonbase. Concepts are reviewed for providing night power for a solar powered moonbase. The categories of solutions considered are electrical storage, physical storage, transmitted power, and innovative concepts. Electrical storage is the most well-developed option. Less developed electrical storage options are capacitors and superconducting inductors. Physical storage options include storage of potential energy and storage of energy in flywheels. Thermal storage has potentially high energy/weight, but problems of conduction and radiation losses during the night need to be addressed. Transmitted power considers use of microwave or laser beams to transmit power either from orbit or directly from the earth. Finally, innovative concepts proposed include reflecting light from orbital mirrors, locating the moonbase at a lunar pole, converting reflected earthlight, or moving the moonbase to follow the sun.

Landis, Geoffrey A.↗
NASA NTRS1991

Laser diagnostics on a hypersonic combustor

NASA-Langley has implemented a laser-based multipoint/multiparameter diagnostics system at its hypersonic direct-connect combustor, in order to measure both temperature and majority species densities in two dimensions, using spatially-scanned CARS; in addition, line-imaged measurements of radical densities are simultaneously generated by LIF at any of several planes downstream of the fuel injector. Initial experimental trials have demonstrated successful detection of one-dimensional images of OH density, as well as CARS N2-temperature measurements, in the turbulent reaction zone of the hypersonic combustor.

Taylor, David J.↗
NASA NTRS1991

Thermocapillary migration of liquid droplets in a temperature gradient in a density matched system

An experimental investigation of thermocapillary flow in droplets of a vegetable oil (partially hydrogenated soybean oil) immersed in silicone oil was conducted in a test cell with a heated top wall and a cooled bottom wall. The liquids are nearly immiscible and have equal densities at a temperature below the room temperature, thus providing a simulation of low-gravity conditions by reducing the buoyancy forces. The interfacial tension between the two oils was measured in the temperature range 20 to 50 C using a capillary tube and (d sigma)/(d T) was determined to be negative. Droplets ranging in sizes from 3 mm to 1 cm diameter were injected into the silicone oil. The vertical temperature profile in the bulk liquid (silicone oil) produces temperature variations along the interface which induce variations in the interfacial tension. The flow inside the droplet driven by the resulting interfacial shear stresses was observed using a laser light-sheet flow visualization technique. The flow direction is consistent with the sign of (d sigma)/(d T). The observed maximum surface velocities are compared to the theoretical predictions of Young et al. (1959).

Rashidnia, N.↗
NASA NTRS1995

Kinetic Kelvin-Helmholtz instability at a finite sized object

Two-dimensional hybrid simulations with particle ions and fluid electrons are used to calculate the kinetic evolution of the self-consistent flow around a two-dimensional obstacle with zero intrinsic magnetic field. Plasma outlfow from the obstacle is used to establish a boundary layer between the incoming solar wind and the outgoing plasma. Because the self-consistent flow solution, a velocity shear is naturally set up at this interface, and since the magnetic field for these simulations is transverse to this flow, the Kelvin-Helmholtz (K-H) instability can be excited at low-velocity shear. Simulations demonstrate the existence of the instability even near the subsolar location, which normally is thought to be stable to this instability. The apparent reason for this result is the overall time dependence at the boundary layer, which gives rise to a Rayleigh-Taylor like instability which provides seed perturbations for the K-H instability. These results are directly applicable to Venus, comets, artificial plasma releases, and laser target experiments. This result has potentially important ramifications for the interpretation of observational results as well as for an estimation of the cross-field transport. The results suggest that the K-H instability may play a role in dayside processes and the Venus ionopause, and may exist within the context of more general situations, for example, the Earth's magnetopause.

Thomas, V. A.↗
NASA NTRS1997

Unsteady Velocity Measurements Taken Behind a Model Helicopter Rotor Hub in Forward Flight

Drag caused by separated flow behind the hub of a helicopter has an adverse effect on aerodynamic performance of the aircraft. To determine the effect of separated flow on a configuration used extensively for helicopter aerodynamic investigations, an experiment was conducted using a laser velocimeter to measure velocities in the wake of a model helicopter hub operating at Mach-scaled conditions in forward flight. Velocity measurements were taken using a laser velocimeter with components in the vertical and downstream directions. Measurements were taken at 13 stations downstream from the rotor hub. At each station, measurements were taken in both a horizontal and vertical row of locations. These measurements were analyzed for harmonic content based on the rotor period of revolution. After accounting for these periodic velocities, the remaining unsteady velocities were treated as turbulence. Turbulence intensity distributions are presented. Average turbulent intensities ranged from approximately 2 percent of free stream to over 15 percent of free stream at specific locations and azimuths. The maximum average value of turbulence was located near the rear-facing region of the fuselage.

Berry, John D.↗
NASA NTRS2010

Progress in Measurement of Carbon Dioxide Using a Broadband LIDAR

Innovative active system using advanced source technology development will enable precise daytime or nighttime measurements of column CO2. Directly responds to NRC DS ASCENDS mission. Number of lasers is reduced compared to competing technologies which reduces the complexity of sensor and thus the cost and risk of failure. Knowledge gained from previously developed passive sensor decreases the risk and cost of the present lidar system development. The instrument can play a significant role as an intercomparison instrument for OCO (Orbiting Carbon Observatory) if it is rebuilt and launched as well as other laser based instruments under development for participation in ASCENDS. It can play a role as an airborne instrument in its own right in addressing the problems of scale arising from differences between point observations by the existing ground based CO2 network and wider area measurements obtained by satellites. Developed 2.0 micron broadband system as well and will compare performance of both systems to choose optimal approach for ASCENDS. Have begun development of approach that uses array detectors instead of APD. This approach will have lower noise than APD and may simplify design of the detector optical train.

Heaps, William S.↗
NASA NTRS2011

Comparison of 16-Channel Laser Photoreceivers for Topographic Mapping

Topographic mapping lidar instruments must be able to detect extremely weak laser return signals from high altitudes including orbital distance. The signals have a wide dynamic range caused by the variability in atmospheric transmission and surface reflectance under a fast moving spacecraft. Ideally, lidar detectors should be able to detect laser signal return pulses at the single photon level and produce linear output for multiple photon events. Silicon avalanche photodiode (APO) detectors have been used in most space lidar receivers to date. Their sensitivity is typically hundreds of photons per pulse, and is limited by the quantum efficiency, APO gain noise, dark current, and preamplifier noise. NASA is pursuing three approaches for a 16-channel laser photoreceiver for use on the next generation direct-detection airborne and spacebome lidars. We present our measurement results and a comparison of their performance.

Krainak, Michael A.↗
NASA NTRS2019

100-kHz Rate Rayleigh Imaging for Combustion and Flow Diagnostics

Two-dimensional (2D) Rayleigh scattering (RS) imaging at an ultrahigh repetition rate of 100 kHz is demonstrated in non-reacting and reacting flows employing a high-energy burst-mode laser system. Image sequences of flow mixture fraction were directly derived from high-speed RS images. Additionally, a 2D instantaneous flow velocity field at 100 kHz was obtained through optical-flow-based analysis of the RS images. The technique was also applied to study turbulent flames having a near-constant Rayleigh cross section. The demonstrated high-speed RS technique in conjunction with optical-flow-based analysis provides non-intrusive, simultaneous measurements of the flow mixing and velocity field, extending the measurement capability of the RS technique to high-speed non-reacting and reacting flows.

Jiang, Naibo↗
NASA NTRS2015

A plasma-based non-intrusive point source for acoustic beamforming applications

A laser-generated plasma acoustic point source is used to directly measure the point spread function (PSF) of a microphone phased array. In beamforming analysis of microphone phased array data, the true acoustic field is convolved with the array's PSF. By directly measuring the PSF, corrections to the array analysis can be computed and applied. The acoustic source is measured in an open-jet aeroacoustic facility to evaluate the effects of sampling rate, microphone installation, source shift, reflections, shear layer refraction and model presence. Results show that measurements exhibit behavior consistent with theory with regard to source shift and shear layer refraction. Application of a measured PSF in beamforming analysis shows the process provides an effective in-situ method for array calibration both with and without flow and allows for corrections to incorporate reflections and scattering. The technique improves the agreement of beamforming results with the true spectrum of a known source, especially in the presence of reflections.

phased array↗