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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Laboratory Simulation of Space Weathering: ESR Measurements of Nanophase Metallic Iron in Laser-irradiated Olivine and Pyroxene Samples

S-type asteroids are believed to be parent bodies of ordinary chondrites. Although both S-type asteroids and ordinary chondrites contain the same mineral assemblage, mainly olivine and pyroxene, the reflectance spectra of the asteroids exhibit more overall depletion (darkening) and reddening, and more weakening of absorption bands relative to the meteorites. This spectral mismatch is explained by space weathering process, where high-velocity dust particle impacts should change the optical properties of the uppermost regolith surface of asteroids. In order to simulate the space weathering, we irradiated nanosecond pulse laser beam onto pellet samples of olivine (8.97wt% FeO) and pyroxene (enstatite: 9.88wt% FeO, hypersthene: 16.70wt%). We got spectral changes in our samples similar to that by space weathering on asteroids and confirmed nanophase alpha-metallic iron particles, which were theoretically predicted, not only on olivine but also on pyroxene samples by Transmission Electron Microscopy (TEM). Nanophase metallic iron particles were widely scattered throughout the amorphous rims developed along the olivine grains, whereas they were embedded in aggregates of amorphous in enstatite samples. Recently, we also measured laser-irradiated samples by ESR (Electron Spin Resonance). Strong ESR signals, characteristic to nanophase iron particles, are observed on irradiated olivine samples. In this paper, we report the quantities of nanophase metallic iron particles in pyroxene samples by ESR observations in addition to olivine samples.

Kurahashi, E.↗
NASA NTRS2012

Computing Radiative Transfer in a 3D Medium

A package of software computes the time-dependent propagation of a narrow laser beam in an arbitrary three- dimensional (3D) medium with absorption and scattering, using the transient-discrete-ordinates method and a direct integration method. Unlike prior software that utilizes a Monte Carlo method, this software enables simulation at very small signal-to-noise ratios. The ability to simulate propagation of a narrow laser beam in a 3D medium is an improvement over other discrete-ordinate software. Unlike other direct-integration software, this software is not limited to simulation of propagation of thermal radiation with broad angular spread in three dimensions or of a laser pulse with narrow angular spread in two dimensions. Uses for this software include (1) computing scattering of a pulsed laser beam on a material having given elastic scattering and absorption profiles, and (2) evaluating concepts for laser-based instruments for sensing oceanic turbulence and related measurements of oceanic mixed-layer depths. With suitable augmentation, this software could be used to compute radiative transfer in ultrasound imaging in biological tissues, radiative transfer in the upper Earth crust for oil exploration, and propagation of laser pulses in telecommunication applications.

Von Allmen, Paul↗
NASA NTRS1974

Development and testing of laser Doppler system components for wake vortex monitoring. Volume 1: Scanner development, laboratory and field testing and system modeling

A servo-controlled range/elevation scanner for the laser Doppler velocimeter (LDV) was developed and tested in the field to assess its performance in detecting and monitoring aircraft trailing vortices in an airport environment. The elevation scanner provides a capability to manually point the LDV telescope at operator chosen angles from 3.2 deg. to 89.6 deg within 0.2 deg, or to automatically scan the units between operator chosen limits at operator chosen rates of 0.1 Hz to 0.5 Hz. The range scanner provides a capability to manually adjust the focal point of the system from a range of 32 meters to a range of 896 meters under operator control, or to scan between operator chosen limits and at rates from 0.1 Hz to 6.9 Hz. The scanner controls are designed to allow simulataneous range and elevation scanning so as to provide finger scan patterns, arc scan patterns, and vertical line scan patterns. The development and testing of the unit is discussed, along with a fluid dynamic model of the wake vortex developed in a laser Doppler vortex sensor simulation program.

Wilson, D. J.↗
NASA NTRS1978

Estimability and simple dynamical analyses of range (range-rate range-difference) observations to artificial satellites

Non-Bayesian statistics were used in simulation studies centered around laser range observations to LAGEOS. The capabilities of satellite laser ranging especially in connection with relative station positioning are evaluated. The satellite measurement system under investigation may fall short in precise determinations of the earth's orientation (precession and nutation) and earth's rotation as opposed to systems as very long baseline interferometry (VLBI) and lunar laser ranging (LLR). Relative station positioning, determination of (differential) polar motion, positioning of stations with respect to the earth's center of mass and determination of the earth's gravity field should be easily realized by satellite laser ranging (SLR). The last two features should be considered as best (or solely) determinable by SLR in contrast to VLBI and LLR.

Vangelder, B. H. W.↗
NASA NTRS1982

Shuttle lidar resonance fluorescence investigations. I - Analysis of Na and K measurements. II - Analysis of thermospheric Mg/+/ measurements

Optical radar systems (lidar) have a number of advantages compared to passive techniques with respect to applications involving the measurement of alkali atoms (Na and K) in the atmosphere. By using Shuttle-borne optical radar systems, analytical capabilities can be extended to cover wider geographic areas. One of the objectives of the present investigation is to assess the performance and application of a recently defined Shuttle optical radar system for the measurements of sodium and potassium in the 80-110-km region. A second objective is related to a study of the effects of high-intensity laser beams on the optical radar measurements, giving particular attention to the saturation in the atomic absorption of laser photons. A numerical simulation is conducted of the measurements of magnesium ions (Mg/+/) over the 80-500-km altitude range using recently defined Shuttle optical radar system parameters to study the performance of such a system.

Yeh, S.-D.↗
NASA NTRS1982

A theoretical study of a two-wavelength lidar technique for the measurement of atmospheric temperature profiles

The theory of differential absorption lidar measurements for lines with a Voigt profile is given and applied to a two-wavelength technique for measuring the atmospheric temperature profile using a high J line in the oxygen A band. Explicit expressions for the temperature and pressure dependence of the absorption coefficient are developed for lines with a Voigt profile. An iteration procedure for calculating the temperature for narrow laser bandwidths is described which has an accuracy better than 0.2 K for bandwidths less than 0.01/cm. To reduce the errors in lidar measurements due to uncertainties in pressure, a method for estimating the pressure from the temperature profile is described. A procedure for extending the differential absorption technique to the case of finite laser bandwidth with good accuracy is also described. Simulation results show that a knowledge of the laser frequency is needed to 0.005/cm for accurate temperature measurements. Evaluation of the sensitivity for both ground- and Shuttle-based measurements shows accuracies generally better than 1 K. This technique allows up to an order of magnitude improvement in sensitivity compared to other differential absorption lidar techniques.

Korb, C. L.↗
NASA NTRS1985

Transfer-Function Simulator

Transfer function simulator constructed from analog or both analog and digital components substitute for device that has faults that confound analysis of feedback control loop. Simulator is substitute for laser and spectrophone.

Kavaya, M. J.↗
NASA NTRS1987

A theoretical study of photovoltaic converters

The final phase of research was performed in the model simulation for the solar simulator pumped atomic iodine laser. The geometry for the steady state laser operation with axial lasant flow is illustrated. The chemical kinetics for this laser are described.

Heinbockel, John H.↗
NASA NTRS1988

High-temperature shock formation of N2 and organics on primordial Titan

Theoretical models suggest that the initial form of nitrogen in Titan's atmosphere may have been NH3. The possible importance of strong shocks produced during high-velocity impacts accompanying the late stages of accretion are investigated as a method for converting NH3 to N2, of which Titan's atmosphere is now primarily composed. The focused beam of a high-power laser is used to simulate the effects of an impact in Titan's atmosphere. For mixtures of 10, 50, and 90 percent NH3, yields of 0.25, 1, and 6 x 20 to the 17th molecules of N2 per joule, respectively, were obtained. It is also found that the yield of HCN is comparable to that for N2. Several other hydrocarbons are produced, many with yields in excess of theoretical high-temperature-equilibrium models. The above yields, when combined with models of the satellite's accretion, result in a total N2 production comparable to that present in TItan's atmosphere and putative ocean.

Mckay, Christopher P.↗
NASA NTRS1991

Precluding nonlinear ISI in direct detection long-haul fiber optic systems

Long-distance, high-rate fiber optic systems employing directly modulated 1.55-micron single-mode lasers and conventional single-mode fiber suffer severe intersymbol interference (ISI) with a large nonlinear component. A method of reducing the nonlinearity of the ISI, thereby making linear equalization more viable, is investigated. It is shown that the degree of nonlinearity is highly dependent on the choice of laser bias current, and that in some cases the ISI nonlinearity can be significantly reduced by biasing the laser substantially above threshold. Simulation results predict that an increase in signal-to-nonlinear-distortion ratio as high as 25 dB can be achieved for synchronously spaced samples at an optimal sampling phase by increasing the bias current from 1.2 times threshold to 3.5 times threshold. The high SDR indicates that a linear tapped delay line equalizer could be used to mitigate ISI. Furthermore, the shape of the pulse response suggests that partial response precoding and digital feedback equalization would be particularly effective for this channel.

Swenson, Norman L.↗
NASA NTRS2004

Development and Testing of Ceramic Thermal Barrier Coatings

Ceramic thermal barrier coatings will play an increasingly important role in future gas turbine engines because of their ability to effectively protect the engine components and further raise engine temperatures. Durability of the coating systems remains a critical issue with the ever-increasing temperature requirements. Thermal conductivity increase and coating degradation due to sintering and phase changes are known to be detrimental to coating performance. There is a need to characterize the coating behavior and temperature limits, in order to potentially take full advantage of the current coating capability, and also accurately assess the benefit gained from advanced coating development. In this study, thermal conductivity behavior and cyclic durability of plasma-sprayed ZrO2-8wt%Y2O3 thermal barrier coatings were evaluated under laser heat-flux simulated high temperature, large thermal gradient and thermal cycling conditions. The coating degradation and failure processes were assessed by real-time monitoring of the coating thermal conductivity under the test conditions. The ceramic coating crack propagation driving forces and resulting failure modes will be discussed in light of high temperature mechanical fatigue and fracture testing results.

Zhu, Dongming↗
NASA NTRS2005

Improvements in Near-Terminator and Nocturnal Cloud Masks using Satellite Image Data over the Atmospheric Radiation Measurement Sites

Cloud detection using satellite measurements presents a big challenge near the terminator where the visible (VIS; 0.65 (micro)m) channel becomes less reliable and the reflected solar component of the solar infrared 3.9-(micro)m channel reaches very low signal-to-noise ratio levels. As a result, clouds are underestimated near the terminator and at night over land and ocean in previous Atmospheric Radiation Measurement (ARM) Program cloud retrievals using Geostationary Operational Environmental Satellite (GOES) imager data. Cloud detection near the terminator has always been a challenge. For example, comparisons between the CLAVR-x (Clouds from Advanced Very High Resolution Radiometer (AVHRR)) cloud coverage and Geoscience Laser Altimeter System (GLAS) measurements north of 60 degrees N indicate significant amounts of missing clouds from AVHRR because this part of the world was near the day/night terminator viewed by AVHRR. Comparisons between MODIS cloud products and GLAS at the same regions also shows the same difficulty in the MODIS cloud retrieval (Pavolonis and Heidinger 2005). Consistent detection of clouds at all times of day is needed to provide reliable cloud and radiation products for ARM and other research efforts involving the modeling of clouds and their interaction with the radiation budget. To minimize inconsistencies between daytime and nighttime retrievals, this paper develops an improved twilight and nighttime cloud mask using GOES-9, 10, and 12 imager data over the ARM sites and the continental United States (CONUS).

Detection↗
NASA NTRS2006

Lightweight Ablative and Ceramic Thermal Protection System Materials for NASA Exploration Systems Vehicles

As a collaborative effort among NASA Centers, the "Lightweight Nonmetallic Thermal Protection Materials Technology" Project was set up to assist mission/vehicle design trade studies, to support risk reduction in thermal protection system (TPS) material selections, to facilitate vehicle mass optimization, and to aid development of human-rated TPS qualification and certification plans. Missions performing aerocapture, aerobraking, or direct aeroentry rely on advanced heatshields that allow reductions in spacecraft mass by minimizing propellant requirements. Information will be presented on candidate materials for such reentry approaches and on screening tests conducted (material property and space environmental effects tests) to evaluate viable candidates. Seventeen materials, in three classes (ablatives, tiles, and ceramic matrix composites), were studied. In additional to physical, mechanical, and thermal property tests, high heat flux laser tests and simulated-reentry oxidation tests were performed. Space environmental effects testing, which included exposures to electrons, atomic oxygen, and hypervelocity impacts, was also conducted.

Valentine, Peter G.↗
NASA NTRS2017

Radiation Hardening by Software Techniques on FPGAs: Flight Experiment Evaluation and Results

We present our work on implementing Radiation Hardening by Software (RHBSW) techniques on the Xilinx Virtex5 FPGAs PowerPC 440 processors on the SpaceCube 2.0 platform. The techniques have been matured and tested through simulation modeling, fault emulation, laser fault injection and now in a flight experiment, as part of the Space Test Program- Houston 4-ISS SpaceCube Experiment 2.0 (STP-H4-ISE 2.0). This work leverages concepts such as heartbeat monitoring, control flow assertions, and checkpointing, commonly used in the High Performance Computing industry, and adapts them for use in remote sensing embedded systems. These techniques are extremely low overhead (typically <1.3%), enabling a 3.3x gain in processing performance as compared to the equivalent traditionally radiation hardened processor. The recently concluded STP-H4 flight experiment was an opportunity to upgrade the RHBSW techniques for the Virtex5 FPGA and demonstrate them on-board the ISS to achieve TRL 7. This work details the implementation of the RHBSW techniques, that were previously developed for the Virtex4-based SpaceCube 1.0 platform, on the Virtex5-based SpaceCube 2.0 flight platform. The evaluation spans the development and integration with flight software, remotely uploading the new experiment to the ISS SpaceCube 2.0 platform, and conducting the experiment continuously for 16 days before the platform was decommissioned. The experiment was conducted on two PowerPCs embedded within the Virtex5 FPGA devices and the experiment collected 19,400 checkpoints, processed 253,482 status messages, and incurred 0 faults. These results are highly encouraging and future work is looking into longer duration testing as part of the STP-H5 flight experiment.

Hybrid Flight Architectures↗
NASA NTRS2011

Improving Single Event Effects Testing Through Software

Radiation encountered in space environments can be damaging to microelectronics and potentially cause spacecraft failure. Single event effects (SEE) are a type of radiation effect that occur when an ion strikes a device. Single event gate rupture (SEGR) is a type of SEE that can cause failure in power transistors. Unlike other SEE rates in which a constant linear energy transfer (LET) can be used, SEGR rates sometimes require a non-uniform LET to be used to be accurate. A recent analysis shows that SEGR rates are most easily calculated when the environment is described as a stopping rate per unit volume for each ion species. Stopping rates in silicon for pertinent ions were calculated using the Stopping and Range of Ions in Matter (SRIM) software and CREME-MC software. A reference table was generated and can be used by others to calculate SEGR rates for a candidate device. Additionally, lasers can be used to simulate SEEs, providing more control and information at lower cost than heavy ion testing. The electron/hole pair generation rate from a laser pulse in a semiconductor can be related to the LET of an ion. MATLAB was used to generate a plot to easily make this comparison.

generation equation↗
NASA NTRS1977

Atmospheric lidar research applying to H2O, O2 and aerosols

Experimental research on a near infrared tunable dye laser was reported, and theoretical simulations were presented for various lidar configurations. The visible and nearinfrared wavelengths considered were suitable for observations of aerosols, water vapor, molecular oxygen pressure and temperature in the troposphere and above. The first phase of development work was described on a ruby pumped, tunable dye laser for the wavelength region 715 to 740 nanometers. Lidar simulations were summarized for measurements of H2O and for two color lidar observations of aerosols in the atmosphere.

Mcilrath, T. J.↗
NASA NTRS2020

Laser Based Remote and Rapid Inspection for Composite Plates

Composites have been extensively used in aero structure and become the predominate components in the new airframes. Thus, rapid and effective inspection for composite structures is highly desired in aerospace engineering in order to shorten the certificate cycle for new structures or provide safety guarantee for existing ones. In this paper, a laser based remote Lamb wave inspection system is presented and implemented on composite plates for simulated damage detection. The system employs pulsed laser (PL) and scanning laser Doppler vibrometer (SLDV) for noncontact and remote Lamb wave actuation and wavefield sensing. A composite plate with simulated defect (surface bonded quartz rod) is inspected with the PL-SLDV laser system. Wave scattering are observed in the SLDV acquired wavefield and the damage is further evaluated with wavefield imaging and frequency wavenumber analysis. Potential application towards automatic PL Lamb wave excitation is also explored through employing an industry robotic arm towards rapid inspection.

Lamb waves↗