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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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NASA NTRS1992

Multi-Mode Excitation and Data Reduction for Fatigue Crack Characterization in Conducting Plates

Advances in the technique of fatigue crack characterization by resonant modal analysis have been achieved through a new excitation mechanism and data reduction of multiple resonance modes. A non-contacting electromagnetic device is used to apply a time varying Lorentz force to thin conducting sheets. The frequency and direction of the Lorentz force are such that resonance modes are generated in the test sample. By comparing the change in frequency between distinct resonant modes of a sample, detecting and sizing of fatigue cracks are achieved and frequency shifts caused by boundary condition changes can be discriminated against. Finite element modeling has been performed to verify experimental results.

Wincheski, B.↗
NASA NTRS2004

Automated Guided-Wave Scanning Developed to Characterize Materials and Detect Defects

The Nondestructive Evaluation (NDE) Group of the Optical Instrumentation Technology Branch at the NASA Glenn Research Center has developed a scanning system that uses guided waves to characterize materials and detect defects. The technique uses two ultrasonic transducers to interrogate the condition of a material. The sending transducer introduces an ultrasonic pulse at a point on the surface of the specimen, and the receiving transducer detects the signal after it has passed through the material. The aim of the method is to correlate certain parameters in both the time and frequency domains of the detected waveform to characteristics of the material between the two transducers. The scanning system is shown. The waveform parameters of interest include the attenuation due to internal damping, waveform shape parameters, and frequency shifts due to material changes. For the most part, guided waves are used to gauge the damage state and defect growth of materials subjected to various mechanical or environmental loads. The technique has been applied to polymer matrix composites, ceramic matrix composites, and metal matrix composites as well as metallic alloys. Historically, guided wave analysis has been a point-by-point, manual technique with waveforms collected at discrete locations and postprocessed. Data collection and analysis of this type limits the amount of detail that can be obtained. Also, the manual movement of the sensors is prone to user error and is time consuming. The development of an automated guided-wave scanning system has allowed the method to be applied to a wide variety of materials in a consistent, repeatable manner. Experimental studies have been conducted to determine the repeatability of the system as well as compare the results obtained using more traditional NDE methods. The following screen capture shows guided-wave scan results for a ceramic matrix composite plate, including images for each of nine calculated parameters. The system can display up to 18 different wave parameters. Multiple scans of the test specimen demonstrated excellent repeatability in the measurement of all the guided-wave parameters, far exceeding the traditional point-by-point technique. In addition, the scan was able to detect a subsurface defect that was confirmed using flash thermography This technology is being further refined to provide a more robust and efficient software environment. Future hardware upgrades will allow for multiple receiving transducers and the ability to scan more complex surfaces. This work supports composite materials development and testing under the Ultra-Efficient Engine Technology (UEET) Project, but it also will be applied to other material systems under development for a wide range of applications.

Martin, Richard E.↗
NASA NTRS2002

Novel Optical Technique Developed and Tested for Measuring Two-Point Velocity Correlations in Turbulent Flows

A novel technique for characterizing turbulent flows was developed and tested at the NASA Glenn Research Center. The work is being done in collaboration with the University of Pittsburgh, through a grant from the NASA Microgravity Fluid Physics Program. The technique we are using, Homodyne Correlation Spectroscopy (HCS), is a laser-light-scattering technique that measures the Doppler frequency shift of light scattered from microscopic particles in the fluid flow. Whereas Laser Doppler Velocimetry gives a local (single-point) measurement of the fluid velocity, the HCS technique measures correlations between fluid velocities at two separate points in the flow at the same instant of time. Velocity correlations in the flow field are of fundamental interest to turbulence researchers and are of practical importance in many engineering applications, such as aeronautics.

Zimmerli, Gregory A.↗
NASA NTRS2005

Analysis of variability in the burst oscillations of the accreting millisecond pulsar XTE J1814-338

The accreting millisecond pulsar XTE J1814-338 exhibits oscillations at the known spin frequency during Type I X-ray bursts. The properties of the burst oscillations reflect the nature of the thermal asymmetry on the stellar surface. We present an analysis of the variability of the burst oscillations of this source, focusing on three characteristics: fractional amplitude, harmonic content and frequency. Fractional amplitude and harmonic content constrain the size, shape and position of the emitting region, whilst variations in frequency indicate motion of the emitting region on the neutron star surface. We examine both long-term variability over the course of the outburst, and short-term variability during the bursts. For most of the bursts, fractional amplitude is consistent with that of the accretion pulsations, implying a low degree of fuel spread. There is however a population of bursts whose fractional amplitudes are substantially lower, implying a higher degree of fuel spread, possibly forced by the explosive burning front of a precursor burst. For the first harmonic, substantial differences between the burst and accretion pulsations suggest that hotspot geometry is not the only mechanism giving rise to harmonic content in the latter. Fractional amplitude variability during the bursts is low; we can only rule out the hypothesis that the fractional amplitude remains constant at the l(sigma) level for bursts that do not exhibit photospheric radius expansion (PRE). There are no significant variations in frequency in any of the bursts except for the one burst that exhibits PRE. This burst exhibits a highly significant but small (= 0.1Hz) drop in frequency in the burst rise. The timescale of the frequency shift is slower than simple burning layer expansion models predict, suggesting that other mechanisms may be at work.

Watts, Anna L.↗
NASA NTRS2005

Cycom 977-2 Composite Material: Impact Test Results

The reaction frequency data from 13A testing by MSFC and WSTF appear well behaved for the sample number used by each and exhibit the same type of energy level dependency. The reaction frequency shift in energy level is unexplained at this time. All the 13A data suggest that only a small amount of material is consumed when reactions take place. At ambient pressure, most of not all reactions are quenched as indicated by the small mass loss. As test pressure is increased in LOX using 13B results. Cycom does not support initiation of reactions or propagations of reactions in GOX at 100 psis based on tests at MSFC and WSTF at 72 ft-lb impact energy. No batch effect was identified in LOX or GOX.

Engel, Carl D.↗
NASA NTRS2005

Proposal to Simultaneously Profile Wind and CO2 on Earth and Mars With 2-micron Pulsed Lidar Technologies

2-micron lidar technology has been in use and under continued improvement for many years toward wind measurements. But the 2-micron wavelength region is also rich in absorption lines of CO2 (and H2O to a lesser extent) that can be exploited with the differential absorption lidar (DIAL) technique to make species concentration measurements. A coherent detection receiver offers the possibility of making combined wind and DIAL measurements with wind derived from frequency shift of the backscatter spectrum and species concentration derived from power of the backscatter spectrum. A combined wind and CO2 measurement capability is of interest for applications on both Earth and Mars. CO2 measurements in the Earth atmosphere are of importance to studies of the global carbon cycle. Data on vertically-resolved CO2 profiles over large geographical observations areas are of particular interest that could potentially be made by deploying a lidar on an aircraft or satellite. By combining CO2 concentration with wind measurements an even more useful data product could be obtained in the calculation of CO2 flux. A challenge to lidar in this application is that CO2 concentration measurements must be made with a high level of precision and accuracy to better than 1%. The Martian atmosphere also presents wind and CO2 measurement problems that could be met with a combined DIAL/Doppler lidar. CO2 concentration in this scenario would be used to calculate atmospheric density since the Martian atmosphere is composed of 95% CO2. The lack of measurements of Mars atmospheric density in the 30-60 km range, dust storm formation and movements, and horizontal wind patterns in the 0-20 km range pose significant risks to aerocapture, and entry, descent, and landing of future robotic and human Mars missions. Systematic measurement of the Mars atmospheric density and winds will be required over several Mars years, supplemented with day-of-entry operational measurements. To date, there have been 5 successful robotic landings on Mars. Atmospheric density and wind reconstruction has been performed for 3 of these entries (the two Viking landers and Mars Pathfinder). At present, all Mars atmospheric density and wind models have these 3 entries (at widely scattered positions and seasons) as their basis, supplemented by coarse orbital measurements of atmospheric opacity and temperature. This lack of data leads to a large uncertainty in prediction of the Mars atmospheric density and winds in the altitude regime where deceleration of landers will occur. This uncertainty will have a dramatically large impact on mass, cost and risk. The precision and accuracy for application to Mars is not as stringent as Earth, but Mars does pose a challenge in needing a high level of wavelength stability and control in order to reference wavelength to the narrow linewidths found in the low atmospheric pressure of Mars, as illustrated in Figure 1.

Singh, Upendra N.↗
NASA NTRS2005

Development of a Coherent Lidar for Aiding Precision Soft Landing on Planetary Bodies

Coherent lidar can play a critical role in future planetary exploration missions by providing key guidance, navigation, and control (GNC) data necessary for navigating planetary landers to the pre-selected site and achieving autonomous safe soft-landing. Although the landing accuracy has steadily improved over time to approximately 35 km for the recent Mars Exploration Rovers due to better approach navigation, a drastically different guidance, navigation and control concept is required to meet future mission requirements. For example, future rovers will require better than 6 km landing accuracy for Mars and better than 1 km for the Moon plus maneuvering capability to avoid hazardous terrain features. For this purpose, an all-fiber coherent lidar is being developed to address the call for advancement of entry, descent, and landing technologies. This lidar will be capable of providing precision range to the ground and approach velocity data, and in the case of landing on Mars, it will also measure the atmospheric wind and density. The lidar obtains high resolution range information from a frequency modulated-continuous wave (FM-CW) laser beam whose instantaneous frequency varies linearly with time, and the ground vector velocity is directly extracted from the Doppler frequency shift. Utilizing the high concentration of aerosols in the Mars atmosphere (approx. two order of magnitude higher than the Earth), the lidar can measure wind velocity with a few watts of optical power. Operating in 1.57 micron wavelength regime, the lidar can use the differential absorption (DIAL) technique to measure the average CO2 concentration along the laser beam using, that is directly proportional to the Martian atmospheric density. Employing fiber optics components allows for the lidar multi-functional operation while facilitating a highly efficient, compact and reliable design suitable for integration into a spacecraft with limited mass, size, and power resources.

Amzajerdian, Farzin↗
NASA NTRS2005

A Simple Semaphore Signaling Technique for Ultra-High Frequency Spacecraft Communications

For planetary lander missions such as the upcoming Phoenix mission to Mars, the most challenging phase of the spacecraft-to-ground communications is during the critical phase termed entry, descent, and landing (EDL). At 8.4 GHz (X-band), the signals received by the largest Deep Space Network (DSN) antennas can be too weak for even 1 bit per second (bps) and therefore not able to communicate critical information to Earth. Fortunately, the lander s ultra-high frequency (UHF) link to an orbiting relay can meet the EDL requirements, but the data rate needs to be low enough to fit the capability of the UHF link during some or all of EDL. On Phoenix, the minimum data rate of the as-built UHF radio is 8 kbps and requires a signal level at the Odyssey orbiter of at least -120 dBm. For lower signaling levels, the effective data rate needs to be reduced, but without incurring the cost of rebuilding and requalifying the equipment. To address this scenario, a simple form of frequency-shift keying (FSK) has been devised by appropriately programming the data stream that is input to the UHF transceiver. This article describes this technique and provides performance estimates. Laboratory testing reveals that input signal levels at -140 dBm and lower can routinely be demodulated with the proposed signaling scheme, thereby providing a 20-dB and greater margin over the 8-kbps threshold.

Butman, S.↗
NASA NTRS1999

Experimental Line Parameters of the Oxygen A-Band at 760 nanm

To support atmospheric remote sensing applications, line positions, intensities, self- and nitrogen-broadened line widths and their temperature dependence and pressure-induced frequency shift at room temperature were measured up to J' and N' = 22 for the oxygen A-band at 13122 cm-1.

oxygen line parameters A-band intensities pressure↗
NASA NTRS2009

Ground Vibration Test of the Aerostructure Test Wing 2

The Aerostructures Test Wing (ATW) was developed to test unique concepts for flutter prediction and control synthesis. A follow-on to the successful ATW, denoted ATW2, was fabricated as a test bed to validate a variety of instrumentation in flight and to collect data for development of advanced signal processing algorithms for flutter prediction and aviation safety. As a means to estimate flutter speed, a ground vibration test (GVT) was performed. The results of a GVT are typically utilized to update structural dynamics finite element (FE) models used for flutter analysis. In this study, two GVT methodologies were explored to determine which nodes provide the best sensor locations: (i) effective independence and (ii) kinetic energy sorting algorithms. For measurement, ten and twenty sensors were used for three and 10 target test modes. A total of six accelerometer configurations measured frequencies and mode shapes. This included locations used in the original ATW GVT. Moreover, an optical measurement system was used to acquire data without mass effects added by conventional sensors. A considerable frequency shift was observed in comparing the data from the accelerometers to the optical data. The optical data provided robust data for use of the ATW2 finite element model update.

Herrera, Claudia↗
NASA NTRS2010

Cryogenic Flow Sensor

An acousto-optic cryogenic flow sensor (CFS) determines mass flow of cryogens for spacecraft propellant management. The CFS operates unobtrusively in a high-pressure, high-flowrate cryogenic environment to provide measurements for fluid quality as well as mass flow rate. Experimental hardware uses an optical plane-of-light (POL) to detect the onset of two-phase flow, and the presence of particles in the flow of water. Acousto-optic devices are used in laser equipment for electronic control of the intensity and position of the laser beam. Acousto-optic interaction occurs in all optical media when an acoustic wave and a laser beam are present. When an acoustic wave is launched into the optical medium, it generates a refractive index wave that behaves like a sinusoidal grating. An incident laser beam passing through this grating will diffract the laser beam into several orders. Its angular position is linearly proportional to the acoustic frequency, so that the higher the frequency, the larger the diffracted angle. If the acoustic wave is traveling in a moving fluid, the fluid velocity will affect the frequency of the traveling wave, relative to a stationary sensor. This frequency shift changes the angle of diffraction, hence, fluid velocity can be determined from the diffraction angle. The CFS acoustic Bragg grating data test indicates that it is capable of accurately determining flow from 0 to 10 meters per second. The same sensor can be used in flow velocities exceeding 100 m/s. The POL module has successfully determined the onset of two-phase flow, and can distinguish vapor bubbles from debris.

Justak, John↗
NASA NTRS2010

Ultra-High Resolution Spectroscopic Remote Sensing: A Microscope on Planetary Atmospheres

Remote sensing of planetary atmospheres is not complete without studies of all levels of the atmosphere, including the dense cloudy- and haze filled troposphere, relatively clear and important stratosphere and the upper atmosphere, which are the first levels to experience the effects of solar radiation. High-resolution spectroscopy can provide valuable information on these regions of the atmosphere. Ultra-high spectral resolution studies can directly measure atmospheric winds, composition, temperature and non-thermal phenomena, which describe the physics and chemistry of the atmosphere. Spectroscopy in the middle to long infrared wavelengths can also probe levels where dust of haze limit measurements at shorter wavelength or can provide ambiguous results on atmospheric species abundances or winds. A spectroscopic technique in the middle infrared wavelengths analogous to a radio receiver. infrared heterodyne spectroscopy [1], will be describe and used to illustrate the detailed study of atmospheric phenomena not readily possible with other methods. The heterodyne spectral resolution with resolving power greater than 1,000.000 measures the true line shapes of emission and absorption lines in planetary atmospheres. The information on the region of line formation is contained in the line shapes. The absolute frequency of the lines can be measured to I part in 100 ,000,000 and can be used to accurately measure the Doppler frequency shift of the lines, directly measuring the line-of-sight velocity of the gas to --Im/s precision (winds). The technical and analytical methods developed and used to measure and analyze infrared heterodyne measurements will be described. Examples of studies on Titan, Venus, Mars, Earth, and Jupiter will be presented. 'These include atmospheric dynamics on slowly rotating bodies (Titan [2] and Venus [3] and temperature, composition and chemistry on Mars 141, Venus and Earth. The discovery and studies of unique atmospheric phenomena will also be described, such as non-thermal and lasing phenomena on Mars and Venus, mid-infrared aurora on Jupiter [5], and results of small body impacts on Jupiter [6]. The heterodyne technique can also be applied for detailed study of the Earth's stratosphere and mesosphere by measuring trace constituent abundances and temporal and spatial variability as well as winds, which provide information of transport. All ground-based measurements will be described as complementary and supporting studies for on-going and future space missions [7] (Mars Express, Venus Express, Cassini Huygens, JUNO, ExoMars Trace Gas Orbiter, and the Europa Jupiter System Mission, an Earth Science Venture Class missions), Proposed instrument and technology development for a space flight infrared heterodyne spectrometer will be described.

Kostiuk, Theodor↗
NASA NTRS2006

Automatic Alignment of Displacement-Measuring Interferometer

A control system strives to maintain the correct alignment of a laser beam in an interferometer dedicated to measuring the displacement or distance between two fiducial corner-cube reflectors. The correct alignment of the laser beam is parallel to the line between the corner points of the corner-cube reflectors: Any deviation from parallelism changes the length of the optical path between the reflectors, thereby introducing a displacement or distance measurement error. On the basis of the geometrical optics of corner-cube reflectors, the length of the optical path can be shown to be L = L(sub 0)cos theta, where L(sub 0) is the distance between the corner points and theta is the misalignment angle. Therefore, the measurement error is given by DeltaL = L(sub 0)(cos theta - 1). In the usual case in which the misalignment is small, this error can be approximated as DeltaL approximately equal to -L(sub 0)theta sup 2/2. The control system (see figure) is implemented partly in hardware and partly in software. The control system includes three piezoelectric actuators for rapid, fine adjustment of the direction of the laser beam. The voltages applied to the piezoelectric actuators include components designed to scan the beam in a circular pattern so that the beam traces out a narrow cone (60 microradians wide in the initial application) about the direction in which it is nominally aimed. This scan is performed at a frequency (2.5 Hz in the initial application) well below the resonance frequency of any vibration of the interferometer. The laser beam makes a round trip to both corner-cube reflectors and then interferes with the launched beam. The interference is detected on a photodiode. The length of the optical path is measured by a heterodyne technique: A 100- kHz frequency shift between the launched beam and a reference beam imposes, on the detected signal, an interferometric phase shift proportional to the length of the optical path. A phase meter comprising analog filters and specialized digital circuitry converts the phase shift to an indication of displacement, generating a digital signal proportional to the path length.

Halverson, Peter↗
NASA NTRS2005

Coherent Laser Instrument Would Measure Range and Velocity

A proposed instrument would project a narrow laser beam that would be frequency-modulated with a pseudorandom noise (PN) code for simultaneous measurement of range and velocity along the beam. The instrument performs these functions in a low mass, power, and volume package using a novel combination of established techniques. Originally intended as a low resource- footprint guidance sensor for descent and landing of small spacecraft onto Mars or small bodies (e.g., asteroids), the basic instrument concept also lends itself well to a similar application guiding aircraft (especially, small unmanned aircraft), and to such other applications as ranging of topographical features and measuring velocities of airborne light-scattering particles as wind indicators. Several key features of the instrument s design contribute to its favorable performance and resource-consumption characteristics. A laser beam is intrinsically much narrower (for the same exit aperture telescope or antenna) than a radar beam, eliminating the need to correct for the effect of sloping terrain over the beam width, as is the case with radar. Furthermore, the use of continuous-wave (CW), erbium-doped fiber lasers with excellent spectral purity (narrow line width) permits greater velocity resolution, while reducing the laser s power requirement compared to a more typical pulsed solid-state laser. The use of CW also takes proper advantage of the increased sensitivity of coherent detection, necessary in the first place for direct measurement of velocity using the Doppler effect. However, measuring range with a CW beam requires modulation to "tag" portions of it for time-of-flight determination; typically, the modulation consists of a PN code. A novel element of the instrument s design is the use of frequency modulation (FM) to accomplish both the PN-modulation and the Doppler-bias frequency shift necessary for signed velocity measurements. This permits the use of a single low-power waveguide electrooptic phase modulator, while simultaneously mitigating the effects of speckle as a noise source in the coherent detection.

Chang, Daniel↗
NASA NTRS2015

Nanostructure Diffraction Gratings for Integrated Spectroscopy and Sensing

The present disclosure pertains to metal or dielectric nanostructures of the subwavelength scale within the grating lines of optical diffraction gratings. The nanostructures have surface plasmon resonances or non-plasmon optical resonances. A linear photodetector array is used to capture the resonance spectra from one of the diffraction orders. The combined nanostructure super-grating and photodetector array eliminates the use of external optical spectrometers for measuring surface plasmon or optical resonance frequency shift caused by the presence of chemical and biological agents. The nanostructure super-gratings can be used for building integrated surface enhanced Raman scattering (SERS) spectrometers. The nanostructures within the diffraction grating lines enhance Raman scattering signal light while the diffraction grating pattern of the nanostructures diffracts Raman scattering light to different directions of propagation according to their wavelengths. Therefore, the nanostructure super-gratings allows for the use of a photodetector array to capture the surface enhanced Raman scattering spectra.

Guo, Junpeng↗
NASA NTRS2011

MIRO Observation of Comet C/2002 T7 (LINEAR) Water Line Spectrum

Comet C/2002 T7 (LINEAR) was observed with the Microwave Instrument for Rosetta Orbiter (MIRO) on April 30, 2004, between 5 hr and 16 hr UT. The comet was 0.63AU distance from the Sun and 0.68AU distance from the MIRO telescope at the time of the observations. The water line involving the two lowest rotational levels at 556.936 GHz is observed at 557.070 GHz due to a large Doppler frequency shift. The detected water line spectrum is interpreted using a non local thermal equilibrium (Non-LTE) molecular excitation and radiative transfer model. Several synthetic spectra are calculated with various coma profiles that are plausible for the comet at the time of observations. The coma profile is modeled with three characteristic parameters: outgassing rate, a constant expansion velocity, and a constant gas temperature. The model calculation result shows that for the distant line observation where contributions from a large coma space is averaged, the combination of the outgassing rate and the gas expansion velocity determines the line shape while the gas temperature has a negligible effect. The comparison between the calculated spectra and the MIRO measured spectrum suggests that the outgassing rate of the comet is about 2.0x1029 molecules/second and its gas expansion velocity about 1.2 km/s at the time of the observations.

spectral line↗
NASA NTRS2014

Wireless Capacitive Pressure Sensor Operating up to 400 Celcius from 0 to 100 psi Utilizing Power Scavenging

In this paper, a wireless capacitive pressure sensor developed for the health monitoring of aircraft engines has been demonstrated. The sensing system is composed of a Clapp-type oscillator that operates at 131 MHz. The Clapp oscillator is fabricated on a alumina substrate and consists of a Cree SiC (silicon carbide) MESFET (Metal Semiconductor Field Effect Transistors), this film inductor, Compex chip capacitors and Sporian Microsystem capacitive pressure sensor. The resonant tank circuit within the oscillator is made up of the pressure sensor and a spiral thin film inductor, which is used to magnetically couple the wireless pressure sensor signal to a coil antenna placed over 1 meter away. 75% of the power used to bias the sensing system is generated from thermoelectric power modules. The wireless pressure sensor is operational at room temperature through 400 C from 0 to 100 psi and exhibits a frequency shift of over 600 kHz.

Scardelletti, Maximilian C.↗