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At least 163 records · Page 9

Tunable optical lens array using viscoelastic material and acoustic radiation force

A movable optical lens array that uses acoustic radiation force was investigated. The lens array consists of a glass plate, two piezoelectric bimorph transducers, and a transparent viscoelastic gel film. A cylindrical lens array with a lens pitch of 4.6 mm was fabricated using the acoustic radiation force generated by the flexural vibration of the glass plate. The focal point and the positioning of the lenses can be changed using the input voltage and the driving phase difference between the two transducers, respectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Selected OAST/OSSA space experiment activities in support of Space Station Freedom

The Space Experiments Division at NASA Lewis Research Center is developing technology and science space experiments for the Office of Aeronautics and Space Technology (OAST) and the Office of Space Sciences and Applications (OSSA). Selected precursor experiments and technology development activities supporting the Space Station Freedom (SSF) are presented. The Tank Pressure Control Experiment (TPCE) is an OAST-funded cryogenic fluid dynamics experiment, the objective of which is to determine the effectiveness of jet mixing as a means of equilibrating fluid temperatures and controlling tank pressures, thereby permitting the design of lighter cryogenic tanks. The information from experiments such as this will be utilized in the design and operation of on board cryogenic storage for programs such as SSF. The Thermal Energy Storage Flight Project (TES) is an OAST-funded thermal management experiment involving phase change materials for thermal energy storage. The objective of this project is to develop and fly in-space experiments to characterize void shape and location in phase change materials used in a thermal energy storage configuration representative of an advanced solar dynamic system design. The information from experiments such as this will be utilized in the design of future solar dynamic power systems. The Solar Array Module Plasma Interaction Experiment (SAMPIE) is an OAST-funded experiment to determine the environmental effects of the low earth orbit (LEO) space plasma environment on state-of-the-art solar cell modules biased to high potentials relative to the plasma. Future spacecraft designs and structures will push the operating limits of solar cell arrays and other high voltage systems. SAMPIE will provide key information necessary for optimum module design and construction. The Vibration Isolation Technology (VIT) Advanced Technology Development effort is funded by OSSA to provide technology necessary to maintain a stable microgravity environment for sensitive payloads on board spacecraft. The proof of concept will be demonstrated by laboratory tests and in low-gravity aircraft flights. VIT is expected to be utilized by many SSF microgravity science payloads. The Space Acceleration Measurement System (SAMS) is an OSSA-funded instrument to measure the microgravity acceleration environment for OSSA payloads on the shuttle and SSF.

Delombard, Richard↗

Electric Motor Noise from Small Quadcopters: Source Characteristics - Part II

The increased interest in electric motors for propulsion systems has driven interest in quantifying the contribution of electric motor noise to the overall sound levels and possible human annoyance of the propulsion system. This work presents acoustic measurements of electric motors used for small quadcopters to quantify the sound produced by a number of outrunning motors with different types of controllers. Results are presented for loaded and unloaded motors as installed and uninstalled configurations. Motor resonance frequencies were measured and computed. Current probe measurements showed that the supply current from the controllers contained significant harmonic content for the conventional and sinewave controllers. Acoustic results showed motor noise is typically radiated at frequencies near the mode 2 vibration frequency at roughly 5000 Hz. Electric motor noise was evident in the spectra produced by many of the motor-controller combinations for motors loaded with propellers with levels often greater than those for the motor alone due to increase in the stator magnetic flux density with increased current. An installed configuration produced increases in acoustic radiation over that of the uninstalled motor in a frequency range near the mode 1 vibration frequency near 1200 Hz. A companion paper (Part I - Acoustic Measurements), focuses on source identification using a phased array and directivity characteristics for a baseline configuration.

Motor Resonance Frequencies↗

BOK-Underfill Optimization for FPGA Package/Assembly

Commercial-off-the-shelf area array package technologies in high-reliability versions are being considered for NASA electronic systems. These packages are prone to early failure due to the severe mechanical shock and vibration of launch, as well as other less severe conditions, such as mechanical loading during descent, rough terrain mobility, handling, and ground tests. As the density of these packages increases and the size of ball interconnections decrease, susceptibility to mechanical loading and cycling fatigue grows. This report presents a summary of the body of knowledge developed for the evaluation of area array packages and is based on surveys of literature from industry and academia. For high-reliability applications, the limited data that exists will be presented. Most data from industry deals with mechanical fatigue caused by four-point bend tests, as well as from drop tests for hand-held electronics; the most recent data will be presented, along with a brief background of prior literature. Understanding the key design guidelines and failure mechanisms from past tests is critical to developing an approach that will minimize future failures. Additional specific testing enables low-risk insertion of these advanced electronic packages.

mechanical fatigue↗

Modeling and Simulation of Phased Array Antennas to Support Next-Generation Satellite Design

Developing enhanced simulation capabilities has become a significant priority for the Space Communications and Navigation (SCaN) project at NASA as new space communications technologies are proposed to replace aging NASA communications assets, such as the Tracking and Data Relay Satellite System (TDRSS). When developing the architecture for these new space communications assets, it is important to develop updated modeling and simulation methodologies, such that competing architectures can be weighed against one another and the optimal path forward can be determined. There have been many simulation tools developed here at NASA for the simulation of single RF link budgets, or for the modeling and simulation of an entire network of spacecraft and their supporting SCaN network elements. However, the modeling capabilities are never fully complete and as new technologies are proposed, gaps are identified. One such gap is the ability to rapidly develop high fidelity simulation models of electronically steerable phased array systems. As future relay satellite architectures are proposed that include optical communications links, electronically steerable antennas will become more desirable due to the reduction in platform vibration introduced by mechanically steerable devices. In this research, we investigate how modeling of these antennas can be introduced into out overall simulation and modeling structure. The ultimate goal of this research is two-fold. First, to enable NASA engineers to model various proposed simulation architectures and determine which proposed architecture meets the given architectural requirements. Second, given a set of communications link requirements for a proposed satellite architecture, determine the optimal configuration for a phased array antenna. There is a variety of tools available that can be used to model phased array antennas. To meet our stated goals, the first objective of this research is to compare the subset of tools available to us, trading-off modeling fidelity of the tool with simulation performance. When comparing several proposed architectures, higher- fidelity modeling may be desirable, however, when iterating a proposed set of communication link requirements across ranges of phased array configuration parameters, the practicality of performance becomes a significant requirement. In either case, a minimum simulation - fidelity must be met, regardless of performance considerations, which will be discussed in this research. Given a suitable set of phased array modeling tools, this research then focuses on integration with current SCaN modeling and simulation tools. While properly modeling the antenna elements of a system are vital, this is only a small part of the end-to-end communication path between a satellite and the supporting ground station and/or relay satellite assets. To properly model a proposed simulation architecture, this toolset must be integrated with other commercial and government development tools, such that the overall architecture can be examined in terms of communications, reliability, and cost. In this research, integration with previously developed communication tools is investigated.

Phased Array↗

Short range laser obstacle detector

A short range obstacle detector for surface vehicles is described which utilizes an array of laser diodes. The diodes operate one at a time, with one diode for each adjacent azimuth sector. A vibrating mirror a short distance above the surface provides continuous scanning in elevation for all azimuth sectors. A diode laser is synchronized with the vibrating mirror to enable one diode laser to be fired, by pulses from a clock pulse source, a number of times during each elevation scan cycle. The time for a given pulse of light to be reflected from an obstacle and received is detected as a measure of range to the obstacle.

Kuriger, W. L.↗

Final Qualification and Early On-Orbit Performance of the HESSI Cryocooler

The High Energy Solar Spectroscopic Imager (HESSI) spacecraft was launched on February 5, 2002. It now observes the Sun with the finest angular and energy resolutions ever achieved from a few keV to hundreds of keV, using an array of nine germanium detectors operating at 75K. The spacecraft was originally scheduled for launch in July 2000, but a vibration facility mishap damaged the primary structure of the spacecraft, along with the cryocooler, This paper describes issues in the qualification of a replacement for the original flight cooler, and describes early on-orbit performance.

Boyle, R. F.↗

Properties of Noise Cross-Correlation Functions Obtained from a Distributed Acoustic Sensing Array at Garner Valley, California

A field test that was conducted at Garner Valley, California, on 11 and 12 September 2013 using distributed acoustic sensing (DAS) to sense ground vibrations provided a continuous overnight record of ambient noise. Furthermore, the energy of ambient noise was concentrated between 5 and 25 Hz, which falls into the typical traffic noise frequency band. A standard procedure (Bensen et al., 2007) was adopted to calculate noise cross-correlation functions (NCFs) for 1-min intervals. The 1-min-long NCFs were stacked using the time–frequency domain phase-weighted-stacking method, which significantly improves signal quality. The obtained NCFs were asymmetrical, which was a result of the nonuniform distributed noise sources. A precursor appeared on NCFs along one segment, which was traced to a strong localized noise source or a scatterer at a nearby road intersection. NCF for the radial component of two surface accelerometers along a DAS profile gave similar results to those from DAS channels. Here, we calculated the phase velocity dispersion from DAS NCFs using the multichannel analysis of surface waves technique, and the result agrees with active-source results. We then conclude that ambient noise sources and the high spatial sampling of DAS can provide the same subsurface information as traditional active-source methods.

58 GEOSCIENCES↗

Far-infrared tangential interferometer/polarimeter design and installation for NSTX-U

The Far-infrared Tangential Interferometer/Polarimeter (FIReTIP) system has been refurbished and is being reinstalled on the National Spherical Torus Experiment—Upgrade (NSTX-U) to supply real-time line-integrated core electron density measurements for use in the NSTX-U plasma control system (PCS) to facilitate real-time density feedback control of the NSTX-U plasma. Inclusion of a visible light heterodyne interferometer in the FIReTIP system allows for real-time vibration compensation due to movement of an internally mounted retroreflector and the FIReTIP front-end optics. Real-time signal correction is achieved through use of a National Instruments CompactRIO field-programmable gate array.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Brady's Geothermal Field DAS Vibroseis Data

The submitted data correspond to the monitored vibrations caused by a vibroseis seismically exciting the ground in the vertical direction and captured by the DAS horizontal and vertical arrays during the PoroTomo Experiment. The data also include a file with the acceleration record at the Vibroseis. Vibroseis Sweep Details: Sweep on location T84 Stage 4 (Mode P 60 s long record ) Time: 2016-03-25 14:01:15 (UTC) Location: 39.80476089N, -119.0027625W Elevation: 1272.0M (on ground surface at the site) Sweep length: 20 seconds Frequencies: 5 Hz to 20 Hz

15 GEOTHERMAL ENERGY↗

Optical signal processing

The article discusses several optical configurations used for signal processing. Electronic-to-optical transducers are outlined, noting fixed window transducers and moving window acousto-optic transducers. Folded spectrum techniques are considered, with reference to wideband RF signal analysis, fetal electroencephalogram analysis, engine vibration analysis, signal buried in noise, and spatial filtering. Various methods for radar signal processing are described, such as phased-array antennas, the optical processing of phased-array data, pulsed Doppler and FM radar systems, a multichannel one-dimensional optical correlator, correlations with long coded waveforms, and Doppler signal processing. Means for noncoherent optical signal processing are noted, including an optical correlator for speech recognition and a noncoherent optical correlator.

Casasent, D.↗

Cameras Would Withstand High Accelerations

Very rugged cameras with all-reflective optics proposed for use in presence of high accelerations. Optics consist of four coaxial focusing mirrors in Cassegrain configuration. Mirrors are conics or aspherics. Optics achromatic,and imaging system overall passes light from extreme ultraviolet to far infrared. Charge-coupled-device video camera, film camera, or array of photodetectors placed at focal plane. Useful as portable imagers subject to rough handling, or instrumentation cameras mounted on severely vibrating or accelerating vehicles.

Meinel, Aden B.↗

Atmospheric Trace Gas Abundances and Stable Isotope Ratios via IR-LIF

We propose to develop new technologies with support provided by PIDDP that will enable the in situ measurements of abundances and stable isotope ratios in important radiatively and biogenically active gases such as carbon dioxide, carbon monoxide, water, methane, nitrous oxide, and hydrogen sulfide to very high precision (0.1 per mil or better for the isotopic ratios, for example). Such measurements, impossible at present, could provide pivotal new constraints on the global (bio)geochemical budgets of these critical species, and could also be used to examine the dynamics of atmospheric transport on Mars, Titan, and other solar system bodies. We believe the combination of solid state light sources with imaging of the IR laser induced fluorescence (IR-LIF) via newly available detector arrays will make such in situ measurements possible for the first time. Even under ambient terrestrial conditions, the LIF yield from vibrational excitation of species such as water and carbon dioxide should produce emission measures well in excess of ten billion photons/sec from samples volumes of order 1 c.c. These count rates can, in principle, yield detection limits into the sub-ppt range that are required for the in situ isotopic study of atmospheric trace gases. While promising, such technologies are relatively immature, but developing rapidly, and there are a great many uncertainties regarding their applicability to in situ IR-LIF planetary studies. We therefore feel PIDDP support will be critical to developing these new tools, and propose a three-year program to combine microchip near-IR lasers with low background detection axes and state-of-the-art HgCdTe detectors developed for astronomical spectroscopy to investigate the sensitivity of IR-LIF under realistic planetary conditions, to optimize the optical pumping and filtering schemes for important species, and to apply the spectrometer to the non-destructive measurement of stable isotopes in a variety of test samples. These studies form the necessary precursors to the development of compact, lightweight stable isotope/trace gas sensors for future planetary missions.

Blake, Geoffrey A.↗

Nancy Grace Roman Space Telescope Observatory Implementation and Challenges

NASA’s Nancy Grace Roman Space Telescope (Roman), previously referred to as Wide Field Infrared Survey Telescope (WFIRST), was named after Dr. Nancy Grace Roman, an astronomer and NASA pioneer of modern space-based astronomy who is known as the “mother of the Hubble Space Telescope”. Roman is a deep space infrared observatory with a Hubble-sized telescope and wide field of view instrument (greater than 100 times that of Hubble’s) that will conduct a high latitude time-domain survey, a high latitude imaging and spectroscopic survey, and a galactic bulge time-domain survey to characterize dark energy and expand the census of exoplanets in our galaxy while allowing a broad range of astrophysics research. Roman will also demonstrate exoplanet coronagraphy with active wave front control technology and provide general investigator programs for the science community. Roman is finishing the critical design phase and is planning for launch in 2026. It will operate in a quasi-halo orbit about Sun-Earth L2, 1.5 million kilometers from Earth, for a five-year primary mission life. The Observatory features an Optical Telescope Assembly with an existing, repurposed 2.4m primary mirror, a Wide Field Instrument with a focal plane array comprised of 18 HgCdTe near-infrared detectors and a grism, prism and filter elements for imaging and spectroscopy in support of the primary surveys, as well as a Coronagraph instrument technology demonstration with starlight suppression technology for direct imaging and spectroscopy of exoplanets. The telescope is mounted to the Instrument Carrier composite truss structure which also optically meters each instrument, includes a Launch Load and Vibration Isolation System to provide passive isolation of spacecraft jitter sources while also supporting the payload during launch and is attached to the Spacecraft Bus. The Spacecraft also includes a Solar Array Sunshield ,Deployable Aperture Cover, Lower Instrument Sunshade, High Gain Antenna System, and Outer Barrel Assembly. Figure 1 shows an overview of the Roman Observatory. When fully integrated, Roman will be the largest Observatory assembled and tested at NASA’s Goddard Space Flight Center. Figure 1. Roman Observatory Overview Development of scientific satellites is challenging by nature, as the pursuit to broaden scientific knowledge always pushes the boundary of what has come before. The implementation of the Roman mission is a prime example and expected challenges have been augmented by the foundational decision to use the existing telescope components, developed in the early 2000s by another Government agency for a different application. Other unique aspects of the Roman mission, such as its survey nature, the vast amount of data required to meet science objectives, and packaging of the Observatory elements around the existing telescope components, create constrained design spaces that drive competing requirements across Observatory subsystems. Given these challenges, systems engineering has been a critical discipline in balancing implementation decisions for the Roman mission and will continue to play a key role going forward. This paper will discuss details of the Roman Observatory configuration, as well as some of the systems engineering challenges and the decision-making process used to mature the Roman Space Telescope preliminary design to implementation.

Lisa Ml Bartusek↗

Enhanced Raman scattering from aromatic dithiols electrosprayed into plasmonic nanojunctions

We describe surface enhanced Raman spectroscopy (SERS) experiments in which molecular coverage is systematically varied from 3.8 x 105 to 3.8 x 102 to 0.38 molecules/μm2 using electrospray deposition of ethanolic 4,4’-dimercaptostilbene (DMS) solutions. The plasmonic SERS substrate used herein consists of a well-characterized 2-dimensional (2D) array of silver nanospheres [see El-Khoury et al., J. Chem. Phys., 2014, 141, 214308], previously shown to feature uniform topography and plasmonic response, as well as intense SERS activity. When compared to their ensemble averaged analogues, the spatially and temporally averaged spectra of a single molecule exhibit several unique features including: (i) distinct relative intensities of the observable Raman-active vibrational states, (ii) more pronounced SERS backgrounds, and (iii) broader Raman lines indicative of faster vibrational dephasing. The first observation may be understood on the basis of an intuitive physical picture in which removal of averaging over multiple molecules exposes the tensorial nature of Raman scattering. When an oriented single molecule gives rise to the recorded SERS spectra, the relative orientation of the molecule with respect to vector components of the local electric field determines the relative intensities of the observable vibrational states. Using a single molecule SERS framework described herein, we derive a unique molecular orientation in which a single DMS molecule is isolated at a nanojunction formed between two silver nanospheres in the 2D array. The DMS molecule is found lying nearly flat with respect to the metal surface. The derived orientation of a single molecule at a plasmonic nanojunction is consistent with observations (ii) and (iii). In particular, a careful inspection of the temporal spectral variations along the recorded single molecule SERS time sequences reveals that the time-averaged SERS backgrounds arise from individual molecular events, marked by broadened SERS signatures. We assign the broadened spectra along the SERS time sequence – which sum up to a SERS background in the averaged spectra – to instances in which the π-framework of the DMS molecule is parallel to the metal surface. This also accounts for Raman line broadening as a result of fast vibrational dephasing and driven by molecular reorientation at a plasmonic nanojunction. Furthermore, we report on the orientation dependence of single molecule SERS enhancement factors. We find that in the case of a single DMS molecule isolated at a plasmonic nanojunction, molecular orientation may affect the derived single molecule SERS enhancement factor by up to 5 orders of magnitude. Taking both chemical effects as well as molecular orientation into account, we were able to estimate a single molecule enhancement factor of ~1010 in our measurements.

Environmental Molecular Sciences Laboratory↗

HgCdTe Avalanche Photodiode Array Detectors with Single Photon Sensitivity and Integrated Detector Cooler Assemblies for Space Lidar Applications

A HgCdTe avalanche photodiode (APD) focal plane array assembly with linear mode photon-counting capability has been developed for space lidar applications. An integrated detector cooler assembly (IDCA) has been built using a miniature Stirling cooler. A microlens array has been included to improve the fill factor. The HgCdTe APD has a spectral response from 0.9- to 4.3-μm wavelengths, a photon detection efficiency as high as 70%, and a dark count rate of <250 kHz at 110 K. The mass of the IDCA is 0.8 kg and the total electrical power consumption is about 7 W. The HgCdTe APD arrays have been characterized at NASA Goddard Space Flight Center. A series of environmental tests have been conducted for the IDCAs, including vibration, thermal cycling, and thermal vacuum tests. A description of the device and the test results at NASA are given in this paper.

Sun, Xiaoli↗

Wind Turbine Gearbox Condition Monitoring Vibration Analysis Benchmarking Datasets

Wind turbine condition monitoring (CM) can potentially help the wind industry reduce turbine downtime and operation and maintenance (O&M) cost. NREL CM research has investigated various condition-monitoring techniques such as acoustic emission (AE specifically stress wave), vibration, electrical signature, lubricant and debris monitoring based on the Gearbox Reliability Collaborative dynamometer and field tests, and other test turbines and resources accessible by NREL. During the past several years, NREL CM research has shown that there are very few validation and verification efforts on commercial wind turbine CM systems. One of the reasons might be limited benchmarking datasets accessible by stakeholders. To fill this gap, NREL executed a data collection effort. The targeted users of these datasets include those investigating vibration-based wind turbine CM research, evaluating commercially available vibration-based CM systems, or testing prototyped vibration-based CM systems. NREL collected data from a healthy and a damaged gearbox of the same design tested by the GRC. Vibration data were collected by accelerometers along with high-speed shaft RPM signals during the dynamometer testing. The healthy gearbox was only tested in the dynamometer. The damaged gearbox was first tested in the dynamometer and later sent to a wind farm close to NREL for field testing. In the field test, it experienced two loss-of-oil events that damaged its internal bearings and gear elements. The gearbox was brought back to NREL and it was retested in the dynamometer with CM systems deployed under controlled loading conditions that would not cause catastrophic failure of the gearbox. The objective of releasing these datasets to the public along with information about the real damage that occurred to the damaged gearbox is to provide the wind industry with some benchmarking datasets. These datasets will benefit research, development, validation, verification, and advancement of vibration-based wind condition-monitoring techniques. By accessing this data you acknowledge the terms outlined in the "License Information" document. Please contract Shawn Sheng (NREL) if you have any questions on the data or would like to collaborate on publications based on the datasets.

Array↗

VIBRATIONALLY EXCITED C{sub 4}H

Rotational spectra in four new excited vibrational levels of the linear carbon chain radical C{sub 4}H were observed in the millimeter band between 69 and 364 GHz in a low pressure glow discharge, and two of these were observed in a supersonic molecular beam between 19 and 38 GHz. All have rotational constants within 0.4% of the X{sup 2}Σ{sup +} ground vibrational state of C{sub 4}H and were assigned to new bending vibrational levels, two each with {sup 2}Σ and {sup 2}Π vibrational symmetry. The new levels are tentatively assigned to the 1ν{sub 6} and 1ν{sub 5} bending vibrational modes (both with {sup 2}Π symmetry), and the 1ν{sub 6}+1ν{sub 7} and 1ν{sub 5}+1ν{sub 6} combination levels ({sup 2}Σ symmetry) on the basis of the derived spectroscopic constants, relative intensities in our discharge source, and published laser spectroscopic and quantum calculations. Prior spectroscopic constants in the 1ν{sub 7} and 2ν{sub 7} levels were refined. Also presented are interferometric maps of the ground state and the 1ν{sub 7} level obtained with the Submillimeter Array (SMA) near 257 GHz which show that C{sub 4}H is present near the central star in IRC+10216. We found no evidence with the SMA for the new vibrationally excited levels of C{sub 4}H at a peak flux density averaged over a 3{sup ′′} synthesized beam of ⩾0.15 Jy/beam in the 294–296 and 304–306 GHz range, but it is anticipated that rotational lines in the new levels might be observed in IRC+10216 when ALMA attains its full design capability.

74 ATOMIC AND MOLECULAR PHYSICS↗