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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Primary and secondary ice production: interactions and their relative importance

A discrepancy of up to 5 orders of magnitude between ice crystal and ice nucleating particle (INP) number concentrations was found in the measurements, indicating the potentially important role of secondary ice production (SIP) in the clouds. However, the interactions between primary and SIP processes and their relative importance remain unexplored. In this study, we implemented five different ice nucleation schemes as well as physical representations of SIP processes (i.e., droplet shattering during rain freezing, ice-ice collisional break-up, and rime splintering) in the Community Earth System Model version 2 (CESM2). We ran CESM2 in the single column mode for model comparisons with the DOE Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Cloud Experiment (M-PACE) observations. We found that the model experiments with aerosol-aware ice nucleation schemes and SIP processes yield the best simulation results for the M-PACE single-layer mixed-phase clouds. We further investigated the relative importance of ice nucleation and SIP to ice number and cloud phase as well as interactions between ice nucleation and SIP in the M-PACE single-layer mixed-phase clouds. Our results show that SIP contributes 80 % to the total ice formation and transforms ~30 % of pure liquid-phase clouds simulated in the model experiments without considering SIP into mixed-phase clouds. The SIP is not only a result of ice crystals produced from ice nucleation, but also competes with the ice nucleation by reducing the number concentrations of cloud droplets and cloud-borne dust INPs. Conversely, strong ice nucleation also suppresses SIP by glaciating mixed-phase clouds and thereby reducing the amount of precipitation particles (rain and graupel).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1981

Noise suppression characteristics of peripherally segmented duct liners

The acoustic fields and transmission losses produced in semi-infinite circular ducts with peripherally segmented liners are analyzed using a series expansion of hard-wall duct modes. The coefficients of the series are computed using Galerkin's method. Unlike finite element approaches, this analysis includes the effects of realistic sources and the number of peripheral strips need not be small. It is shown that peripherally segmented liners redistribute the acoustic energy in waves composed of only a single circumferential mode at the source into other waves which contain a multitude of circumferential modes in the lined section. The accuracy of eigenfunctions computed from the analysis was observed to increase as either the frequency or radial mode order increased. The transmission losses were found to be accurate at frequencies above the cut-on value of the first-order radial mode in a hard-wall duct. The results show that for plane wave sources, peripherally segmented liners may attenuate as much sound as an optimized uniform liner at the optimal point while giving more noise suppression at most other frequencies.

Watson, W. R.↗
NASA NTRS2018

Lunar and Mars Ascent and Descent/Entry Crew Abort Modes for the Hercules Single-Stage Reusable Vehicle

The Hercules single-stage reusable vehicle is designed to support crewed missions to both the lunar surface and Mars surface. The design maximizes crew safety by providing full coverage crew abort capability during ascent and entry/descent, either through abort-to-surface or abort-to-orbit. This paper outlines each of the abort modes and discuss the Hercules vehicle design along with the base and orbital infrastructure required to enable the full coverage abort capability. For each abort mode, trajectory simulations are flown that illustrate the requisite design capabilities and highlight the sensitivity to key design variables.

Komar, David R.↗
NASA NTRS1988

Efficient second harmonic generation of a diode-laser-pumped CW Nd:YAG laser using monolithic MgO:LiNbO3 external resonant cavities

56-percent efficient external-cavity-resonant second-harmonic generation of a diode-laser pumped, CW single-axial-mode Nd:YAG laser is reported. A theory of external doubling with a resonant fundamental is presented and compared to experimental results for three monolithic cavities of nonlinear MgO:LiNbO3. The best conversion efficiency was obtained with a 12.5-mm-long monolithic ring cavity doubler, which produced 29.7 mW of CW, single-axial model 532-nm radiation from an input of 52.5 mW.

Kozlovsky, William J.↗
NASA NTRS1980

New PbSnTe heterojunction laser diode structures with improved performance

Several recent advances in the state-of-the-art of lead tin telluride double heterojunction laser diodes are summarized. Continuous Wave operation to 120 K and pulsed operation to 166 K with single, lowest order transverse mode emission to in excess of four times threshold at 80 K were achieved in buried stripe lasers fabricated by liquid phase epitaxy in the lattice-matched system, lead-tin telluride-lead telluride selenide. At the same time, liquid phase epitaxy was used to produce PbSnTe distributed feedback lasers with much broader continuous single mode tuning ranges than are available from Fabry-Perot lasers. The physics and philosophy behind these advances is as important as the structures and performance of the specific devices embodying the advances, particularly since structures are continually being evolved and the performance continues to be improved.

Fonstad, C. G.↗
NASA NTRS2009

Fiber Laser Development for LISA

We have developed a linearly-polarized Ytterbium-doped fiber ring laser with single longitudinal-mode output at 1064nm for LISA and other space applications. Single longitudinal-mode selection was achieved by using a fiber Bragg grating (FBG) and a fiber Fabry-Perot (FFP). The FFP also serves as a frequency-reference within our ring laser. Our laser exhibits comparable low frequency and intensity noise to Non-Planar Ring Oscillator (NPRO). By using a fiber-coupled phase modulator as a frequency actuator, the laser frequency can be electro-optically tuned at a rate of 100kHz. It appears that our fiber ring laser is promising for space applications where robustness of fiber optics is desirable.

Numata, Kenji↗
NASA NTRS1994

Parabolized stability equations

The parabolized stability equations (PSE) are a new approach to analyze the streamwise evolution of single or interacting Fourier modes in weakly nonparallel flows such as boundary layers. The concept rests on the decomposition of every mode into a slowly varying amplitude function and a wave function with slowly varying wave number. The neglect of the small second derivatives of the slowly varying functions with respect to the streamwise variable leads to an initial boundary-value problem that can be solved by numerical marching procedures. The PSE approach is valid in convectively unstable flows. The equations for a single mode are closely related to those of the traditional eigenvalue problems for linear stability analysis. However, the PSE approach does not exploit the homogeneity of the problem and, therefore, can be utilized to analyze forced modes and the nonlinear growth and interaction of an initial disturbance field. In contrast to the traditional patching of local solutions, the PSE provide the spatial evolution of modes with proper account for their history. The PSE approach allows studies of secondary instabilities without the constraints of the Floquet analysis and reproduces the established experimental, theoretical, and computational benchmark results on transition up to the breakdown stage. The method matches or exceeds the demonstrated capabilities of current spatial Navier-Stokes solvers at a small fraction of their computational cost. Recent applications include studies on localized or distributed receptivity and prediction of transition in model environments for realistic engineering problems. This report describes the basis, intricacies, and some applications of the PSE methodology.

Herbert, Thorwald↗
NASA NTRS2013

Single and Multi-Pulse Low-Energy Conical Theta Pinch Inductive Pulsed Plasma Thruster Performance

Impulse bits produced by conical theta-pinch inductive pulsed plasma thrusters possessing cone angles of 20deg, 38deg, and 60deg, were quantified for 500J/pulse operation by direct measurement using a hanging-pendulum thrust stand. All three cone angles were tested in single-pulse mode, with the 38deg model producing the highest impulse bits at roughly 1 mN-s operating on both argon and xenon propellants. A capacitor charging system, assembled to support repetitively-pulsed thruster operation, permitted testing of the 38deg thruster at a repetition-rate of 5 Hz at power levels of 0.9, 1.6, and 2.5 kW. The average thrust measured during multiple-pulse operation exceeded the value obtained when the single-pulse impulse bit is multiplied by the repetition rate.

Hallock, A. K.↗
NASA NTRS1998

A Very High Resolution Mid Infrared Spectrograph for SOFIA

The purpose of this project was to study the design of a high resolution mid-infrared spectrograph for the SOFIA airborne observatory. The primary motivation for the construction and use of such an instrument is the study of vibrational transitions of molecules in molecular clouds, circumstellar inflows and outflows, and planetary atmospheres, which are blocked from ground-based observations by absorption by the Earth's atmosphere. The instrument design studied is a cross-dispersed grating spectrograph with several modes of operation giving spectral resolving powers of approximately 4000, 20,000, and 100,000. In the two lower resolution modes a single grating is used in a long-slit spectrograph. At high resolution that grating serves as the cross-disperser for a 1-m long echelon, a very coarsely and steeply ruled grating, diamond-machined in aluminum. Several design study tasks were carried out: 1. An optical and mechanical design was developed. It differed from the preliminary design by using a reflecting focal reducer in the fore-optics and by rearranging the echelon and cross-dispersing chambers to improve the efficiency of the long-slit modes. 2. A finite-element analysis of the dewar and echelon support structures was done. It led us to change the echelon support to improve its rigidity. 3. Further information was obtained which convinced us that Hyperfine Inc. was capable of diamond-machining the echelon. 4. Several possible vendors of readout electronics and software were identified. It was decided that it is more cost-effective to purchase these items rather than developing them ourselves. 5. Observing and calibration procedures were studied. we did not identify significant changes needed from procedures used previously. 6. Possible expansions of instrument capabilities, including wavelength coverage, were studied. It appears unlikely that the echelon will perform well at wavelengths shortward of 5 microns, but the spectral coverage could be extended longward of 28 microns with the use of an Si:Sb detector. No patentable inventions were made during this study. Based on this design study, a proposal was submitted to construct the instrument. It was chosen as one of the first-light instruments for SOFIA.

Lacy, John H.↗
NASA NTRSDate not supplied

Photonic Integrated Circuit TUned for Reconnaissance and Exploration (PICTURE)

The mid-infrared (MIR) spectral range (3-5 μm) is of particular interest for remotely sensing gaseous molecules such as H2O, CO2, CH4, N2O, CO, NH3, and other compounds. The infrared spectra of planets, moons, comets, and asteroids are rich in information, including gas composition and surface mineralogy. Significant advances in technology have emerged for ground-based telescopes, including the higher spectral resolution permitted by cross-dispersed instruments and heterodyne techniques. New technologies offer the opportunity to break this barrier, by using solid- state photonics. In the past three years, under the NASA ROSES PICASSO program, we have been developing key components for a revolutionary MIR spectrometer: Photonic Integrated Circuit TUned for Reconnaissance and Exploration (PICTURE), which is based on integrated photonics technology that offers ultra-small size, weight, and power (SWaP) with non-moving parts and low cost for future planetary missions. In this paper, we will describe our science and technology development progress leading to demonstrating the concept and functionalities of the PICTURE instrument. The photonic integrated circuit spectrometer (PICS) of the PICTURE instrument uses an integrated heterodyne detection scheme to significantly reduce SWaP and improve sensitivity. Our program goals are to advance the building blocks needed for the PICS, which include arrayed waveguide gratings (AWGs), quantum cascade lasers (QCLs) as local oscillators, and quantum cascade detectors (QCDs) as heterodyne detectors. In addition, we are leveraging a NASA SBIR program to develop the toolsets needed to fabricate MIR photonics lanterns (PL). The PL is a critical component that enables PICTURE to bring a signal from the collecting telescope to the PICS, which requires single optical mode inputs. PICTURE focuses on the CO spectral band at 4.6-4.8 μm that is of key importance to cometary science. We also continue to explore future instrument concepts that exploit the broad wavelength potential of the PICS design to perform spectroscopy spanning the full MIR and longwave IR (LWIR) bands. This will have wide applicability in planetary science, for example, to probe the strongest CO2, H2O, and CH4 transitions that are difficult (CH4) or impossible (CO2, H2O) to detect using Earth-based telescopes due to atmospheric opacity. Each integrated-photonics-spectrometer chip will feature a single heterodyne room-temperature laser with a wide wavelength tuning range, or multiple local-oscillator lasers for much broader spectral coverage. The fully developed PICTURE instrument will provide a cost-effective, high-resolution spectrometer for future space applications.

Anthony W Yu↗
NASA NTRSDate not supplied

Photonic Integrated Circuit TUned for Reconnaissance and Exploration (PICTURE)

The mid-infrared (MIR) spectral range (3-5 μm) is of particular interest for remotely sensing gaseous molecules such as H2O, CO2, CH4, N2O, CO, NH3, and other compounds. The infrared spectra of planets, moons, comets, and asteroids are rich in information, including gas composition and surface mineralogy. Significant advances in technology have emerged for ground-based telescopes, including the higher spectral resolution permitted by cross-dispersed instruments and heterodyne techniques. New technologies offer the opportunity to break this barrier, by using solid-state photonics. In the past three years, under the NASA ROSES PICASSO program, we have been developing key components for a revolutionary MIR spectrometer: Photonic Integrated Circuit TUned for Reconnaissance and Exploration (PICTURE), which is based on integrated photonics technology that offers ultra-small size, weight, and power (SWaP) with non-moving parts and low cost for future planetary missions. In this paper, we will describe our science and technology development progress leading to demonstrating the concept and functionalities of the PICTURE instrument. The photonic integrated circuit spectrometer (PICS) of the PICTURE instrument uses an integrated heterodyne detection scheme to significantly reduce SWaP and improve sensitivity. Our program goals are to advance the building blocks needed for the PICS, which include arrayed waveguide gratings (AWGs), quantum cascade lasers (QCLs) as local oscillators, and quantum cascade detectors (QCDs) as heterodyne detectors. In addition, we are leveraging a NASA SBIR program to develop the toolsets needed to fabricate MIR photonics lanterns (PL). The PL is a critical component that enables PICTURE to bring a signal from the collecting telescope to the PICS, which requires single optical mode inputs. PICTURE focuses on the CO spectral band at 4.6-4.8 μm that is of key importance to cometary science. We also continue to explore future instrument concepts that exploit the broad wavelength potential of the PICS design to perform spectroscopy spanning the full MIR and longwave IR (LWIR) bands. This will have wide applicability in planetary science, for example, to probe the strongest CO2, H2O, and CH4 transitions that are difficult (CH4) or impossible (CO2, H2O) to detect using Earth-based telescopes due to atmospheric opacity. Each integrated-photonics-spectrometer chip will feature a single heterodyne room-temperature laser with a wide wavelength tuning range, or multiple local-oscillator lasers for much broader spectral coverage. The fully developed PICTURE instrument will provide a cost-effective, high-resolution spectrometer for future space applications.

Anthony W Yu↗
NASA NTRSDate not supplied

Photonic Integrated Circuit TUned for Reconnaissance and Exploration (PICTURE)

The mid-infrared (MIR) spectral range (3-5 μm) is of particular interest for remotely sensing gaseous molecules such as H2O, CO2, CH4, N2O, CO, NH3, and other compounds. The infrared spectra of planets, moons, comets, and asteroids are rich in information, including gas composition and surface mineralogy. Significant advances in technology have emerged for ground-based telescopes, including the higher spectral resolution permitted by cross-dispersed instruments and heterodyne techniques. New technologies offer the opportunity to break this barrier, by using solid-state photonics. In the past three years, under the NASA ROSES PICASSO program, we have been developing key components for a revolutionary MIR spectrometer: Photonic Integrated Circuit TUned for Reconnaissance and Exploration (PICTURE), which is based on integrated photonics technology that offers ultra-small size, weight, and power (SWaP) with non-moving parts and low cost for future planetary missions. In this paper, we will describe our science and technology development progress leading to demonstrating the concept and functionalities of the PICTURE instrument. The photonic integrated circuit spectrometer (PICS) of the PICTURE instrument uses an integrated heterodyne detection scheme to significantly reduce SWaP and improve sensitivity. Our program goals are to advance the building blocks needed for the PICS, which include arrayed waveguide gratings (AWGs), quantum cascade lasers (QCLs) as local oscillators, and quantum cascade detectors (QCDs) as heterodyne detectors. In addition, we are leveraging a NASA SBIR program to develop the toolsets needed to fabricate MIR photonics lanterns (PL). The PL is a critical component that enables PICTURE to bring a signal from the collecting telescope to the PICS, which requires single optical mode inputs. PICTURE focuses on the CO spectral band at 4.6-4.8 μm that is of key importance to cometary science. We also continue to explore future instrument concepts that exploit the broad wavelength potential of the PICS design to perform spectroscopy spanning the full MIR and longwave IR (LWIR) bands. This will have wide applicability in planetary science, for example, to probe the strongest CO2, H2O, and CH4 transitions that are difficult (CH4) or impossible (CO2, H2O) to detect using Earth-based telescopes due to atmospheric opacity. Each integrated-photonics-spectrometer chip will feature a single heterodyne room-temperature laser with a wide wavelength tuning range, or multiple local-oscillator lasers for much broader spectral coverage. The fully developed PICTURE instrument will provide a cost-effective, high-resolution spectrometer for future space applications.

Anthony W. Yu↗
NASA NTRS1992

A new hue capturing technique for the quantitative interpretation of liquid crystal images used in convective heat transfer studies

A new image processing based color capturing technique for the quantitative interpretation of liquid crystal images used in convective heat transfer studies is presented. This method is highly applicable to the surfaces exposed to convective heating in gas turbine engines. It is shown that, in the single-crystal mode, many of the colors appearing on the heat transfer surface correlate strongly with the local temperature. A very accurate quantitative approach using an experimentally determined linear hue vs temperature relation is found to be possible. The new hue-capturing process is discussed in terms of the strength of the light source illuminating the heat transfer surface, the effect of the orientation of the illuminating source with respect to the surface, crystal layer uniformity, and the repeatability of the process. The present method is more advantageous than the multiple filter method because of its ability to generate many isotherms simultaneously from a single-crystal image at a high resolution in a very time-efficient manner.

Camci, C.↗
NASA NTRS2001

Optical Sensors Based on Single Arm Thin Film Waveguide Interferometer

Single-arm double-mode double-order optical waveguide interferometer utilizes interference between two propagating modes of different orders. Sensing effect results from the change in propagation conditions of the modes caused by the environment. The waveguide is made as an open asymmetric slab structure containing a dye-doped polymer film onto a fused quartz substrate. It is more sensitive to the change of environment than its conventional polarimetric analog using orthogonal modes (TE and TM) of the same order. The sensor still preserves the option of operating in polarimetric regime using a variety of mode combinations such as TE(sub 0)/TM(sub 0) (conventional), TE(sub 0)/TM(sub 1), TE(sub 1)/TM(sub 0), or TE(sub 1)/TM(sub 1) but can also work in nonpolarimetric regime using combinations TE(sub 0)/TM(sub 1) or TE(sub 0)/TM(sub 1). Utilization of different mode combinations simultaneously makes the device more versatile. Application of the sensor to gas sensing is based on doping polymer film with an organic indicator dye sensitive to a particular gas. Change of optical absorption spectrum of the dye caused by the gaseous pollutant results change of the reactive index of the dye-doped polymer film that can be detected by the sensor. As an indicator dyes, we utilize Bromocresol Purple doped into polymer poly(methyl) methacrylate, which shows a reversible growth of the absorption peak neat 600 nm after exposure to wet ammonia. We have built a breadboard prototype of the sensor with He-Ne laser as a light source and with a single mode fiber input and a multimode fiber output. The prototype showed sensitivity to temperature change of the order of 2 C per one full oscillation of the signal. The sensitivity of the sensor to the presence of wet ammonia is 200 ppm per one full oscillation of the signal. The further improvements include switching to a longer wavelength laser source (750-nm semiconductor laser), substitution of poly(methyl) methacrylate with hydrophilic high-temperature polyimide, and increase the doping rate of indicator dye. All these improvements are expected to bring sensitivity to 10 ppm of ammonia per one full oscillation of signal independent on the humidity of ambient air. The proposed sensor can be used as a robust and inexpensive stand-alone instrument for continuous environment pollution monitoring.

Sarkisov, S. S.↗
NASA NTRS1998

Ducted-Fan Engine Acoustic Predictions Using a Navier-Stokes Code

A Navier-Stokes computer code is used to predict one of the ducted-fan engine acoustic modes that results from rotor-wake/stator-blade interaction. A patched sliding-zone interface is employed to pass information between the moving rotor row and the stationary stator row. The code produces averaged aerodynamic results downstream of the rotor that agree well with a widely used average-passage code. The acoustic mode of interest is generated successfully by the code and is propagated well upstream of the rotor, temporal and spatial numerical resolution are fine enough such that attenuation of the signal is small. Two acoustic codes are used to find the far-field noise. Near-field propagation is computed by using Eversman's wave envelope code, which is based on a finite-element model. Propagation to the far field is accomplished by using the Kirchhoff formula for moving surfaces with the results of the wave envelope code as input data. Comparison of measured and computed far-field noise levels show fair agreement in the range of directivity angles where the peak radiation lobes from the inlet are observed. Although only a single acoustic mode is targeted in this study, the main conclusion is a proof-of-concept: Navier Stokes codes can be used both to generate and propagate rotor-stator acoustic modes forward through an engine, where the results can be coupled to other far-field noise prediction codes.

Rumsey, C. L.↗
NASA NTRS1998

Ducted-Fan Engine Acoustic Predictions using a Navier-Stokes Code

A Navier-Stokes computer code is used to predict one of the ducted-fan engine acoustic modes that results from rotor-wake/stator-blade interaction. A patched sliding-zone interface is employed to pass information between the moving rotor row and the stationary stator row. The code produces averaged aerodynamic results downstream of the rotor that agree well with a widely used average-passage code. The acoustic mode of interest is generated successfully by the code and is propagated well upstream of the rotor; temporal and spatial numerical resolution are fine enough such that attenuation of the signal is small. Two acoustic codes are used to find the far-field noise. Near-field propagation is computed by using Eversman's wave envelope code, which is based on a finite-element model. Propagation to the far field is accomplished by using the Kirchhoff formula for moving surfaces with the results of the wave envelope code as input data. Comparison of measured and computed far-field noise levels show fair agreement in the range of directivity angles where the peak radiation lobes from the inlet are observed. Although only a single acoustic mode is targeted in this study, the main conclusion is a proof-of-concept: Navier-Stokes codes can be used both to generate and propagate rotor/stator acoustic modes forward through an engine, where the results can be coupled to other far-field noise prediction codes.

Rumsey, C. L.↗
NASA NTRS2000

Optical Sensors Based on Single on Arm Thin Film Waveguide Interferometer

Single-arm dual-mode optical waveguide interferometer utilizes interference between two modes of different order. Sensing effect results from the change in propagation conditions of the modes caused by the environment. The waveguide is made as an open asymmetric structure containing a dye-doped polymer film onto a quartz substrate. It is more sensitive to the change of environment than its conventional polarimetric analog using orthogonal modes (TE and TM) of the same order. The sensor still preserves the option of operating in polarimetric regime using a variety of mode combinations such as TE(sub 0)/TM(sub 0) (conventional) TE(sub 0)/TM(sub 1), TE(sub 1)/TM(sub 0), or TE(sub 1)/TM(sub 1) but can also work in nonpolarimetric regime using combinations TE(sub 0)/TE(sub 1) or TM(sub 0)/TM(sub 1). Utilization of different mode combinations simultaneously makes the device more versatile. Application of the sensor to gas sensing is based on doping polymer film with an organic indicator dye targeting a particular gaseous reagent. Change of the optical absorption spectrum of the dye caused by the gaseous pollutant results in change of the reactive index of the dye-doped polymer film that can be detected by the sensor. As indicator dyes we utilize Bromocresol Purple doped into polymer poly(methyl) methacrylate that is sensitive to small concentrations of ammonia. The indicator dye demonstrated an irreversible increase in optical absorption near the peak at 350 nm being exposed to 5% ammonia in pure nitrogen at 600 Torr. The dye also showed reversible growth of the absorption peak near 600 nm after exposure to a vapor of standard medical ammonia spirit (65% alcohol). We have built a breadboard prototype of the sensor with He-Ne laser as a light source and with a single mode fiber input and a multimode fiber output. The prototype showed a sensitivity to temperature change of the order of 2 C per 2pi phase shift. The sensitivity of the sensor to the presence of dTy ammonia is not less than 300 ppm per 2pi phase shift. The proposed sensor can be used as a robust stand-alone instrument for continuous environment pollution monitoring.

Sarkisov, S. S.↗