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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

An Investigation into Quantifying Micron-G Changes in a Gravitational Field of 1G

This project called for the development of an accelerometer designed to be used in conjunction with gravity shielding experiments. The device had to measure local gravitational changes on the order of a few micro-G's (micron-G) with a spatial resolution greater than one measurement per ten square centimeters. Measurements had to be made at a minimum rate of two per second. Tasks included the design, development and demonstration of a prototype. The deliverable consisted of three copies of this final report. The study resulted in the development of a Transversely Suspended Accelerometer (TSA) which met all of the technical specifications. Different generations of the device were demonstrated to NASA/MSFC personnel as they were developed. The final prototype is available for further demonstration and future use. The study draws attention to the fact that the magnetic fields required to produce gravitational shielding may result in apparent decreases in the weights of suspended objects on the order of those attributed to the effect itself. This observation reinforces the need to quantify the influences of the magnetic field on any measurement device used to study gravitational shielding. This task was accomplished for the TSA.

Gauthier, Richard R.↗
NASA NTRS1996

Effectiveness of Interaural Delays Alone as Cues During Dynamic Sound Localization

The contribution of interaural time differences (ITDs) to the localization of virtual sound sources with and without head motion was examined. Listeners estimated the apparent azimuth, elevation and distance of virtual sources presented over headphones. Stimuli (3 sec., white noise) were synthesized from minimum-phase representations of nonindividualized head-related transfer functions (HRTFs); binaural magnitude spectra were derived from the minimum phase estimates and ITDs were represented as a pure delay. During dynamic conditions, listeners were encouraged to move their heads; head position was tracked and stimuli were synthesized in real time using a Convolvotron to simulate a stationary external sound source. Two synthesis conditions were tested: (1) both interaural level differences (ILDs) and ITDs correctly correlated with source location and head motion, (2) ITDs correct, no ILDs (flat magnitude spectrum). Head movements reduced azimuth confusions primarily when interaural cues were correctly correlated, although a smaller effect was also seen for ITDs alone. Externalization was generally poor for ITD-only conditions and was enhanced by head motion only for normal HRTFs. Overall the data suggest that, while ITDs alone can provide a significant cue for azimuth, the errors most commonly associated with virtual sources are reduced by location-dependent magnitude cues.

Wenzel, Elizabeth M.↗
NASA NTRS2006

Comets, Asteroids, Meteorites, and the Origin of the Biosphere

During the past few decades, the delivery of water, organics, and prebiotic chemicals to the Biosphere of Earth during the Hadean (4.5-3.8 Ga) period of heavy bombardment by comets and asteroids has become more widely accepted. Comets are still largely regarded as frigid, pristine bodies of protosolar nebula material that are devoid of liquid water and therefore unsuitable for life. Complex organic compounds have been observed in comets and on the water-rich asteroid 1998 KY26 and near IR observations have indicated the presence of crystalline water ice and ammonia hydrate on the large Kuiper Belt object (50000) Quaoar that has resurfacing suggesting cryovolcanic outgassing. Spacecraft observations of the chemical compositions and characteristics of the nuclei of several comets (Halley, Borrelly, Wild 2, and Tempel 1) have shown that comets contain complex organic chemicals; that water is the predominant volatile; and that extremely high temperatures (approx. 350-400 K) can be reached on the surfae of the very black (albedo approx. 0.03) nuclei of comets when they approach the Sun. Impact craters and pinnacles observed on comet Wild 2 suggest a thick crust. Episodic outbursts and jets from the nuclei of several comets indicate that localized regimes of liquid water and water vapor can periodically exist beneath the comet crust. The Deep Impact mission found the temperature of the nucleus of comet Tempel 1 at 1.5 AU varied from a minimum of 280 plus or minus 8 K the 330K (57 C) on the sunlit side. In this paper it is argued that that pools and films of liquid water exist (within a wide range of temperatures) in cavities and voids just beneath the hot, black crust. The possibility of liquid water existing over a wide range of temperatures significantly enhances the possibility that comets might contain niches suitable for the growth of microbial communities and ecosystems. These regimes would be ideal for the growth of psychrophilic, mesophilic, and thermophilic photoautotrophs and chemolithotrophs such as the motile filamentous cyanobacteria (e.g., Calothrix, Oscillatoria, Phormidium, and Spirulina) that grow in geothermal springs and geysers of Earth at temperatures ranging fiom 320K to 345K and are also found growing in cold polar desert soils. The mineralized remains of morphotypes of all of these cyanobacteria have also been found in the Orgueil CI1 and the Murchison CN2 carbonaceous meteorites that may derive from cometary parent bodies. Observational results that support the hypothesis that liquid water can in active regions just beneath the surface of comets and that comets, carbonaceous meteorites, and asteroids may have played a significant role in the origin and evolution of the Biosphere and in the distribution of microbial life throughout the Solar System.

Hoover, Richard B.↗
NASA NTRS2010

Cassini/CIRS Observations of Water Vapor in Saturn's Stratosphere

The Composite Infrared Spectrometer (CIRS) on the Cassini spacecraft has obtained numerous spectra of Saturn at varying spectral and spatial resolutions since Saturn Orbit Insertion in 2001. Emission lines due to water vapor in Saturn's stratosphere were first detected using whole-disk observations from the Infrared Space Observatory [1] and subsequently confirmed by the Submillimeter Wave Astronomy Satellite [2], CIRS has detected water and the data permit the retrieval of the latitudinal variation of water on Saturn. Emission lines of H2O on Saturn are very weak in the CIRS data. Thus, large spectral averages as well as improvements in calibration are necessary to detect water vapor. long integrations at the full 0.5/cm spectral resolution were performed at targeted latitudes on Saturn. High emission angles were chosen to enhance stratospheric emission. Over the course of the prime and extended mission a set of observations has been built up spaced roughly every 10 degrees of latitude. Stratospheric temperatures in the 0.5 - 5.0 mbar range were obtained by inverting spectra of CH4 in the v'4 band centered at 1501/cm. The origin of water vapor is believed to be from the ablation of micrometeorites containing eater ice, followed by photochemistry. This external source of oxygen originates either from the Saturn system (from the rings or perhaps from Enceladus) or from the interplanetary medium. Connerney [3] proposed a mechanism to transport water from the inner edge of the B-ring along magnetic field lines to specific latitudes (50N and 44S) on Saturn. Prange et al [4] interpreted a minimum in the abundance of acetylene from ultraviolet spectra gear 41S on Saturn as possibly due to an enhanced influx of water. We will be able to test the "ring rain" mechanism by searching, for localized water vapor enhancement at mid-latitudes. Our results may be used to constrain photochemical models of Saturn's stratosphere [5].

Bjoraker, Gordon↗
NASA NTRS1981

Auroral kilometric radiation source region observations from ISIS 1

The ISIS 1 observations of the high-frequency portion of the auroral kilometric radiation (AKR) spectrum are considered, that is, from the minimum frequency encountered for the extraordinary mode cut-off (approximately 450 kHz) to the upper frequency cut-off (approximately 800 kHz). AKR is found to be generated in the extraordinary mode just above the local cutoff frequency and to emanate in a direction that is nearly perpendicular to the magnetic field. It occurs within local depletions of electron density, where the ratio of plasma frequency to cyclotron frequency is below 0.2. The density depletion is restricted to altitudes above approximately 2,000 km, and the upper AKR frequency limit corresponds to the extraordinary cutoff frequency at this altitude.

Benson, R. F.↗
NASA NTRS1992

Application of Face-Gear Drives in Helicopter Transmissions

The use of face gears in helicopter transmissions was explored. A light-weight, split torque transmission design utilizing face gears was described. Face-gear design and geometry were investigated. Topics included tooth generation, limiting inner and outer radii, tooth contact analysis, contact ratio, gear eccentricity, and structural stiffness. Design charts were developed to determine minimum and maximum face-gear inner and outer radii. Analytical study of transmission error showed face-gear drives were relatively insensitive to gear misalignment, but tooth contact was affected by misalignment. A method of localizing bearing contact to compensate for misalignment was explored. The proper choice of shaft support stiffness enabled good load sharing in the split torque transmission design. Face-gear experimental studies were also included and the feasibility of face gears in high-speed, high-load applications such as helicopter transmissions was demonstrated.

Litvin, F. L.↗
NASA NTRS2002

Changes in Earth 360 380 nm Reflectivity: 1980 2000

The Total Ozone Mapping Spectrometer (TOMS) reflectivity time series 1980 to 1992 and 1997 to 2000 have been combined to estimate change that have occurred over a 21 year period. The relative calibration of the two TOMS (Nimbus-7, N7 and Earth-Probe, EP) has been adjusted using the measured minimum reflectivity over mid-latitude ocean and land locations (50o). The result is that the N7 reflectivity has been decreased by 0.02 to match the better-calibrated Earth-Probe/TOMS. Most of the local trend features seen in the N7 time series (1980 to 1992) have been continued in the combined time series, but the overall zonal average and global trends have changed. The correlation of cloud cover with solar activity (measured by the 10.7 cm solar radiation) that was present during the Nimbus-7 period (1980 to 1992) is no longer evident for the period 1980 to 2000. The UV reflectivity data are compared with changes in the Advanced Very High Resolution Radiometer (AVHRR) Outgoing Long-wavelength Radiation (OLR) and show an expected anti-correlation with cloud-cover changes over the same period for many, but not all, features. The key results include a continuing decrease in cloud cover over Europe and North America and an increase in reflectivity near climatology should be reduced by 0.02. The TOMS reflectivity time series 1980 to 1992 and 1997 to 2000 have been Antarctica. This also means that the previously published N7 UV surface reflectivity.

Herman, J. R.↗
NASA NTRS2007

Optimal Electrodynamic Tether Phasing Maneuvers

We study the minimum-time orbit phasing maneuver problem for a constant-current electrodynamic tether (EDT). The EDT is assumed to be a point mass and the electromagnetic forces acting on the tether are always perpendicular to the local magnetic field. After deriving and non-dimensionalizing the equations of motion, the only input parameters become current and the phase angle. Solution examples, including initial Lagrange costates, time of flight, thrust plots, and thrust angle profiles, are given for a wide range of current magnitudes and phase angles. The two-dimensional cases presented use a non-tilted magnetic dipole model, and the solutions are compared to existing literature. We are able to compare similar trajectories for a constant thrust phasing maneuver and we find that the time of flight is longer for the constant thrust case with similar initial thrust values and phase angles. Full three-dimensional solutions, which use a titled magnetic dipole model, are also analyzed for orbits with small inclinations.

Bitzer, Matthew S.↗
NASA NTRS2011

Comparisons of Supergranule Characteristics During the Solar Minima of Cycles 22/23 and 23/24

Supergranulation is a component of solar convection that manifests itself on the photosphere as a cellular network of around 35 Mm across, with a turnover lifetime of 1 2 days. It is strongly linked to the structure of the magnetic field. The horizontal, divergent flows within supergranule cells carry local field lines to the cell boundaries, while the rotational properties of supergranule upflows may contribute to the restoration of the poloidal field as part of the dynamo mechanism, which controls the solar cycle. The solar minimum at the transition from cycle 23 to 24 was notable for its low level of activity and its extended length. It is of interest to study whether the convective phenomena that influence the solar magnetic field during this time differed in character from periods of previous minima. This study investigates three characteristics (velocity components, sizes and lifetimes) of solar supergranulation. Comparisons of these characteristics are made between the minima of cycles 22/23 and 23/24 using MDI Doppler data from 1996 and 2008, respectively. It is found that whereas the lifetimes are equal during both epochs (around 18 h), the sizes are larger in 1996 (35.9 plus or minus 0.3 Mm) than in 2008 (35.0 plus or minus 0.3 Mm), while the dominant horizontal velocity flows are weaker (139 plus or minus m per second in 1996; 141 plus or minus 1 m per second in 2008). Although numerical differences are seen, they are not conclusive proof of the most recent minimum being inherently unusual.

Williams, Peter E.↗
NASA NTRS2015

The 27-Day Rotational Variations in Total Solar Irradiance Observations: from SORCE-TIM, ACRIMSAT-ACRIM III, and SOHO-VIRGO

During the last decade, observations from SORCE (Solar Radiation and Climate Experiment)/TIM (Total Irradiance Monitor), ACRIMSAT (Active Cavity Radiometer Irradiance Monitor Satellite)/ACRIM III, and SOHO (Solar and Heliospheric Observatory)VIRGO (Variability of IRradiance and Gravity Oscillations Sun PhotoMeter) provided the Total Solar Irradiance (TSI) measurements with unprecedented accuracy and stability to determine the amount of solar irradiance reaching the top of the atmosphere and how solar irradiance varies in different time scales. These three independent measurements are analyzed using the EEMD (Ensemble Empirical Mode Decomposition) method to characterize the phase and amplitude of 27-day solar rotational variation in TSI. The mode decomposition clearly identifies a 27-day solar rotational signature in TSI measurements. The rotational variations of TSI from the three independent observations are generally consistent with each other, despite different mean TSI values. During the declining phase of solar cycle 23, the amplitude of TSI 27-day variations is as high as 0.8 watts per square meter (approximately 0.05 percent), while during the rising phase of solar cycle 24, the amplitude is up to 0.4 watts per square meter (approximately 0.04 percent). During the minimum phase (2008-2009), the amplitude of the rotational mode is only 0.1 watts per square meter. The correlation of this rotational mode between TIM and ACRIM III is approximately 0.92 and the slope of the local peak values is approximately 0.98. The correlation between TIM and VIRGO is approximately 0.96 and the slope of the local peak values isapproximately 0.98, very similar to the slope with ACRIM III.

ACRIM III↗
NASA NTRS1979

The 63 micron radiation field in the earth's thermosphere and its influence on the atomic hydrogen temperature

The thermal escape of hydrogen from the earth's atmosphere is strongly affected by its temperature at the exobase. It has been suggested recently that the hydrogen temperature might be significantly lower than the thermospheric temperature as a result of a collisional exchange of energy with atomic oxygen. The tendency is to cool the hydrogen since the energy of the excited 3P1 level of oxygen can be lost from the atmosphere via magnetic dipole emission of the micron line (3P2-3P1). A detailed calculation of the net cooling effect as a function of altitude throughout the thermosphere is presented. The calculations have been performed for both day and night conditions and for periods of maximum and minimum solar activity conditions. It is found that its effect on Delta T/T varies from a very small value to a maximum of about 3%. The theoretical framework for describing deviations of the 63 micron emission from local thermodynamic equilibrium is given and it is shown that these effects can cause the emission to be reduced by as much as 40% near 500 km.

Durrance, S. T.↗
NASA NTRS1982

Multilevel optimum design of structures with fiber-composite stiffened-panel components

The multilevel approach to minimum weight structural design is extended to wing box structures with fiber-composite stiffened-panel components. Strength, deflection, and panel buckling constraints are treated at the system level with equivalent-thickness-type design variables. Local buckling and panel buckling constraints are guarded against at the component level, employing detailed component dimensions as design variables. A key feature of the method is selection of change in stiffness as the component level objective function to be minimized. Numerical results are given for wing box structures with sandwich and hat-stiffened fiber-composite panels.

Schmit, L. A.↗
NASA NTRS1993

F region plasma drifts over Arecibo - Solar cycle, seasonal, and magnetic activity effects

Characteristics of low-latitude F region plasma drifts are determined on the basis of Arecibo incoherent scatter measurements from 1981 to 1990. The measurements show large day-to-day variability even during magnetically quiet periods. The average poleward/perpendicular plasma drifts do not change significantly with season and solar cycle except in the midnight-morning sector. The zonal drifts show clear solar cycle and seasonal effects. The plasma drifts along the magnetic field lines exhibit large altitudinal and seasonal variations, particularly near solar minimum, and are generally anticorrelated with the perpendicular/north drifts. The drift patterns observed by the Arecibo and the middle and upper atmosphere radars have significantly different seasonal dependences. This is explained by electrodynamic effects in the corresponding local and conjugate ionospheres.

Fejer, B. G.↗
NASA NTRS2002

Changes in Earth 360 to 380 nm Reflectivity: 1980 to 2000

The TOMS reflectivity time series 1980 to 1992 and 1997 to 2000 have been combined to estimate change that have occurred over a 21 year period. The relative calibration of the two TOMS (Nimbus-7, N7 and Earth-Probe, EP) has been adjusted using the measured minimum reflectivity over mid-latitude ocean and land locations (50 deg.). The result is that the N7 reflectivity has been decreased by 0.02 to match the better-calibrated Earth-Probe/TOMS. Most of the local trend features seen in the N7 time series (1980 to 1992) have been continued in the combined time series, but the overall zonal average and global trends have changed. The correlation of cloud cover with solar activity (measured by the 10.7 cm solar radiation) that was present during the Nimbus-7 period (1980 to 1992) is no longer evident for the period 1980 to 2000. The UV reflectivity data are compared with changes in the AVHRR outgoing long-wavelength radiation (OLR) and show an expected anti-correlation with cloud-cover changes over the same period for many, but not all, features. The key results include a continuing decrease in cloud cover over Europe and North America and an increase in reflectivity near Antarctica. This also means that the previously published N7 UV surface reflectivity climatology should be reduced by 0.02.

Herman, J. R.↗
NASA NTRS2008

Using Wind and Temperature Fields to Study Dehydration Mechanisms in the Tropical Tropopause Layer

The tropics are the main region for troposphere-to-stratosphere transport (TST) of air. One of the dominant mechanisms that control tropical TST of water vapor is freeze-drying by the cold tropical tropopause. This mechanism is supported by evidence from satellite observations of the "tape recorder", where seasonal changes in stratospheric water vapor are in phase with seasonal changes in tropopause temperatures in the tropics. Over the last few years, however, the concept of the tropical tropopause has evolved from a single material surface to a layer called the Tropical Tropopause Layer (TTL). A recent hypothesis on dehydration mechanisms suggests that dehydration and entry point into the stratosphere are not always co-located (Holton and Gettelman, 2001). Instead, dehydration can occur during horizontal advection through Lagrangian 'cold pools', or coldest regions along a parcel's trajectory, as air ascends within the TTL while the entry point into the stratosphere occurs at a different geographical location. In this study, we investigate the impact that these Lagrangian cold pools have on TTL moisture. For this purpose, we use in situ measurements of TTL water vapor obtained aboard NASA's WB-57 aircraft over the Eastern Tropical Pacific, and we compare these measurements to minimum saturation water vapor mixing ratios obtained from three-dimensional backward trajectory calculations. Aircraft measurements show frequent unsaturated conditions, which suggest that the entry value of stratospheric water vapor in this region was not set by local saturation conditions. Trajectory calculations, driven by both ECMWF operational analysis and reanalysis winds and temperature fields, are used to explore the impact (e.g., geographical location, timing, dehydration magnitude) of the Lagrangian cold pools intercepted by the parcels sampled by the aircraft. We find noteworthy differences in the location of the Lagrangian cold pools using the two ECMWF data sets, namely influence of the Western Tropical Pacific region when using operational analysis fields versus influence of the Eastern Tropical Pacific and South America regions when using reanalysis fields. These results have a significant impact on our scientific conclusions on dehydration mechanisms affecting the air sampled by the aircraft, given that these regions have different thermodynamic and convective properties.

Pittman, Jasna↗
NASA NTRS2002

GOES Cloud Detection at the Global Hydrology and Climate Center

The bi-spectral threshold (BTH) for cloud detection and height assignment is now operational at NASA's Global Hydrology and Climate Center (GHCC). This new approach is similar in principle to the bi-spectral spatial coherence (BSC) method with improvements made to produce a more robust cloud-filtering algorithm for nighttime cloud detection and subsequent 24-hour operational cloud top pressure assignment. The method capitalizes on cloud and surface emissivity differences from the GOES 3.9 and 10.7-micrometer channels to distinguish cloudy from clear pixels. Separate threshold values are determined for day and nighttime detection, and applied to a 20-day minimum composite difference image to better filter background effects and enhance differences in cloud properties. A cloud top pressure is assigned to each cloudy pixel by referencing the 10.7-micrometer channel temperature to a thermodynamic profile from a locally -run regional forecast model. This paper and supplemental poster will present an objective validation of nighttime cloud detection by the BTH approach in comparison with previous methods. The cloud top pressure will be evaluated by comparing to the NESDIS operational CO2 slicing approach.

Laws, Kevin↗
NASA NTRS2003

Vacancy Mediated Mechanism of Nitrogen Substitution in Carbon Nanotubes

Nitrogen substitution reaction in a graphene sheet and carbon nanotubes of different diameter are investigated using the generalized tight-binding molecular dynamics method. The formation of a vacancy in curved graphene sheet or a carbon nanotube is found to cause a curvature dependent local reconstruction of the surface. Our simulations and analysis show that vacancy mediated N substitution (rather than N chemisorption) is favored on the surface of nanotubes with diameter larger than 8 nm. This predicted value of the critical minimum diameter for N incorporation is confirmed by experimental results presented.

Srivastava, Deepak↗
NASA NTRS1987

The minimum bandwidths of auroral kilometric radiation

The bandwidths of the discrete spectral components of the auroral kilometric radiation can sometimes be as narrow as 5 Hz. Since this would imply an apparent source thickness of substantially less than the wavelength, it is inconsistent with the previous explanation for such discrete components based simply upon vertical localization of a cyclotron source. Instead, such narrow bandwidths can only be explained by radio lasing.

Baumback, M. M.↗