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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Test Analysis Correlation of the Single Stringer Bending Tests for the Space Shuttle ET-137 Intertank Stringer Crack Investigation

On November 5, 2010, Space Shuttle mission STS-133 was scrubbed due to a hydrogen leak at the Ground Umbilical Carrier Plate (GUCP). After the scrub, a crack in the foam thermal protection system (TPS) was observed on the External Tank (ET) near the interface between the liquid oxygen (LOX) tank and the Intertank. When the damaged foam was removed, two 9-in. long cracks were found on the feet of Intertank stringer S7-2, and the stringer failure was the cause of the TPS crack. An investigation was conducted to determine the root cause of the cracks, establish a remedy/repair for the stringers, and provide flight rationale for the damaged tank, ET-137. The Space Transportation System (STS) Super Lightweight ET (SLWT) is comprised of two propellant tanks (an aft liquid hydrogen (LH2) tank and a forward LOX tank) and an Intertank. The Intertank serves as the structural connection between the two propellant tanks and also functions to receive and distribute all thrust loads from the solid rocket boosters . The Intertank is a stiffened cylinder structure consisting of eight mechanically joined panels (two integrally-stiffened, machined thrust panels to react the booster loads and six stringer-stiffened skin panels). There are one main ring frame, four intermediate ring frames, and forward and aft flange chords that mate to the respective propellant tanks.. The skin/stringer panels utilize external hat-section stringers that are mechanically attached with rivets along most of their length and with specialty fasteners, such as GP Lockbolts and Hi-Loks, at the forward and aft ends where the stringers attach to the flange chords. During the STS-133 Intertank stringer crack investigation, cracks were found on a total of five stringers. All of the cracks were at the LOX end, in the feet of the stringers, and near the forward fasteners (GP Lockbolts). Video of tanking for the November 5 launch attempt was used to determine that the TPS failure, and thus the stringer failure, occurred as the LOX liquid level crossed the LOX tank / Intertank interface ring frame. Hence, cryogenically-induced displacements were suspected as a contributing cause of the stringer cracks. To study the behavior of Intertank stringers subjected to similar displacements, static load tests of individual stringers, colloquially known as "single stringer bending tests" were performed. Approximately thirty stringers were tested, many of which were cut from the partially completed Intertank for what would have been ET-139. In addition to the tests, finite element (FE) analyses of the test configuration were also performed. In this paper, the FE analyses and test-analysis correlation for stringer test S6-8 are presented. Stringer S6-8 is a "short chord" configuration with no doubler panels.

Phillips, Dawn R.↗
NASA NTRS2021

Variabilities in Pm2.5 and Black Carbon Surface Concentrations Reproduced by Aerosol Optical Properties Estimated by In-Situ Data, Ground Based Remote Sensing and Modeling

Because of the increased temporal and spatial resolutions of the sensors onboard recently launched satellites, satellite-based surface aerosol concentration, which is usually estimated from the aerosol optical depth (AOD), is expected to become a strategic tool for air quality studies in the future. By further exploring the relationships of aerosol concentrations and their optical properties using ground observations, the accuracies of these products can be improved. Here, we analyzed collocated observations of surface mass concentrations of fine particulate matter (PM2.5) and black carbon (BC), as well as columnar aerosol optical properties from a sky radiometer and aerosol extinction profiles obtained by multi-axis differential optical absorption spectroscopy (MAX-DOAS), during the 2019–2020 period. We focused the analyses on a daily scale, emphasizing the role of the ultraviolet (UV) spectral region. Generally, the correlation between the AOD of the fine fraction (i.e., fAOD) and the PM2.5 surface concentration was moderately strong, regardless of considerations of boundary layer humidity and altitude. In contrast, the fAOD of the partial column below 1 km, which was obtained by combining sky radiometer and MAX-DOAS retrievals, better reproduced the variability of the PM2.5 and resulted in a linear relationship. In the same manner, we demonstrated that the absorption AOD of the fine fraction (fAAOD) of the partial column was related to the variability of the BC concentration. Analogous analyses based on aerosol products from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) confirmed these findings and highlighted the importance of the shape of the aerosol profile. Overall, our results indicated a remarkable consistency among the retrieved datasets, and between the datasets and MERRA-2 products. These results confirmed the well-known sensitivity to aerosol absorption in the UV spectral region; they also highlighted the efficacy of combined MAX-DOAS and sky radiometer observations.

Alessandro Damiani↗
NASA NTRS1992

Multiple symbol partially coherent detection of MPSK

It is shown that by using the known (or estimated) value of carrier tracking loop signal to noise ratio (SNR) in the decision metric, it is possible to improve the error probability performance of a partially coherent multiple phase-shift-keying (MPSK) system relative to that corresponding to the commonly used ideal coherent decision rule. Using a maximum-likeihood approach, an optimum decision metric is derived and shown to take the form of a weighted sum of the ideal coherent decision metric (i.e., correlation) and the noncoherent decision metric which is optimum for differential detection of MPSK. The performance of a receiver based on this optimum decision rule is derived and shown to provide continued improvement with increasing length of observation interval (data symbol sequence length). Unfortunately, increasing the observation length does not eliminate the error floor associated with the finite loop SNR. Nevertheless, in the limit of infinite observation length, the average error probability performance approaches the algebraic sum of the error floor and the performance of ideal coherent detection, i.e., at any error probability above the error floor, there is no degradation due to the partial coherence. It is shown that this limiting behavior is virtually achievable with practical size observation lengths. Furthermore, the performance is quite insensitive to mismatch between the estimate of loop SNR (e.g., obtained from measurement) fed to the decision metric and its true value. These results may be of use in low-cost Earth-orbiting or deep-space missions employing coded modulations.

Simon, M. K.↗
NASA NTRS1981

Venus gravity - A high-resolution map

The Doppler data from the radio tracking of the Pioneer Venus Orbiter (PVO) have been used in a two-stage analysis to develop a high-resolution map of the gravitational potential of Venus, represented by a central mass and a surface mass density. The two-stage procedure invokes a Kalman filter-smoother to determine the orbit of the spacecraft, and a stabilized linear inverter to estimate the surface mass density. The resultant gravity map is highly correlated with the topographic map derived from the PVO radar altimeter data. However, the magnitudes of the gravity variations are smaller than would be expected if the topography were uncompensated, indicating that at least partial compensation has taken place.

Reasenberg, R. D.↗
NASA NTRS1990

Sparse distributed memory overview

The Sparse Distributed Memory (SDM) project is investigating the theory and applications of massively parallel computing architecture, called sparse distributed memory, that will support the storage and retrieval of sensory and motor patterns characteristic of autonomous systems. The immediate objectives of the project are centered in studies of the memory itself and in the use of the memory to solve problems in speech, vision, and robotics. Investigation of methods for encoding sensory data is an important part of the research. Examples of NASA missions that may benefit from this work are Space Station, planetary rovers, and solar exploration. Sparse distributed memory offers promising technology for systems that must learn through experience and be capable of adapting to new circumstances, and for operating any large complex system requiring automatic monitoring and control. Sparse distributed memory is a massively parallel architecture motivated by efforts to understand how the human brain works. Sparse distributed memory is an associative memory, able to retrieve information from cues that only partially match patterns stored in the memory. It is able to store long temporal sequences derived from the behavior of a complex system, such as progressive records of the system's sensory data and correlated records of the system's motor controls.

Raugh, Mike↗
NASA NTRS2003

Kernel PLS-SVC for Linear and Nonlinear Discrimination

A new methodology for discrimination is proposed. This is based on kernel orthonormalized partial least squares (PLS) dimensionality reduction of the original data space followed by support vector machines for classification. Close connection of orthonormalized PLS and Fisher's approach to linear discrimination or equivalently with canonical correlation analysis is described. This gives preference to use orthonormalized PLS over principal component analysis. Good behavior of the proposed method is demonstrated on 13 different benchmark data sets and on the real world problem of the classification finger movement periods versus non-movement periods based on electroencephalogram.

Rosipal, Roman↗
NASA NTRS1981

Nitridation of silicon

Silicon powders with three levels of impurities, principally Fe, were sintered in He or H2. Non-densifying mechanisms of material transport were dominant in all cases. High purity Si showed coarsening in He while particle growth was suppressed in H2. Lower purity powder coarsened in both He and H2. The same three Si powders and Si /111/ single crystal wafers were nitrided in both N2 and N2/H2 atmospheres. Hydrogen increased the degree of nitridation of all three powders and the alpha/beta ratio of the lower purity powder. Some Si3N4 whiskers and open channels through the surface nitride layer were observed in the presence of Fe, correlating with the nitridation-enhancing effects of Fe. Thermodynamic calculations showed that when SiO2 is present on the Si, addition of H2 to the nitriding atmosphere decreases the amount of SiO2 and increases the partial pressure of Si-containing vapor species, that is, Si and SiO. Large amounts of NH3 and SiH4 were also predicted to form.

Shaw, N. J.↗
NASA NTRS1995

Changes in chemical and optical properties of thin film metal mirrors on LDEF

Thin films of the metals Cu, Ni, Pt, Au, Sn, Mo, and W deposited on fused silica flats were exposed at ambient temperature on the leading and trailing faces of the LDEF. Reflectances of these films were measured from 250 to 2500 nm and compared with controls. The exposed films were subjected to the LDEF external environment including atomic oxygen, molecular contamination, and solar ultraviolet. Major changes in optical and infrared reflectance were seen for Cu, Mo, Ni, and W films on the leading face of LDEF and are attributed to partial conversion of metal to metal oxide. Smaller changes in optical properties are seen on all films and are probably caused by thin contaminant films deposited on top of the metal. The optical measurements are correlated with film thickness measurements, x-ray photoelectron spectroscopy, optical calculations, and, in the case of Cu, with x-ray diffraction measurements. In a few cases, comparisons with results from a similar UAH experiment on STS-8 have been drawn.

Peters, Palmer N.↗
NASA NTRS2021

Inter-comparison of snow depth over Arctic sea ice from reanalysis reconstructions and satellite retrieval

In this study, we compare eight recently developed snow depth products over Arctic sea ice, which use satellite observations, modeling, or a combination of satellite and modeling approaches. These products are further compared against various ground-truth observations, including those from ice mass balance observations and airborne measurements. Large mean snow depth discrepancies are observed over the Atlantic and Canadian Arctic sectors. The differences between climatology and the snow products early in winter could be in part a result of the delaying in Arctic ice formation that reduces early snow accumulation, leading to shallower snowpacks at the start of the freeze-up season. These differences persist through spring despite overall more winter snow accumulation in the reanalysis-based products than in the climatologies. Among the products evaluated, the University of Washington (UW) snow depth product produces the deepest spring (March–April) snowpacks, while the snow product from the Danish Meteorological Institute (DMI) provides the shallowest spring snow depths. Most snow products show significant correlation with snow depths retrieved from Operational IceBridge (OIB) while correlations are quite low against buoy measurements, with no correlation and very low variability from University of Bremen and DMI products. Inconsistencies in reconstructed snow depth among the products, as well as differences between these products and in situ and airborne observations, can be partially attributed to differences in effective footprint and spatial–temporal coverage, as well as insufficient observations for validation/bias adjustments. Our results highlight the need for more targeted Arctic surveys over different spatial and temporal scales to allow for a more systematic comparison and fusion of airborne, in situ and remote sensing observations.

Lu Zhou↗
NASA NTRS1982

Infrared spectra of protostars - Composition of the dust shells

Nearly complete 2 to 13 micron spectra are presented for 13 compact infrared sources associated with molecular clouds, along with partial spectra of six additional objects. The spectra are found to resemble blackbodies with superposed absorption features from 2.8 to 3.5 microns, at 6.0 and 6.8 microns, and in the silicate band centered near 9.7 microns. Correlations among the features are investigated in an attempt to confirm possible identifications. A good correlation between the deepest part of the absorption at 3.1 microns, its long wavelength wing, and the 6.0 micron features suggests that all may derive from large amorphous water ice particles. The relatively poor correlation between the 3.4 and 6.8 micron optical depths adds no evidence in support of the suggestion that these bands may be due to CH bonds

Willner, S. P.↗
NASA NTRS1984

Interpretation of radar returns from the mesosphere, part 2.3A

The study of VHF radar signals from the mesosphere has shown that neutral atmosphere turbulence plays a central role in generating the refractive index irregularities that backscatter the radio waves. It follows that an increase in the turbulent energy dissipation rate will result in a decrease in signal correlation time and an increase in scattered signal power. Thus, in turbulence-generated radar echoes a negative correlation between echo power and signal correlation time (P/C) is expected. P/C also changes as a function of altitude, i.e., it is negative in the upper mesosphere but largely positive in the lower, with the latter thought to be a manifestation of partial reflection from stratified layers of refractive index gradient. Partial reflection would also explain the vertical aspect sensitivity of the scattered signal in the lower mesosphere.

Royrvik, O.↗
NASA NTRS2014

Liquefied Bleed for Stability and Efficiency of High Speed Inlets

A mission analysis code was developed to perform a trade study on the effectiveness of liquefying bleed for the inlet of the first stage of a TSTO vehicle. By liquefying bleed, the vehicle weight (TOGW) could be reduced by 7 to 23%. Numerous simplifying assumptions were made and lessons were learned. Increased accuracy in future analyses can be achieved by: Including a higher fidelity model to capture the effect of rescaling (variable vehicle TOGW). Refining specific thrust and impulse models ( T m a and Isp) to preserve fuel-to-air ratio. Implementing LH2 for T m a and Isp. Correlating baseline design to other mission analyses and correcting vehicle design elements. Implementing angle-of-attack effects on inlet characteristics. Refining aerodynamic performance (to improve L/D ratio at higher Mach numbers). Examining the benefit with partial cooling or densification of the bleed air stream. Incorporating higher fidelity weight estimates for the liquefied bleed system (heat exchange and liquid storage versus bleed duct weights) could be added when more fully developed. Adding trim drag or 6-degree-of-freedom trajectory analysis for higher fidelity. Investigating vehicle optimization for each of the bleed configurations.

Saunders, J. David↗
NASA NTRSDate not supplied

Developing Mass Spectrometry for Water Quantitation and Volatiles Analysis from In-Situ Regolith

With a revived focus to create a sustainable hu-man presence on the moon, and in preparation for future Mars exploration, it is imperative that all resources are utilized to their fullest potential [1]. In-Situ Resource Utilization (ISRU) will be critical for future mission success as it would enable in-dependent operation of missions while reducing the dependence on the complex supply chain created between the Earth, the moon and Mars. One of the most critical resources that has been identified for ISRU on the lunar surface is water [2]. Water is a versatile resource that can be used in various space operations, such as ra-diation shielding and conversion to oxygen (O2) for propellant [3,4]. One of the most water rich resources is thought to be within the regolith lo-cated in the permanently shadowed regions (PSR) of the Moon; several upcoming missions, such as PRIME-1 and VIPER, are already sched-uled to confirm this hypothesis [5,6]. However, there are currently no missions planned to quanti-fy the abudance of water at these regions. The quantity of water contained in the ice will inform and help the development of future ISRU plants and operation. Water and other volatile gases can be detect-ed upon controlled heating of icy lunar regolith for an accurate quantification of water. This method is similar to thermogravimetric analysis, which was used to analyze Apollo lunar regolith sam-ples. However, losses via sublimation/evaporation or contamination may have occurred with the samples due to the transit and exposure to the terrestrial environment. Furthermore, water would not be expected for these samples since they were not collected from a PSR. Thus, for more accurate results, icy lunar regolith should be ana-lyzed in situ to provide the most representative composition of both water and other volatile gas-es. The Light Water Analysis and Volatile Extract (LightWAVE) project aims to address this knowledge gap. A system has been developed to collect, heat and analyze evolved gases from lu-nar regolith on the lunar surface. The gases will be analyzed by a modified commercial off the shelf (COTS) residual gas analyzer (RGA) quad-rupole mass spectrometer. Evolved gases from heated regolith samples can be identified by the observed mass-to-charge (m/z) ratios, and the peak intensities correlate to the abundances of the observed gases for quantitation. Therefore, our group is developing a calibration methodology utilizing a COTS RGA to quantitate water from in-situ regolith samples on the lunar surface. The partial pressure of water and ideal gas law will be used to quantify the total water evolved from a regolith sample. Here we present our methodol-ogy for the design and calibration for water quan-titation using a COTS RGA.

Nilab Azim↗
NASA NTRS2001

Highly Siderophile Element Abundances in Martian Meteorites

Critical evaluation of new and literature data for highly siderophile elements (HSE) in Martian (SNC) meteorites allows several first order conclusions to be drawn. (i) Re concentrations in SNC meteorites are nearly constant (within a factor of two) and do not correlate with rock type. Exceptions to this rule are Chassigny and Dar al Gani (DaG) 476, both of which are inferred to have experienced terrestrial Re contamination. (ii) Fractionations between Rh and Pd are small. Excluding Shergotty, the Rh/Pd ratio of the SNC suite is 0.22\pm0.05. (iii) Os and Ir contents vary by about four orders of magnitude; and positive correlations with MgO, Cr, and Ni suggest that these variations are not controlled by sulfide fractionation. A possible exception is the orthopyroxenite ALH84001, whose HSE's (including Ni, which is compatible in opx) are very low. (iv) Zagami, Shergotty, and Nakhla have nearly identical HSE signatures. Shergotty and Zagami have experienced assimilation-fractional crystallization (AFC) and have "crustal" Sr and Nd isotopic signatures. Conversely, the Nakhla parent was a small degree partial melt of a depleted mantle that interacted little with the Martian crust. These observations suggest that "evolved" HSE signatures can be produced by either fractional crystallization or small degrees of partial melting. (v) Chassigny and other mafic SNC's have HSE signatures that are very distinct from those of Nakhla-Zagami-Shergotty. The HSE elemental ratios of mafic SNC's approach chondritic, implying that the Martian mantle has nearly chondritic relative abundances of the HSE's. (vi) This chondritic HSE signature is observed in SNC's of various ages, suggesting that this is an ancient feature that has not evolved over time. (vii) No correlation is observed between HSE's and signatures of crustal contamination (e.g., Sr isotopes), indicating that the HSE signatures of the SNC suite are not derived from the crust. (vii) The Ru/Pd for the SNC suite ratio is about 0.5 chondritic. We attribute this depletion of Ru to the presence of spinel in the SNC source regions. (viii) Assignment of this depletion of Ru to spinel seems to also imply that spinel is not the cause of Os and Ir fractionations, requiring some other mafic phase to account for the observed variations. -----.

Jones, J. H.↗
NASA NTRS1987

Copper and nickel partitioning in iron meteorites

Trace element analyses using proton induced X-ray emission and synchrotron X-ray fluorescence have been made on metal and troilite from nine iron meteorites representing five geochemical groups. Nickel and copper distribution coefficients D (troilite/metal) vary by factors of 600 and 20, respectively, correlate positively with kamacite bandwidth and correlate negatively with bulk nickel content. Meteorites with bulk Ni of less than 10 percent have Cu-enriched troilite while those with Ni greater than 10 percent have Cu-depleted troilite. Since magmatic evolution and partial melting will produce Cu-enriched troilite only, the observation of Cu-depleted troilite in Ni-rich meteorites is evidence for subsolidus reequilibration, a process which reduces D(Cu) by transfer of Cu to exsolving metal. Elemental redistribution may have played an important role in establishing the present chemical trends in iron meteorites.

Sutton, S. R.↗
NASA NTRS2017

Measuring N2 Pressure Using Cyanobacteria Discipline: Geomicrobiology

The evolution of Earth's atmosphere has been governed by biological evolution. Dinitrogen (N2) has been a major constituent of Earth's atmosphere throughout the planet's history, yet only a few constraints exist for the partial pressure of N2 (pN2). In this study we evaluate two new potential proxies for pN2: the physical spacing between heterocysts and the isotopic signature of nitrogen fixation in filamentous cyanobacteria. Heterocyst-forming filamentous cyanobacteria are some of the oldest photosynthetic microorganisms on Earth, and debated fossilized specimens have been found in sedimentary rocks as old as 2 Ga. These organisms overcome nitrogen limitation in their aqueous environment through cellular differentiation along their filaments. The specialized cells that develop, known as heterocysts, fix the nitrogen and laterally distribute it to neighboring cells along the filaments. Because the concentration of the dissolved N2 available to the filaments correlates directly with pN2, any preservable physiological response of the organism to the changed N2 availability constitutes a potential proxy for pN2. In the laboratory, we have examined how pN2 is reflected in the heterocyst spacing pattern and in the isotopic signature of nitrogen fixation by subjecting the representative species Anabaena cylindrica and Anabaena variabilis to different N2 partial pressures during growth at constant temperature and lighting (in media free of combined nitrogen). We show experimentally that the distance between heterocysts and the nitrogen isotope fractionation measured in bulk biomass reflect the pN2 experienced by Anabaena cylindrica. Current work is investigating these responses in Anabaena variabilis. When heterocystous cyanobacteria fossilize, these morphological and isotopic signatures should preserve information about pN2 at that time. Application of this relationship to the rock record may provide a paleoproxy to complement the two existing geobarometers.

nitrogen↗
NASA NTRSDate not supplied

Thermal, Structural, and Rotordynamics Refinements to the Superconducting Rotor of A 1.4 Mw Partially Superconducting Machine for Electrified Aircraft

NASA is developing the high efficiency megawatt motor (HEMM), a 1.4 MW partially superconducting machine, to ad-dress the need for highly efficient, lightweight, MW-class ma-chines to support aviation sustainability efforts. This paper presents progress on the thermal, structural, and rotordynamics aspects of HEMM’s superconducting rotor. Emissivity measurements of gold coated cobalt iron and titanium parts are presented and then used to correlate a thermal model of the rotor to existing data from a thermo-electrical test of the full-scale rotor. Lessons learned from the correlated model are presented, including a rank ordering of the contributors to the temperature of the superconducting coils. An updated structural design of the HEMM rotor is presented and compared to the prior design. Finite element analysis demonstrates that the updated design improves stress margins while reducing magnetic flux leakage and retaining thermal performance. The key conclusions of the rotordynamics design are presented.

electrified aircraft propulsion↗
NASA NTRS1982

Analytical and experimental evaluations of Space Shuttle TPS tile vibration response

Analytical studies and laboratory experiments have been performed to evaluate the vibration response of the Space Shuttle Thermal Protection System (TPS) tiles due to the intense rocket generated acoustic noise during lift-off. The TPS tiles are mounted over the exterior of the Space Shuttle Orbiter structure through Strain Isolation Pads (SIP) which protect the tiles from thermal induced shear loads at their interface. The analytical predictions indicate that the response of a typical tile is governed by the structural vibration inputs through the SIP under the tile at frequencies below 250 Hz, and by the direct acoustic excitation over the exterior surface of the tile at frequencies above 250 Hz. An evaluation of the laboratory test data for this same tile, in which conditioned (partial) coherent output spectral analysis procedures were used, leads to exactly the same conclusion. The results demonstrate the power of conditioned spectral analysis procedures in identifying vibration response mechanisms when two or more of the inputs are highly correlated.

Piersol, A. G.↗