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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Thermal fatigue behavior of T-111 and ASTAR 811C in ultrahigh vacuum

The thermal fatigue behavior of the tantalum alloys T-111 (Ta-8W-2Hf) and ASTAR 811C (Ta-8W-1Re-0.7Hf-0.025C) has been evaluated using completely reversed push-pull fatigue tests conducted in ultrahigh vacuum with independently programmed temperature and strain cycles. Test results showed that cycling of the test temperature simultaneously with the mechanical strain in most cases significantly reduced the cycles to failure of both alloys compared to isothermal testing. Notched specimens had reduced lives under isothermal conditions, but the presence of a notch or use of a 1-h holdtime provided only a small further decrease in life for the temperature cycled tests. Compressive stress at the maximum temperature produced longer lives than tensile stress. ASTAR 811C was more fatigue resistant than T-111 isothermally and did not have as great a decrease in life with thermal cycling. Results are analyzed by partition of plastic strains into creep and creep-independent components and considering where each component was active in the hysteresis cycle.

Sheffler, K. D.↗
NASA NTRS1981

Orbiter global positioning system design and Ku-band problems investigation, exhibit B, revision 1

The LinCom effort in supporting the JSC study of the use of the Global Positioning System (GPS) on the space shuttle and in Ku-band problem investigation is documented. LinCom was tasked to evaluate system implementation, performance, and integration aspects of the shuttle GPS and to provide independent technical assessment of reports submitted to JSC regarding integration studies, system studies and navigation analyses.

Chie, C. M.↗
NASA NTRS1983

NASA mechanical impact testing in high-pressure oxygen

Three independently developed high-pressure gaseous oxygen mechanical impact testers have been used to evaluate materials for the Space Shuttle Program. A test program evaluating the performance of these test systems is described. The gaseous and liquid oxygen test procedures and equipment are considered along with the material selection procedures. The results of the NASA mechanical impact tester variability study are presented, including penetration function curves and curve parameters and equivalent energies and comparisons of high-pressure testers at ambient pressure and temperature, ambient temperature and 34 MPa, and cryogenic temperature and 34 MPa. Finally, a summary of NASA mechanical impact test data is presented.

Bryan, C. J.↗
NASA NTRS1991

Ultraviolet interstellar lines in the spectrum of Pi Scorpii recorded at 2 kilometers per second resolution

A spectrum of Pi Scorpii has been recorded from 1003 to 1172 A with a maximum SNR of about 20 and a velocity resolution of 2.4 km/s. Three types of H I as well as two discrete H II regions are distinguished in velocity space, allowing independent analyses of physical conditions and abundances for the individual gas components. A direct evaluation of optical depths and column densities across the absorption features is applied for the first time to the dominant ionization stage of Fe, Si, and P. Based on an analysis of the spectrum, it is concluded that all of the Ti II absorption seen toward Pi Sco arises in the warm, neutral intercloud medium while the other elements have their maximum absorption associated with cold clouds. A conservative value of log delta less than -3.4 is inferred for the Ti depletion in the cold clouds, a value more extreme than any integrated, line-of-sight measurement made to date.

Joseph, Charles L.↗
NASA NTRS1992

The link evaluation terminal for the advanced communications technology satellite experiments program

The experimental NASA satellite, Advanced Communications Technology Satellite (ACTS), introduces new technology for high throughput 30 to 20 GHz satellite services. Contained in a single communication payload is both a regenerative TDMA system and multiple 800 MHz 'bent pipe' channels routed to spot beams by a switch matrix. While only one mode of operation is typical during any experiment, both modes can operate simultaneously with reduced capability due to sharing of the transponder. NASA-Lewis instituted a ground terminal development program in anticipation of the satellite launch to verify the performance of the switch matrix mode of operations. Specific functions are built into the ground terminal to evaluate rain fade compensation with uplink power control and to monitor satellite transponder performance with bit error rate measurements. These functions were the genesis of the ground terminal's name, Link Evaluation Terminal, often referred to as LET. Connectors are included in LET that allow independent experimenters to run unique modulation or network experiments through ACTS using only the RF transmit and receive portions of LET. Test data indicate that LET will be able to verify important parts of ACTS technology and provide independent experimenters with a useful ground terminal. Lab measurements of major subsystems integrated into LET are presented. Bit error rate is measured with LET in an internal loopback mode.

May, Brian D.↗
NASA NTRS1992

The Link Evaluation Terminal for the Advanced Communications Technology Satellite Experiments Program

The experimental NASA satellite, Advanced Communications Technology Satellite (ACTS), introduces new technology for high throughput 30 to 20 GHz satellite services. Contained in a single communication payload is both a regenerative TDMA system and multiple 800 MHz 'bent pipe' channels routed to spot beams by a switch matrix. While only one mode of operation is typical during any experiment, both modes can operate simultaneously with reduced capability due to sharing of the transponder. NASA-Lewis instituted a ground terminal development program in anticipation of the satellite launch to verify the performance of the switch matrix mode of operations. Specific functions are built into the ground terminal to evaluate rain fade compensation with uplink power control and to monitor satellite transponder performance with bit error rate measurements. These functions were the genesis of the ground terminal's name, Link Evaluation Terminal, often referred to as LET. Connectors are included in LET that allow independent experimenters to run unique modulation or network experiments through ACTS using only the RF transmit and receive portions of LET. Test data indicate that LET will be able to verify important parts of ACTS technology and provide independent experimenters with a useful ground terminal. Lab measurements of major subsystems integrated into LET are presented. Bit error rate is measured with LET in an internal loopback mode.

May, Brian D.↗
NASA NTRS1992

Intense laser beams; Proceedings of the Meeting, Los Angeles, CA, Jan. 23, 24, 1992

Various papers on intense laser beams are presented. Individual topics addressed include: novel methods of copper vapor laser excitation, UCLA IR FEL, lasing characteristics of a large-bore copper vapor laser (CVL), copper density measurement of a large-bore CVL, high-power XeCl excimer laser, solid state direct-drive circuit for pumping gas lasers, united energy model for FELs, intensity and frequency instabilities in double-mode CO2 lasers, comparison of output power stabilities of CO and CO2 lasers, increasing efficiency of sealed-off CO lasers, thermal effects in singlet delta oxygen generation, optical extraction from the chemical oxygen-iodine laser medium, generation and laser diagnostic analysis of bismuth fluoride. Also discussed are: high-Q resonator design for an HF overtone chemical lasers, improved coatings for HF overtone lasers, scaled atmospheric blooming experiment, simulation on producing conjugate field using deformable mirrors, paraxial theory of amplitude correction, potential capabilities of adaptive optical systems in the atmosphere, power beaming research at NASA, system evaluations of laser power beaming options, performance projections for laser beam power to space, independent assessment of laser power beaming options, removal of atmospheric CFCs by lasers, efficiency of vaporization cutting by CVL.

Wade, Richard C.↗
NASA NTRS1994

Search for extraterrestrial intelligence/High Resolution Microwave Survey team member

This final report summarizes activities conducted during the three years of the NASA High Resolution Microwave Survey (HRMS). With primary interest in the Sky Survey activity, the principal investigator attended nine Working Group meetings and traveled independently to conduct experiments or present results at other meetings. The major activity involved evaluating the effects of spaceborne radio frequency interference (RFI) on both the SETI sky survey and targeted search. The development of a database of all unclassified earth or biting and deep space transmitters, along with accompanying search software, was a key accomplishment. The software provides information about potential sources of interference and gives complete information regarding the frequencies, positions and levels of interference generated by the spacecraft. A complete description of this search system (called HRS, or HRMS RFI Search) is provided. Other accomplishments include development of a 32,000 channel Fast-Fourier-Transform Spectrum analyzer for use in studies of interference from satellites and in a 1.4 mm SETI observational study. The latest revision of HRS has now been distributed to the extended radio astronomy and SETI community.

Steffes, Paul G.↗
NASA NTRS1997

Application of the Finite-Element Z-Matrix Method to e-H2 Collisions

The present study adapts the Z-matrix formulation using a mixed basis of finite elements and Gaussians. This is a energy-independent basis which allows flexible boundary conditions and is amenable to efficient algorithms for evaluating the necessary matrix elements with molecular targets.

Huo, Winifred M.↗
NASA NTRS1997

A model for the kinetics of homotypic cellular aggregation under static conditions

We present the formulation and testing of a mathematical model for the kinetics of homotypic cellular aggregation. The model considers cellular aggregation under no-flow conditions as a two-step process. Individual cells and cell aggregates 1) move on the tissue culture surface and 2) collide with other cells (or aggregates). These collisions lead to the formation of intercellular bonds. The aggregation kinetics are described by a system of coupled, nonlinear ordinary differential equations, and the collision frequency kernel is derived by extending Smoluchowski's colloidal flocculation theory to cell migration and aggregation on a two-dimensional surface. Our results indicate that aggregation rates strongly depend upon the motility of cells and cell aggregates, the frequency of cell-cell collisions, and the strength of intercellular bonds. Model predictions agree well with data from homotypic lymphocyte aggregation experiments using Jurkat cells activated by 33B6, an antibody to the beta 1 integrin. Since cell migration speeds and all the other model parameters can be independently measured, the aggregation model provides a quantitative methodology by which we can accurately evaluate the adhesivity and aggregation behavior of cells.

Non-NASA Center↗
NASA NTRS2013

Piloted Simulation Assessment of the Impact of Flexible Structures on Handling Qualities of Generic Supersonic Aircraft

The NASA Langley Research Center Cockpit Motion Facility (CMF) was used to conduct a piloted simulation assessment of the impact of flexible structures on flying qualities. The CMF was used because of its relatively high bandwidth, six degree-of-freedom motion capability. Previous studies assessed and attempted to mitigate the effects of multiple dynamic aeroservoelastic modes (DASE). Those results indicated problems existed, but the specific cause and effect was difficult to ascertain. The goal of this study was to identify specific DASE frequencies, damping ratios, and gains that cause degradation in handling qualities. A generic aircraft simulation was developed and designed to have Cooper-Harper Level 1 handling qualities when flown without DASE models. A test matrix of thirty-six DASE modes was implemented. The modes had frequencies ranging from 1 to 3.5 Hz and were applied to each axis independently. Each mode consisted of a single axis, frequency, damping, and gain, and was evaluated individually by six subject pilots with test pilot backgrounds. Analysis completed to date suggests that a number of the DASE models evaluated degrade the handling qualities of this class of aircraft to an uncontrollable condition.

Stringer, Mary T.↗
NASA NTRS2014

A New Study of Sea Spray Optical Properties from Multi-Sensor Spaceborne Observations

Retrievals of aerosol optical depth (AOD) from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite sensor require the assumption of an extinction-to-backscatter ratio, also known as the lidar ratio. This paper evaluates a new method to calculate lidar ratio of sea spray aerosol using two independent sources: the AOD from Synergized Optical Depth of Aerosols (SODA) and the integrated attenuated backscatter from CALIOP. The method applied in this study allows particulate lidar ratio to be calculated for individual CALIOP retrievals of single aerosol layer columns over the ocean. Analyses are carried out using CALIOP level 2, 5km sea spray aerosol layer products and collocated SODA nighttime data from December 2007 to December 2009. The global mean lidar ratio for sea spray aerosols was found to be 26 sr, roughly 30 higher than the one prescribed by CALIOP. Data analysis also showed considerable spatiotemporal variability in calculated lidar ratio over different parts of the remote oceans. The calculated aerosol lidar ratios are shown to be inversely related to the mean ocean surface wind speed: increase in ocean surface wind speed (U10) from 0 to 15 ms-1 reduces the mean lidar ratios for sea spray particles from 32 sr (for 0 U10 4 ms-1) to 22 sr (for U10 15 ms-1). Such changes in the lidar ratio are expected to have a corresponding effect on sea spray AOD. The outcomes of this study are relevant for future improvements of the SODA and CALIOP operational product and could lead to more accurate retrievals of sea spray AOD.

aerosol optical depth↗
NASA NTRS2019

Joint Assimilation of the Aura Microwave Limb Sounder and Ozone Mapping and Profiler Suite Limb Profiler Data: Towards a Reanalysis of Stratospheric Ozone for Trend Studies

The future trajectory of the stratospheric ozone recovery will be sensitive to greenhouse gas concentrations through thermal control of chemical loss and via stratospheric circulation changes. The latter in particular is subject to considerable uncertainty meriting continuing monitoring of the evolution of ozone throughout the depth of the stratosphere. Atmospheric reanalyses utilize the data assimilation methodology to obtain comprehensive representations of the state of the atmosphere, including its composition, on multidecadal scales by combining diverse measurements from satellite-borne and conventional data sources. Systematic biases among these various data types pose a challenge for assimilation by introducing spurious discontinuities that affect the utility of reanalyses for studies of long-term variability and trends.In this presentation we will outline an approach, developed at NASA's Global Modeling and Assimilation Office (GMAO), that allows joint assimilation of stratospheric ozone profiles from the Microwave Limb Sounder (MLS) on EOS Aura and the Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP) currently flying on the Suomi-NPP satellite with future missions projected into the 2030s. We will demonstrate that a simple offline correction significantly reduces biases between MLS and OMPS-LP ozone data providing a strategy for generating a long-term vertically resolved homogenized representation of stratospheric ozone in future reanalyses. One novel element of our approach compared to previous GMAO reanalysis is the use of a version of the Goddard Earth Observing System model with full stratospheric chemistry. We will show selected comparisons of MLS and OMPS-LP assimilation experiments with independent ozonesonde and satellite data as well as two examples of process-based evaluation focused on the 2016 QBO disruption and Arctic winter ozone loss focusing on the relative performance of the MLS and OMPS-LP analyses.

Wargan, K.↗
NASA NTRS2021

Multi-Resolution Elevation Mapping and Safe Landing Site Detection with Applications to Planetary Rotorcraft

In this paper, we propose a resource-efficient approach to provide an autonomous UAV with an on-board perception method to detect safe, hazard-free landing sites during flights over complex 3D terrain. We aggregate 3D measurements acquired from a sequence of monocular images by a Structure-from-Motion approach into a local, robot-centric, multi-resolution elevation map of the overflown terrain, which fuses depth measurements according to their lateral surface resolution (pixel-footprint) in a probabilistic framework based on the concept of dynamic Level of Detail. Map aggregation only requires depth maps and the associated poses, which are obtained from an on-board Visual Odometry algorithm. An efficient landing site detection method then exploits the features of the underlying multi-resolution map to detect safe landing sites based on the slope, roughness, and quality of the reconstructed terrain surface. The evaluation of the performance of the mapping and landing site detection modules are analyzed independently and jointly in simulated and realworld experiments in order to establish the efficacy of the proposed approach.

Brockers, Roland↗
NASA NTRSDate not supplied

Machine learning based noise reduction for satellite products: application to solar-induced fluorescence retrievals using simulated and real data

In the past two decades, global satellite measurements of terrestrial chlorophyll solar-induced fluorescence (SIF) have been used widely for a number of different applications related to physiology, phenology, and productivity of plants. However, SIF retrievals are inherently noisy due to the relatively small SIF spectral signature in comparison with observational noise. In this work, we examine how a spectral-based approach that employs principal component analysis along with a relatively shallow artificial neural network can be used to reduce noise and other artifacts in satellite level 2 (L2) products. We first apply the approach in a controlled environment in which radiance spectra are simulated with a full atmospheric and surface radiative transfer model for different scenarios including various SIF values that are known. Various levels of noise can be added to the simulated spectra. Resulting noisy and noise-reduced SIF retrievals are compared with the true values to assess performance. We then apply the noise reduction approach to real SIF derived from instruments flying on meteorological satellites. The results are evaluated by comparing SIF retrievals from different platforms with each other and with other independent data sets, showing enhanced capability to capture seasonal and interannual variability in SIF.

Chlorophyll fluorescence↗
NASA NTRS2024

Increasing Prevalence of Hot Drought Across Western North America Since the 16th Century

Across western North America (WNA), 20th-21st century anthropogenic warming has increased the prevalence and severity of concurrent drought and heat events, also termed hot droughts. However, the lack of independent spatial reconstructions of both soil moisture and temperature limits the potential to identify these events in the past and to place them in a long-term context. We develop the Western North American Temperature Atlas (WNATA), a data-independent 0.5° gridded reconstruction of summer maximum temperatures back to the 16th century. Our evaluation of the WNATA with existing hydroclimate reconstructions reveals an increasing association between maximum temperature and drought severity in recent decades, relative to the past five centuries. The synthesis of these paleo-reconstructions indicates that the amplification of the modern WNA megadrought by increased temperatures and the frequency and spatial extent of compound hot and dry conditions in the 21st century are likely unprecedented since at least the 16th century.

Drought↗
NASA NTRSDate not supplied

Validation of Self-Scheduling Countermeasures in NASA's HERA Campaign 6

Enhancing crew capabilities for planning and scheduling activities is critical for periods of increased crew autonomy in future long-duration missions where communication delays preclude real-time ground support from Earth. Our study focuses on how to empower astronauts to manage their timelines independently from the experts in the mission control center (MCC). Our objective was to evaluate the impact of scheduling countermeasures on crew scheduling performance, workload, and usability in an analog mission environment. The study involved 16 crew members across four missions in the Limited Autonomy phase of Human Exploration Research Analog (HERA) Campaign 6. Crew members used Playbook to schedule one operational day for the entire crew. Half the participants accessed scheduling aids, and we compared their performance to a control group with no aids. Performance, workload, and usability were assessed using time on task, violation counts, NASA Task Load Index (NASA-TLX), and System Usability Scale (SUS). Participants using scheduling aids completed sessions 20% faster and committed 33% fewer violations. While these differences were not statistically significant due to the study’s operational limitations, trends indicate that scheduling aids may reduce errors and improve efficiency. These results can inform the design of scheduling tools to enhance astronauts’ autonomy in long-duration space missions, contributing to improved crew performance and reduced reliance on ground support.

space robotics↗
NASA NTRSDate not supplied

Validation of Self-Scheduling Countermeasures in NASA's HERA Campaign 6

Enhancing crew capabilities for planning and scheduling activities is critical for periods of increased crew autonomy in future long-duration missions where communication delays preclude real-time ground support from Earth. Our study focuses on how to empower astronauts to manage their timelines independently from the experts in the mission control center (MCC). Our objective was to evaluate the impact of scheduling countermeasures on crew scheduling performance, workload, and usability in an analog mission environment. The study involved 16 crew members across four missions in the Limited Autonomy phase of Human Exploration Research Analog (HERA) Campaign 6. Crew members used Playbook to schedule one operational day for the entire crew. Half the participants accessed scheduling aids, and we compared their performance to a control group with no aids. Performance, workload, and usability were assessed using time on task, violation counts, NASA Task Load Index (NASA-TLX), and System Usability Scale (SUS). Participants using scheduling aids completed sessions 20% faster and committed 33% fewer violations. While these differences were not statistically significant due to the study’s operational limitations, trends indicate that scheduling aids may reduce errors and improve efficiency. These results can inform the design of scheduling tools to enhance astronauts’ autonomy in long-duration space missions, contributing to improved crew performance and reduced reliance on ground support.

space robotics↗