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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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The objective of the program is to demonstrate that the Stirling engine is a practical efficient and reliable energy converter when integrated with a parabolic dish concentrator, and that it has the potential of being cost competitive with fossil fueled electric generating systems of today. The engine, with its receiver (solar heat exchanger), alternator and control system, is described.
A simple, nearly passive technique is described that allows a spacecraft sensor to be driven to a potential close to that of a plasma where the ion concentration exceeds about 100 per cu cm even in the presence of a large vehicle potential. Such a technique may become increasingly useful in the event that compatibility constraints in the Space Shuttle demand a 28-V negative ground spacecraft system.
The survey covers the various optical elements that are considered in a fly-by-light flight control system including optical sensors and transducers, optical data links, so-called optical actuators, and optical/electro-optical processing. It also addresses airframe installation, maintenance, and repair issues. Rather than an in-depth treatment of optical technology, the survey concentrates on technology readiness and the potential advantages/disadvantages of applying the technology. The information was assembled from open literature, personal interviews, and responses to a questionnaire distributed specifically for this survey. Not all of the information obtained was consistent, particularly with respect to technology readiness. The synthesis of information into the perception of the state-of-technology is presented.
The Space Shuttle Challenger accident is thought to have been caused by the failure of one of the tang-clevis joints which join together the casing segments of the Solid Rocket Motors (SRM). Excessive displacement between the tang and clevis, possibly unseating the O-ring seals, may have initiated the resulting accident. An effort was undertaken at NASA's Langley Research Center to design an alternative concept for mating the casing segments. A bolted flanged joint concept was designed and analyzed to determine if the concept would effectively maintain a seal while minimizing joint weight and controlling stress levels. It is shown that under the loading condition analyzed the seal area of the joint remains seated. The only potential stress problem is a stress concentration in the flange at the edge of the bolt hole, which is highly localized. While heavier than the existing joint, this concept does have some advantages which make the bolted joint an attractive alternative.
The Space Shuttle Challenger accident is thought to have been caused by the failure of one of the tang-clevis joints joining together the casing segments of the Solid Rocket Motors (SRM). Excessive displacement between the tang and clevis, possibly unseating the O-ring seals, may have initiated the resulting accident. An effort was made at NASA Langley Research Center to design an alternative concept for mating the casing segments. A bolted flange joint concept was designed and analyzed to determine if the concept would effectively maintain a seal while minimizing joint weight and controlling stress levels. It is shown that under the loading conditions analyzed the seal area of the joint remains seated. The only potential stress problem is a stress concentration in the flange at the edge of the bolt hole, which is highly localized. While heavier than the existing joint, this concept does have some advantages making the bolted joint an attractive alternative.
The laser atmospheric wind sounder (LAWS) will provide a new space based capability for the direct measurement of atmospheric winds in the troposphere. LAWS will make a major contribution toward advancing the understanding and prediction of the total Earth system and NASA's Earth Observing System (EOS) Program. LAWS is designed to measure a fundamental atmospheric parameter required to advance weather forecasting accuracies and investigate global climatic change. LAWS has a potential added benefit of providing (global) concentration profiles of large aerosols including visible and subvisible cirrus clouds, volcanic dust, smoke, and other pollutants. The objective of this Phase One study was to develop a LAWS concept and configuration. The instrument design is outlined in this first volume of three.
Application of developments in imaging spectrometry to the study of terrestrial ecosystems, which began in 1983, demonstrate the potential to estimate lignin and nitrogen concentrations of plant canopies by remote-sensing techniques. Estimation of these parameters from the first principles of radiative transfer and the interactions of light with plant materials is not presently possible, principally because of lack of knowledge about internal leaf scattering and specific absorption involving biochemical compounds. From the perspective of remote-sensing instrumentation, sensors are needed to support derivative imaging spectroscopy. Biochemical absorption features tend to occur in functional groupings throughout the 1100- to 2500-nm region. Derivative spectroscopy improves the information associated with the weaker, narrower absorption features of biochemical absorption that are superimposed on the strong absolute variations due to foliar biomass, pigments, and leaf water content of plant canopies. Preliminary sensor specifications call for 8-nm bandwidths at 2-nm centers in four spectral regions (about 400 bands total) and a signal-to-noise performance of at least 1000:1 for 20 percent albedo targets in the 2000-nm region.
A new metal-semiconductor-metal (MSM) photodetector geometry is proposed. The new device has concentric metal electrodes which exhibit a high degree of symmetry and a design flexibility absent in the conventional MSM device. The concentric electrodes are biased to alternating potentials as in the conventional interdigitated device. Because of the high symmetry configuration, however, the new device also has a lower effective capacitance. This device and the conventional MSM structure are analyzed within a common theoretical framework which allows for the comparison of the important performance characteristics.
An overview of the piezoelectric activity in amorphous piezoelectric polymers is presented. The criteria required to render a polymer piezoelectric are discussed. Although piezoelectricity is a coupling between mechanical and electrical properties, most research has concentrated on the electrical properties of potentially piezoelectric polymers. In this work, we present comparative mechanical data as a function of temperature and offer a summary of polarization and electromechanical properties for each of the polymers considered.
BACKGROUND: Data currently available on HIV-1-induced cytopathology is unclear regarding the mechanism of cell killing. OBJECTIVE: To clarify the extent to which apoptosis or necrosis is involved in HIV-1-induced cell death in view of conflicting existing data. METHODS: T lymphoblastoid cells or peripheral blood mononuclear cells were infected by various strains of HIV-1 and the numbers of apoptotic or necrotic cells were quantified at various times after infection using video-image analysis techniques; the results were compared with the amount of fragmented DNA using a quantitative method. Measurement of mitochondrial transmembrane potential (deltapsi(m)) and intracellular calcium concentrations [Ca2+]i was performed with fluorescent probes and fluorescence concentration analysis (FCA). RESULTS: Although lymphoblastoid and monocytoid cells acutely infected by HIV-1 had increased levels of fragmented DNA, a marker of apoptotic cell death, few (<12%) had condensed chromatin and fragmented nuclei, the morphological features of apoptosis. The predominant alterations in acutely infected cells were distended endoplasmic reticulum and abnormal mitochondria; these ultrastructural changes are consistent with necrosis, although some infected cells simultaneously displayed features of both necrosis and apoptosis. Viability of cells persistently infected by HIV-1 was only minimally reduced from that of uninfected cells. This reduction was accounted for by an increased propensity of the persistently infected cells to die by apoptosis. Alterations in [Ca2+]i and deltapsi(m) occurred in both acutely and persistently infected cells. CONCLUSION: Both necrosis and apoptosis contribute to HIV-1-induced killing of CD4 cells.
Universally, life must be characterized by a characteristic level of order and complexity. In the most general sense, habitability could then be defined as the set of factors required to allow the creation and maintenance of molecular complexity. These factors are: chemical raw materials; energy with which to assemble those materials into complex molecules and sustain the resultant state of complexity; a solvent that allows the interaction of complex molecules, promotes tertiary structure, and permits compartmentalization; and environmental conditions that permit the assembly and maintenance of complex molecules. On Earth, these general requirements correspond to the major biogenic elements C, H, O, N, P, S; chemical or light energy; the solvent water; and specific ranges of temperature, pH, radiation, ionic strength, and so forth, which have thus far been determined on and exclusively empirical basis. Importantly, while the complete absence of any of these factors ensures uninhabitable conditions, the mere presence of all four does not guarantee habitability. In each case - even that of water - it is a question of degree. This question can be couched in quantitative terms by considering the impact of each of these factors on cellular energy balance. More "extreme" conditions (e.g., high temperature, high or low pH, etc.), lower water activity, and low concentrations of nutrients incur or have potential to be addressed by increased investment of energy on the part of the cell. This must be balanced by energy conservation in the cell, noting that biochemical, mass transport, and abiotic chemical limitations intervene between environmental energy availability and biological energy capture. Similarly, lower boundary conditions are emplaced on useful environmental energy yields by the "quantized" nature of biological energy conservation, and upper boundary conditions are emplaced by energy levels or fluxes that are destructive with respect to complexity. This energetic framework, with boundary conditions supplied by the specifics of the biochemistry in question, offers a generalized, yet quantitative means of assessing the habitability of any system with respect to complex life.
Spacecraft materials selection is based on an upward flammability test conducted in a quiescent environment in the highest-expected oxygen-concentration environment. However, NASA s advanced space exploration program is anticipating using various habitable environments. Because limited data is available to support current program requirements, a different test logic is suggested to address these expanded atmospheric environments through the determination of materials self-extinguishment limits. This paper provides additional pressure effects data on oxygen concentration and partial pressure self-extinguishment limits under quiescent conditions. For the range of total pressures tested, the oxygen concentration and oxygen partial pressure flammability thresholds show a near linear function of total pressure. The oxygen concentration/oxygen partial pressure flammability thresholds depend on the total pressure and appear to increase with increasing oxygen concentration (and oxygen partial pressure). For the Constellation Program, the flammability threshold information will allow NASA to identify materials with increased flammability risk because of oxygen concentration and total pressure changes, minimize potential impacts, and allow for development of sound requirements for new spacecraft and extraterrestrial landers and habitats.
After the loss of Columbia, there was great concern in the Space Shuttle program for the impact of debris against the leading edges of the Orbiter wings. It was quickly recognized that, in addition to impacts by foam, ice that formed on the liquid-oxygen bellows running down the outside of the External Tank could break free during launch and hit this sensitive area. A Center Director s Discretionary Fund (CDDF) project would concentrate on novel ideas that were potentially applicable. The most successful of the new concepts for ice mitigation involved shape memory alloy materials. These materials can be bent into a given shape and, when heated, will return to their original shape.
Spacecraft fire safety emphasizes fire prevention, which is achieved primarily through the use of fire-resistant materials. Materials selection for spacecraft is based on conventional flammability acceptance tests, along with prescribed quantity limitations and configuration control for items that are non-pass or questionable. ISO 14624-1 and -2 are the major methods used to evaluate flammability of polymeric materials intended for use in the habitable environments of spacecraft. The methods are upward flame-propagation tests initiated in static environments and using a well-defined igniter flame at the bottom of the sample. The tests are conducted in the most severe flaming combustion environment expected in the spacecraft. The pass/fail test logic of ISO 14624-1 and -2 does not allow a quantitative comparison with reduced gravity or microgravity test results; therefore their use is limited, and possibilities for in-depth theoretical analyses and realistic estimates of spacecraft fire extinguishment requirements are practically eliminated. To better understand the applicability of laboratory test data to actual spacecraft environments, a modified ISO 14624 protocol has been proposed that, as an alternative to qualifying materials as pass/fail in the worst-expected environments, measures the actual upward flammability limit for the material. A working group established by NASA to provide recommendations for exploration spacecraft internal atmospheres realized the importance of correlating laboratory data with real-life environments and recommended NASA to develop a flammability threshold test method. The working group indicated that for the Constellation Program, the flammability threshold information will allow NASA to identify materials with increased flammability risk from oxygen concentration and total pressure changes, minimize potential impacts, and allow for development of sound requirements for new spacecraft and extravehicular landers and habitats. Furthermore, recent research has shown that current normal gravity materials flammability tests do not correlate with flammability in ventilated, micro- or reduced-gravity conditions. Currently, the materials selection for spacecraft is based on the assumption of commonality between ground flammability test results and spacecraft environments, which does not appear to be valid. Materials flammability threshold data acquired in normal gravity can be correlated with data obtained in microgravity or reduced-gravity experiments, and consequently a more accurate assessment of the margin of safety of the material in the real environment can be made. In addition, the method allows the option of selecting better or best space system materials, as opposed to what would be considered just acceptable from a flammability point of view and realistic assessment of spacecraft fire extinguishment needs, which could result in significant weight savings. The knowledge afforded by this technique allows for limited extrapolations of flammability behavior to conditions not specifically tested and that could potentially result in significant cost and time savings. The intent of this Technical Specification is to bring to the attention of International Aerospace Community the importance of correlating laboratory test data with real-life space systems applications. The method presented is just one of the possibilities that are believed will lead to better understanding the applicability of laboratory aerospace materials flammability test data. International feedback on improving the proposed method, as well as suggestions for correlating other laboratory aerospace test data with real-life applications relevant to space systems are being sought.
PM2.5 (particulate matter with diameter less than 2.5um) is one of the major air pollutants in many regions around the globe. Column integrated aerosol optical depth (AOD) measurement provides a potential way to estimate surface PM2.5 concentration from the remote sensing technics. In this analysis, we compiled hourly measurements of surface PM2.5 and AOD made in Beijing, China and meteorological conditions provided by NASA Global Modeling and Assimilation Office's Modern-Era Retrospective Analysis for Research and Applications (MERRA) product in recent years. On daily basis, hourly PM2.5 and AOD show positive correlation, i.e. correlation coefficient (R) is higher than 0.5 on about 50% of days. We apply multi-variant analysis to this dataset and estimate the magnitude of AOD variance that can be explained by or related to PM2.5 and relevant meteorological conditions changes.
Aerosols influence climate through their direct and indirect effects. The aerosol indirect effect is based on the way they interact with surrounding clouds. During cloud formation and development, aerosols act as cloud nucleation nuclei (CCN) or ice nuclei, which modifies cloud micro-, macro-physical and radiative properties, and hence helps to shape the Earth's radiation budget. Dominant sources of ocean-derived aerosols that may serve as CCN include sea spray and biogenic aerosol. In this study, we used 10-years global observations from the A-Train satellites to show seasonal variations of cloud droplet number concentrations (CDNC), ocean chlorophyll concentrations, aerosol angstrom parameter, and rainfall. Potential cloud-aerosol interactions are further discussed based on seasonal and spatial correlations between microphysics of clouds and aerosols. Emphasis for this study is placed on the southern ocean and tropical Pacific.
The stable isotope composition of soluble and insoluble organic compounds in carbonaceous chondrites can be used to determine the provenance of organic molecules in space. Deuterium enrichment in meteoritic organics could be a residual signal of synthetic reactions occurring in the cold interstellar medium or an indicator of hydrothermal parent-body reactions. δD values have been measured in grains and bulk samples for a wide range of meteorites; however, these reservoirs are highly variable and may have experienced fractionation during thermal and/or aqueous alteration. Among the plethora of organic compounds in meteorites are polycyclic aromatic hydrocarbons (PAHs), which are stable and abundant in carbonaceous chondrites, and their δD ratio may preserve evidence about their formation environment as well as the influence of parent-body processes. This study tests hypotheses about the potential links between PAHs-deuteration concentrations and their formation conditions by examining the δD ratio of PAHs in three CM carbonaceous chondrites representing an aqueous alteration gradient. We use deuterium enrichments in soluble 2–5-ring PAHs as an indicator of either photon-driven deuteration due to unimolecular photodissociation in warm regions of space, gas-phase ion–molecule reactions in cold interstellar regions of space, or UV photolysis in ices. We also test hypothesized reaction pathways during parent-body processing that differ between partially and fully aromatized PAHs. New methodological approaches were developed to extract small, volatile PAHs without fractionation. Our results suggest that meteoritic PAHs could have formed through reactions in cold regions, with possible overprinting of deuterium enrichment during aqueous parent-body alteration, but the data could not rule out PAH alteration in icy mantles as well.
Climate change has the potential to increase surface ozone (O3) concentrations, known as the “ozone–climate penalty”, through changes to atmospheric chemistry, transport and dry deposition. In the tropics, the response of surface O3 to changing climate is relatively understudied but has important consequences for air pollution and human and ecosystem health. In this study, we evaluate the change in surface O3 due to climate change over South America and Africa using three state-of-the-art Earth system models that follow the Shared Socioeconomic Pathway 3-7.0 emission scenario from CMIP6. In order to quantify changes due to climate change alone, we evaluate the difference between simulations including climate change and simulations with a fixed present-day climate. We find that by 2100, models predict an ozone–climate penalty in areas where O3 is already predicted to be high due to the impacts of precursor emissions, namely urban and biomass burning areas, although on average, models predict a decrease in surface O3 due to climate change. We identify a small but robust positive trend in annual mean surface O3 over polluted areas. Additionally, during biomass burning seasons, seasonal mean O3 concentrations increase by 15 ppb (model range 12 to 18 ppb) in areas with substantial biomass burning such as the arc of deforestation in the Amazon. The ozone–climate penalty in polluted areas is shown to be driven by an increased rate of O3 chemical production, which is strongly influenced by NOx concentrations and is therefore specific to the emission pathway chosen. Multiple linear regression finds the change in NOx concentration to be a strong predictor of the change in O3 production, whereas increased isoprene emission rate is positively correlated with increased O3 destruction, suggesting NOx-limited conditions over the majority of tropical Africa and South America. However, models disagree on the role of climate change in remote, low-NOx regions, partly because of significant differences in NOx concentrations produced by each model. We also find that the magnitude and location of the ozone–climate penalty in the Congo Basin has greater inter-model variation than that in the Amazon, so further model development and validation are needed to constrain the response in central Africa. We conclude that if the climate were to change according to the emission scenario used here, models predict that forested areas in biomass burning locations and urban populations will be at increasing risk of high O3 exposure, irrespective of any direct impacts on O3 via the prescribed emission scenario.