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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Interfacial chemistry of a perfluoropolyether lubricant studied by X-ray photoelectron spectroscopy and temperature desorption spectroscopy

The interfacial chemistry of Fomblin Z25, a commercial perfluoropolyether used as lubricant for space applications was studied with different metallic surfaces: 440C steel, gold, and aluminum. Thin layers of Fomblin Z25 were evaporated onto the oxide-free substrates, and the interfacial chemistry was studied using XPS and TDS. The reactions were induced by heating the substrate and by rubbing the substrate with a steel ball. Gold was found to be completely unreactive towards Fomblin at any temperature. Reaction at room temperature was observed only in the case of the aluminum substrate, the most reactive towards Fomblin Z25 of the substrates studied. It was necessary to heat the 440C steel substrate to 190 C to induce decomposition of the fluid. The degradation of the fluid was indicated by the formation of a debris layer at the interface. This debris layer, composed of inorganic and organic reaction products, when completely formed, passivated the surface from further attack to the Fromblin on top. The tribologically induced reactions on 440C steel formed a debris layer of similar chemical characteristics to the thermally induced layer. In all cases, the degradation reaction resulted in preferential consumption of the difluoroformyl carbon (-OCF2O-).

Herrera-Fierro, Pilar↗
NASA NTRS1992

Interfacial chemistry of a perfluoropolyether lubricant studied by XPS and TDS

The interfacial chemistry of Fomblin Z25, a commercial perfluoropolyether used as lubricant for space applications, with different metallic surfaces: 440C steel, gold and aluminum was studied. Thin layers of Fomblin Z25 were evaporated onto the oxide-free substrates and the interfacial chemistry studied using XPS and TDS. The reactions were induced by heating the substrate and by rubbing the substrate with a steel ball. Gold was found to be completely unreactive towards Fomblin at any temperature. Reaction at room temperature was observed only in the case of the aluminum substrate, the most reactive towards Fomblin Z25 of the substrates studied. It was necessary to heat the 440C steel substrate to 190 degree C to induce decomposition of the fluid. The degradation of the fluid was indicated by the formation of a debris layer at the interface. This debris layer, composed of inorganic and organic reaction products, when completely formed, passivated the surface from further attack to the Fromblin on top. The tribologically induced reactions on 440C steel formed a debris layer of similar chemical characteristics to the thermally induced layer. In all cases, the degradation reaction resulted in preferential consumption of the difluoroformyl carbon (-OCF2O-).

Herrera-Fierro, Pilar C.↗
NASA NTRS2008

Recent Progress in Characterization of Dust over Land Surfaces with Space-borne Passive Remote Sensing

Among the many components that contribute to air pollution, airborne mineral dust plays an important role due to its biogeochemical impact on the ecosystem and its radiative-forcing effect on the climate system. In East Asia, dust storms frequently accompany the cold and dry air masses that occur as part of springtime cold front systems. Outbreaks of Asian dust storms occur often in the arid and semi-arid areas of northwestern China -about 1.6x10(exp 6) square kilometers including the Gobi and Taklimakan deserts- with continuous expanding of spatial coverage. These airborne dust particles, originating in desert areas far from polluted regions, interact with anthropogenic sulfate and soot aerosols emitted from Chinese mega-cities during their transport over the mainland. Adding the intricate effects of clouds and marine aerosols, dust particles reaching the marine environment can have drastically different properties than those from their sources. Furthermore, these aerosols, once generated over the source regions, can be transported out of the boundary layer into the free troposphere and can travel thousands of kilometers across the Pacific into the United States and beyond. In this paper, we will demonstrate the capability of a new satellite algorithm to retrieve aerosol properties (e.g., optical thickness, single scattering albedo) over bright-reflecting surfaces such as urban areas and deserts. Such retrievals have been difficult to perform using previously available algorithms that use wavelengths from the mid-visible to the near IR because they have trouble separating the aerosol signal from the contribution due to the bright surface reflectance. This new algorithm, called Deep Blue, utilizes blue-wavelength measurements from instruments such as SeaWiFS and MODIS to infer the properties of aerosols, since the surface reflectance over land in the blue part of the spectrum is much lower than for longer wavelength channels. Reasonable agreements have been achieved between Deep Blue retrievals of aerosol optical thickness and those directly from AERONET sunphotometers over desert and semi-desert regions. New Deep Blue products will allow scientists to determine quantitatively the aerosol properties near sources using high spatial resolution measurements from SeaWiFS and MODIS-like instruments. Long-term satellite measurements (1998 - 2007) from SeaWiFS will be utilized to investigate the interannual variability of source, pathway, and dust loading associated with the Asian dust storm outbreaks. In addition, monthly averaged aerosol optical thickness during the springtime from SeaWiFS will also be compared with the MODIS Deep Blue products.

Hsu, N. Christina↗
NASA NTRS2007

Remote Sensing of Terrestrial Water Storage and Application to Drought Monitoring

Terrestrial water storage (TWS) consists of groundwater, soil moisture and permafrost, surface water, snow and ice, and wet biomass. TWS variability tends to be dominated by snow and ice in polar and alpine regions, by soil moisture in mid-latitudes, and by surface water in wet, tropical regions such as the Amazon (Rodell and Famiglietti, 2001; Bates et al., 2007). Drought may be defined as a period of abnormally dry weather long enough to cause significant deficits in one or more of the TWS components. Thus, along with observations of the agricultural and socioeconomic impacts, measurements of TWS and its components enable quantification of drought severity. Each of the TWS components exhibits significant spatial variability, while installation and maintenance of sufficiently dense monitoring networks is costly and labor-intensive. Thus satellite remote sensing is an appealing alternative to traditional measurement techniques. Several current remote sensing instruments are able to detect variations in one or more TWS variables, including the Advanced Microwave Scanning Radiometer (AMSR) on NASA's Aqua satellite and the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra and Aqua. Future satellite missions have been proposed to improve this capability, including the European Space Agency's Soil Moisture Ocean Salinity mission (SMOS) and the Soil Moisture Active Passive (SMAP), Surface Water Ocean Topography (SWOT), and Snow and Cold Land Processes (SCLP) missions recommended by the US National Academy of Science's Decadal Survey for Earth Science (NRC, 2007). However, only one remote sensing technology is able to monitor changes in TWS from the land surface to the base of the deepest aquifer: satellite gravimetry. This paper focuses on NASA's Gravity Recovery and Climate Experiment mission (GRACE; http://www.csr.utexas.edu/grace/) and its potential as a tool for drought monitoring.

Rodell, Matt↗
NASA NTRS1994

Ice surface temperature retrieval from AVHRR, ATSR, and passive microwave satellite data: Algorithm development and application

One essential parameter used in the estimation of radiative and turbulent heat fluxes from satellite data is surface temperature. Sea and land surface temperature (SST and LST) retrieval algorithms that utilize the thermal infrared portion of the spectrum have been developed, with the degree of success dependent primarily upon the variability of the surface and atmospheric characteristics. However, little effort has been directed to the retrieval of the sea ice surface temperature (IST) in the Arctic and Antarctic pack ice or the ice sheet surface temperature over Antarctica and Greenland. The reason is not one of methodology, but rather our limited knowledge of atmospheric temperature, humidity, and aerosol vertical, spatial and temporal distributions, the microphysical properties of polar clouds, and the spectral characteristics of snow, ice, and water surfaces. Over the open ocean the surface is warm, dark, and relatively homogeneous. This makes SST retrieval, including cloud clearing, a fairly straightforward task. Over the ice, however, the surface within a single satellite pixel is likely to be highly heterogeneous, a mixture of ice of various thicknesses, open water, and snow cover in the case of sea ice. Additionally, the Arctic is cloudy - very cloudy - with typical cloud cover amounts ranging from 60-90 percent. There are few observations of cloud cover amounts over Antarctica. The goal of this research is to increase our knowledge of surface temperature patterns and magnitudes in both polar regions, by examining existing data and improving our ability to use satellite data as a monitoring tool. Four instruments are of interest in this study: the AVHRR, ATSR, SMMR, and SSM/I. Our objectives are as follows. Refine the existing AVHRR retrieval algorithm defined in Key and Haefliger (1992; hereafter KH92) and applied elsewhere. Develop a method for IST retrieval from ATSR data similar to the one used for SST. Further investigate the possibility of estimating surface temperature from passive microwave data (in conjunction with AVHRR clear sky samples) through the use of 'effective emissivities' and physical relationships between skin temperature and subsurface temperature. Use the general method outlined in MK93 to calculate a 12-year record of clear sky equivalent surface temperatures, or possibly all-sky snow-ice interface physical temperatures, from SMMR and SSM/I, compare these temperatures to climatologies, ECMWF modeled surface temperatures, and surface temperatures predicted by a 2-D ice model. And intercompare several ice surface retrieval methods and validate them against ground measurements from the Swiss Camp on the Greenland ice sheet. Additionally, we intend to develop a surface temperature product based on AVHRR data and possibly blended with drifting buoy and meteorological station temperatures.

Key, Jeff↗
NASA NTRS1972

Structural active cooling applications for the Space Shuttle.

Analytic and experimental studies have been conducted to evaluate a number of active cooling approaches to structural thermal protection for the Space Shuttle. The primary emphasis was directed toward the thermal protection system. Trade study results are presented for various heat shield material and TPS arrangements. Both metallic and reusable surface insulation (RSI) concepts were considered. Active systems heat sinks consisted of hydrogen, phase change materials, and expendable water. If consideration is given only to controlling the surface temperature, passive TPS was found to provide the most efficient system. Use of active cooling which incorporates some interior temperature control made the thermally less efficient RSI system more attractive.

Masek, R. V.↗
NASA NTRS1984

Technology needs of advanced Earth observation spacecraft

Remote sensing missions were synthesized which could contribute significantly to the understanding of global environmental parameters. Instruments capable of sensing important land and sea parameters are combined with a large antenna designed to passively quantify surface emitted radiation at several wavelengths. A conceptual design for this large deployable antenna was developed. All subsystems required to make the antenna an autonomous spacecraft were conceptually designed. The entire package, including necessary orbit transfer propulsion, is folded to package within the Space Transportation System (STS) cargo bay. After separation, the antenna, its integral feed mast, radiometer receivers, power system, and other instruments are automatically deployed and transferred to the operational orbit. The design resulted in an antenna with a major antenna dimension of 120 meters, weighing 7650 kilograms, and operating at an altitude of 700 kilometers.

Herbert, J. J.↗
NASA NTRS1983

A concept for an advanced earth observation spacecraft

Remote sensing missions have been synthesized which could contribute significantly to the understanding of global environmental parameters. Instruments capable of sensing important land and sea parameters are combined with a large antenna designed to passively quantify surface emitted radiation at several wavelengths. A conceptual design for this large deployable antenna has been developed. All subsystems required to make the antenna an autonomous spacecraft have been conceptually designed. The entire package, including necessary orbit transfer propulsion, is folded to package within the Space Transportation System (STS) cargo bay. After separation the antenna, its integral feed mast, radiometer receivers, power system, and other instruments are automatically deployed and transferred to the operational orbit. The design resulted in an antenna with a major antenna dimension of 120 meters, weighting 7650 kilograms, and operating at an altitude of 700 kilometers.

Lovelace, U. M.↗
NASA NTRS1989

Turbulent flow separation control through passive techniques

Several passive separation control techniques for controlling moderate two-dimensional turbulent flow separation over a backward-facing ramp are studied. Small transverse and swept grooves, passive porous surfaces, large longitudinal grooves, and vortex generators were among the techniques used. It was found that, unlike the transverse and longitudinal grooves of an equivalent size, the 45-deg swept-groove configurations tested tended to enhance separation.

Lin, J. C.↗
NASA NTRS1997

Passive Microwave Observation of Diurnal Surface Soil Moisture

Microwave radiometers operating at low frequencies are sensitive to surface soil moisture changes. Few studies have been conducted that have involved multifrequency observations at frequencies low enough to measure a significant soil depth and not be attenuated by the vegetation cover. Another unexplored aspect of microwave observations at low frequencies has been the impact of diurnal variations of the soil moisture and temperature on brightness temperature. In this investigation, observations were made using a dual frequency radiometer (1.4 and 2.65 GHz) over bare soil and corn for extended periods in 1994. Comparisons of emissivity and volumetric soil moisture at four depths for bare soils showed that there was a clear correspondence between the 1 cm soil moisture and the 2.65-GHz emissivity and between the 3-5 cm soil moisture and the 1.4-GHZ emissivity, which confirms previous studies. Observations during drying and rainfall demonstrate that new and unique information for hydrologic and energy balance studies can be extracted from these data.

Jackson, Thomas J.↗
NASA NTRS2007

Design and Fabrication of High-Efficiency CMOS/CCD Imagers

An architecture for back-illuminated complementary metal oxide/semiconductor (CMOS) and charge-coupled-device (CCD) ultraviolet/visible/near infrared- light image sensors, and a method of fabrication to implement the architecture, are undergoing development. The architecture and method are expected to enable realization of the full potential of back-illuminated CMOS/CCD imagers to perform with high efficiency, high sensitivity, excellent angular response, and in-pixel signal processing. The architecture and method are compatible with next-generation CMOS dielectric-forming and metallization techniques, and the process flow of the method is compatible with process flows typical of the manufacture of very-large-scale integrated (VLSI) circuits. The architecture and method overcome all obstacles that have hitherto prevented high-yield, low-cost fabrication of back-illuminated CMOS/CCD imagers by use of standard VLSI fabrication tools and techniques. It is not possible to discuss the obstacles in detail within the space available for this article. Briefly, the obstacles are posed by the problems of generating light-absorbing layers having desired uniform and accurate thicknesses, passivation of surfaces, forming structures for efficient collection of charge carriers, and wafer-scale thinning (in contradistinction to diescale thinning). A basic element of the present architecture and method - the element that, more than any other, makes it possible to overcome the obstacles - is the use of an alternative starting material: Instead of starting with a conventional bulk-CMOS wafer that consists of a p-doped epitaxial silicon layer grown on a heavily-p-doped silicon substrate, one starts with a special silicon-on-insulator (SOI) wafer that consists of a thermal oxide buried between a lightly p- or n-doped, thick silicon layer and a device silicon layer of appropriate thickness and doping. The thick silicon layer is used as a handle: that is, as a mechanical support for the device silicon layer during micro-fabrication.

Pain, Bedabrata↗
NASA NTRS2016

Genesis Solar Wind Science Canister Components Curated as Potential Solar Wind Collectors and Reference Contamination Sources

The Genesis mission collected solar wind for 27 months at Earth-Sun L1 on both passive and active collectors carried inside of a Science Canister, which was cleaned and assembled in an ISO Class 4 cleanroom prior to launch. The primary passive collectors, 271 individual hexagons and 30 half-hexagons of semiconductor materials, are described in. Since the hard landing reduced the 301 passive collectors to many thousand smaller fragments, characterization and posting in the online catalog remains a work in progress, with about 19% of the total area characterized to date. Other passive collectors, surfaces of opportunity, have been added to the online catalog. For species needing to be concentrated for precise measurement (e.g. oxygen and nitrogen isotopes) an energy-independent parabolic ion mirror focused ions onto a 6.2 cm diameter target. The target materials, as recovered after landing, are described in. The online catalog of these solar wind collectors, a work in progress, can be found at: http://curator.jsc.nasa.gov/gencatalog/index.cfm This paper describes the next step, the cataloging of pieces of the Science Canister, which were surfaces exposed to the solar wind or component materials adjacent to solar wind collectors which may have contributed contamination.

Allton, J. H.↗
NASA NTRS2017

Improved Mirror Coatings for Use in the Lyman Ultraviolet to Enhance Astronomical Instrument Capabilities

This paper will describe efforts at developing broadband mirror coatings with high performance that will extend from infrared wavelengths down to the Far-Ultraviolet (FUV) spectral region. These mirror coatings would be realized by passivating the surface of freshly made aluminum coatings with XeF2 gas in order to form a thin AlF3 overcoat that will protect the aluminum from oxidation and, hence, realize the high-reflectance of this material down to its intrinsic cut-off wavelength of 90 nm. Improved reflective coatings for optics, particularly in the FUV region (90-120 nm), could yield dramatically more sensitive instruments and permit more instrument design freedom.

reflectance↗
NASA NTRS2017

Improved Lyman Ultraviolet Astronomy Capabilities through Enhanced Coatings

This paper will describe efforts at developing broadband mirror coatings with high performance that will extend from infrared wavelengths down to the Far-Ultraviolet (FUV) spectral region. These mirror coatings would be realized by passivating the surface of freshly made aluminum coatings with XeF2 gas in order to form a thin AlF$_3$ overcoat that will protect the aluminum from oxidation and, hence, realize the high-reflectance of this material down to its intrinsic cut-off wavelength of 90 nm. Improved reflective coatings for optics, particularly in the FUV region (90-120 nm), could yield dramatically more sensitive instruments and permit more instrument design freedom.

Lyman-Ultraviolet↗
NASA NTRSDate not supplied

Global Precipitation Means and Variations with the New Version of GPCP

Knowledge of global precipitation means, patterns and variations is essential for understanding the global water cycle. The observation-based global analysis of the Global Precipitation Climatology Project (GPCP) has been a key input to many such studies, including those related to means of the global (and regional) water and energy cycles. A new version (Version 3.1) of the GPCP monthly analysis is now available (1983-2019), with finer spatial resolution (0.5º latitude/longitude), updated satellite algorithms, latest gauge analysis over land from the Global Precipitation Climatology Center (GPCC), and with ocean climatologies adjusted using information from the Tropical Rainfall Measuring Mission (TRMM), the Global Precipitation Measurement (GPM) mission and CloudSat. The presentation will give key findings from the new analysis, compare with the previous version, link to studies of the water cycle and compare to CMIP6 climate model results. The GPCP Monthly V3.1 analysis uses a Tropical Composite Climatology (TCC) using 22 years (1998-2019) of TRMM and GPM-based surface precipitation estimates from passive microwave, radar and combined passive microwave and radar observations to adjust the long-term mean values in the tropics over ocean. At higher latitudes over ocean climatological values of merged CloudSat and GPM combined passive microwave and radar surface precipitation estimates are used. The result of the new algorithms and procedures is an ocean mean value 60º N to 60º S of 3.2 mm/d, an increase of 7% from the older V2.3. Over land the gauge analysis (from GPCC in Germany), combined with satellite estimates results in a small decrease (~ 0.5%) from the previous version, giving a total global precipitation mean of 2.81 mm/d for V3.1, an increase of 4.5%. Variations from inter-annual to trend scales over most of the ocean are driven by the Colorado State University (CSU) Goddard Profiling (GPROF) algorithm applied to SSMI/SSMIS satellite data. The new GPCP version retains a near zero trend of global precipitation, with significant positive trends in the deep tropics along the Pacific ITCZ and elsewhere, countered by middle latitude decreases, very similar to the previous version of the GPCP Monthly analysis. The pattern of trends is similar to that of AMIP climate model results, driven by observed SSTs for the period in question, but very different from results for “free-running” CMIP historical ensembles, likely due in part to the relatively short comparison period and effects of inter-decadal variations in the GPCP and AMIP results that are not in the “history” models. Interannual variations are also nearly the same in the new version, but with finer detail, although ENSO variations over the ocean have slightly larger amplitude than before, an effect likely related to the change in ocean satellite algorithm used in Version 3. For precipitation intensity (percentiles) at the monthly scale, especially in the tropics, GPCP shows a positive trend for the upper one third of the percentiles (Pct ≥ 70th) and a much weaker positive trend for the lowest percentiles (Pct ≤ 10th), while negative trends appear for the middle one-half percentiles (20th-65th). AMIP results agree with those from the GPCP in terms of the sign of the changes/trends for high and intermediate percentiles. The CMIP historical results also agree in the sign of the trends, but the trends are weaker. Comparisons with other types of CMIP historical simulations including the GHG-only, aerosol-only, and nature-only runs suggest that the observed changes/trends in precipitation amount and intensity during the GPCP period are dominated by a combination of the effects of the Pacific Decadal Oscillation (PDO) and anthropogenic GHG-related surface warming.

Robert Adler↗