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NASA NTRS1985

Methyl halide production associated with kelp

Methyl halides (MeX) are important trace constituents of the atmosphere because they, mostly MeCl, have a major impact on the atmospheric ozone layer. Also, MeCl may account for 5 pct. of the total Cl budget and MeI may have a central role in the biogeochemical cycling of iodine. High MeI concentrations were found in seawater from kelp beds and it has been suggested that MeI is produced by kelps and that MeI and MeBr along with numerous other halocarbons were released by non-kelp marine macroalgae. The objective was to determine if kelps (and other seaweeds) are sources of MeX and to assess their contribution to the estimated global source strength (EGSS) of MeX. Although the production of MeX appears to be associated with kelp, microbes involved with kelp degradation also produce MeX. Microbial MeX production may be of global significance. The microbial MeX production potential, assuming annual kelp production equals kelp degradation and 100 pct. conversion of kelp halides to MeX, is approx. 2 x the EGSS. This is not achieved but indicates that microbial production of MeX may be of global significance.

Dastoor, Minoo N.↗

NASA NTRS1993

Al-26 production profile and model comparisons in Canyon Diablo

The large preatmospheric size of the Canyon Diablo meteorite, a radius of about 15 m, makes it especially suitable for systematic studies of cosmogenic nuclide production rates of iron objects in a 2 pi geometry. To reconstruct the exposure history of the meteoroid, Heymann et al. investigated several fragments recovered from known geographic locations around the crater for their shock features and cosmogenic nobel gases. They applied the Signer-Nier noble gas production rate model to establish the preatmospheric depth of the specimens in the meteoroid. Cosmic ray exposure ages suggested a multi-episodic irradiation, with 170 or 540 Ma being inferred for most of the samples studied while two anomalous specimens indicated a possible third exposure age at 940 Ma. Be-10 and Cl-36 have been measured in a number of these same samples by accelerator mass spectrometry (AMS), with use being made of the preatmospheric depths determined in Heymann et al. to construct production profiles. The present study extends the cosmogenic radionuclide data to Al-26 and compares the results with both the production rate model of Reedy and Arnold and production rates determined from the cross sections used by the Reedy-Arnold model (for the major nuclear reactions making Al-26) in combination with differential fluxes calculated using the Los Alamos High Energy Transport (LAHET) Code System. Model calculations for Be-10 and Cl-36 have also been obtained.

Michlovich, E.↗

NASA NTRS1993

Production of O2 on the Moon: A lab-top demonstration of ilmenite reduction with hydrogen

Estimates of the costs of transporting materials from Earth to the Moon are around $25,000 per pound. Therefore, it is imperative that we learn to utilize the resources on the Moon to partially offset these 'astronomical' expenses. The production of oxygen on the Moon utilizing indigenous materials is crucial to the establishment and development of an autonomous lunar colony. Besides obvious biologic needs, this lunar liquid oxygen (LLOX) could result in tremendous cost savings on fuel for effective transportation systems, particularly with its export to low-Earth orbit. Over 20 different process concepts were proposed and evaluated for the production of oxygen from lunar materials. Simplicity, low energy, easily attainable feedstock, and low resupply mass are the keywords for the process(es) which will ultimately be selected for the initial production of oxygen on the Moon. One of these schemes, which has received considerable study to date, is the hydrogen reduction of ilmenite. In fact, Carbotek, Inc. (Houston, TX) patented an ilmenite, hydrogen-reduction technique involving a three-stage, fluidized-bed process for the production of LLOX. A lab-top demonstration unit of the basic concepts of this oxygen generation process that was constructed by our group at the University of Tennessee is explained. It utilizes many of the principles which must be addressed in designing an effective production plant for operation on the Moon.

Taylor, Lawrence A.↗

NASA NTRS1993

Characteristics of products generated by selective sintering and stereolithography rapid prototyping processes

The trend in the modern global economy towards free market policies has motivated companies to use rapid prototyping technologies to not only reduce product development cycle time but also to maintain their competitive edge. A rapid prototyping technology is one which combines computer aided design with computer controlled tracking of focussed high energy source (eg. lasers, heat) on modern ceramic powders, metallic powders, plastics or photosensitive liquid resins in order to produce prototypes or models. At present, except for the process of shape melting, most rapid prototyping processes generate products that are only dimensionally similar to those of the desired end product. There is an urgent need, therefore, to enhance the understanding of the characteristics of these processes in order to realize their potential for production. Currently, the commercial market is dominated by four rapid prototyping processes, namely selective laser sintering, stereolithography, fused deposition modelling and laminated object manufacturing. This phase of the research has focussed on the selective laser sintering and stereolithography rapid prototyping processes. A theoretical model for these processes is under development. Different rapid prototyping sites supplied test specimens (based on ASTM 638-84, Type I) that have been measured and tested to provide a data base on surface finish, dimensional variation and ultimate tensile strength. Further plans call for developing and verifying the theoretical models by carefully designed experiments. This will be a joint effort between NASA and other prototyping centers to generate a larger database, thus encouraging more widespread usage by product designers.

Cariapa, Vikram↗

NASA NTRS1994

The effects of temporal variability of mixed layer depth on primary productivity around Bermuda

Temporal variations in primary production and surface chlorophyll concentrations, as measured by ship and satellite around Bermuda, were simulated with a numerical model. In the upper 450 m of the water column, population dynamics of a size-fractionated phytoplankton community were forced by daily changes of wind, light, grazing stress, and nutrient availability. The temporal variations of production and chlorophyll were driven by changes in nutrient introduction to the euphotic zone due to both high- and low-frequency changes of the mixed layer depth within 32 deg-34 deg N, 62 deg-64 deg W between 1979 and 1984. Results from the model derived from high-frequency (case 1) changes in the mixed layer depth showed variations in primary production and peak chlorophyll concentrations when compared with results from the model derived from low-frequency (case 2) mixed layer depth changes. Incorporation of size-fractionated plankton state variables in the model led to greater seasonal resolution of measured primary production and vertical chlorophyll profiles. The findings of this study highlight the possible inadequacy of estimating primary production in the sea from data of low-frequency temporal resolution and oversimplified biological simulations.

Bissett, W. Paul↗

NASA NTRS1994

Factors affecting the estimate of primary production from space

Remote sensing of primary production in the euphotic zone has been based mostly on visible-band and water-leaving radiance measured with the coastal zone color scanner. There are some robust, simple relationships for calculating integral production based on surface measurements, but they also require knowledge for photoadaptive parameters such as maximum photosynthesis which currently cannot be obtained from spave. A 17,000-station data set is used to show that space-based estimates of maximum photosynthesis could improve predictions of psi, the water column light utiliztion index, which is an important term in many primary productivity models. Temperature is also examined as a factor for predicting hydrographic structure and primary production. A simple model is used to relate temperature and maximum photosynthesis; the model incorporates (1) the positive relationship between maximum photosynthesis and temperature and (2) the strongly negative relationship between temperature and nitrate in the ocean (which directly affects maximum growth rates via nitrogen limitation). Since these two factors relate to carbon and nitrogen, 'balanced carbon/nitrogen assimilation' was calculated using the Redfield ratio, It is expected that the relationship between maximum balanced carbon assimilation versus temperature is concave-down, with the peak dependent on nitrate uptake kinetics, temperature-nitrate relationships,a nd the carbon chlorophyll ration. These predictions were compared with the sea truth data. The minimum turnover time for nitrate was also calculated using this approach. Lastly, sea surface temperature gradients were used to predict the slope of isotherms (a proxy for the slope of isopycnals in many waters). Sea truth data show that at size scales of several hundred kilometers, surface temperature gradients can provide information on the slope of isotherms in the top 200 m of the water column. This is directly relevant to the supply of nutrients into the surface mixed layer, which is useful for predicting integral biomass and primary production.

Balch, W. M.↗

NASA NTRS1994

The trend of production rates with heliocentric distance for comet P/Halley

Comet P/Halley was observed spectroscopically in the wavelength range 5200-10,400 A during 10 observing runs, roughly a month apart from 1985 August 28 to 1986 June 6. The observations span a heliocentric distance from 0.73 to 2.52 AU. This data set is analyzed to determine the course of the production rate with heliocentric distance for C2, NH2, CN, and the continuum. The effect of changing the Haser scale lengths and their heliocentric distance dependence is examined. The production rate ratios to water change only in a minor way, but the absolute values of the production rates are more severely affected. Fluorescent efficiencies, or g-factors for the CN red system are calculated, and band intensity ratios for NH2 and CN are presented. Using presently available fluorescence efficiencies and Haser scale lengths, mixing ratios for the parents of C2, CN, and NH2 with respect to water are: 0.34 +/- 0.07%, 0.15 +/- 0.04%, and 0.13 +/- 0.05%. It is found that these mixing ratios are essentially constant over the heliocentric distance range of the observations, implying a rather uniform nucleus and uniform outgassing characteristics, although there are indications of smaller scale day-to-day variations. The results provide strong observational confirmation that water evaporation controls the activity of the comet over the distance range studied. Continuum values Af rho are determined, and their ratios to QH2O are found to have a clear dependence with heliocentric distance approximately r(exp -1.0) with a post-perihelion enhancement. No correlation of the production rate ratios with light curve of P/Halley were found, nor was there any correlation of the C2 or CN production with the dust.

Fink, Uwe↗

NASA NTRS1996

Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) Data Products User's Guide

Two data products from the Total Ozone Mapping Spectrometer (TOMS) onboard Nimbus-7 have been archived at the Distributed Active Archive Center, in the form of Hierarchical Data Format files. The instrument measures backscattered Earth radiance and incoming solar irradiance; their ratio is used in ozone retrievals. Changes in the instrument sensitivity are monitored by a spectral discrimination technique using measurements of the intrinsically stable wavelength dependence of derived surface reflectivity. The algorithm to retrieve total column ozone compares measured Earth radiances at sets of three wavelengths with radiances calculated for different total ozone values, solar zenith angles, and optical paths. The initial error in the absolute scale for TOMS total ozone is 3 percent, the one standard deviation random error is 2 percent, and drift is less than 1.0 percent per decade. The Level-2 product contains the measured radiances, the derived total ozone amount, and reflectivity information for each scan position. The Level-3 product contains daily total ozone amount and reflectivity in a I - degree latitude by 1.25 degrees longitude grid. The Level-3 product also is available on CD-ROM. Detailed descriptions of both HDF data files and the CD-ROM product are provided.

McPeters, Richard D.↗

NASA NTRS1995

Clouds and the Earth's Radiant Energy System (CERES) algorithm theoretical basis document: Determination of surface and atmosphere fluxes and temporally and spatially averaged products (subsystems 5-12) - volume 4

The theoretical bases for the Release 1 algorithms that will be used to process satellite data for investigation of the Clouds and the Earth's Radiant Energy System (CERES) are described. The architecture for software implementation of the methodologies is outlined. Volume 4 details the advanced CERES techniques for computing surface and atmospheric radiative fluxes (using the coincident CERES cloud property and top-of-the-atmosphere (TOA) flux products) and for averaging the cloud properties and TOA, atmospheric, and surface radiative fluxes over various temporal and spatial scales. CERES attempts to match the observed TOA fluxes with radiative transfer calculations that use as input the CERES cloud products and NOAA National Meteorological Center analyses of temperature and humidity. Slight adjustments in the cloud products are made to obtain agreement of the calculated and observed TOA fluxes. The computed products include shortwave and longwave fluxes from the surface to the TOA. The CERES instantaneous products are averaged on a 1.25-deg latitude-longitude grid, then interpolated to produce global, synoptic maps to TOA fluxes and cloud properties by using 3-hourly, normalized radiances from geostationary meteorological satellites. Surface and atmospheric fluxes are computed by using these interpolated quantities. Clear-sky and total fluxes and cloud properties are then averaged over various scales.

Wielicki, Bruce A.↗

NASA NTRS1996

Measurement of proton production cross sections of (sup 10)Be and (sup 26)Al from elements found in lunar rocks

Cosmic rays penetrate the lunar surface and interact with the lunar rocks to produce both radionuclides and stable nuclides. Production depth profiles for long-lived radionuclides produce in lunar rocks are measured using Accelerator Mass Spectrometry (AMS). For a particular radionuclide these production depth profiles can be interpreted to give an estimate for the solar proton flux over a time period characterized by the half life of the radionuclide under study. This analysis is possible if and only if all the cross sections for the interactions of all cosmic ray particles with all elements found in lunar rocks are well known. In practice, the most important cross sections needed are the proton production cross sections, because 98% of solar cosmic rays and (similar to)87% of galactic cosmic rays are protons. The cross sections for the production of long-lived radionuclides were very difficult to measure before the development of AMS and only in recent years has significant progress been made in determining these essential cross sections. Oxygen and silicon are major constituents of lunar rocks. We have reported already C-14 production cross sections from O and Si for proton energies 25-500 MeV, and O(p,x)(sup 10)Be from 58 160 MeV[6]. Here we present new measurements for the cross sections O(p,x)Be-10,O(p,x)Be-7, Si(p,x)Be-7,Si(p,x)Al-26, and Si(p,x)Na-22 from approximately 30 - 500 MeV.

Sisterson, J. M.↗

NASA NTRS1997

Balloon-Borne Measurements of Stratospheric Radicals and their Precursors: Implications for the Production and Loss of Ozone

Measurements of hydrogen, nitrogen and chlorine radicals from a balloon flight on 25 September 1993 from Ft. Sumner, NM provide an opportunity to quantify photochemical production and loss of stratospheric ozone. Ozone loss rates determined using measured radical concentrations agree fairly well with loss rates calculated using a photochemical model. Catalytic cycles involving OH and HO2 are shown to dominate photochemical loss of ozone for altitudes between 44 and 50 km. Reactions involving NO and NO2 are the dominant sink for ozone between 25 and 38 km. The total ozone loss rate determined from the measurements balances calculated production rates for altitudes between 30 and 40 km. However, loss of ozone exceeds production by -35% between 42 and 50 km. The imbalance between production and loss of ozone above 42 km is larger than the uncertainty of any one of the critical kinetic parameters or species concentrations. No single adjustment to any of these parameters can simultaneously resolve the imbalance and satisfy constraints imposed by measured OH, HO2, NO2 and ClO. Our results are consistent with an additional mechanism for ozone production above 40 km other than photolysis of ground state O2.

Osterman, G. B.↗

NASA NTRS1996

Ethylene Production by Plants in a Closed Environment

Ethylene production by 20-sq m stands of wheat, soybean, lettuce and potato was monitored throughout growth and development in NASA's Controlled Ecological Life Support System (CELSS) Biomass Production Chamber. Chamber ethylene concentrations rose during periods of rapid growth for all four species, reaching 120 parts per billion (ppb) for wheat, 60 ppb for soybean, and 40 to 50 ppb for lettuce and potato. Following this, ethylene concentrations declined during seed fill and maturation (wheat and soybean), or remained relatively constant (potato). Lettuce plants were harvested during rapid growth and peak ethylene production. The highest ethylene production rates (unadjusted for chamber leakage) ranged from 0.04 to 0.06 ml/sq m/day during rapid growth of lettuce and wheat stands, or approximately 0.8 to 1.1 ml/g fresh weight/h. Results suggest that ethylene production by plants is a normal event coupled to periods of rapid metabolic activity, and that ethylene removal or control measures should be considered for growing crops in a tightly closed CELSS.

Wheeler, R. M.↗

NASA NTRS1998

Hydrogen Radicals, Nitrogen Radicals, and the Production of O3 in the Upper Troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HO, required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production Of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about I part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more 03 than expected.

Wennberg, P. O.↗

NASA NTRS1998

Hydrogen Radicals, Nitrogen Radicals, and the Production of O3 in the Upper Troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HO(sub x) required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.

Wennberg, P. O.↗

NASA NTRS1998

Hydrogen Radicals, Nitrogen Radicals, and the Production of O3 in the Upper Troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3, in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HO(x) required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of 03 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day.This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more 03 than expected.

Wennberg, P. O.↗

NASA NTRS1999

In-Situ Production of Solar Power Systems for Exploration

Current proposals for developing an extended human presence, beyond space stations, on the Moon and Mars increasingly consider the processing of non-terrestrial materials essential for keeping the Earth launch burden reasonable. Utilization of in-situ resources for construction of lunar and Mars bases will initially require assessment of resource availability followed by the development of economically acceptable and technically feasible extractive processes. In regard to materials processing and fabrication the lower gravity level on the Moon (0.125 g) and Mars (0.367 g) will dramatically change the presently accepted hierarchy of materials in terms of specific properties, a factor which must be understood and exploited. Furthermore, significant changes are expected in the behavior of liquid materials during processing. In casting, for example, mold filling and associated solidification processes have to be reevaluated. Finally microstructural development and therefore material properties, presently being documented through on-going research in microgravity science and applications, needs to be understood and scaled to the reduced gravity environments. One of the most important elements of a human planetary base is power production. Lunar samples and geophysical measurements returned by the Apollo missions provide detailed data on the composition and physical characteristics of the lunar materials and environment. Based on this knowledge and extrapolations of terrestrial industrial experience it is clear that several types of solar-to-electric converters can be manufactured on the Moon. It is conceivable that well over 90% of a solar-to- electric power system could be made from lunar materials. Production and utilization of photovoltaic devices for solar energy production on Earth is primarily driven by the market economy. On Earth a production plant for photovoltaic devices is intimately linked to the planets massive industrial base. A selection of off the shelf refined materials are available as well as cheap fast transportation on demand. The processes takes place (except for the few seconds reprieve in shot towers etc.) under one gravity, with solar radiation significantly modulated by weather, and under conditions where one atmosphere is free and high vacuum is cumbersome and expensive. Off Earth, on lunar or Mars bases, the cost of photovoltaic power is driven by transport costs - Earth launch, deep space transport, landing on the planetary surface. Thus there is a premium for processes that are materials self-sufficient or for closed loop in-situ processes. The lack of differentiated ores on the Moon, and lack of explored minerals on Mars and interplanetary space give a premium to universal/non-ore-specific mineral extractive processes. Initially a semiconductor/photovoltaic production facility will build on no conveniently located industrial base, further increasing the premium on closed loop self sufficient processes.

Curreri, Peter A.↗

NASA NTRS1999

Gas Sensor Evaluations in Polymer Combustion Product Atmospheres

Toxic gases produced by the combustion or thermo-oxidative degradation of materials such as wire insulation, foam, plastics, or electronic circuit boards in space shuttle or space station crew cabins may pose a significant hazard to the flight crew. Toxic gas sensors are routinely evaluated in pure gas standard mixtures, but the possible interferences from polymer combustion products are not routinely evaluated. The NASA White Sands Test Facility (WSTF) has developed a test system that provides atmospheres containing predetermined quantities of target gases combined with the coincidental combustion products of common spacecraft materials. The target gases are quantitated in real time by infrared (IR) spectroscopy and verified by grab samples. The sensor responses are recorded in real time and are compared to the IR and validation analyses. Target gases such as carbon monoxide, hydrogen cyanide, hydrogen chloride, and hydrogen fluoride can be generated by the combustion of poly(vinyl chloride), polyimide-fluoropolymer wire insulation, polyurethane foam, or electronic circuit board materials. The kinetics and product identifications for the combustion of the various materials were determined by thermogravimetric-IR spectroscopic studies. These data were then scaled to provide the required levels of target gases in the sensor evaluation system. Multisensor toxic gas monitors from two manufacturers were evaluated using this system. In general, the sensor responses satisfactorily tracked the real-time concentrations of toxic gases in a dynamic mixture. Interferences from a number of organic combustion products including acetaldehyde and bisphenol-A were minimal. Hydrogen bromide in the products of circuit board combustion registered as hydrogen chloride. The use of actual polymer combustion atmospheres for the evaluation of sensors can provide additional confidence in the reliability of the sensor response.

Delgado, Rafael H.↗

NASA NTRS1999

Seasonal-to-Interannual Variability in Antarctic Sea-Ice Dynamics, and Its Impact on Surface Fluxes and Water Mass Production

Strong seasonal and interannual signals in Antarctic bottom-water outflow remain unexplained yet are highly correlated with anomalies in net sea-ice growth in coastal polynyas. The mechanisms responsible for driving salination and replenishment and rejuvenation of the dense shelf "source" waters likely also generate pulses of bottom water outflow. The objective of this research is to investigate time-scales of variability in the dynamics of sea-ice in the Southern Ocean in order to determine the primary sites for production of dense shelf waters. We are using a merged satellite/buoy sea-ice motion data set for the period 1978-present day to compute the dynamics of opening and closing of coastal polynyas over the continental shelf. The Ocean Circulation and Climate Advanced Model (OCCAM) ocean general circulation model with coupled sea-ice dynamics is presently forced using National Center for Environmental Prediction (NCEP) data to simulate fluxes and the salination impact of the ocean shelf regions. This work is relevant in the context of measuring the influence of polar sea-ice dynamics upon polar ocean characteristics, and thereby upon global thermohaline ocean circulation. Interannual variability in simulated net freezing rate in the Southern Weddell Sea is shown for the period 1986-1993. There is a pronounced maximum of ice production in 1988 and minimum in 1991 in response to anomalies in equatorward meridional wind velocity. This follows a similar approximate 8-year interannual cycle in Sea Surface Temperature (SST) and satellite-derived ice-edge anomalies reported elsewhere as the "Antarctic Circumpolar Wave." The amplitude of interannual fluctuations in annual net ice production are about 40% of the mean value, implying significant interannual variance in brine rejection and upper ocean heat loss. Southward anomalies in wind stress induce negative anomalies in open water production, which are observed in passive microwave satellite images. Thus, cycles of enhanced poleward wind stress reduce ice growth by compacting the ice along the coastline and closing open water in leads and polynyas. Model simulations confirm that years of low ice production, such as 1991, coincide with years of lower than normal bottom water outflow. Future plans include the assimilation of satellite ice concentrations and ice drift dynamics to more accurately constrain boundary conditions in the model.

Drinkwater, Mark R.↗