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NASA NTRS2002

Comprehension of Navigation Directions

Subjects were shown navigation instructions varying in length directing them to move in a space represented by grids on a computer screen. They followed the instructions by clicking on the grids in the locations specified. Some subjects repeated back the instructions before following them, some did not, and others repeated back the instructions in reduced form, including only the critical words. The commands in each message were presented simultaneously for half of the subjects and sequentially for the others. For the longest messages, performance was better on the initial commands and worse on the final commands with simultaneous than with sequential presentation. Instruction repetition depressed performance, but reduced repetition removed this disadvantage. Effects of presentation format were attributed to visual scanning strategies. The advantage for reduced repetition was attributable either to enhanced visual scanning or to reduced output interference. A follow-up study with auditory presentation supported the visual scanning explanation.

Healy, Alice F.↗

NASA NTRS2002

Effects of Thermomechanical History on the Tensile Behavior of Nitinol Ribbon

Shape memory alloys (SMAs) have enormous potential for a wide variety of applications. A large body of work exists on the characterization of the microstructure and stress-strain behavior of these alloys, Nitinol (NiTi) in particular. However, many attributes of these materials are yet to be fully understood. Previous work at NASA Langley Research Center (LaRC) has included fabrication of hybrid composite specimens with embedded Nitinol actuators and modeling of their thermomechanical behavior. An intensive characterization effort has been undertaken to facilitate fundamental understanding of this alloy and to promote implementation of Nitinol in aerospace applications. Previous work revealed attributes of the Nitinol ribbon that were not easily rationalized with existing data in the literature. In particular, tensile behavior at ambient temperature showed significant dependence on the thermomechanical history prior to testing. The present work is focused on characterizing differences in the microstructure of Nitinol ribbons exposed to four different thermomechanical histories and correlation of the microstructure with tensile properties. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) analysis were employed to rationalize the microstructures present after exposure to various thermomechanical histories. Three of the Nitinol ribbon conditions were reversible upon heating (in the DSC) through the reverse transformation temperature (A(sub f) to transform the microstructure to austenite. However, the prior thermomechanical conditioning for the Nitinol ribbon that reflected the entire fabrication procedure (4% thermal cycle condition) was found to have an irreversible effect on the microstructure, as it remained unchanged after repeated complete thermal cycles. Tensile tests were conducted to determine the effect of prior thermomechancal conditioning on both the tensile behavior of the Nitinol ribbons and the stress state of the microstructure. The stress-strain behavior of the Nitinol actuators appears to be governed by the interplay between two major variables: namely, microstructural constituents such as the R-phase and the martensite; and the stress state of these constituents (whether twinned with low residual stresses, or detwinned with high residual stresses). The most significant difference in the stress-strain behavior of the four conditions, the critical stress required to achieve an initial stress plateau, was found to depend on both the amount and stress state (twinned or detwinned) of R-phase present in the initial microstructure. Thus, the effect of prior thermomechanical processing is critical to the resulting tensile behavior of the Nitinol actuator. For numerical modeling inputs one must take into account the entire fabrication process on the Nitinol actuator.

Lach, Cynthia L.↗

NASA NTRS2003

Flightweight Carbon Nanotube Magnet Technology

Virtually all plasma-based systems for advanced airborne/spaceborne propulsion and power depend upon the future availability of flightweight magnet technology. Unfortunately, current technology for resistive and superconducting magnets yields system weights that tend to counteract the performance advantages normally associated with advanced plasma-based concepts. The ongoing nanotechnology revolution and the continuing development of carbon nanotubes (CNT), however, may ultimately relieve this limitation in the near future. Projections based on recent research indicate that CNTs may achieve current densities at least three orders of magnitude larger than known superconductors and mechanical strength two orders of magnitude larger than steel. In fact, some published work suggests that CNTs are superconductors. Such attributes imply a dramatic increase in magnet performance-to-weight ratio and offer real hope for the construction of true flightweight magnets. This Technical Publication reviews the technology status of CNTs with respect to potential magnet applications and discusses potential techniques for using CNT wires and ropes as a winding material and as an integral component of the containment structure. The technology shortfalls are identified and a research and technology strategy is described that addresses the following major issues: (1) Investigation and verification of mechanical and electrical properties, (2) development of tools for manipulation and fabrication on the nanoscale, (3) continuum/molecular dynamics analysis of nanotube behavior when exposed to practical bending and twisting loads, and (4) exploration of innovative magnet fabrication techniques that exploit the natural attributes of CNTs.

Chapman, J. N.↗

NASA NTRS2003

Enhanced Weather Radar (EWxR) System

An airborne weather radar system, the Enhanced Weather Radar (EWxR), with enhanced on-board weather radar data processing was developed and tested. The system features additional weather data that is uplinked from ground-based sources, specialized data processing, and limited automatic radar control to search for hazardous weather. National Weather Service (NWS) ground-based Next Generation Radar (NEXRAD) information is used by the EWxR system to augment the on-board weather radar information. The system will simultaneously display NEXRAD and on-board weather radar information in a split-view format. The on-board weather radar includes an automated or hands-free storm-finding feature that optimizes the radar returns by automatically adjusting the tilt and range settings for the current altitude above the terrain and searches for storm cells near the atmospheric 0-degree isotherm. A rule-based decision aid was developed to automatically characterize cells as hazardous, possibly-hazardous, or non-hazardous based upon attributes of that cell. Cell attributes are determined based on data from the on-board radar and from ground-based radars. A flight path impact prediction algorithm was developed to help pilots to avoid hazardous weather along their flight plan and their mission. During development the system was tested on the NASA B757 aircraft and final tests were conducted on the Rockwell Collins Sabreliner.

Kronfeld, Kevin M.↗

NASA NTRS2003

Analysis of Near Simultaneous Jimsphere and AMPS High Resolution Wind Profiles

The high-resolution wind profile of the Automated Meteorological Profiling System (HRAMPS) is the proposed replacement for the Jimsphere measurement system used to support NASA Shuttle launches from the Eastern Test Range (ETR). Samples of twenty-six ETR near simultaneous Jimsphere and HRAMPS wind profiles were obtained for Shuttle program HRAMPS certification studies. Shuttle systems engineering certification is to ensure that spacecraft and launch vehicle systems performance and safety evaluations for each launch (derived from flight simulations with Jimsphere wind profile data bases) retain their validity when HRAMPS profiles are used on day-of-launch (DOL) in trajectory and loads simulations to support the commit-to-launch decision. This paper describes a statistical analysis of the near simultaneous profiles. In principle the differences between a Jimsphere profile and an HRAMPS profile should be attributed to tracking technology (radar versus GPS tracking of a Jimsphere flight element) and the method for derivation of wind vectors from the raw tracking data. In reality, it is not technically feasible to track the same Jimsphere balloon with the two systems. The aluminized Mylar surface of the standard Jimsphere flight element facilitates radar tracking, but it interferes with HRAMPS during simultaneous tracking. Suspending a radar reflector from an HRAMPS flight element (Jimsphere without aluminized coating) does not produce satisfactory Jimsphere profiles because of intermittent radar returns. Thus, differences between the Jimsphere and HRAMPS profiles are also attributed to differences in the trajectories of separate flight elements. Because of small sample size and a test period limited to one winter season, test measurements during extreme high winds aloft could not have been expected and did not occur. It is during the highest winds that the largest differences between Jimsphere and HRAMPS would occur because the distance between flight elements would be larger. Jimsphere radar tracking noise increases as a function of balloon displacement downrange. The Jimsphere data processing compensates for tracking signal/noise degradation by increasing the smoothing interval. The Jimsphere wind profile effective resolution is a function of downrange distance and altitude, whereas the effective resolution of the HRAMPS should be independent of those variables. The procedure used for editing Jimsphere spikes in Shuttle DOL profiles was not implemented for the Jimsphere profile measurements during the AMPS field tests. For this analysis a code was developed that essentially mimics DOL Jimsphere spike editing. Jimsphere profiles have somewhat more noise in the wavelength range less than 200m defined as the noise floor. No differences between Jimsphere and HRAMPS wind profile pairs have been found that would support denial of HRAMPS certification for application in Shuttle DOL applications. The reliability of the HRAMPS system, which is an important certification issue, is not addressed in this study.

Adelfang, S. I.↗

NASA NTRS2003

Development and Engineering Design in Support of "Rover Ranch": A K-12 Outreach Software Project

A continuation of the initial development started in the summer of 1999, the body of work performed in support of 'ROVer Ranch' Project during the present fellowship dealt with the concrete concept implementation and resolution of the related issues. The original work performed last summer focused on the initial examination and articulation of the concept treatment strategy, audience and market analysis for the learning technologies software. The presented work focused on finalizing the set of parts to be made available for building an AERCam Sprint type robot and on defining, testing and implementing process necessary to convert the design engineering files to VRML files. Through reverse engineering, an initial set of mission critical systems was designed for beta testing in schools. The files were created in ProEngineer, exported to VRML 1.0 and converted to VRML 97 (VRML 2.0) for final integration in the software. Attributes for each part were assigned using an in-house developed JAVA based program. The final set of attributes for each system, their mutual interaction and the identification of the relevant ones to be tracked, still remain to be decided.

Pascali, Raresh↗

NASA NTRS2003

Wind Tunnel Testing of Various Disk-Gap-Band Parachutes

Two Disk-Gap-Band model parachute designs were tested in the NASA Langley Transonic Dynamics Tunnel. The purposes of these tests were to determine the drag and static stability coefficients of these two model parachutes at various subsonic Mach numbers in support of the Mars Exploration Rover mission. The two model parachute designs were designated 1.6 Viking and MPF. These model parachute designs were chosen to investigate the tradeoff between drag and static stability. Each of the parachute designs was tested with models fabricated from MIL-C-7020 Type III or F-111 fabric. The reason for testing model parachutes fabricated with different fabrics was to evaluate the effect of fabric permeability on the drag and static stability coefficients. Several improvements over the Viking-era wind tunnel tests were implemented in the testing procedures and data analyses. Among these improvements were corrections for test fixture drag interference and blockage effects, and use of an improved test fixture for measuring static stability coefficients. The 1.6 Viking model parachutes had drag coefficients from 0.440 to 0.539, while the MPF model parachutes had drag coefficients from 0.363 to 0.428. The 1.6 Viking model parachutes had drag coefficients 18 to 22 percent higher than the MPF model parachute for equivalent fabric materials and test conditions. Model parachutes of the same design tested at the same conditions had drag coefficients approximately 11 to 15 percent higher when manufactured from F-111 fabric as compared to those fabricated from MIL-C-7020 Type III fabric. The lower fabric permeability of the F-111 fabric was the source of this difference. The MPF model parachutes had smaller absolute statically stable trim angles of attack as compared to the 1.6 Viking model parachutes for equivalent fabric materials and test conditions. This was attributed to the MPF model parachutes larger band height to nominal diameter ratio. For both designs, model parachutes fabricated from F-111 fabric had significantly greater statically stable absolute trim angles of attack at equivalent test conditions as compared to those fabricated from MILC-7020 Type III fabric. This reduction in static stability exhibited by model parachutes fabricated from F-111 fabric was attributed to the lower permeability of the F-111 fabric. The drag and static stability coefficient results were interpolated to obtain their values at Mars flight conditions using total porosity as the interpolating parameter.

Cruz, Juan R.↗

NASA NTRS2003

Palagonitic (Not Andesitic) Mars: Evidence from Thermal Emission and VNIR Spectra of Palgonitic Alteration Rinds on Basaltic Rock

Visible and near-IR (VNIR) spectra of both Martian bright and dark regions are characterized by a ferric absorption edge extending from approx. 400 to 750 nm, with bright regions having about twice the reflectivity at 750 nm as dark regions. Between 750 nm to beyond 2000 nm, bright and dark regions have nearly constant and slightly negative spectral slopes, respectively. Depending on location, bright regions have shallow reflectivity minima in the range 850-910 nm that are attributed to ferric oxides. Similarly, dark regions have shallow reflectivity minima near approx. 950 and 1700-2000 nm that are attributed to ferrous silicate minerals (pyroxene). Among terrestrial geologic materials, the best spectral analogues for Martian bright regions are certain palagonitic tephras from Mauna Kea Volcano (Hawaii). By definition, palagonite is a "yellow or orange isotropic mineraloid formed by hydration and devitrification of basaltic glass". The ferric pigment in palagonite is nanometer-sized ferric oxide particles (np-Ox) dispersed throughout the hydrated basaltic glass matrix. The hydration state of the np-Ox particles is not known, but the best Martian spectral analogues contain allophane-like materials and not crystalline phyllosilicates.

R V Morris↗

NASA NTRS2003

The MODIS Aerosol Algorithm, Products and Validation

The MODerate resolution Imaging Spectroradiometer (MODIS) aboard both NASA's Terra and Aqua satellites is making near global daily observations of the earth in a wide spectral range. These measurements are used to derive spectral aerosol optical thickness and aerosol size parameters over both land and ocean. The aerosol products available over land include aerosol optical thickness at three visible wavelengths, a measure of the fraction of aerosol optical thickness attributed to the fine mode and several derived parameters including reflected spectral solar flux at top of atmosphere. Over ocean, the aerosol optical thickness is provided in seven wavelengths from 0.47 microns to 2.13 microns. In addition, quantitative aerosol size information includes effective radius of the aerosol and quantitative fraction of optical thickness attributed to the fine mode. Spectral aerosol flux, mass concentration and number of cloud condensation nuclei round out the list of available aerosol products over the ocean. The spectral optical thickness and effective radius of the aerosol over the ocean are validated by comparison with two years of AERONET data gleaned from 133 AERONET stations. 8000 MODIS aerosol retrievals colocated with AERONET measurements confirm that one-standard deviation of MODIS optical thickness retrievals fall within the predicted uncertainty of delta tauapproximately equal to plus or minus 0.03 plus or minus 0.05 tau over ocean and delta tay equal to plus or minus 0.05 plus or minus 0.15 tau over land. 271 MODIS aerosol retrievals co-located with AERONET inversions at island and coastal sites suggest that one-standard deviation of MODIS effective radius retrievals falls within delta r_eff approximately equal to 0.11 microns. The accuracy of the MODIS retrievals suggests that the product can be used to help narrow the uncertainties associated with aerosol radiative forcing of global climate.

Remer, L. A.↗

NASA NTRS2003

Next Generation of Hall Thrusters for Space Propulsion

During the previous year, grant activity research focused on demonstrating high thrust/power operation of Hall thrusters. Performance of a low power and a high power Hall thruster was experimentally investigated at discharge voltages from 100 to 150 volts. Discharge efficiencies dropped significantly as discharge voltage was decreased over this range. Reductions in discharge efficiency with decreasing discharge voltage were attributed to reductions in ionization efficiency and/or ion acceleration through a potential less that the applied discharge voltage relative to the performance of state-of-art Hall thrusters operating at discharge voltages of 300 Volts and above. The low power Hall thruster exhibited a more pronounced reduction in discharge efficiency with decreasing discharge voltage. This was attributed to increased electron leakage related to the axial distribution of the radial magnetic field. These data demonstrated that the thrust benefit of operating at discharge voltages below 130 Volts was offset by a corresponding decrease in discharge efficiency for a given input power. Additional activities included continued support of on-going Hall thruster propulsion research within the On-Board Propulsion Branch at NASA Glenn Research Center.

Keith, Theo G., Jr.↗

NASA NTRS2003

Looking for Speed!! Go Optical Ultra-Fast Photonic Logic Gates for the Future Optical Communication and Computing

Recently, we developed two ultra-fast all-optical switches in the nanosecond and picosecond regimes. The picosecond switch is made of a polydiacetylene thin film coated on the interior wall of a hollow capillary of approximately 50 micron diameter by a photo-polymerization process. In the setup a picosecond Nd:YAG laser at 10 Hz and at 532 nm with a pulse duration of approximately 40 ps was sent collinearly along a cw He-Ne laser beam and both were waveguided through the hollow capillary. The setup functioned as an Exclusive OR gate. On the other hand, the material used in the nanosecond switch is a phthalocyanine thin film, deposited on a glass substrate by a vapor deposition technique. In the setup a nanosecond, 10 Hz, Nd:YAG laser of 8 ns pulse duration was sent collinearly along a cw He-Ne laser beam and both were wave-guided through the phthalocyanine thin film. The setup in this case functioned as an all-optical AND logic gate. The characteristic table of the ExOR gate in polydiacetylene film was attributed to an excited state absorption process, while that of the AND gate was attributed to a saturation process of the first excited state. Both mechanisms were thoroughly investigated theoretically and found to agree remarkably well with the experimental results. An all-optical inverter gate has been designed but has not yet been demonstrated. The combination of all these three gates form the foundation for building all the necessary gates needed to build a prototype of an all-optical system.

Abdeldayem, Hossin↗

NASA NTRS2004

Impact Processes in the Solar System

Our laboratory has previously conducted impact fracture and dynamic failure tests. Polanskey and Ahrens [1990] mapped the fractures from a series of laboratory craters (Fig. 1) and Ahrens and Rubin [ 1993] inferred that the usually further extending radial cracks resulted from tensional failure during the compression of the shock propagation. The radial spreading induced by the particle velocity field caused the stresses perpendicular to the shock front to become sufficiently large and tensile. This induces "radial fractures." The concentric fractures are attributed to the tensional failure occurring after the initial compressive phase. Upon radial propagation of the stress wave the negative tension behind the stress-wave front caused failure along the quasi-spherical concentric fractures. The near-surface and spall fractures are attributed to the fractures described by Melosh [1984]. These are activated by impact and can launch relatively unshocked samples of planetary surfaces to speeds exceeding escape velocity. In the case of Mars, some of these surface samples presumably become the SNC (Mars) meteorites.

Ahrens, Thomas J.↗

NASA NTRS2004

Analysis of Orientation-dependence of Martian Gullies

The recent discovery of small Martian gullies has stimulated debate about the role that water plays on the Martian surface under current or recent conditions. Of critical importance in evaluating various gully hypotheses is reliable morphometric and orientation data. The former centers on such questions as whether the water (or another fluid) emanated from a surface or sub-surface source and the duration of flow. The latter ties into whether solar insolation has an important effect on formation of the initial water source and subsequent mobilization. Initial studies of gullies indicated a poleward orientation dependence, an observation which has recently been challenged. Herein we investigate the orientation of Martian gullies and the dependence of various parameters on the orientation. Whereas previous studies have been global or through most of the southern hemisphere, we focus on several specific regions. This approach offers some advantages in that regional variations are factored out, such that of lithology, ground water table depth (if any), surface thermal properties, and other parameters are more or less the same in a given region. Differences in gully attributes as a function of orientation within a region can more easily be attributable to solar insolation effects than is the case for global statistics. We use the orientation to constrain several classes of gully formation hypotheses. 1) A favored orientation toward the pole across all regions could indicate a process dominated by melting of cold trapped ice, snow, or condensed volatiles from incident sunlight during summer under current conditions. 2) Variations among all regions would be more consistent with mechanisms less strongly tied to current solar insolation, such as geothermal heating of ice. 3) Favored orientations within specific regions, but differing among regions, could indicate a preference for poleward ices and melting, with orientation being a function of age and dependent on variations in obliquity and precision. We find that the gullies fall into either categories 2 or 3, but not 1, indicating the recent melting of cold trapped condensates is unlikely the sole formation mechanism.

Mohan, S.↗

NASA NTRS2003

Records of our Early Biosphere Illuminate our Origins and Guide our Search for Life Beyond Earth

A scientific "mission of exploration to early Earth" will help us chart the distribution of life elsewhere. We must discriminate between attributes of biospheres that are universal versus those attributes that represent principally the outcomes of long-term survival specifically on Earth. In addition to the basic physics and chemistry of matter, the geologic evolution of rocky habitable planets and their climates might be similar elsewhere in the Universe. Certain key agents that drive long-term environmental change (e.g., stellar evolution, impacts, geothermal heat flow, tectonics, etc.) can help us to reconstruct ancient climates and to compare their evolution among populations of Earth- like planets. Early Earth was tectonically more active than today and therefore it exhaled reduced chemical species into the more oxidized surface environment at greater rates. This tectonic activity thus sustained oxidation-reduction reactions that provided the basis for the development of biochemical pathways that harvest chemical energy ("bioenergetics"). Most examples of bioenergetics today that extract energy by reacting oxidized and reduced chemicals in the environment were likely more pervasive among our microbial ancestors than are the presently known examples of photosynthesis. The geologic rock record indicates that, as early as 3.5 billion years ago (3.5 Ga), microbial biofilms were widespread within the coastal environments of small continents and tectonically unstable volcanic islands. Non oxygen-producing (non-oxygenic) photosynthesis preceded oxygenic photosynthesis, but all types of photosynthesis contributed substantially to the long-term increase in global primary biological productivity. Evidence of photosynthesis is tentative by 3.5 Ga and compelling by 2.7 Ga. Evidence of oxygenic photosynthesis is strong by 2.7 Ga and compelling by 2.3 Ga. These successive innovations transformed life from local communities that survived principally by catalyzing chemical equilibration to a globally dominant agent that created and sustained widespread chemical disequilibria in the environment and shallow crust. Major biogeochemical perturbations ca. 2.3 to 2.0 Ga, 1.3 Ga, and also 0.8 to 0.6 Ga, contributed to the irreversible oxidation of the global environment and perhaps also triggered evolutionary innovations (e.g., the development of multi-cellular biota) that became the foundations of our modern biosphere. Understanding the nature and timing of this ascent of life is crucial for discerning our o m beginnings. This understanding also empowers OUT search for the origins, evolution and distribution of life elsewhere in our solar system and beyond.

DesMarais, David J.↗

NASA NTRS2003

Thermal Effects on the Compressive Behavior of IM7/PET15 Laminates

The effect of changing operating temperature on the compressive response of IM7/PETI5 composite laminates is investigated within this paper. The three temperatures evaluated for this study were 129 C, 21 C, and 177 C, a spectrum from cryogenic to an elevated operating temperature. Laminate compressive strength property testing was conducted using the Wyoming Combined Load Compression fixture to generate strength data at the three operating temperatures of interest for several lay-ups. A three-dimensional finite element analysis model of a [90/0]8s composite laminate subject to compressive loading is developed. The model is used to study the key attributes of the laminate that significantly influence the state of stress in the laminate. Both the resin rich layer located between lamina and the thermal residual stresses present in the laminate due to curing are included in the analysis model. For the laminate modeled, the effect of modeling temperature dependent material properties was determined to be insignificant for the operating temperatures studied. Simply using the material properties measured at the operating temperature of interest was sufficient for predicting stresses accurately in a linear analysis for the current problem. The three-dimensional analysis results revealed that the application of an applied compressive axial load in the 0-degree direction decreased the interlaminar stresses present in the laminate initially due to curing. Therefore, failure was concluded not be attributable to the interlaminar stresses in the composite laminate being studied when a compressive load is applied. The magnitude of the measured laminate compressive strength change with a change in temperature is concluded to be dominated by the change in the lamina compressive axial strength with a change in temperature.

Walker, Sandra Polesky↗

NASA NTRS2000

Al-Li Alloy 1441 for Fuselage Applications

A cooperative investigation was conducted to evaluate Al-Cu-Mg-Li alloy 1441 for long service life fuselage applications. Alloy 1441 is currently being used for fuselage applications on the Russian Be-103 amphibious aircraft, and is expected to be used for fuselage skin on a new Tupolev business class aircraft. Alloy 1441 is cold-rollable and has several attributes that make it attractive for fuselage skin applications. These attributes include lower density and higher specific modulus with similar strength as compared to conventional Al-Cu-Mg alloys. Cold-rolled 1441 Al-Li sheet specimens were tested at NASA Langley Research Center (LaRC) and at the All-Russia Institute of Aviation Materials (VIAM) in Russia to evaluate tensile properties, fracture toughness, impact resistance, fatigue life and fatigue crack growth rate. In addition, fuselage panels were fabricated by Tupolev Design Bureau (TDB) using 1441 skins and Al-Zn-Mg-Cu alloy stiffeners. The panels were subjected to cyclic pressurization fatigue tests at TDB and at LaRC to simulate fuselage pressurization/depressurization during aircraft service. This paper discusses the results from this investigation.

Bird, R. K.↗

NASA NTRS2002

Space flight and oxidative stress

Space flight is associated with an increase in oxidative stress after return to 1g. The effect is more pronounced after long-duration space flight. The effects lasts for several weeks after landing. In humans there is increased lipid peroxidation in erythrocyte membranes, reduction in some blood antioxidants, and increased urinary excretion of 8-iso-prostaglandin F(2alpha) and 8-oxo-7,8 dihydro-2 deoxyguanosine. Isoprostane 8-iso-prostaglandin F(2alpha) and 8-oxo-7,8 dihydro-2 deoxyguanosine are markers for oxidative damage to lipids and DNA, respectively. The changes have been attributed to a combination of the energy deficiency that occurs during flight and substrate competition for amino acids occurring between repleting muscle and other tissues during the recovery phase. The observations in humans have been complemented by rodent studies. Most rodent studies showed increased production of lipid peroxidation products postflight and decreased antioxidant enzyme activity postflight. The rodent observations were attributed to the stress associated with reentry into Earth's gravity. Decreasing the imbalance between the production of endogenous oxidant defenses and oxidant production by increasing the supply of dietary antioxidants may lessen the severity of the postflight increase in oxidative stress.

long duration↗

NASA NTRS2002

Effects of perfluorohexane vapor on relative blood flow distribution in an animal model of surfactant-depleted lung injury

OBJECTIVE: To test the hypothesis that treatment with vaporized perfluorocarbon affects the relative pulmonary blood flow distribution in an animal model of surfactant-depleted acute lung injury. DESIGN: Prospective, randomized, controlled trial. SETTING: A university research laboratory. SUBJECTS: Fourteen New Zealand White rabbits (weighing 3.0-4.5 kg). INTERVENTIONS: The animals were ventilated with an FIO(2) of 1.0 before induction of acute lung injury. Acute lung injury was induced by repeated saline lung lavages. Eight rabbits were randomized to 60 mins of treatment with an inspiratory perfluorohexane vapor concentration of 0.2 in oxygen. To compensate for the reduced FIO(2) during perfluorohexane treatment, FIO(2) was reduced to 0.8 in control animals. Change in relative pulmonary blood flow distribution was assessed by using fluorescent-labeled microspheres. MEASUREMENTS AND MAIN RESULTS: Microsphere data showed a redistribution of relative pulmonary blood flow attributable to depletion of surfactant. Relative pulmonary blood flow shifted from areas that were initially high-flow to areas that were initially low-flow. During the study period, relative pulmonary blood flow of high-flow areas decreased further in the control group, whereas it increased in the treatment group. This difference was statistically significant between the groups (p =.02) as well as in the treatment group compared with the initial injury (p =.03). Shunt increased in both groups over time (control group, 30% +/- 10% to 63% +/- 20%; treatment group, 37% +/- 20% to 49% +/- 23%), but the changes compared with injury were significantly less in the treatment group (p =.03). CONCLUSION: Short treatment with perfluorohexane vapor partially reversed the shift of relative pulmonary blood flow from high-flow to low-flow areas attributable to surfactant depletion.

NASA Discipline Cardiopulmonary↗