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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Polymeric Coatings for Electrodynamic Tethers

Two polymeric coatings have been developed for the Propulsive Small Expendable Deployer System (ProSEDS) mission. ProSEDS is designed to provide an on-orbit demonstration of the electrodynamic propulsion capabilities of tethers in space. The ProSEDS experiment will be a secondary payload on a Delta II unmanned expendable booster scheduled for launch in August 2000. A 5-km conductive tether is attached to the Delta 11 second stage and collects current from the low Earth orbit (LEO) plasma to facilitate de-orbit of the spent stage. The conductive tether is attached to a 10-km non-conductive tether, the other end of which is attached to an endmass containing several scientific instruments. A bare metal tether would have the best conductivity but thermal concerns preclude this design. A conductive polymer developed by Triton Systems has been optimized for conductivity and thermo-optical properties. The current design for the ProSEDS conductive tether is seven strands of 28 AWG aluminum wire individually coated with 8.7 micrometers (0.35 mil) of an atomic oxygen-resistant conductive polymer composed of a mixture of 87% Clear Oxygen-Resistant polymer (COR) and 13% polyanaline (PANi), wrapped around a braided Kevlar (TM) 49 core. Extensive testing has been performed at the Marshall Space Flight Center (MSFC) to qualify this material for flight on ProSEDS. Atomic oxygen exposure was performed, with solar absorptance and infrared emittance measured before and after exposure. Conductivity was measured before and after atomic oxygen exposure. High voltage tests, up to 1500 V, of the current collecting ability of the COR/PANi have been completed. Approximately 160 meters of the conductive tether closest to the Delta 11 second stage is insulated to prevent any electron reconnection to the tether from the plasma contactor. The insulation is composed of polyimide overcoated with TOR-BP, another polymeric coating developed by Triton for this mission. TOR-BP acts as both insulator and a protective coating against atomic oxygen erosion. The insulation has been tested to withstand 5000 V.

Vaughn, Jason A.↗
NASA NTRS1994

Theoretical Study of Electron Scattering By Small Clusters and Adsorbates

Current interest in clusters stems from their role as novel materials as well as a possible extension of cluster results to bulk systems. Experimental investigations on clusters have been carried out using laser spectroscopy, microwave spectroscopy, heavy-particle collisions, as well as electron collisions with earlier experimental work on electron attachment and ionization having been reviewed previously. Recently, Mark and coworkers studied the decay channels of cluster ions following electron impact ionization. Rauth et al. reported the formation of the superhalogen ion SF7(-) and other nonstoichiometric cluster ions in their study of electron attachment to SF6 clusters. Kresin et al. measured the absolute electron-impact depletion cross section of metal clusters Na8, Na(20), and Na(40). They found that the inelastic scattering cross section increased with cluster size and was considerably greater than the hard sphere collision cross sections. They hypothesized that electron attachment and collision-induced fragmentation were the dominant physical processes responsible for this effect. For the two smaller clusters, they also found a sharp increase in the cross section near threshold. Most theoretical studies of clusters have been devoted to their electronic structures, vibrational relaxation, and predissociation while investigations of electron scattering from clusters has been lacking. In view of this, we recently undertook an ab initio study of electron scattering from small Be clusters and BeCO. Beryllium was chosen because it is readily amenable to ab t'nitio calculations. Moreover, the electronic structure of Be clusters has been studied extensively, showing that the Be-Be bond is relatively weak in comparison with a normal chemical bond. Our investigation focuses on how the cross sections change with cluster size and geometry. The range of energy studied, 0.05 - 5.0 eV, is chosen because of the ubiquitous resonance in the low-energy scattering of Be. Hence it can be determined if it is possible, as a consequence of the weaker bonds in the Be clusters, to identify the atomic origin of the cluster resonance.

Huo, Winifred M.↗
NASA NTRS2001

Beagle 2: The Next Exobiology Mission to Mars

Beagle 2 is a 60 kg probe (with a 30 kg lander) developed in the United Kingdom for inclusion on the European Space Agency's 2003 Mars Express. Beagle 2 will deliver to the Martian surface a payload which consists of a high percentage of science instruments to landed spacecraft mass. Beagle 2 will be launched in June, 2003 with Mars Express on a Soyuz-Fregat rocket from the Baikonur Cosmodrome in Kazakhstan. Beagle 2 will land on Mars on December 26, 2003 in the Isidis Planitia basin (approximately 10 degrees N and 275 degrees W), a large sedimentary basin that overlies the boundary between ancient highlands and northern plains. Isidis Planitia, the third largest basin on Mars, which is possibly filled with sediment deposited at the bottom of long-standing lakes or seas, offers an ideal environment for preserving traces of life. Beagle 2 was developed to search for organic material and other volatiles on and below the surface of Mars in addition to the study of the inorganic chemistry and mineralogy. Beagle 2 will utilize a mechanical mole and grinder to obtain samples from below the surface, under rocks and inside rocks. A pair of stereo cameras will image the landing site along with a microscope for examination of surface and rock samples. Analyses will include both rock and soil samples at various wavelengths, X-ray spectrometer and Mossbauer spectrometer as well as a search for organics and other light element species (e.g. carbonates and water) and measurement of their isotopic compositions. Beagle 2 has as its focus the goal of establishing whether evidence for life existed in the past on Mars at the Isidis Planitia site or at least establishing if the conditions were ever suitable. Carbonates and organic components were first recognized as existing on Mars when they were found in the Martian meteorite Nakhla. Romanek et al showed the carbonates in ALH84001 were formed at low temperatures. McKay et al noted possible evidence of early life on Mars within the ALH84001 meteorite. Thomas-Keprta et al showed the magnetite biomarkers in ALH84001's carbonates are indistinguishable from those formed by magnetotactic bacteria found on Earth. Gibson et al showed there was significant evidence for liquid water and biogenic products present on Mars across a 3.9 billion year period. A mechanical arm (PAW) operates from the lander and is used for science operations along with sample acquisition. Instruments attached to the PAW include: stereo cameras, Mossbauer instrument, X-ray fluorescence instrument, microscope, environmental sensors, rock corer/grinder, a spoon, mirror, brushes, a mole attachment for acquisition of subsurface to depths of 1 to 2 meters and an illumination device. Each camera has 14 filters which have been optimized for mineralogy composition, dust and water vapor detection. The microscope's camera is designed for viewing the size and shape of dust particles, rock surfaces, microfossils, and characteristics of the samples prior to introduction into the gas analysis package (GAP). The camera has a resolution of 4 microns/pixel, features four color capability (red, green, blue and UV (ultraviolet) fluoresence), a depth of focus of 40 micrometers and translation stage of +3 millimeters. The heart of the Beagle 2's life detection package is the gas analysis package (GAP), which consists of a mass spectrometer with collectors at fixed masses for precise isotopic ratio measurements and voltage scanning for spectral analysis. Primary aim of the GAP is to search for the presence of bulk constituents, individual species, and isotopic fractionations for both extinct and extent life along with studying the low-temperature geochemistry of the hydrogen, carbon, nitrogen and oxygen components on Mars from both the surface and atmosphere. GAP is a magnetic sector mass spectrometer with the range of 1 to 140 amu which can be operated in both the static and dynamic modes. A triple Faraday collector array will be used for C, N and O ratios along with a double Faraday array for H/D. Pulse counting electron multiplier will be utilized for noble gases and selected organics. Anticipated detection limits are at the picomole level for operation in the static mode of operation and high precision isotopic measurements will be made in the dynamic mode. Sample processing and preparation system consists of reaction vessels along with references. Sample ovens capable of being heated are attached to the manifold for sample combustion. Surface, subsurface materials and interior rock specimens will be combusted in pure oxygen gas at various temperature intervals to release organic matter and volatiles. Combustion process will permit detection of all forms and all atoms of carbon present in the samples. A chemical processing system is capable of a variety of conversion reactions. Gases are manipulated either by cryogenic or chemical reactions and passed through the gas handling portion of the vacuum system. There are two modes of operation: quantitative analysis and precise isotopic measurements. Additional information is contained in the original extended abstract.

Gibson, Everett K., Jr.↗
NASA NTRS2002

The Surface Interface Characteristics of Vertically Aligned Carbon Nanotube and Graphitic Carbon Fiber Arrays Grown by Thermal and Plasma Enhanced Chemical Vapor Deposition

The development of nano-arrays for sensors and devices requires the growth of arrays with the proper characteristics. One such application is the growth of vertically aligned carbon nanotubes (CNTs) and graphitic carbon fibers (GCFs) for the chemical attachment of probe molecules. The effectiveness of such an array is dependent not only upon the effectiveness of the probe and the interface between that probe and the array, but also the array and the underlaying substrate. If that array is a growth of vertically aligned CNTs or GCFs then the attachment of that array to the surface is of the utmost importance. This attachment provides the mechanical stability and durability of the array, as well as, the electrical properties of that array. If the detection is to be acquired through an electrical measurement, then the appropriate resistance between the array and the surface need to be fabricated into the device. I will present data on CNTs and GCFs grown from both thermal and plasma enhanced chemical vapor deposition. The focus will be on the characteristics of the metal film from which the CNTs and GCFs are grown and the changes that occur due to changes within the growth process.

Delzeit, Lance↗
NASA NTRS2002

Initial Flight Tests of the NASA F-15B Propulsion Flight Test Fixture

Flights of the F-15B/Propulsion Flight Test Fixture (PFTF) with a Cone Drag Experiment (CDE) attached have been accomplished at NASA Dryden Flight Research Center. Mounted underneath the fuselage of an F-15B airplane, the PFTF provides volume for experiment systems and attachment points for propulsion experiments. A unique feature of the PFTF is the incorporation of a six-degree-of-freedom force balance. The force balance mounts between the PFTF and experiment and measures three forces and moments. The CDE has been attached to the force balance for envelope expansion flights. This experiment spatially and inertially simulates a large propulsion test article. This report briefly describes the F-15B airplane, the PFTF, and the force balance. A detailed description of the CDE is provided. Force-balance ground testing and stiffness modifications are described. Flight profiles and selected flight data from the envelope expansion flights are provided and discussed, including force-balance data, the internal PFTF thermal and vibration environment, a handling qualities assessment, and performance capabilities of the F-15B airplane with the PFTF installed.

Palumbo, Nathan↗
NASA NTRS2003

Subsurface Stress Fields in Single Crystal (Anisotropic) Contacts

Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and fatigue stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. Techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts are presented in this report. Figure 1 shows typical damper contact locations in a turbine blade. The subsurface stress results are used for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades.

Arakere, Nagaraj K.↗
NASA NTRS2003

Changes in Polymeric Tether Properties Due to Atomic Oxygen

The Propulsive Small Expendable Deployer System (ProSEDS) mission is designed to provide an on-orbit demonstration of the electrodynamic propulsion capabilities of tethers in space. The ProSEDS experiment will be a secondary payload on a Delta II unmanned expendable booster. A 5-km conductive tether is attached to the Delta II second stage and collects current fiom the low Earth orbit (LEO) plasma to facilitate de-orbit of the spent stage. The conductive tether is attached to a 10-km non-conductive tether, which is then attached to an endmass containing several scientific instruments. Atomic oxygen (AO) erodes most organic materials. As the orbit of the Delta II second stage decas, the AO flux (atoms/sq cm sec) increases. A nominal AO fluence of 1 x l0(exp 21) atoms/sq cm was agreed upon by the investigators as an adequate level for evaluating the performance of the tether materials. A test series was performed to determine the effect of atomic oxygen (AO) on the mechanical integrity and possible strength loss of ProSEDS tether materials. The tether materials in this study were Dyneema, an ultra-high molecular weight polyethylene material used as the non-conducting portion of the ProSEDS tether, and the Kevlar core strength fiber used in the conductive tether. Samples of Dyneema and Kevlar were exposed to various levels of atomic oxygen up to 1.07 x 10(exp 21) atoms/sq cm in the Marshall Space Flight Center Atomic Oxygen Beam Facility (AOBF). Changes in mass were noted after AO exposure. The tethers were then tensile-tested until failure. AO affected both the Dyneema and Kevlar tether material strength. Dyneema exposed to 1.07 x 10(exp 21) atoms/sq cm of atomic oxygen failed due to normal handling when removed fiom the AOBF and was not tensile-tested. Another test series was performed to determine the effect of AO on the electrical properties of the ProSEDS conductive tether. The conductive tether consists of seven individually coated strands of 28 AWG 1350-0 aluminum wire. The conductive coating, developed by Triton Systems, Inc., is a mix of polyanaline and COR, a clear AO-resistant polymer.

Finckenor, Miria M.↗
NASA NTRS2004

Subsurface Stress Fields In Single Crystal (Anisotropic) Contacts

Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is , presented, for evaluating the subsurface stresses in the elastic half-space, using a complex potential method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis. Effects of crystal orientation on stress response and fatigue life are examined.

Arakere, Nagaraj K.↗
NASA NTRS2004

Subsurface Stress Fields in FCC Single Crystal Anisotropic Contacts

Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent high cycle fatigue (HCF) failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and non-crystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is presented for evaluating the subsurface stresses in the elastic half-space, based on the adaptation of a stress function method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis (FEA). Effects of crystal orientation on stress response and fatigue life are examined. Obtaining accurate subsurface stress results for anisotropic single crystal contact problems require extremely refined three-dimensional (3-D) finite element grids, especially in the edge of contact region. Obtaining resolved shear stresses (RSS) on the principal slip planes also involves considerable post-processing work. For these reasons it is very advantageous to develop analytical solution schemes for subsurface stresses, whenever possible.

Arakere, Nagaraj K.↗
NASA NTRS1999

Periodic Excitation for Jet Vectoring and Enhanced Spreading

The effects of periodic excitation on the evolution of a turbulent jet were studied experimentally. A short, wide-angle diffuser was attached to the jet exit and excitation was introduced at the junction between the jet exit and the diffuser inlet. The introduction of high amplitude periodic excitation at the jet exit enhances the mixing and promotes attachment of the jet shear-layer to the diffuser wall. Vectoring is achieved by applying the excitation over a fraction of the circumference of the circular jet, enhancing its spreading rate on the excited side and its tendency to reattach to that side. Static deflection studies demonstrate that the presence of the wide-angle diffuser increases the effectiveness of the added periodic momentum due to a favorable interaction between the excitation, the jet shear-layer and the diffuser wall. This point was further demonstrated by the evolution of a wave packet that was excited in the jet shear-layer. Strong amplification of the wave packet was measured with a diffuser attached to the jet exit. The turbulent jet responds quickly (10-20 msec) to step changes in the level of the excitation input. The response scales with the jet exit velocity and is independent of the Reynolds number. Jet deflection angles were found to be highly sensitive to the relative direction between the excitation and the jet flow and less sensitive to the excitation frequency. The higher jet deflection angles were obtained for a diffuser length of about two diameters and for diffusers with half-angles greater than 15 degrees.

Pack, LaTunia G.↗
NASA NTRS1995

Removal of Burkholderia cepacia biofilms with oxidants

Iodine is used to disinfect the water system aboard US space shuttles and is the anticipated biocide for the international space station. Water quality on spacecraft must be maintained at the highest possible levels for the safety of the crew. Furthermore, the treatment process used to maintain the quality of water on research must be robust and operate for long periods with minimal crew intervention. Biofilms are recalcitrant and pose a major threat with regard to chronic contamination of spacecraft water systems. We measured the effectiveness of oxidizing biocides on the removal and regrowth of Burkholderia (Pseudomonas) cepacia biofilms. B. cepacia, isolated from the water distribution system of the space shuttle Discovery, was grown in continuous culture to produce a bacterial contamination source for biofilm formation and removal studies. A 10(7) CFU ml-1 B. cepacia suspension, in distilled water, was used to form biofilms on 3000 micrometers2 glass surfaces. Rates of attachment were measured directly with image analysis and were found to be 7.8, 15.2, and 22.8 attachment events h-1 for flow rates of 20.7, 15.2, and 9.8 ml min-1, respectively. After 18 h of formation, the B. cepacia biofilms were challenged with oxidants (ozone, chlorine, and iodine) and the rates of biofilm removal determined by image analysis. Fifty percent of the biofilm material was removed in the first hour of continous treatment with 24 mg l-1 chlorine or 2 mg l-1 ozone. Iodine (48 mg l-1) did not remove any measurable cellular material after 6 h continuous contact. After this first removal of biofilms by the oxidants, the surface was allowed to refoul and was again treated with the biocide. Iodine was the only compound that was unable to remove cellular debris from either primary or secondary biofilms. Moreover, treating primary biofilms with iodine increased the rate of formation of secondary biofilms, from 4.4 to 5.8 attachment events h-1. All the oxidants tested inactivated the B. cepacia associated with both primary and secondary biofilms. The amount of biocide needed to inactivate 50% of planktonic B. cepacia in 10 min at 25 degrees C was 8.4, 0.5, and 0.2 mg l-1 for iodine, chlorine, and ozone, respectively. The data suggest that iodine maynot be the best chemical for treating of biofilms when removal of cellular material is required.

NASA Discipline Environmental Health↗
NASA NTRS1995

Effect of microgravity and hypergravity on embryo axis alignment during postencystment embryogenesis in Artemia franciscana (Anostraca)

Cysts of brine shrimp attached with a liquid adhesive to 12-mm diameter glass coverslips in a syringe-type fluid processing apparatus were flown aboard the NASA space shuttle Discovery, flight STS-60, from 3-11 February 1994, and were allowed to undergo postencystment embryogenesis and to hatch in microgravity. The shuttle flight and the ground-based control coverslips with attached cysts were parallel to the earth's surface during incubation in salt water. Based on the position of the cyst shell crack in the attached cyst population, the ground-control nauplii emerged mostly upward. On the shuttle in microgravity, although our method of detection of orientation would not reveal emergence toward the coverslip, the ratio of the position of the cyst shell crack in the population after hatching best fit the predicted values of a random direction for nauplii emergence. Centrifugation on earth was then used to create hypergravity forces of up to 73 g during postencystment embryogenesis and hatching. The upward orientation of emerging nauplii showed a high degree of correlation (r(2) =98.8%) with a linear relationship to the log of g, with 78.2% of the total hatching upward at 1 g and 91.0% hatching upward at 73 g.

NASA Program NSCORT↗
NASA NTRS1999

Peptide-formation on cysteine-containing peptide scaffolds

Monomeric cysteine residues attached to cysteine-containing peptides by disulfide bonds can be activated by carbonyldiimidazole. If two monomeric cysteine residues, attached to a 'scaffold' peptide Gly-Cys-Glyn-Cys-Glu10, (n = 0, 1, 2, 3) are activated, they react to form the dipeptide Cys-Cys. in 25-65% yield. Similarly, the activation of a cysteine residue attached to the 'scaffold' peptide Gly-Cys-Gly-Glu10 in the presence of Arg5 leads to the formation of Cys-Arg5 in 50% yield. The significance of these results for prebiotic chemistry is discussed.

NASA Discipline Exobiology↗
NASA NTRS1993

The effect of hypogravity and hypergravity on cells of the immune system

This article reviews the gravity effects discovered in T lymphocytes and other cells of the immune system. The strong depression of mitogenic activation first observed in an experiment conducted in Spacelab 1 in 1983 triggered several other investigations in space and on the ground in the clinostat and in the centrifuge in the past 10 years. During this period, great progress was made in our knowledge of the complex mechanism of T cell activation as well as the technology to analyze the lymphokines produced during stimulation. Nevertheless, several aspects of the steps leading to activation are not yet clear. Studies in hypogravity and hypergravity may contribute to answering some of the questions. A recent investigation in the U.S. Spacelab SLS-1, based on a new technology in which leukocytes are attached to microcarrier beads, showed that the strong inhibition of activation in microgravity is due to a malfunction of monocytes acting as accessory cells. In fact, interleukin-1 production is nearly nil in resuspended monocytes, whereas T cell activation is doubled in attached cells. In hypergravity, but not at 1g, concanavalin A bound to erythrocytes activates B lymphocytes in addition to T cells. The activation of Jurkat cells is also severely impaired in space. These recent results have raised new questions that have to be answered in experiments to be conducted in space and on Earth in this decade. The experimental system, based on the mitogenic activation of T lymphocytes and accessory cells attached to microcarriers, offers an optimum model for studying basic biological mechanisms of the cell to assess the immunological fitness of humans in space and to test the feasibility of bioprocesses in space as well as on Earth.

NASA Discipline Regulatory Physiology↗
NASA NTRS1947

Free-Spinning-Tunnel Tests of a 1/16-Scale Model of the Chance Vought XF5U-1 Airplane, TED No. NACA 2349

Spin tests of a 1/16-scale model of the Chance Vought XF5U-1 airplane have been performed in the Langley 20-foot free-spinning tunnel. The effect of control position and movement upon the erect and inverted spin and recovery characteristics ae well as the effects of propellers, of stability flaps, and of various revisions to the design configuration have been determined for the normal fighter loading. The investigation also included spin recovery parachute, tumbling, and pilot-escape tests. For the original design configuration, with or without windmilling propellers, the recovery characteristics of the model were considered unsatisfactory. Increasing the maximum upward deflection of the ailavators from 45 deg to 65 deg resulted in greatly improved recovery characteristics. Dimensional revisions to the original airplane configuration, which satisfactorily improved the general spin and recovery characteristics of the model, consisted of: (1) a supplementary vertical tail 34 inches by 59 inches (full-scale) attached to a boom 80 inches aft of the trailing edge of the airplane in the plane of symmetry, (2) a large semispan undersurface spoiler placed along the airplane quarter-chord line and opened on the outboard side in a spin, or (3) two additional vertical tails 64 inches by 52 inches (full-scale) located at the tips of the ailavators. A satisfactory parachute arrangement for emergency spin recovery from demonstration spins was found to be an arrangement consisting of a 13.3-foot parachute attached by a 30-foot towline to the arresting gear mast on the airplane and opened simultaneously with an 8-foot parachute on the outboard end of the wing attached by a 3-foot towline. Tests indicated that pilot escape from a spin would be extremely hazardous unless the pilot is mechanically ejected from the cockpit. Model tumbling tests indicated that the airplane would not tumble.

White, Richard P.↗
NASA NTRS2004

Experiments with osteoblasts cultured under hypergravity conditions

To understand further the role of gravity in osteoblast attachment, osteoblasts were subjected to hypergravity conditions in vitro. Scanning electron microscopy of all confluent coverslips from FPA units show that the number of attached osteoblasts was similar among gravitational levels and growth durations (~90 cells/microscopic field). Specifically, confluent 1.0 G control cultures contained an average of 91 +/- 8 cells/field, 3.3 G samples had 88 +/- 8 cells/field, and 4.0 G cultures averaged 90 +/- 7 cells/field. The sparsely plated cultures assessed by immunohistochemistry also had similar numbers of cells at each time point (l.0 G was similar to 3.3 and 4.0 G), but cell number changed from one time point to the next as those cells proliferated. Immunohistochemistry of centrifuged samples showed an increase in number (up to 160% increase) and thickness (up to 49% increase) of actin fibers, a decrease in intensity of fibronectin fluorescence (18-23% decrease) and an increase in number of vinculin bulbs (202-374% increase in number of vinculin bulbs/area). While hypergravity exposure did not alter the number of attached osteoblasts, it did result in altered actin, fibronectin, and vinculin elements, changing some aspects of osteoblast- substrate adhesion.

NASA Program Fundamental Space Biology↗
NASA NTRS1998

Electron Beam Welder Used to Braze Sapphire to Platinum

A new use for electron beam brazing was recently developed by NASA Lewis Research Center's Manufacturing Engineering Division. This work was done to fabricate a fiberoptic probe (developed by Sentec Corporation) that could measure high temperatures less than 600 deg C of vibrating machinery, such as in jet engine combustion research. Under normal circumstances, a sapphire fiber would be attached to platinum by a ceramic epoxy. However, no epoxies can adhere ceramic fibers to platinum under such high temperatures and vibration. Also, since sapphire and platinum have different thermal properties, the epoxy bond is subjected to creep over time. Therefore, a new method had to be developed that would permanently and reliably attach a sapphire fiber to platinum. Brazing a sapphire fiber to a platinum shell. The fiber-optic probe assembly consists of a 0.015-in.-diameter sapphire fiber attached to a 0.25-in.-long, 0.059-in.-diameter platinum shell. Because of the small size of this assembly, electron beam brazing was chosen instead of conventional vacuum brazing. The advantage of the electron beam is that it can generate a localized heat source in a vacuum. Gold reactive braze was used to join the sapphire fiber and the platinum. Consequently, the sapphire fiber was not affected by the total heat needed to braze the components together.

Forsgren, Roger C.↗
NASA NTRS2004

An Overview of My 2004 Summer Internship

This summer I have been working with the Non-destructive evaluation (NDE) group and NASA Glenn Research Center. As this is my second summer with the group, I was able to begin working as soon as I arrived. My first task was to develop a system to acquire an impedance analyzer. The basic setup of the system is as follows: a piezo- electric patch is attached to a sample, and a lead is attached to that patch. Another lead is attached directly to the sample, and the leads are connected to the impedance analyzer. The system then puts a voltage through the material over a range of frequencies, and the corresponding impedances are measured for each frequency. After data is collected, it can be compared to another data set, and through a series of calculations a damage parameter is produced. For the time being, we are using a correlation calculation to find the damage parameter. The hope for this project is that a baseline measurement can be taken, and then sometime later another measurement could be taken, and the damage parameter would determine how much damage had been done to the sample. To test this hypothesis, we took baseline data from a sample, and then sent it out to have a notch cut into it. When it was returned, we again took measurements on the sample, and the damage parameter was significantly lower. Another project that I have been working on pertains to the group's newly acquired acoustography system. This system creates a full field ultrasonic signal on one side of a sample, and an acousto-optic sensor is placed on the other side of the sample.

Hertert, Lucien↗