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NASA NTRS2003

Interaction of Comets and the Solar Wind

We had originally planned to analyze UVCS observations of Comet Machholz, but we obtained higher quality observations of Comet Kudo-Fujikawa in January 2003 at its 0.19 AU perihelion. Besides a large and rapidly increasing water outgassing rate, we detected a bright tail in doubly ionized carbon. The amount of carbon was greater than could be accounted for by GO photodissociation, and we attribute the carbon to evaporation of organics from dust. A spectacular disconnection event was apparent in the C III tail, and it coincides within the uncertainties with the position of the heliospheric current sheet. A paper is in press in Science, and it will be the subject of a press release. We are also analyzing two sungrazing comets. Comet C/2001 C2 shows evidence for sub-fragments and for a very long lasting source of neutrals, which we tentatively identify as evaporation of pyroxene dust grains. Comet C/2002 S2 shows a sudden 2 magnitude drop in optical brightness and an equally sudden recovery. UVCS observations during that time show a steadily increasing outgassing rate. We have derived solar wind densities for both comets, but we are still sorting out the ambiguities involving the fragmentation and optical behavior. We are collaborating with Philippe Lamy on the LASCO measurements.

Wagner, William↗

NASA NTRS1998

Impact of resistance exercise during bed rest on skeletal muscle sarcopenia and myosin isoform distribution

Because resistance exercise (REx) and bed-rest unloading (BRU) are associated with opposing adaptations, our purpose was to test the efficacy of REx against the effects of 14 days of BRU on the knee-extensor muscle group. Sixteen healthy men were randomly assigned to no exercise (NoEx; n = 8) or REx (n = 8). REx performed five sets of leg press exercise with 80-85% of one repetition maximum (1 RM) every other day during BRU. Muscle samples were removed from the vastus lateralis muscle by percutaneous needle biopsy. Myofiber distribution was determined immunohistochemically with three monoclonal antibodies against myosin heavy chain (MHC) isoforms (I, IIa, IIx). MHC distribution was further assessed by quantitative gel electrophoresis. Dynamic 1-RM leg press and unilateral maximum voluntary isometric contraction (MVC) were determined. Maximal neural activation (root mean squared electromyogram) and rate of torque development (RTD) were measured during MVC. Reductions (P < 0.05) in type I (15%) and type II (17%) myofiber cross-sectional areas were found in NoEx but not in REx. Electrophoresis revealed no changes in MHC isoform distribution. The percentage of type IIx myofibers decreased (P < 0.05) in REx from 9 to 2% and did not change in NoEx. 1 RM was reduced (P < 0.05) by 9% in NoEx but was unchanged in REx. MVC fell by 15 and 13% in NoEx and REx, respectively. The agonist-to-antagonist root mean squared electromyogram ratio decreased (P < 0.05) 19% in REx. RTD slowed (P < 0.05) by 54% in NoEx only. Results indicate that REx prevented BRU-induced myofiber atrophy and also maintained training-specific strength. Unlike spaceflight, BRU did not induce shifts in myosin phenotype. The reported benefits of REx may prove useful in prescribing exercise for astronauts in microgravity.

NASA Discipline Musculoskeletal↗

NASA NTRS1997

Effects of static fingertip loading on carpal tunnel pressure

The purpose of this study was to explore the relationship between carpal tunnel pressure and fingertip force during a simple pressing task. Carpal tunnel pressure was measured in 15 healthy volunteers by means of a saline-filled catheter inserted percutaneously into the carpal tunnel of the nondominant hand. The subjects pressed on a load cell with the tip of the index finger and with 0, 6, 9, and 12 N of force. The task was repeated in 10 wrist postures: neutral; 10 and 20 degrees of ulnar deviation; 10 degrees of radial deviation; and 15, 30, and 45 degrees of both flexion and extension. Fingertip loading significantly increased carpal tunnel pressure for all wrist angles (p = 0.0001). Post hoc analyses identified significant increase (p < 0.05) in carpal tunnel pressure between unloaded (0 N) and all loaded conditions, as well as between the 6 and 12 N load conditions. This study demonstrates that the process whereby fingertip loading elevates carpal tunnel pressure is independent of wrist posture and that relatively small fingertip loads have a large effect on carpal tunnel pressure. It also reveals the response characteristics of carpal tunnel pressure to fingertip loading, which is one step in understanding the relationship between sustained grip and pinch activities and the aggravation or development of median neuropathy at the wrist.

NASA Center ARC↗

NASA NTRS1993

Changes in plasma volume and baroreflex function following resistance exercise

The dynamics of change in plasma volume (PV) and baroreflex responses have been reported over 24 h immediately following maximal cycle exercise. The purpose of this study was to determine if PV and baroreflex showed similar changes for 24 h after resistance exercise. Eight men were studied on 2 test days, 1 week apart. On 1 day, per cent change (% delta) in PV was estimated at 0,3, and 6 h after resistance exercise using haematocrit and haemoglobin. Baseline PV was measured 24 h after exercise using Evans blue dye. The carotid baroreceptor-cardiac reflex response was measured before, and 3, 6, 9, 12, and 24 h post-exercise. Each subject performed six sets of the bench press and leg press with 10 repetitions per set with a load that induced failure within each set. On a control day, the protocol was used without exercise. Plasma volume did not change during the control day. There was a 20% decrease in PV immediately post-exercise; the recovery of the PV was rapid and complete within 3 h. PV was 20% greater 24 h post-exercise than on the control day. There were no differences in any of the baroreflex measurements. Therefore, it is suggested that PV shifts may occur without altering baroreflex sensitivity.

NASA Program Space Physiology and Countermeasures↗

NASA NTRS1989

Effects of restricted feeding schedules on circadian organization in squirrel monkeys

Free running circadian rhythms of motor activity, food-motivated lever-pressing, and either drinking (N = 7) or body temperature (N = 3) were recorded from 10 squirrel monkeys maintained in constant illumination with unlimited access to food. Food availability was then restricted to a single unsignaled 3-hour interval each day. The feeding schedule failed to entrain the activity rhythms of 8 monkeys, which continued to free-run. Drinking was almost completely synchronized by the schedule, while body temperature showed a feeding-induced rise superimposed on a free-running rhythm. Nonreinforced lever-pressing showed both a free-running component and a 24-hour component that anticipated the time of feeding. At the termination of the schedule, all recorded variables showed free-running rhythms, but in 3 animals the initial phase of the postschedule rhythms was advanced by several hours, suggesting relative coordination. Of the remaining 2 animals, one exhibited stable entrainment of all 3 recorded rhythms, while the other appeared to entrain temporarily to the feeding schedule. These results indicate that restricted feeding schedules are only a weak zeitgeber for the circadian pacemaker generating free-running rhythms in the squirrel monkey. Such schedules, however, may entrain a separate circadian system responsible for the timing of food-anticipatory changes in behavior and physiology.

Non-NASA Center↗

NASA NTRS2006

STS-121: Discovery Post Flight Readiness Review Briefing

This post Flight Readiness Review (FRR) briefing begins with NASA Press Secretary Dean Acosta, introducing the panel who consist of: NASA Administrator, Dr. Michael Griffin; Associate Administrator for Space Operations, Bill Gerstenmaier; Space Shuttle Program Manager, Wayne Hale; and NASA Launch director, Mike Leinbach. The discussion begins with Dr. Michael Griffin, who expresses his gladness to be a part of the FRR. Bill Gerstenmaier talks about how they were very thorough about the subjects reviewed and that they wanted to make sure that they were ready to fly. He discusses and presents two slides. The first slide is a description of the LO2 intertank and LH2 ice/frost ramps staging location and the second are the top ten LH2 Ice/Frost Ramp Foam Loss events. Wayne Hale gives his thoughts on the human element that came into play during the FRRs. He talks about the willingness of everyone to speak their mind, instead of giving short comments. He expressed that this element is a huge step forward for NASA. Mike Leinbach reports on the processing of the vehicle and expresses that everything is going well and there is nothing to prohibit the launch. He also gives a good report on Atlantis, in case there is a need to use the vehicle. This FRR briefing ends with a short question and answer period from the press on topics such as debris, foam loss, ice/frost ramp redesign, crew risks, and launch date.

Source record↗

NASA NTRS2006

NASA Agency Overview Briefing

The briefing opened with Dean Acosta (NASA Press Secretary) introducing Michael Griffin (NASA Administrator) and Bill Gerstenmaier (Associate Administrator for Space Operations). Bill Griffin stated that they would resume the Shuttle Fight to Return process, that the vehicle was remarkably clean and if the weather was good, the Shuttle would be ready to launch as scheduled. Bill Gerstenmaier stated that the preparations and processing of the vehicle went extremely well and they are looking forward to increasing the crew size to three. Then the floor was open to questions from the press.

Source record↗

NASA NTRS2002

Thermoelectric properties of n-type polycrystalline BixSb2-xTe3 alloys

(BixSbl-x)2Te3(.5 = x = .7) polycrystalline samples were synthesized using a combination of melting and powder metallurgy techniques. The samples were hot pressed in graphite dies and cut perpendicular and parallel to the pressing direction. Samples were examined by microprobe analysis to determine their atomic composition. The thermoelectric properties were measured at room temperature in both directions. These properties include Seebeck coefficient, thermal conductivity, electrical resistivity, and Hall effect. The thermoelectric figure-of-merit, ZT, was calculated fiom these properties.

thermoelectric power generation segmented↗

NASA NTRS2007

High Temperature Stability of Dissimilar Metal Joints in Fission Surface Power Systems

Future generations of power systems for spacecraft and lunar surface systems will likely require a strong dependence on nuclear power. The design of a space nuclear power plant involves integrating together major subsystems with varying materia1 requirements. Refractory alloys are repeatedly considered for major structural components in space power reactor designs because refractory alloys retain their strength at higher temperatures than other classes of metals. The relatively higher mass and lower ductility of the refractory alloys make them less attractive for lower temperature subsystems in the power plant such as the power conversion system. The power conversion system would consist more likely of intermediate temperature Ni-based superalloys. One of many unanswered questions about the use of refractory alloys in a space power plant is how to transition from the use of the structural refractory alloy to more traditional structural alloys. Because deleterious phases can form when complex alloys are joined and operated at elevated temperatures, dissimilar material diffusion analyses of refractory alloys and superalloys are needed to inform designers about options of joint temperature and operational lifetime. Combinations of four superalloys and six refractory alloys were bonded and annealed at 1150 K and 1300 K to examine diffusional interactions in this study. Joints formed through hot pressing and hot isostatic pressing were compared. Results on newer alloys compared favorably to historical data. Diffusional stability is promising for some combinations of Mo-Re alloys and superalloys at 1150 K, but it appears that lower joint temperatures would be required for other refractory alloy couples.

Locci, Ivan E.↗

NASA NTRS2000

Gas storage using fullerene based adsorbents

This invention is directed to the synthesis of high bulk density high gas absorption capacity adsorbents for gas storage applications. Specifically, this invention is concerned with novel gas absorbents with high gravimetric and volumetric gas adsorption capacities which are made from fullerene-based materials. By pressing fullerene powder into pellet form using a conventional press, then polymerizing it by subjecting the fullerene to high temperature and high inert gas pressure, the resulting fullerene-based materials have high bulk densities and high gas adsorption capacities. By pre-chemical modification or post-polymerization activation processes, the gas adsorption capacities of the fullerene-based adsorbents can be further enhanced. These materials are suitable for low pressure gas storage applications, such as oxygen storage for home oxygen therapy uses or on-board vehicle natural gas storage. They are also suitable for storing gases and vapors such as hydrogen, nitrogen, carbon dioxide, and water vapor.

Loutfy, Raouf O.↗

NASA NTRS1976

Ternary boride product and process

A hard, tough, strong ceramic body is formed by hot pressing a mixture of a powdered metal and a powdered metal diboride. The metal employed is zirconium, titanium or hafnium and the diboride is the diboride of a different member of the same group of zirconium, titanium or hafnium to form a ternary composition. During hot pressing at temperatures above about 2,000.degree.F., a substantial proportion of acicular ternary monoboride is formed.

Clougherty, Edward V.↗

NASA NTRS2008

Oxide Fiber Cathode Materials for Rechargeable Lithium Cells

LiCoO2 and LiNiO2 fibers have been investigated as alternatives to LiCoO2 and LiNiO2 powders used as lithium-intercalation compounds in cathodes of rechargeable lithium-ion electrochemical cells. In making such a cathode, LiCoO2 or LiNiO2 powder is mixed with a binder [e.g., poly(vinylidene fluoride)] and an electrically conductive additive (usually carbon) and the mixture is pressed to form a disk. The binder and conductive additive contribute weight and volume, reducing the specific energy and energy density, respectively. In contrast, LiCoO2 or LiNiO2 fibers can be pressed and sintered to form a cathode, without need for a binder or a conductive additive. The inter-grain contacts of the fibers are stronger and have fewer defects than do those of powder particles. These characteristics translate to increased flexibility and greater resilience on cycling and, consequently, to reduced loss of capacity from cycle to cycle. Moreover, in comparison with a powder-based cathode, a fiber-based cathode is expected to exhibit significantly greater ionic and electronic conduction along the axes of the fibers. Results of preliminary charge/discharge-cycling tests suggest that energy densities of LiCoO2- and LiNiO2-fiber cathodes are approximately double those of the corresponding powder-based cathodes.

Rice, Catherine E.↗

NASA NTRS2008

Joining of Zirconium Diboride-Based Ceramic Composites to Metallic Systems for High-Temperature Applications

Three types of hot-pressed zirconium diboride (ZrB2)-based ultra-high-temperature ceramic composites (UHTCC), ZrB2-SiC (ZS), ZrB2-SiC-C (ZSC), and ZrB2-SCS9-SiC (ZSS), were joined to Cu-clad-Mo using two Ag-Cu brazes (Cusil-ABA and Ticusil, T(sub L) approx.1073-1173 K) and two Pd-base brazes (Palco and Palni, T(sub L) approx.1493-1513 K). Scanning Electron Microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS) revealed greater chemical interaction in joints made using Pd-base brazes than in joints made using Ag-Cu based active brazes. The degree of densification achieved in hot pressed composites influenced the Knoop hardness of the UHTCC and the hardness distribution across the braze interlayer. The braze region in Pd-base system displayed higher hardness in joints made using fully-dense ZS composites than in joints made using partially-dense ZSS composites and the carbon-containing ZSC composites. Calculations indicate a small negative elastic strain energy and an increase in the UHTCC's fracture stress up to a critical clad layer thickness . Above this critical thickness, strain energy in the UHTCC is positive, and it increases with increasing clad layer thickness. Empirical projections show a reduction in the effective thermal resistance of the joints and highlight the potential benefits of joining the UHTCC to Cu-clad-Mo.

Asthana, R.↗

NASA NTRS2007

Electromechanically Actuated Valve for Controlling Flow Rate

A proposed valve for controlling the rate of flow of a fluid would include an electric-motor-driven ball-screw mechanism for adjusting the seating element of the valve to any position between fully closed and fully open. The motor would be of a type that can be electronically controlled to rotate to a specified angular position and to rotate at a specified rate, and the ball screw would enable accurate linear positioning of the seating element as a function of angular position of the motor. Hence, the proposed valve would enable fine electronic control of the rate of flow and the rate of change of flow. The uniqueness of this valve lies in a high degree of integration of the actuation mechanism with the flow-control components into a single, relatively compact unit. A notable feature of this integration is that in addition to being a major part of the actuation mechanism, the ball screw would also be a flow-control component: the ball screw would be hollow so as to contain part of the main flow passage, and one end of the ball screw would be the main seating valve element. The relationships among the components of the valve are best understood by reference to the figure, which presents meridional cross sections of the valve in the fully closed and fully open positions. The motor would be supported by a bracket bolted to the valve body. By means of gears or pulleys and a timing belt, motor drive would be transmitted to a sleeve that would rotate on bearings in the valve body. A ball nut inside the sleeve would be made to rotate with the sleeve by use of a key. The ball screw would pass through and engage the ball nut. A key would prevent rotation of the ball screw in the valve body while allowing the ball screw to translate axially when driven by the ball nut. The outer surface of the ball screw would be threaded only in a mid-length region: the end regions of the outer surface of the ball screw would be polished so that they could act as dynamic sealing surfaces. The inlet end (the right end as depicted in the figure) of the ball screw would be the main seating valve element: in the fully closed position, it would be pressed against the valve seat, as depicted in the upper part of the figure. A retainer would hold the valve seat in an inlet fitting. In addition, the retainer would be contoured to obtain a specified flow rate as a function of axial position of the ball screw. In the fully closed position, little force would be needed to press the ball screw against the seat because the push bore area upon which the upstream pressure would act would be small. The motor would position and hold the ball screw against the seat, providing the force necessary for sealing. To open the valve to a particular position, the motor would be commanded to rotate to a particular angular position (equivalently, a particular number of revolutions) at a particular rate of rotation within its torque limitations. Once the valve was open, fluid would flow through the inlet fitting and the chamber in the inlet housing, past the seat and its retainer, along the hollow core of the ball screw, and through the outlet housing and outlet fitting. The net force generated from fluid pressure in the open position would be small because the pressure exposed to the push bore areas at the inlet and outlet are nearly equal and the forces generated would be in opposing directions.

Patterson, Paul↗

NASA NTRS2007

Mechanical Alloying for Making Thermoelectric Compounds

An economical room-temperature mechanical alloying process has been shown to be an effective means of making a homogeneous powder that can be hot-pressed to synthesize a thermoelectric material having reproducible chemical composition. The synthesis of a given material consists of the room temperature thermomechanical-alloying process followed b y a hot-pressing process. Relative to synthesis of nominally the same material by a traditional process that includes hot melting, this s ynthesis is simpler and yields a material having superior thermoelect ric properties.

Huang, Chen-Kuo↗

NASA NTRS2009

Recent Developments in Ultra High Temperature Ceramics at NASA Ames

NASA Ames is pursuing a variety of approaches to modify and control the microstructure of UHTCs with the goal of improving fracture toughness, oxidation resistance and controlling thermal conductivity. The overall goal is to produce materials that can perform reliably as sharp leading edges or nose tips in hypersonic reentry vehicles. Processing approaches include the use of preceramic polymers as the SiC source (as opposed to powder techniques), the addition of third phases to control grain growth and oxidation, and the use of processing techniques to produce high purity materials. Both hot pressing and field assisted sintering have been used to make UHTCs. Characterization of the mechanical and thermal properties of these materials is ongoing, as is arcjet testing to evaluate performance under simulated reentry conditions. The preceramic polymer approach has generated a microstructure in which elongated SiC grains grow in the form of an in-situ composite. This microstructure has the advantage of improving fracture toughness while potentially improving oxidation resistance by reducing the amount and interconnectivity of SiC in the material. Addition of third phases, such as Ir, results in a very fine-grained microstructure, even in hot-pressed samples. The results of processing and compositional changes on microstructure and properties are reported, along with selected arcjet results.

Johnson, Sylvia M.↗

NASA NTRS2010

Multivariate Methods for Prediction of Geologic Sample Composition with Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) uses pulses of laser light to ablate a material from the surface of a sample and produce an expanding plasma. The optical emission from the plasma produces a spectrum which can be used to classify target materials and estimate their composition. The ChemCam instrument on the Mars Science Laboratory (MSL) mission will use LIBS to rapidly analyze targets remotely, allowing more resource- and time-intensive in-situ analyses to be reserved for targets of particular interest. ChemCam will also be used to analyze samples that are not reachable by the rover's in-situ instruments. Due to these tactical and scientific roles, it is important that ChemCam-derived sample compositions are as accurate as possible. We have compared the results of partial least squares (PLS), multilayer perceptron (MLP) artificial neural networks (ANNs), and cascade correlation (CC) ANNs to determine which technique yields better estimates of quantitative element abundances in rock and mineral samples. The number of hidden nodes in the MLP ANNs was optimized using a genetic algorithm. The influence of two data preprocessing techniques were also investigated: genetic algorithm feature selection and averaging the spectra for each training sample prior to training the PLS and ANN algorithms. We used a ChemCam-like laboratory stand-off LIBS system to collect spectra of 30 pressed powder geostandards and a diverse suite of 196 geologic slab samples of known bulk composition. We tested the performance of PLS and ANNs on a subset of these samples, choosing to focus on silicate rocks and minerals with a loss on ignition of less than 2 percent. This resulted in a set of 22 pressed powder geostandards and 80 geologic samples. Four of the geostandards were used as a validation set and 18 were used as the training set for the algorithms. We found that PLS typically resulted in the lowest average absolute error in its predictions, but that the optimized MLP ANN and the CC ANN often gave results comparable to PLS. Averaging the spectra for each training sample and/or using feature selection to choose a small subset of wavelengths to use for predictions gave mixed results, with degraded performance in some cases and similar or slightly improved performance in other cases. However, training time was significantly reduced for both PLS and ANN methods by implementing feature selection, making this a potentially appealing method for initial, rapid-turn-around analyses necessary for Chemcam's tactical role on MSL. Choice of training samples has a strong influence on the accuracy of predictions. We are currently investigating the use of clustering algorithms (e.g. k-means, neural gas, etc.) to identify training sets that are spectrally similar to the unknown samples that are being predicted, and therefore result in improved predictions

Morris, Richard↗

NASA NTRS2011

Fabrication and Characterization of Brazed Joints for SiC-Metallic Systems Utilizing Refractory Metals

Metal to ceramic joining plays a key role for the integration of ceramics into many nuclear, ground and aero based technologies. In order to facilitate these technologies, the active metal brazing of silicon carbide (CVD beta-SiC, 1.1 mm thick, and hot-pressed alpha-SiC, 3 mm thick) to the refractory metals molybdenum and tungsten using active braze alloys was studied. The joint microstructure, composition, and microhardness were evaluated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Knoop hardness testing. The braze alloys, Cusil-ABA, Ticusil and Copper-ABA, all formed sound joints with excellent wetting and chemical bonding with the SiC substrate. Despite the close thermal expansion match between the metal substrates and SiC, hairline cracks formed in alpha-SiC while beta-SiC showed no signs of residual stress cracking. The use of ductile interlayers to reduce the effect from residual stresses was investigated and joints formed with copper as an interlayer produced crack free systems utilizing both CVD and hot-pressed SiC.

Coddington, Bryan↗