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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Effects of microgravity and tail suspension on enzymes of individual soleus and tibialis anterior fibers

Selected enzymes of energy metabolism were measured in random individual fibers of soleus and tibialis anterior (TA) muscles from rats exposed for 2 wk to spaceflight (F) aboard Cosmos 2044 or tail suspension (T) and from synchronous controls. Average size of soleus fibers (dry weight per unit length) was reduced 37 percent in F and T fibers; there was little change in Ta fibers. Enzyme changes were more pronounced in soleus than in TA fibers. Three enzymes characteristic of fast-twitch muscles, pyruvate kinase, glycerol-3-phosphate dehydrogenase, and 1-phosphofructokinase, were elevated in F and T soleus fibers, but changes in phosphofructokinase were not statistically significant. In TA fibers analyzed for hexokinase, malate dehydrogenase, phosphohexoisomerase, and pyruvate kinase, only hexokinase and malate dehydrogenase showed significant changes. Hexokinase incresed 83 percent in one of two T muscles. Enzyme data for TA fibers typed by myosin adenosinetriphosphatase were more informative: phosphofructokinase, phosphorylase, and glycerol-3-phosphate dehydrogenase were increased in type IIn fibers of either F or T muscles or both. Malate dehydrogenase was not changed in fibers of any type in either F or T muscle.

Chi, Maggie M.-Y.↗
NASA NTRS1994

Hot gas ingestion effects on fuel control surge recovery and AH-1 rotor drive train torque spikes

This report summarizes the work accomplished through computer simulation to understand the impact of the hydromechanical turbine assembly (TA) fuel control on rocket gas ingestion induced engine surges on the AH-1 (Cobra) helicopter. These surges excite the lightly damped torsional modes of the Cobra rotor drive train and can cause overtorqueing of the tail rotor shaft. The simulation studies show that the hydromechanical TA control has a negligible effect on drive train resonances because its response is sufficiently attenuated at the resonant frequencies. However, a digital electronic control working through the TA control's separate, emergency fuel metering system has been identified as a solution to the overtorqueing problem. State-of-the-art software within the electronic control can provide active damping of the rotor drive train to eliminate excessive torque spikes due to any disturbances including engine surges and aggressive helicopter maneuvers. Modifications to the existing TA hydromechanical control are relatively minor, and existing engine sensors can be utilized by the electronic control. Therefore, it is concluded that the combination of full authority digital electronic control (FADEC) with hydromechanical backup using the existing TA control enhances flight safety, improves helicopter performance, reduces pilot workload, and provides a substantial payback for very little investment.

Tokarski, Frank↗
NASA NTRS2000

Multisorbent tubes for collecting volatile organic compounds in spacecraft air

The sampling capability of Tenax-TA tubes, used in the National Aeronautics and Space Administration's solid sorbent air sampler to trap and concentrate contaminants from air aboard spacecraft, was improved by incorporating two sorbents within the tubes. Existing tubes containing only Tenax-TA allowed highly volatile compounds to "break through" during collection of a 1.5 L air sample. First the carbon molecular sieve-type sorbents Carboxen 569 and Carbosieve S-III were tested for their ability to quantitatively trap the highly volatile compounds. Breakthrough volumes were determined with the direct method, whereby low ppm levels of methanol or Freon 12 in nitrogen were flowed through the sorbent tubes at 30 mL/min, and breakthrough was detected by gas chromatography. Breakthrough volumes for methanol were about 9 L/g on Carboxen 569 and 11 L/g on Carbosieve S-III; breakthrough volumes for Freon 12 were about 7 L/g on Carboxen 569 and > 26 L/g on Carbosieve S-III. Next, dual-bed tubes containing either Tenax-TA/Carbosieve S-III, Tenax-TA/Carboxen 569, or Carbotrap/Carboxen 569 to a 10-component gas mixture were exposed, in dry and in humidified air (50% relative humidity), and percentage recoveries of each compound were determined. The Tenax-TA/Carboxen 569 combination gave the best overall recoveries (75-114% for the 10 compounds). Acetaldehyde had the lowest recovery (75%) of the 10 compounds, but this value was still an improvement over either the other two sorbent combinations or the original single-sorbent tubes.

NASA Center JSC↗
NASA NTRS1999

Effects of spaceflight on rhesus quadrupedal locomotion after return to 1G

Effects of spaceflight on Rhesus quadrupedal locomotion after return to 1G. Locomotor performance, activation patterns of the soleus (Sol), medial gastrocnemius (MG), vastus lateralis (VL), and tibialis anterior (TA) and MG tendon force during quadrupedal stepping were studied in adult Rhesus before and after 14 days of either spaceflight (n = 2) or flight simulation at 1G (n = 3). Flight simulation involved duplication of the spaceflight conditions and experimental protocol in a 1G environment. Postflight, but not postsimulation, electromyographic (EMG) recordings revealed clonus-like activity in all muscles. Compared with preflight, the cycle period and burst durations of the primary extensors (Sol, MG, and VL) tended to decrease postflight. These decreases were associated with shorter steps. The flexor (TA) EMG burst duration postflight was similar to preflight, whereas the burst amplitude was elevated. Consequently, the Sol:TA and MG:TA EMG amplitude ratios were lower following flight, reflecting a "flexor bias." Together, these alterations in mean EMG amplitudes reflect differential adaptations in motor-unit recruitment patterns of flexors and extensors as well as fast and slow motor pools. Shorter cycle period and burst durations persisted throughout the 20-day postflight testing period, whereas mean EMG returned to preflight levels by 17 days postflight. Compared with presimulation, the simulation group showed slight increases in the cycle period and burst durations of all muscles. Mean EMG amplitude decreased in the Sol, increased in the MG and VL, and was unchanged in the TA. Thus adaptations observed postsimulation were different from those observed postflight, indicating that there was a response unique to the microgravity environment, i.e., the modulations in the nervous system controlling locomotion cannot merely be attributed to restriction of movement but appear to be the result of changes in the interpretation of load-related proprioceptive feedback to the nervous system. Peak MG tendon force amplitudes were approximately two times greater post- compared with preflight or presimulation. Adaptations in tendon force and EMG amplitude ratios indicate that the nervous system undergoes a reorganization of the recruitment patterns biased toward an increased recruitment of fast versus slow motor units and flexor versus extensor muscles. Combined, these data indicate that some details of the control of motor pools during locomotion are dependent on the persistence of Earth's gravitational environment.

Bion 11 Project↗
NASA NTRS2012

The Aquarius Salinity Retrieval Algorithm: Early Results

The Aquarius L-band radiometer/scatterometer system is designed to provide monthly salinity maps at 150 km spatial scale to a 0.2 psu accuracy. The sensor was launched on June 10, 2011, aboard the Argentine CONAE SAC-D spacecraft. The L-band radiometers and the scatterometer have been taking science data observations since August 25, 2011. The first part of this presentation gives an overview over the Aquarius salinity retrieval algorithm. The instrument calibration converts Aquarius radiometer counts into antenna temperatures (TA). The salinity retrieval algorithm converts those TA into brightness temperatures (TB) at a flat ocean surface. As a first step, contributions arising from the intrusion of solar, lunar and galactic radiation are subtracted. The antenna pattern correction (APC) removes the effects of cross-polarization contamination and spillover. The Aquarius radiometer measures the 3rd Stokes parameter in addition to vertical (v) and horizontal (h) polarizations, which allows for an easy removal of ionospheric Faraday rotation. The atmospheric absorption at L-band is almost entirely due to O2, which can be calculated based on auxiliary input fields from numerical weather prediction models and then successively removed from the TB. The final step in the TA to TB conversion is the correction for the roughness of the sea surface due to wind. This is based on the radar backscatter measurements by the scatterometer. The TB of the flat ocean surface can now be matched to a salinity value using a surface emission model that is based on a model for the dielectric constant of sea water and an auxiliary field for the sea surface temperature. In the current processing (as of writing this abstract) only v-pol TB are used for this last process and NCEP winds are used for the roughness correction. Before the salinity algorithm can be operationally implemented and its accuracy assessed by comparing versus in situ measurements, an extensive calibration and validation (cal/val) activity needs to be completed. This is necessary in order to tune the inputs to the algorithm and remove biases that arise due to the instrument calibration, foremost the values of the noise diode injection temperatures and the losses that occur in the feedhorns. This is the subject of the second part of our presentation. The basic tool is to analyze the observed difference between the Aquarius measured TA and an expected TA that is computed from a reference salinity field. It is also necessary to derive a relation between the scatterometer backscatter measurements and the radiometer emissivity that is induced by surface winds. In order to do this we collocate Aquarius radiometer and scatterometer measurements with wind speed retrievals from the WindSat and SSMIS F17 microwave radiometers. Both of these satellites fly in orbits that have the same equatorial ascending crossing time (6 pm) as the Aquarius/SAC-D observatory. Rain retrievals from WindSat and SSMIS F 17 can be used to remove Aquarius observations that are rain contaminated. A byproduct of this analysis is a prediction for the wind-induced sea surface emissivity at L-band.

Meissner, Thomas↗
NASA NTRS1971

Technology assessment: What should it be?

A report on technology assessment (TA) is presented. Topics discussed include: the nature of TA, TA used as an analytical method for natural and social sciences, and the uncertain consequences of TA.

Black, G.↗
NASA NTRS1976

Development and study of chemical vapor deposited tantalum base alloys

A technique for the chemical vapor deposition of alloys was developed. The process, termed pulsing, involves the periodic injection of reactant gases into a previously-evacuated reaction chamber where they blanket the substrate almost instantaneously. Formation of alternating layers of the alloy components and subsequent homogenization allows the formation of an alloy of uniform composition with the composition being determined by the duration and relative numbers of the various cycles. The technique has been utilized to produce dense alloys of uniform thickness and composition (Ta- 10 wt % W) by depositing alternating layers of Ta and W by the hydrogen reduction of TaCl5 and WCl6. A similar attempt to deposit a Ta - 8 wt % W - 2 wt% Hf alloy was unsuccessful because of the difficulty in reducing HfCl4 at temperatures below those at which gas phase nucleation of Ta and W occurred.

Meier, G. H.↗
NASA NTRS1984

Influence of cobalt, tantaum and tungsten on the high temperature mechanical properties of single crystal nickel-base superalloys

For alloys with the baseline refractory metal level of 3 percent Ta and 10 percent W, decreases in Co level from 10 to 0 percent resulted in increased tensile strength and creep resistance. Substitution of W for Ta resulted in decreased creep life at high stresses but improved life at low stresses. Substitution of Ni for Ta caused large reductions in tensile strength and creep resistance, and corresponding increases in ductility. For these alloys with low Ta plus W totals, strength was independent of Co level. The increases in tensile strength with increases in refractory metal content were related to the increases in gamma volume fraction and solid solution hardening. Increases in strength as Co level decreased were considered to be the result of coherency strain hardening from the increased lattice mismatch. Dislocation shear through the gamma-gamma interface is considered to be the rate limiting step in the deformation process.

Nathal, M. V.↗
NASA NTRS1985

The influence of cobalt, tantalum, and tungsten on the elevated temperature mechanical properties of single crystal nickel-base superalloys

The influence of composition on the tensile and creep strength of 001-line oriented nickel-base superalloy single crystals at temperatures near 1000 C was investigated. Cobalt, tantalum, and tungsten concentrations were varied according to a matrix of compositions based on the single crystal version of MAR-M247. For alloys with the baseline refractory metal level of 3 wt pct Ta and 10 wt pct W, decreases in Co level from 10 to 0 wt pct resulted in increased tensile and creep strength. Substitution of 2 wt pct W for 3 wt pct Ta resulted in decreased creep life at high stresses, but improved life at low stresses. Substitution of Ni for Ta caused large reductions in tensile strength and creep resistance, and corresponding increases in ductility. For these alloys with low Ta-plus-W totals, strength was independent of Co level. The effects of composition on properties were related to the microstructural features of the alloys. In general, high creep strength was associated with high levels of gamma-prime volume fraction, gamma-gamma-prime lattice mismatch, and solid solution hardening.

Nathal, M. V.↗
NASA NTRS1987

Size and metabolic properties of fibers in rat fast-twitch muscles after hindlimb suspension

The effect of hind-limb suspension (HS) on single fibers of the medial gastrocnemius (MG) and the tibialis anterior (TA) muscles were studied in rats. Fiber area and the activities of succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPD) were determined in tissue sections using an image analysis system. After 28 days of HS, the MG atrophied 28 percent, whereas the TA weight was maintained. Both dark- and light-ATPase fibers in the deep region of the MG had decreased cross-sectional areas following HS, with the atrophic response being twice as great in the light-ATPase fibers than in the dark-ATPase fibers. Following HS, mean SDH activities of both fiber types were significantly lower in the MG and TA than in the CON; by contrast, mean GPD activities were either maintained at the CON level or were higher in both MG and TA muscles. The data suggest an independence of the mechanisms determining the muscle fiber size and the metabolic adaptations associated with HS.

Roy, Roland R.↗
NASA NTRS1990

Micromechanical thermal analysis of interphase region in a titanium aluminide MMC

The high reactivity between the fiber and matrix in silicon carbide/titanium aluminide MMCs leads to the formation of brittle reaction products at the fiber/matrix (F/M) interface. Also, the high thermal expansion coefficient mismatch between the fiber and matrix leads to high tensile residual stresses at the F/M interface, and this can lead to premature cracking during cooldown. One solution to these problems is the use of a metallic fiber coating like Ta which acts as an F/M diffusion barrier and reacts with the matrix to form a beta stabilized compliant layer. A finite element micromechanics analysis was performed to study the effects of Ta and beta interphase layers on the thermal residual stresses during consolidation. A 5-micron-thick beta layer reduced cool-down stresses by 8 percent compared to a 2 percent reduction computed for a Ta layer of the same thickness. Plastic yielding in the Ta was not effective in reducing cool-down stresses. Compliant alpha-2 particles next to the stiffer gamma particles reduced stresses in the gamma particles by less than 2 percent. A simple closed form analysis was developed to calculate thermal residual stresses in a fiber/interphase/matrix system. A 2-micron-thick Ag interphase layer was found to reduce residual stresses by about 11 percent.

Naik, R. A.↗
NASA NTRS1994

Processing and Mechanical Properties of NiAl-Based In-Situ Composites

In-situ composites based on the NiAl-Cr eutectic system were successfully produced by containerless processing and evaluated. The NiAl-Cr alloys had a fibrous microstructure while the NiAl-(Cr,Mo) alloys containing 1 at. percent or more molybdenum exhibited a lamellar structure. The NiAl-28Cr-6Mo eutectic displays promising high temperature strength while still maintaining a reasonable room temperature fracture toughness when compared to other NiAl-based materials. The Laves phase NiAlTa was used to strengthen NiAl and very promising creep strengths were found for the directionally solidified NiAl-NiAlTa eutectic. The eutectic composition was found to be near NiAl-15.5Ta (at. percent) and well aligned microstructures were produced at this composition. An off-eutectic composition of NiAl-14.5Ta was also processed, consisting of NiAl dendrites surrounded by aligned eutectic regions. The room temperature toughness of these two phase alloys was similar to that of polycrystalline NiAl even with the presence of the brittle Laves phase NiAlTa. Polyphase in-situ composites were generated by directional solidification of ternary eutectics. The systems investigated were the Ni-Al-Ta-X (X=Cr, Mo, or V) alloys. Ternary eutectics were found in each of these systems and both the eutectic composition and temperature were determined. Of these ternary eutectics, the one in the NiAl-Ta-Cr system was found to be the most promising. The fracture toughness of the NiAl-(Cr,Al)NiTa-Cr eutectic was intermediate between those of the NiAl-NiAlTa eutectic and the NiAl-Cr eutectic. The creep strength of this ternary eutectic was similar to or greater than that of the NiAl-Cr eutectic.

Johnson, David Ray↗
NASA NTRS1994

Trade study plan for Graphite Composite Primary Structure (GCPS)

This TA 2 document (with support from TA 1) describes the trade study plan that will identify the most suitable structural configuration for an SSTO winged vehicle capable of delivering 25,000 lbs to a 220 nm circular orbit at 51.6 degree inclination For this most suitable configuration the structural attachment of the wing, and the most suitable GCPS composite materials for intertank, wing, tail and thrust structure are identified. This trade study analysis uses extensive information derived in the TA 1 trade study plan and is identified within the study plan. In view of this, for convenience, the TA 1 study plan is included as an appendix to this document.

Greenberg, H. S.↗
NASA NTRS1994

Trade study plan for Reusable Hydrogen Composite Tank System (RHCTS)

This TA 1 document describes the trade study plan (with support from TA 2) that will identify the most suitable structural configuration for an SSTO winged vehicle capable of delivering 25,000 lbs to a 220 nm circular orbit at 51.6 degree inclination. The analysis uses information derived in the TA 2 study as identified within the study plan. In view of this, for convenience, the TA 2 study plan is included as an appendix to this document.

Greenberg, H. S.↗
NASA NTRS1994

Adaptation of skeletal muscle to spaceflight: Cosmos rhesus project. Cosmos 2044 and 2229

The proposed experiments were designed to determine the effects of the absence of weight support on hindlimb muscles of the monkey: an ankle flexor (tibialis anterior, TA), two ankle extensors (medial gastrocnemius, MG and soleus, SOL), and a knee extensor (vastus lateralis, VL). These effects were assessed by examining the biochemical and morphological properties of muscle fibers obtained from biopsies in young Rhesus monkeys (3-4 Kg). Biopsies taken from ground base experiments were analyzed to determine: (1) the effects of chair restraint at 1 G on muscle properties and (2) the growth rate of flexor and extensor muscles in the Rhesus. In addition, two sets of biopsies were taken from monkeys which were in the flight pool and the four monkeys that flew on the Cosmos 2044 and 2229 biosatellite missions. Based on data collected in rats it is generally assumed that extensors atrophy to a greater extent than flexors in response to spaceflight or hindlimb suspension. Consequently, the finding that fibers in the TA (a fast flexor) of the flight monkeys atrophied, whereas fibers in the Sol (a predominantly slow extensor) and MG (a fast extensor) grew after a 14-day spaceflight (Cosmos 2044) and 12-day spaceflight (Cosmos 2229) was unexpected. In Cosmos 2044, the TA in both flight monkeys had a 21 percent decrease in fiber size, whereas the Sol and MG both had a 79 percent increase in fiber size. In Cosmos 2229, the TA in both flight monkeys showed significant atrophy, whereas the Sol and MG showed slight growth in one monkey (906) and slight atrophy in the other monkey (151).

Bodine-Fowler, Sue↗
NASA NTRS1992

Intramuscular pressure: A better tool than EMG to optimize exercise for long-duration space flight

A serious problem experienced by astronauts during long-duration space flight is muscle atrophy. In order to develop countermeasures for this problem, a simple method for monitoring in vivo function of specific muscles is needed. Previous studies document that both intramuscular pressure (IMP) and electromyography (EMG) provide quantitative indices of muscle contraction force during isometric exercise. However, at present there are no data available concerning the usefulness of IMP versus EMG during dynamic exercise. Methods: IMP (Myopress catheter) and surface EMG activity were measured continuously and simultaneously in the tibalis anterior (TA) and soleus (SOL) muscles of 9 normal male volunteers (28-54 years). These parameters were recorded during both concentric and eccentric exercises which consisted of plantarflexon and dorsiflexon of the ankle joint. A Lido Active Isokinetic Dynamometer concurrently recorded ankle joint torque and position. Results: Intramuscular pressure correlated linearly with contraction force for both SOL (r exp 2 = 0.037) and TA (R exp 2 = 0.716 and r exp 2 = 0.802, respectively). During eccentric exercises, SOL and TA IMP also correlated linearly with contraction force (r(exp 2) = 0.883 and r(exp 2) = 0.904 respectively), but SOL and TA EMG correlated poorly with force (r(exp 2) = 0.489 and r(exp 2) = 0.702 respectively). Conclusion: IMP measurement provides a better index of muscle contraction force than EMG during concentric and eccentric exercise. IMP reflects intrinsic mechanical properties of individual muscles, such as length tension relationships. Although invasive, IMP provides a more powerful tool and EMG for developing exercise hardware and protocols for astronauts exposed to long-duration space flight.

Hargens, A. R.↗
NASA NTRS1995

Advanced transportation system studies. Technical area 2: Heavy lift launch vehicle development: Technical Results - Volume 2

Sections 10 to 13 of the Advanced Transportation System Studies final report are included in this volume. Section 10 contains a copy of an executive summary that was prepared by Lockheed Space Operations Company (LSOC) to document their support to the TA-2 contract during the first-year period of performance of the contract, May 1992 through May 1993. LSOC participated on the TA-2 contract as part of the concurrent engineering launch system definition team, and provided outstanding heavy lift launch vehicle (HLLV) ground operations requirements and concept assessments for Lockheed Missiles and Space Company (LMSC) through an intercompany work transfer as well as providing specific HLLV ground operations assessments at the direction of NASA KSC through KSC funding that was routed to the TA-2 contract. Section 11 contains a copy of a vehicle-independent, launch system health management requirements assessment. The purpose of the assessment was to define both health management requirements and the associated interfaces between a generic advanced transportation system launch vehicle and all related elements of the entire transportation system, including the ground segment. Section 12 presents the major TA-2 presentations provided to summarize the significant results and conclusions that were developed over the course of the contract. Finally, Section 13 presents the design and assessment report on the first lunar outpost heavy lift launch vehicle.

Source record↗
NASA NTRS1993

Heart Imaging System

Johnson Space Flight Center's device to test astronauts' heart function in microgravity has led to the MultiWire Gamma Camera, which images heart conditions six times faster than conventional devices. Dr. Jeffrey Lacy, who developed the technology as a NASA researcher, later formed Proportional Technologies, Inc. to develop a commercially viable process that would enable use of Tantalum-178 (Ta-178), a radio-pharmaceutical. His company supplies the generator for the radioactive Ta-178 to Xenos Medical Systems, which markets the camera. Ta-178 can only be optimally imaged with the camera. Because the body is subjected to it for only nine minutes, the radiation dose is significantly reduced and the technique can be used more frequently. Ta-178 also enables the camera to be used on pediatric patients who are rarely studied with conventional isotopes because of the high radiation dosage.

Source record↗