SEARCH · Search NASA

Results for “geometrical confinement”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

71 records · Page 4

All sources NASA NTRS DOE OSTI

NASA NTRS1987

Contributions of numerical simulation data bases to the physics, modeling and measurement of turbulence

The use of simulation data bases for the examination of turbulent flows is an effective research tool. Studies of the structure of turbulence have been hampered by the limited number of probes and the impossibility of measuring all desired quantities. Also, flow visualization is confined to the observation of passive markers with limited field of view and contamination caused by time-history effects. Computer flow fields are a new resource for turbulence research, providing all the instantaneous flow variables in three-dimensional space. Simulation data bases also provide much-needed information for phenomenological turbulence modeling. Three dimensional velocity and pressure fields from direct simulations can be used to compute all the terms in the transport equations for the Reynolds stresses and the dissipation rate. However, only a few, geometrically simple flows have been computed by direct numerical simulation, and the inventory of simulation does not fully address the current modeling needs in complex turbulent flows. The availability of three-dimensional flow fields also poses challenges in developing new techniques for their analysis, techniques based on experimental methods, some of which are used here for the analysis of direct-simulation data bases in studies of the mechanics of turbulent flows.

Moin, Parviz↗

NASA NTRS2002

Visualization of Flows in Packed Beds of Twisted Tapes

A videotape presentation of the flow field in a packed bed of 48 twisted tapes which can be simulated by very thin virtual cylinders has been assembled. The indices of refraction of the oil and the Lucite twisted tapes were closely matched, and the flow was seeded with magnesium oxide particles. Planar laser light projected the flow field in two dimensions both along and transverse to the flow axis. The flow field was three dimensional and complex to describe, yet the most prominent finding was flow threads. It appeared that axial flow spiraled along either within the confines of a virtual cylindrical boundary or within the exterior region, between the tangency points, of the virtual cylinders. Random packing and bed voids created vortices and disrupted the laminar flow but minimized the entrance effects. The flow-pressure drops in the packed bed fell below the Ergun model for porous-media flows. Single-twisted-tape results of Smithberg and Landis (1964) were used to guide the analysis. In appendix A the results of several investigators are scaled to the Ergun model. Further investigations including different geometric configurations, computational fluid dynamic (CFD) gridding, and analysis are required.

Hendricks, R. C.↗

NASA NTRS2002

Flow Visualizations in a Packed Bed of Twisted Tapes

Hendricks, R. C.↗

NASA NTRS2011

Locating the Accretion Footprint on a Herbig Ae Star: MWC 480

Accretion is a fundamental process which establishes the dynamics of the protoplanetary disk and the final properties of the forming star. In solar-type stars, the star-disk coupling is determined by the magnetic field structure, which is responsible for funneling material from the disk midplane to higher latitudes on the star. Here, we use pan-chromatic data for the Herbig Ae star MWC 480 to address whether similar processes occur in intermediate-mass stars. MWC 480 has X-ray emission typical of actively accreting Herbig Ae stars, but with 5-9 x more photoelectric absorption than expected from optical and FUV data. We consider 3 sources for the absorption: the disk absorption in a wind or jet, and accretion. While we detect the disk in scattered light in are-analysis of archival HST data. the data are consistent with grazing illumination of the dust disk. We find that MWC 480's disk is stratified, geometrically thin, and is not responsible for the observed photoelectric absorption. MWC 480 drives a bipolar jet, but with a mass loss rate which is low compared to other Herbig Ae stars, where the outflow is more favorably oriented and enhanced photoelectric absorption is not seen. This excludes a jet or wind origin for the enhanced photoelectric absorption. We compare MWC 480's 0 VI emission with other Herbig Ae stars. The distribution of the emission in inclination, and lack of a correlation of profile shape and system inclination excludes equatorially-confined accretion for the FUSE Herbig Ae stars. The photoelectric absorption data further suggest that the accretion footprint on MWC 480 and other Herbig Ae stars is located at high temperate, rather than polar, latitudes. These findings support the presence of funneled accretion in MWC 480 and Herbig Ae stars, strengthening the parallel to T Tauri stars.

Grady, C. A.↗

NASA NTRS2010

The Vertical Distribution of Thin Features Over the Arctic Analysed from CALIPSO Observations: Aerosols - Part 2

Influx of aerosols from the mid-latitudes has a wide range of impacts on the Arctic atmosphere. In this study, the capability of the CALIPSO-CALIOP instrument to provide accurate observations of aerosol layers is exploited to characterize their vertical distribution, probability density functions (PDFs) of aerosol layer thickness, base and top heights, and optical depths over the Arctic for the 4-yr period from June 2006 to May 2010. It is shown that the bulk of aerosols, from about 65% in winter to 45% in summer, are confined below the lowermost kilometer of the troposphere. In the middle troposphere (3-5 km), spring and autumn seasons show slightly higher aerosol amounts compared to other two seasons. The relative vertical distribution of aerosols shows that clean continental aerosol is the largest contributor in all seasons except in summer, when layers of polluted continental aerosols are almost as large. In winter and spring, polluted continental aerosols are the second largest contributor to the total number of observed aerosol layers, whereas clean marine aerosol is the second largest contributor in summer and autumn. The PDFs of the geometrical thickness of the observed aerosol layers peak about 400-700 m. Polluted continental and smoke aerosols, which are associated with the intrusions from mid-latitudes, have much broader distributions of optical and geometrical thicknesses, suggesting that they appear more often optically thicker and higher up in the troposphere.

Devasthale, Abhya↗

NASA NTRS1994

Detection of the SO2 atmosphere on Io with the Hubble Space Telescope

Observations of the trailing hemisphere of Io made with the Faint Object Spectrograph of the Hubble Space Telescope (HST) in March 1992 have resulted in the first detection of atmospheric SO2 absorption bands in the ultraviolet. These observations represent only the third positive means of detection of what is widely believed to be Io's primary atmospheric constituent. Below approximately 2130 A the geometric albedo of the satellite is dominated by SO2 gas absorption band signatures, which have been analyzed using models that include the effects of optical thickness, temperature, and spatial distribution. The disk-intergrated HST data cannot resolve the spatial distribution, but it is possible to define basic properties and set constraints on the atmosphere at the time of the observations. Hemispheric atmospheres with average column density N = 6 - 10 x 10(exp 15)/sq sm and T(gas) = 110 - 500 K fit the data, with preference for temperatures of approximately 200 - 250 K. Better fits are found as the atmosphere is spatially confined, with a limit of approximately 8% hemispheric areal coverage and N approximately equal to 3 x 10(exp 17)/sq cm with colder 110 - 250 K temepratures. A dense (N greater than or equal to 10(exp 16)/sq cm), localized component of SO2 gas, such as that possibly associated with active volcanoes, can generate the observed spectral constrast only when the atmosphere is cold (110 K) and an extended component such as Pele is included. The combination of a dense, localized atmosphere with a tenuous component (N less than 10(exp 16)/sq cm, either patchy or extended) also fits the data. In all cases the best fit models imply a disk-averaged column density larger than exospheric but approximately 10 - 30 times less than the previous upper limit from near-UV observations.

Ballester, G. E.↗

NASA NTRSDate not supplied

Late Accretion of large Dark Asteroids and Their Implantation into the Outer Main Belt

Dark (geometric albedo < 0.09) asteroidsare genetically linked to carbonaceous chondrites. Most of these asteroids are located in the mid-outer main belt (2.5 < a < 4.0 AU)and thought to be remnants of the primary accretion of the first solar system planetesimals. Here we presentnew near-infrared (NIR: ~0.5-4.0 μm) reflectance spectra of dark and large (diameter > 100 km) asteroidsmeasured atNASA Infrared Telescope Facility (IRTF).We place the astronomical observations of these large dark asteroids in the context of the thermal evolution and dynamical models and provide new interpretations for the origin and evolution of these asteroids. The astronomical observations together with thermal evolution and dynamical modeling show late accretion and implantation to a confined heliocentric region (~3.0 < a < 3.4 AU)for these large dark asteroids, in agreement with the dynamical predictions. Average densities of large and dark asteroids suggest highly porous interiors and, consequently, relatively late accretion ata time of 1.5-3.5 Myr relative to the formation of calcium-aluminum-rich inclusions with maximum interior temperatures of < 900 K. This work demonstrates that thederived accretion times of large dark asteroids do not correlate in any way with their current semimajor axes. Large and dark asteroidswere likely implanted from more distant regions of the solar system during the giant planet’s dynamical instability. The discovery of dark large asteroids that are smaller than Ceres near its orbital vicinity suggests that this dwarf planet is not unique in the main belt and its surface composition is not driven by its very large size.

Driss Takir↗

NASA NTRS2011

5 Percent Ares I Scale Model Acoustic Test: Overpressure Characterization and Analysis

During the ignition of a ducted solid rocket motor (SRM), rapid expansion of injected hot gases from the motor into a confined volume causes the development of a steep fronted wave. This low frequency transient wave propagates outward from the exhaust duct, impinging the vehicle and ground structures. An unsuppressed overpressure wave can potentially cause modal excitation in the structures and vehicle, subsequently leading to damage. This presentation details the ignition transient f indings from the 5% Ares I Scale Model Acoustic Test (ASMAT). The primary events of the ignition transient environment induced by the SRM are the ignition overpressure (IOP), duct overpressure (DOP), and source overpressure (SOP). The resulting observations include successful knockdown of the IOP environment through use of a Space Shuttle derived IOP suppression system, a potential load applied to the vehicle stemming from instantaneous asymmetrical IOP and DOP wave impingement, and launch complex geometric influences on the environment. The results are scaled to a full-scale Ares I equivalent and compared with heritage data including Ares I-X and both suppressed and unsuppressed Space Shuttle IOP environments.

Alvord, David↗

NASA NTRS1973

Range of earth structure nonuniqueness implied by body wave observations.

The Herglotz-Wiechert integral for the direct inversion of ray parameter versus distance curves can be manipulated to find the envelope of all possible models consistent with geometrical body wave observations (travel time and ray parameter versus distance). Such an extremal inversion approach has been used to find the uncertainty bounds for the velocity structure in the mantle and core. It is found, for example, that there is an uncertainty of plus or minus 40 km in the radius of the inner core boundary, plus or minus 18 km at the core-mantle boundary, and plus or minus 35 km at the 435-km transition zone. The velocity uncertainty is about plus or minus 0.08 km/sec for P and S waves in the lower mantle and about plus or minus 0.20 km/sec in the core. Experiments with various combinations of ray types in the core indicate that rather crude observations of SKKS-SKS travel times confine the range of possible models far more dramatically than do the most precise estimates of PmKP travel times. Comparisons of results from extremal inversion and linearized perturbation inversions indicate that body wave behavior is too strongly nonlinear for linearized schemes to be effective for predicting uncertainty.

Wiggins, R. A.↗

NASA NTRS1995

RY Scuti: Infrared and radio observations of the mass-loss wind of a massive binary star system

We report infrared (IR) imaging, IR photometry, IR spectroscopy, optical/IR photopolarimetry, and Very Large Array (VLA) radio observations of the peculiar binary star RY Scuti. These observations provide an unprecedented view of the detailed spatial structure of the equatorial mass-loss wind of a massive, luminous, 'overcontact' binary system. The binary star (0.43 AU separation) is surrounded by a flattened equatorial disk with an outer radius of approximately = 3 x 10(exp 16) cm (2000 AU) that emits strongly in the IR and radio. The inside of the disk is ionized and emits free-free radiation from hydrogen and 12.8 micrometers forbidden-line emission from (Ne II); the outside of the disk emits thermal radiation from silicate dust. Radio continuum emission is also produced in a compact H II region surrounding the binary. The dust may have a polycyclic aromatic hydrocarbon (PAH) component. We use a rudimentary geometric model in which the thermal IR and radio emission from the disk are assumed to arise in a pair of concentric toroidal rings to estimate the physical properties of the disk. The mean radius of the ionized gas toroid is approximately = 1.3 x 10(exp 16) cm (870 AU), and the mean radius of the dust toroid is approximately = 2.2 x 10(exp 16) cm (1470 AU). RY Scuti has a small intrinsic polarization, with the electric vector perpendicular to the equatorial disk, that is probably caused by electron scattering from hot gas close to the central binary. We conclude that neon in the nebula is overabundant with respect to hydrogen and helium by a factor of between 1.6 and 10. Our IR/radio image data suggest that the circumstellar disk is part of an extensive radiation driven mass-loss outflow that is strongly confined to the equatorial plane of the binary system. The sharp spatial separation of the outer dust torous from the inner ionized gas torus confirms earlier suggestions that dust formation in the circumstellar ejecta of very hot stars must occur in regions that are shielded from the hard radiation field.

Gehrz, R. D.↗

NASA NTRS1990

Innovative design of composite structures: Axisymmetric deformations of unsymmetrically laminated cylinders loaded in axial compression

The study focuses on the axisymmetric deformation response of unsymmetrically laminate cylinders loaded in axial compression by known loads. A geometrically nonlinear analysis is used. Though buckling is not studied, the deformations can be considered to be the prebuckling response. Attention is directed at three 16 layer laminates: a (90 sub 8/0 sub 8) sub T; a (0 sub 8/90 sub 8) sub T and a (0/90) sub 4s. The symmetric laminate is used as a basis for comparison, while the two unsymmetric laminates were chosen because they have equal but opposite bending-stretching effects. Particular attention is given to the influence of the thermally-induced preloading deformations that accompany the cool-down of any unsymmetric laminate from the consolidation temperature. Simple support and clamped boundary conditions are considered. It is concluded that: (1) The radial deformations of an unsymmetric laminate are significantly larger than the radial deformations of a symmetric laminate, although for both symmetric and unsymmetric laminates the large deformations are confined to a boundary layer near the ends of the cylinder; (2) For this nonlinear problem the length of the boundary layer is a function of the applied load; (3) The sign of the radial deformations near the supported end of the cylinder depends strongly on the sense (sign) of the laminate asymmetry; (4) For unsymmetric laminates, ignoring the thermally-induced preloading deformations that accompany cool-down results in load-induced deformations that are under predicted; and (5) The support conditions strongly influence the response but the influence of the sense of asymmetry and the influence of the thermally-induced preloading deformations are independent of the support conditions.

Hyer, M. W.↗

NASA NTRS2001

A Structural and Molecular Approach for the Study Biomarkers

Investigation of the nucleation and growth of crystals in both abiotic and biotic systems is critical to seemingly diverse disciplines of geology, biology, environmental science, and astrobiology. While there are abundant studies devoted to the determination of the structure and composition of inorganic crystals, as well as to the development of thermodynamic and kinetic models, it is only recently that research efforts have been directed towards understanding mineralization in biological systems (i.e., biomineralization). Biomineralization refers to the processes by which living organisms form inorganic solids. Studies of the processes of biomineralization under low temperature aqueous conditions have focused primarily on magnetite forming bacteria and shell forming marine organisms. Many of the biological building materials consist of inorganic minerals (calcium carbonate, calcium phosphate, silica or iron oxide) intricately combined with organic polymers (like proteins). More recently, efforts have been undertaken to explore the nature of biological activities in ancient rocks. In the absence of well-preserved microorganisms or genetic material required for the polmerase chain reaction (PCR) method in molecular phylogenetic studies, using biominerals as biomarkers offers an alternative approach for the recognition of biogenic activity in both terrestrial and extraterrestrial environments. The primary driving force in biomineralization is the interaction between organic and inorganic phases. Thus, the investigation of the ultrastructure and the nature of reactions at the molecular level occurring at the interface between inorganic and organic phases is essential to understanding the processes leading to the nucleation and growth of crystals. It is recognized that crystal surfaces can serve as the substrate for the organization of organic molecules that lead to the formation of polymers and other complex organic molecules, and in discussions of the origins of life, is referred to as organic synthesis on mineral surfaces. Furthermore, it is suggested that the interaction between mineral surfaces and simple organic molecules resulted in the formation of amino acids, RNA, and perhaps other more complex molecules such as proteins. On the other hand, in natural systems, it is recognized that functional groups on cell walls or membranes of microorganisms serve as sites of nucleation and crystallization. The precise replication of biominerals with controlled structure, morphology, size and texture is not confined to higher organisms as it also occurs in primitive prokaryotic cells such as magnetotactic bacteria and cyanobacteria. This suggests that the principal strategies of biomineralization were established early on in the evolutionary history of organisms. It is critical, therefore, to search for common mechanisms within diverse biological systems. One such common factor is the capability for organization and self-assembly. Organic macromolecules such as proteins and lipids can aggregate and polymerize forming membranes or extracellular matrix. At the organic-inorganic interface, several factors such as lattice geometry, polarity, stereochemistry and topography may act in concert to control nucleation and growth of crystals. Although several models have been proposed that discuss the significance of these factors for biomineralization, no comprehensive experimental data are available. In contrast to crystallization in exclusively inorganic systems, the kinetics of reaction and structural relationships between organic and inorganic phases in biominerals or biomimetic material is poorly understood. For example, it is not clear if the concept of epitactic growth (geometrical matching of unit cells at the interface of a secondary crystal growing on a primary crystal) applies to organic-inorganic systems. In contrast to inorganic templates that often have a smooth and rigid surface that promotes epitactic growth, biological substrates are usually rough and result in a large degree of mismatch. It is apparent that factors controlling the reaction at the crystal-matrix interface are strongly dependent upon the nature of the substrate. Therefore, characterization of the assembled organic surface and surface structure of the inorganic phase is crucial to understanding the processes of biomineralization. The focus of our research is the investigation of the processes leading to the nucleation and growth of crystals on both natural and synthetic systems through an interdisciplinary approach that integrates molecular biology, morphology and mineralogy using advanced preparation and analytical techniques. We have studied run-products, particularly magnetite, siderite and other carbonates, that resulted from extracellular biomineralization by extremophiles isolated from a variety of extreme environments ranging from permafrost to hydrothermal vent systems. The results of this study are critical to recognizing biomarkers in terrestrial and extraterrestrial environments.

Thomas-Keprta, Kathie↗

NASA NTRSDate not supplied

Application of Digital Image Correlation in Wind Tunnel

Digital image correlation (DIC) is a non-contact measurement technique that has been used in various applications in multiple industries, from microscopic specimens all the way to large scale structures. This project involved using DIC to capture wing deflection under simulated wind loading at various angles of attack (AoA). A subscale model of a fixed-wing aircraft, shown in Figure 1, was used in the 14-footby 22-footsubsonicwind tunnel at the NASA Langley Research Center. The setup used two pairs of cameras mounted on the ceiling of the tunnel to view the starboard and port side wings. Aluminum framing was used to rigidly mount the cameras to beams in the ceiling. Camera setup challenges due to the confined space included obtaining even lighting and working around infrared (IR) cameras that were used to capture the flow over the wing. Remote connection was used to access data acquisition computers from computers in the control room. Eight measurement locations on each wing were made of 1-inch-diametercircular silver dry transfer decals that did not alter the air flow across the wing. These circles were speckled with a black ink pen and were used for the IR camera as well as for DIC systems. A mock setup outside the wind tunnel was used to optimize the camera setup and verify that the speckled tape provided sufficient correlation. DIC was used to track the position of seven locations as the AoA of the subscale model changed from −10 degrees to +10 degrees in 1-degree increments. The model was rotated at a fixed height about the center of the fuselage from −7 degrees to +10 degrees. The height of the model had to be lowered to achieve AoA slower than −7degrees due to geometric constraints of the cart supporting the model and the wind tunnel. The source of light was stationary relative to the model, so the exposure time had to be adjusted for different wing regions and AoA values. The three-dimensional (3D) visualization of the markings and the two-dimensional (2D) projection of these points onto the port wing at 0-degree AoA is shown in Figure 2.

Matlock Mennu↗

NASA NTRS2000

Experiment Evaluation of Bifurcation in Sands

The basic principles of bifurcation analysis have been established by several investigators, however several issues remain unresolved, specifically how do stress level, grain size distribution, and boundary conditions affect general bifurcation phenomena in pressure sensitive and dilatant materials. General geometrical and kinematics conditions for moving surfaces of discontinuity was derived and applied to problems of instability of solids. In 1962, the theoretical framework of bifurcation by studying the acceleration waves in elasto-plastic (J2) solids were presented. Bifurcation analysis for more specific forms of constitutive behavior was examined by studying localization in pressure-sensitive, dilatant materials, however, analyses were restricted to plane deformation states only. Bifurcation analyses were presented and applied to predict shear band formations in sand under plane strain condition. The properties of discontinuous bifurcation solutions for elastic-plastic solids under axisymmetric and plane strain loading conditions were studied. The study focused on theory, but also references and comparisons to experiments were made. The current paper includes a presentation of a summary of bifurcation analyses for biaxial and triaxial (axisymmetric) loading conditions. The Coulomb model is implemented using incremental piecewise scheme to predict the constitutive relations and shear band inclination angles. Then, a comprehensive evaluation of bifurcation phenomena is presented based on data from triaxial experiments performed under microgravity conditions aboard the Space Shuttle under very low effective confining pressure (0.05 to 1.30 kPa), in which very high peak friction angles (47 to 75 degrees) and dilatancy angles (30 to 31 degrees) were measured. The evaluation will be extended to include biaxial experiments performed on the same material under low (10 kPa) and moderate (100 kPa) confining pressures. A comparison between the behavior under biaxial and triaxial loading conditions will be presented, and related issues concerning influence of confining pressure will be discussed.

Alshibi, Khalid A.↗

NASA NTRSDate not supplied

Next Generation Exercise Device (NGED): Advancing Exercise Capabilities for Future Space Missions Through Biomechanical Modeling

BACKGROUND As space exploration extends to long-duration missions on the Moon and Mars, maintaining astronaut health and fitness becomes increasingly critical. The Next Generation Exercise Device (NGED), developed and tested by the HumanWorks Lab in NASA Johnson Space Center's (JSC) Software, Robotics, and Simulation Division, aims to address this challenge through innovative approaches. This study presents the development and evaluation of an NGED system, focusing on its adaptability to various mission scenarios, including prospective use in a Lunar Pressurized Rover (LPR). Central to this project is the application of biomechanical modeling to optimize exercise efficacy and safety in microgravity and partial gravity environments. The project is a collaborative effort with the Human Health and Performance group at Johnson Space Center, ensuring a comprehensive approach to astronaut well-being that integrates biomechanical principles with practical exercise solutions. The NGED represents the next generation of exercise capabilities for missions in space, on the Moon and Mars, with a specific focus on applications such as the LPR. METHODS AND RESULTS Data collection for NGED development was conducted with two motor-driven Beyond Power Voltra I [1] systems and a custom test structure to allow placement of the cable-based devices on the ground, at shoulder height, and overhead. The collection was performed in JSC’s Prototype Immersive Technology (PIT) Lab, utilizing an OptiTrack motion capture system and AMTI force platform, to enable detailed biomechanical analysis via OpenSim [2,3]. Motion capture data were collected for three subjects representing different body types and statures. The marker set used was an enhanced version of the full-body Plug-in Gait marker set [4], with additional markers strategically placed for the primary objective of informing exercise volume requirements. Subjects performed a series of 17 exercises, carefully selected to engage various muscle groups, including novel spaceflight exercises such as skiing (ergometer style), lateral pulldowns, wood chops, triceps extensions, and flies, with load variations ranging from 10 to 90 pounds to maintain kinematic form. This comprehensive approach allowed for a thorough evaluation of the NGED's performance across a wide range of motions and loads. The biomechanical modeling and analysis were conducted using a modified OpenSim Full Body Rajagopal Model [4,5] and also scaled to the maximum and minimum anthropometry provided in NASA-STD-3001 [6]. Volumetric convex hulls were generated based on model marker trajectories and aggregated into geometric assemblies. These can be placed in models of vehicle designs to assess fit to protect for exercise as well as to adapt NGED exercise to fit available space. Preliminary findings from the collection indicate that the NGED prototype demonstrates significant adaptability across varying user anthropometrics and exercise types. The device showed consistent performance in load-bearing exercises, with subjects able to perform exercises effectively while maintaining proper biomechanical form. CONCLUSION NGED represents a forward-looking advancement in exercise capabilities for future space missions. In the future, this system can be used to capture valuable metrics (e.g., isometric mid-thigh pull for force output measurements, assessments of postural muscle strength, overall isometric strength). Its versatility in accommodating various exercises and user physiques, coupled with the ability to provide targeted biomechanical loading, makes it a promising approach for maintaining astronaut health during long-duration missions to the Moon and Mars. Future work will focus on refining the NGED based on initial biomechanical findings, leveraging the detailed insights provided by motion capture and analysis techniques. Particular emphasis will be placed on optimizing its use within the confined spaces of a LPR and other space habitats. This work contributes significantly to NASA's goals of supporting human health and performance in deep space exploration, paving the way for sustainable long-term presence beyond Low Earth Orbit through advanced, biomechanically-informed exercise solutions.

C Wang↗

NASA NTRS1994

The stellar population in the core of M15

The inner core of the globular cluster M15 within approximately 2 sec of the geometrical center has been explored with high-resolution images taken through several broad-band UV filter with the Faint Object Camera (FOC) on board the Hubble Space Telescope (HST). Approximately 210 stars in this region down to a 5 sigma detection limit of m(sub 220) = 21.5 were reliably identified and located on a UV - U color magnitude diagram for the first time. A majority of stars (about 70% of the total) observed this way lie above the expected main-sequence turn-off of this cluster and below the sparsely populated horizontal branch. The extension of the main sequence above the turn-off separates this population in two roughly equal components situated to the right and left of this line. Most of the former must be classical blue stragglers while the rest belong to a new, as yet unidentified, population of very blue stars. Possibilities include, but are not restricted to, well-mixed single stars, subdwarfs, and helium white dwarfs. Similar objects are also found just outside the core out to approximately 6 sec from the center, but the brighter, presumably more massive ones, are sharply confined to the core itself. The measured excess of bright blue stars and the relative deficiency of bright red giants in the core are consistent with the blue inward color gradient measured from the ground and imply that dynamical evolution can significantly affect the stellar population in the very dense central regions of a high-concentration globular cluster like M15.

De Marchi, Guido↗

NASA NTRS2010

Miniature Lightweight Ion Pump

This design offers a larger surface area for pumping of active gases and reduces the mass of the pump by eliminating the additional vacuum enclosure. There are three main components to this ion pump: the cathode and anode pumping elements assembly, the vacuum enclosure (made completely of titanium and used as the cathode and maintained at ground potential) containing the assembly, and the external magnet. These components are generally put in a noble diode (or differential) configuration of the ion pump technology. In the present state of the art, there are two cathodes, one made of titanium and the other of tantalum. The anodes are made up of an array of stainless steel cylinders positioned between the two cathodes. All the elements of the pump are in a vacuum enclosure. After the reduction of pressure in this enclosure to a few microns, a voltage is applied between the cathode and the anode elements. Electrons generated by the ionization are accelerated toward the anodes that are confined in the anode space by the axial magnetic field. For the generation of the axial field along the anode elements, the magnet is designed in a C-configuration and is fabricated from rare earth magnetic materials (Nd-B-Fe or Sm-Co) possessing high energy product values, and the yoke is fabricated from the high permeability material (Hiperco-50A composed of Fe-Co-V). The electrons in this region collide with the gas molecules and generate their positive ions. These ions are accelerated into the cathode and eject cathode material (Ti). The neutral atoms deposit on the anode surfaces. Because of the chemical activity of Ti, the atoms combine with chemically active gas molecules (e.g. N2, O2, etc.) and remove them. New layers of Ti are continually deposited, and the pumping of active gases is thus accomplished. Pumping of the inert gases is accomplished by their burial several atomic layers deep into the cathode. However, they tend to re-emit if the entrapping lattice atoms are sputtered away. For stable pumping of inert gases, one side of the cathode is made of Ta. Impaction on Ta produces energetic, neutral atoms that pump the inert gases on the anode structure at the peripheral areas of the cathodes (between anode rings). For inert gases stability, a post design has been implemented. Here, posts of cathode material (Ti) are mounted on the cathode. These protrude into the initial part of the anode elements. Materials sputtered from the posts condense on the anode assembly and on the cathode plane at higher rates than in the normal diodes due to enhanced sputtering at glancing angles from geometrical considerations. This increases pumping by burial. This post design has enhanced pumping rates for both active and inert gases, compared with conventional designs.

Sinha, Mahadeva P.↗