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At least 919 records · Page 51
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NASA NTRS2009

Kinematic and EMG Comparison of Gait in Normal and Microgravity

Astronauts regularly perform treadmill locomotion as a part of their exercise prescription while onboard the International Space Station. Although locomotive exercise has been shown to be beneficial for bone, muscle, and cardiovascular health, astronauts return to Earth after long duration missions with net losses in all three areas [1]. These losses might be partially explained by fundamental differences in locomotive performance between normal gravity (NG) and microgravity (MG) environments. During locomotive exercise in MG, the subject must wear a waist and shoulder harness that is attached to elastomer bungees. The bungees are attached to the treadmill, and provide forces that are intended to replace gravity. However, unlike gravity, which provides a constant force upon all body parts, the bungees provide a spring force only to the harness. Therefore, subjects are subjected to two fundamental differences in MG: 1) forces returning the subject to the treadmill are not constant, and 2) forces are only applied to the axial skeleton at the waist and shoulders. The effectiveness of the exercise may also be affected by the magnitude of the gravity replacement load. Historically, astronauts have difficulty performing treadmill exercise with loads that approach body weight (BW) due to comfort and inherent stiffness in the bungee system. Although locomotion can be executed in MG, the unique requirements could result in performance differences as compared to NG. These differences may help to explain why long term training effects of treadmill exercise may differ from those found in NG. The purpose of this investigation was to compare locomotion in NG and MG to determine if kinematic or muscular activation pattern differences occur between gravitational environments.

DeWitt, John K.↗
NASA NTRS2009

Apollo Recovery Operations

Objectives include: a) Describe the organization of recovery force command and control and landing areas; b) Describe the function and timeline use of the Earth Landing System (ELS); c) Describe Stable 1 vs Stable 2 landing configurations and the function of the Command Module Uprighting System; d) Explain the activities of the helicopter and swimmer teams in egress and recovery of the crew; e)Explain the activities of the swimmer teams and primary recovery ship in recovery of the Command Module; and f) Describe several landing incidents that occurred during Apollo.

Interbartolo, Michael↗
NASA NTRS2008

Modeling Ablation of Fibrous Materials from Bulk to Knudsen Regime

Material-environment interactions are analyzed at microscopic scale to explain the lower than expected density observed by post-flight analysis of the char layer on the Stardust shield. Mass transfer, ablation (oxidation), and surface recession of fibrous material is simulated in 3D using a Monte-Carlo simulation tool. Ablation is found to occur either at the surface or in volume depending on Knudsen and Thiele number values. This study supports the idea of volume ablation followed by possible carbon fiber spallation that may explain post-flight analyses.

Lachaud, Jean↗
NASA NTRS2008

The Cosmic Ray Electron Excess

This slide presentation reviews the possible sources for the apparent excess of Cosmic Ray Electrons. The presentation reviews the Advanced Thin Ionization Calorimeter (ATIC) instrument, the various parts, how cosmic ray electrons are measured, and shows graphs that review the results of the ATIC instrument measurement. A review of Cosmic Ray Electrons models is explored, along with the source candidates. Scenarios for the excess are reviewed: Supernova remnants (SNR) Pulsar Wind nebulae, or Microquasars. Each of these has some problem that mitigates the argument. The last possibility discussed is Dark Matter. The Anti-Matter Exploration and Light-nuclei Astrophysics (PAMELA) mission is to search for evidence of annihilations of dark matter particles, to search for anti-nuclei, to test cosmic-ray propagation models, and to measure electron and positron spectra. There are slides explaining the results of Pamela and how to compare these with those of the ATIC experiment. Dark matter annihilation is then reviewed, which represent two types of dark matter: Neutralinos, and kaluza-Kline (KK) particles, which are next explained. The future astrophysical measurements, those from GLAST LAT, the Alpha Magnetic Spectrometer (AMS), and HEPCAT are reviewed, in light of assisting in finding an explanation for the observed excess. Also the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) could help by revealing if there are extra dimensions.

Chang, J.↗
NASA NTRS2009

The Importance of Technology Readiness in NASA Earth Venture Missions

The first set of Venture-class investigations share the characteristic that the technology should be mature and all investigations must use mature technology that has been modeled or demonstrated in a relevant environment (Technology Readiness Level (TRL) >5). Technology Readiness Levels are a systematic metric/measurement system that supports assessments of the maturity of a particular technology and the consistent comparison of maturity between different types of technology. The TRL is used in NASA technology planning. A major step in the level of fidelity of the technology demonstration follows the completion of TRL 5. At TRL 6, a system or subsystem model or prototype must be demonstrated in a relevant environment (ground or space) representative model or prototype system or system, which would go well beyond ad hoc, "patch-cord," or discrete component level breadboarding. These TRL levels are chosen as target objectives for the Program. The challenge for offerors is that they must identify key aspects (uncertainty, multi subsystem complexity, etc) of the TRL estimate that should be properly explained in a submitted proposal. Risk minimization is a key component of the Earth Venture missions. Experiences of prior airborne missions will be shared. The discussion will address aspects of uncertainty and issues surrounding three areas of airborne earth science missions: (1) Aircraft or proposed flight platform -- Expressing the capability of the aircraft in terms of the supporting mission requirements. These issues include airplane performance characteristics (duration, range, altitude, among others) and multiship complexities. (2) Instruments -- Establishing that the instruments have been demonstrated in a relevant environment. Instruments with heritage in prior space missions meet this requirement, as do instruments tested on the ground. Evidence that the instruments have demonstrated the ability to collect data as advertised will be described. The complexity of the integration of multiple subsystems will also be addressed. Issues associated with tailoring the instrument to meet the specific Venture mission objectives must be thoroughly explained and justified. (3) Aircraft/Instrument Integration -- Explicitly defining what development may be required to harden the instrument and integrate the instrument. The challenges associated with this key aspect of major airborne earth science investigations will be presented.

Wells, James E.↗
NASA NTRS2009

Efficient Model-Based Diagnosis Engine

An efficient diagnosis engine - a combination of mathematical models and algorithms - has been developed for identifying faulty components in a possibly complex engineering system. This model-based diagnosis engine embodies a twofold approach to reducing, relative to prior model-based diagnosis engines, the amount of computation needed to perform a thorough, accurate diagnosis. The first part of the approach involves a reconstruction of the general diagnostic engine to reduce the complexity of the mathematical-model calculations and of the software needed to perform them. The second part of the approach involves algorithms for computing a minimal diagnosis (the term "minimal diagnosis" is defined below). A somewhat lengthy background discussion is prerequisite to a meaningful summary of the innovative aspects of the present efficient model-based diagnosis engine. In model-based diagnosis, the function of each component and the relationships among all the components of the engineering system to be diagnosed are represented as a logical system denoted the system description (SD). Hence, the expected normal behavior of the engineering system is the set of logical consequences of the SD. Faulty components lead to inconsistencies between the observed behaviors of the system and the SD (see figure). Diagnosis - the task of finding faulty components - is reduced to finding those components, the abnormalities of which could explain all the inconsistencies. The solution of the diagnosis problem should be a minimal diagnosis, which is a minimal set of faulty components. A minimal diagnosis stands in contradistinction to the trivial solution, in which all components are deemed to be faulty, and which, therefore, always explains all inconsistencies.

Fijany, Amir↗
NASA NTRS2009

Launching to the Moon and Beyond

This slide presentation reviews the Ares I and Ares V launch vehicles, and includes information about both vehicles. It includes a film that explains the details of the two vehicles, and explains the differences and similarities they have to each other and to other launch vehicles. The presentation also reviews the progress made on the Ares I, and the test of the Ares I-X.

Johnson, Paul↗
NASA NTRS2010

Conditions of Core Formation in the Early Earth: Single Stage or Heterogeneous Accretion?

Since approx.1990 high pressure and temperature (PT) experiments on metal-silicate systems have showed that partition coefficients [D(met/sil)] for siderophile (iron-loving) elements are much different than those measured at low PT conditions [1,2]. The high PT data have been used to argue for a magma ocean during growth of the early Earth [3,4]. In the ensuing decades there have been hundreds of new experiments carried out and published on a wide range of siderophile elements (> 80 experiments published for Ni, Co, Mo, W, P, Mn, V, Cr, Ga, Cu and Pd). At the same time several different models have been advanced to explain the siderophile elements in Earth's mantle: a) shallow depth magma ocean 25-30 GPa [3,5]; b) deep magma ocean; up to 50 GPa [6,7], and c) early reduced and later oxidized magma ocean [8,9]. Some studies have drawn conclusions based on a small subset of siderophile elements, or a set of elements that provides little leverage on the big picture (like slightly siderophile elements), and no single study has attempted to quantitatively explain more than 5 elements at a time. The purpose of this abstract is to identify issues that have lead to a difference in interpretation, and to present updated predictive expressions based on new experimental data. The resulting expressions will be applied to the siderophile element depletions in Earth's upper mantle.

Righter, Kevin↗
NASA NTRS2010

Lunar Meteoroid Impact Observations and the Flux of Kilogram-Size Meteoroids

Meteor showers dominate the environment in this size range and explain the evening/morning flux asymmetry of 1.5:1. With sufficient numbers of impacts, this technique can help determine the population index for some showers. Measured flux of meteoroids in the 100g to kilograms range is consistent with other observations. We have a fruitful observing program underway which has significantly increased the number of lunar impacts observed. Over 200 impacts have been recorded in about 4 years. This analysis reports on the 115 impacts taken under photometric conditions during the first 3 full years of operation. We plan to continue for the foreseeable future as follows: 1) Run detailed model to try explain the concentration near the trailing limb; 2) Build up statistics to better understand the meteor shower environment; 3) Provide support for robotic seismometers and dust missions; and 4) Deploy near-infrared and visible cameras with dichroic beamsplitter to 0.5m telescope in New Mexico.

Suggs, Rob↗
NASA NTRS2010

The Influence of Friction Stir Weld Tool Form and Welding Parameters on Weld Structure and Properties: Nugget Bulge in Self-Reacting Friction Stir Welds

Although friction stir welding (FSW) was patented in 1991, process development has been based upon trial and error and the literature still exhibits little understanding of the mechanisms determining weld structure and properties. New concepts emerging from a better understanding of these mechanisms enhance the ability of FSW engineers to think about the FSW process in new ways, inevitably leading to advances in the technology. A kinematic approach in which the FSW flow process is decomposed into several simple flow components has been found to explain the basic structural features of FSW welds and to relate them to tool geometry and process parameters. Using this modelling approach, this study reports on a correlation between the features of the weld nugget, process parameters, weld tool geometry, and weld strength. This correlation presents a way to select process parameters for a given tool geometry so as to optimize weld strength. It also provides clues that may ultimately explain why the weld strength varies within the sample population.

Schneider, Judy↗
NASA NTRS2010

X-Ray Variation Statistics and Wind Clumping in Vela X-1

We investigate the structure of the wind in the neutron star X-ray binary system Vela X-1 by analyzing its flaring behavior. Vela X-1 shows constant flaring, with some flares reaching fluxes of more than 3.0 Crab between 20-60 keV for several 100 seconds, while the average flux is around 250 mCrab. We analyzed all archival INTEGRAL data, calculating the brightness distribution in the 20-60 keV band, which, as we show, closely follows a log-normal distribution. Orbital resolved analysis shows that the structure is strongly variable, explainable by shocks and a fluctuating accretion wake. Analysis of RXTE ASM data suggests a strong orbital change of N. Accreted clump masses derived from the INTEGRAL data are on the order of 5 x 10(exp 19)-10(exp 21) g. We show that the lightcurve can be described with a model of multiplicative random numbers. In the course of the simulation we calculate the power spectral density of the system in the 20-100 keV energy band and show that it follows a red-noise power law. We suggest that a mixture of a clumpy wind, shocks, and turbulence can explain the measured mass distribution. As the recently discovered class of supergiant fast X-ray transients (SFXT) seems to show the same parameters for the wind, the link between persistent HMXB like Vela X-1 and SFXT is further strengthened.

Furst, Felix↗
NASA NTRS2001

Petrology and Geochemistry of D'Orbigny, Geochemistry of Sahara 99555, and the Origin of Angrites

We have done detailed petrologic study of the angrite, D'Orbigny, and geochemical study of it and Sahara 99555. D'Orbigny is an igneous-textured rock composed of Ca-rich olivine, Al-Ti-diopside-hedenbergite, subcalcic kirschsteinite, two generations of hercynitic spinel and anorthite, with the mesostasis phases ulv6spinel, Ca-phosphate, a silicophosphate phase and Fe-sulfide. We report an unknown Fe-Ca-Al-Ti-silicate phase in the mesostasis not previously found in angrites. One hercynitic spinel is a large, rounded homogeneous grain of a different composition than the euhedral and zoned grains. We believe the former is a xenocryst, the first such described from angrites. The mafic phases are highly zoned; mg# of cores for olivine are approx.64, and for clinopyroxene approx.58, and both are zoned to Mg-free rims. The Ca content of olivine increases with decreasing mg#, until olivine with approx.20 mole% Ca is overgrown by subcalcic kirschsteinite with Ca approx.30-35 mole%. Detailed zoning sequences in olivine-subcalcic kirschsteinite and clinopyroxene show slight compositional reversals. There is no mineralogic control that can explain these reversals, and we believe they were likely caused by local additions of more primitive melt during crystallization of D'Orbigny. D'Orbigny is the most ferroan angrite with a bulk rock mg# of 32. Compositionally, it is virtually identical to Sahara 99555; the first set of compositionally identical angrites. Comparison with the other angrites shows that there is no simple petrogenetic sequence, partial melting with or without fractional crystallization, that can explain the angrite suite. Angra dos Reis remains a very anomalous angrite. Angrites show no evidence for the brecciation, shock, or impact or thermal metamorphism that affected the HED suite and ordinary chondrites. This suggests the angrite parent body may have followed a fundamentally different evolutionary path than did these other parent bodies.

Mittlefehldt, David W.↗
NASA NTRS2010

A Test of Thick-Target Nonuniform Ionization as an Explanation for Breaks in Solar Flare Hard X-Ray Spectra

Solar nonthermal hard X-ray (HXR) flare spectra often cannot be fitted by a single power law, but rather require a downward break in the photon spectrum. A possible explanation for this spectral break is nonuniform ionization in the emission region. We have developed a computer code to calculate the photon spectrum from electrons with a power-law distribution injected into a thick-target in which the ionization decreases linearly from 100% to zero. We use the bremsstrahlung cross-section from Haug (1997), which closely approximates the full relativistic Bethe-Heitler cross-section, and compare photon spectra computed from this model with those obtained by Kontar, Brown and McArthur (2002), who used a step-function ionization model and the Kramers approximation to the cross-section. We find that for HXR spectra from a target with nonuniform ionization, the difference (Delta-gamma) between the power-law indexes above and below the break has an upper limit between approx.0.2 and 0.7 that depends on the power-law index delta of the injected electron distribution. A broken power-law spectrum with a. higher value of Delta-gamma cannot result from nonuniform ionization alone. The model is applied to spectra obtained around the peak times of 20 flares observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI from 2002 to 2004 to determine whether thick-target nonuniform ionization can explain the measured spectral breaks. A Monte Carlo method is used to determine the uncertainties of the best-fit parameters, especially on Delta-gamma. We find that 15 of the 20 flare spectra require a downward spectral break and that at least 6 of these could not be explained by nonuniform ionization alone because they had values of Delta-gamma with less than a 2.5% probability of being consistent with the computed upper limits from the model. The remaining 9 flare spectra, based on this criterion, are consistent with the nonuniform ionization model.

Holman, gordon↗
NASA NTRS2010

Details of Side Load Test Data and Analysis for a Truncated Ideal Contour Nozzle and a Parabolic Contour Nozzle

Two cold flow subscale nozzles were tested for side load characteristics during simulated nozzle start transients. The two test article contours were a truncated ideal and a parabolic. The current paper is an extension of a 2009 AIAA JPC paper on the test results for the same two nozzle test articles. The side load moments were measured with the strain tube approach in MSFC s Nozzle Test Facility. The processing techniques implemented to convert the strain gage signals into side load moment data are explained. Nozzle wall pressure profiles for separated nozzle flow at many NPRs are presented and discussed in detail. The effect of the test cell diffuser inlet on the parabolic nozzle s wall pressure profiles for separated flow is shown. The maximum measured side load moments for the two contours are compared. The truncated ideal contour s peak side load moment was 45% of that of the parabolic contour. The calculated side load moments, via mean-plus-three-standard-deviations at each nozzle pressure ratio, reproduced the characteristics and absolute values of measured maximums for both contours. The effect of facility vibration on the measured side load moments is quantified and the effect on uncertainty is calculated. The nozzle contour designs are discussed and the impact of a minor fabrication flaw in the nozzle contours is explained.

Ruf, Joseph H.↗
NASA NTRS2011

Widespread Nanoflare Variability Detected with Hinode/XRT in a Solar Active Region

It is generally agreed that small impulsive energy bursts called nanoflares are responsible for at least some of the Sun s hot corona, but whether they are the explanation for most of the multi-million degree plasma has been a matter of ongoing debate. We here present evidence that nanoflares are widespread in an active region observed by the X-Ray Telescope on-board the Hinode mission. The distributions of intensity fluctuations have small but important asymmetries, whether taken from individual pixels, multi-pixel subregions, or the entire active region. Negative fluctuations (corresponding to reduced intensity) are greater in number but weaker in amplitude, so that the median fluctuation is negative compared to a mean of zero. Using Monte Carlo simulations, we show that only part of this asymmetry can be explained by Poisson photon statistics. The remainder is explainable with a tendency for exponentially decreasing intensity, such as would be expected from a cooling plasma produced, e.g., from a nanoflare. We suggest that nanoflares are a universal heating process within active regions.

Reale, Fabio↗
NASA NTRS2011

Emission Measure Distribution and Heating of Two Active Region Cores

Using data from the Extreme-ultraviolet Imaging Spectrometer aboard Hinode, we have studied the coronal plasma in the core of two active regions. Concentrating on the area between opposite polarity moss, we found emission measure distributions having an approximate power-law form EM/T(exp 2.4) from log T = 5.55 up to a peak at log T = 6.57. The observations are explained extremely well by a simple nanoflare model. However, in the absence of additional constraints, the observations could possibly also be explained by steady heating.

Tripathi, Durgesh↗
NASA NTRS2011

Human Modeling For Ground Processing Human Factors Engineering Analysis

There have been many advancements and accomplishments over that last few years using human modeling for human factors engineering analysis for design of spacecraft and launch vehicles. The key methods used for this are motion capture and computer generated human models. The focus of this paper is to explain the different types of human modeling used currently and in the past at Kennedy Space Center (KSC) currently, and to explain the future plans for human modeling for future spacecraft designs.

Tran, Donald↗
NASA NTRS2010

Concerning the Motion of FTEs and Attendant Signatures

We employ the Cooling et al. [2001] model to predict the location, orientation, and motion of flux transfer events (FTEs) generated along finite length component and anti parallel reconnection lines for typical solar wind plasma conditions and various interplanetary magnetic field (IMF) orientations in the plane perpendicular to the SunEarth line at the solstices and equinoxes. For duskward and northward or southward IMF orientations, events formed by component reconnection originate along reconnection curves passing through the sub solar point that tilt from southern dawn to northern dusk. They maintain this orientation as they move either northward into the northern dawn quadrant or southward into the southern dusk quadrant. By contrast, events formed by antiparallel reconnection originate along reconnection curves running from northern dawn to southern dusk in the southern dawn and northern dusk quadrants and maintain these orientations as they move anti sunward into both these quadrants. Although both the component and antiparallel reconnection models can explain previously reported event orientations on the southern dusk magnetopause during intervals of northward and dawn ward IMF orientation, only the component model explains event occurrence near the subsolar magnetopause during intervals when the IMF does not point due southward.

Sibeck, David G.↗