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At least 73 records · Page 4

Prestressing Shock Resistant Mechanical Components and Mechanisms Made from Hard, Superelastic Materials

A method and an apparatus confer full superelastic properties to the active surface of a mechanical component constructed of a superelastic material prior to service. A compressive load is applied to the active surface of the mechanical component followed by removing the compressive load from the active surface whereby substantially all load strain is recoverable after applying and removing of subsequent compressive loads.

DellaCorte, Christopher↗

Separation control over an airfoil at high angles of attack by sound emanating from the surface

Active control by sound emanating from a narrow gap in the vicinity of the leading edge of a symmetrical airfoil is used to study the influence of sound on the pressure distribution and the wake at high angles of attack. The results from experiments conducted at a Reynolds number based on the chord of 35,000 show that, with injection of sound at twice the shedding frequency of the shear layer, the region of separation becomes drastically reduced. The shear layer is found to be very sensitive to sound excitation in the vicinity of the separation point. The excitation sufficiently alters the global circulation to cause an increase in lift and reduction in drag. Furthermore, experimental results describing stall and post-stall conditions compare well with the limited data available and indicate that stall is delayed by sound injection into the separated region.

Huang, L. S.↗

Considerations for Health and Performance During Surface Extravehicular Activities

BACKGROUND: NASA’s objectives for expanding human presence beyond low Earth orbit will require Extravehicular Activities (EVAs) on lunar and planetary surfaces. Given the physiological and functional demands of conducting surface EVAs in a pressurized spacesuit in reduced gravity environments, there is a possibility that crew injury and compromised physiological and/or functional performance may present. OVERVIEW: Many human health and performance knowledge gaps exist in regards to exploration EVA that require characterization to ensure safety, reliability, and mission success. To address knowledge gaps, EVA simulations in Earth-based analog environments and/or spacesuit simulators can be utilized to provide valuable insights into task-based physiologic and metabolic costs, cognitive loads, and associated operational limitations to inform future mission concepts. Physical workloads approaching 60% of maximum metabolic rates and 85% age-predicted heart rate maxima; core body temperatures approaching 100o F; and subjective responses indicating limited spare cognitive capacity via Bedford scale have been observed during ground-based exploration EVA simulations in the NASA Active Response Gravity Offload Simulator (ARGOS) and Neutral Buoyancy Lab (NBL) during simulated planetary EVAs in pressurized suits. Further, ground-based EVA analogs vary in their ability to simulate planetary EVA and resulting physical workloads. DISCUSSION: Metabolic costs, thermal burdens, functional strength, and cognitive impacts have been and must continue to be assessed in ground-based analogs to fully characterize operational demands and crew readiness levels for exploration EVA. Considerations should be given to enabling a new concept of high-tempo surface EVA operations and associated work-rest intervals, understanding human health and performance impacts of evolving commercial suit designs and capabilities, and predictive modeling and decision support capabilities to enable safe and successful EVA operations.

EVA↗

Considerations for Health and Performance during Surface Extravehicular Activities

BACKGROUND: NASA’s objectives for expanding human presence beyond low Earth orbit will require Extravehicular Activities (EVAs) on lunar and planetary surfaces. Given the physiological and functional demands of conducting surface EVAs in a pressurized spacesuit in reduced gravity environments, there is a possibility that crew injury and compromised physiological and/or functional performance may present. OVERVIEW: Many human health and performance knowledge gaps exist in regards to exploration EVA that require characterization to ensure safety, reliability, and mission success. To address knowledge gaps, EVA simulations in Earth-based analog environments and/or spacesuit simulators can be utilized to provide valuable insights into task-based physiologic and metabolic costs, cognitive loads, and associated operational limitations to inform future mission concepts. Physical workloads approaching 60% of maximum metabolic rates and 85% age-predicted heart rate maxima; core body temperatures approaching 100° F; and subjective responses indicating limited spare cognitive capacity via Bedford scale have been observed during ground-based exploration EVA simulations in the NASA Active Response Gravity Offload Simulator (ARGOS) and Neutral Buoyancy Lab (NBL) during simulated planetary EVAs in pressurized suits. Further, ground-based EVA analogs vary in their ability to simulate planetary EVA and resulting physical workloads. DISCUSSION: Metabolic costs, thermal burdens, functional strength, and cognitive impacts have been and must continue to be assessed in ground-based analogs to fully characterize operational demands and crew readiness levels for exploration EVA. Considerations should be given to enabling a new concept of high-tempo surface EVA operations and associated work-rest intervals, understanding human health and performance impacts of evolving commercial suit designs and capabilities, and predictive modeling and decision support capabilities to enable safe and successful EVA operations.

P Estep↗

Preliminary catalog of pictures taken on the lunar surface during the Apollo 16 mission

A catalog of all pictures taken from the lunar module or the lunar surface during the Apollo 16 lunar stay is presented. The tabulations are arranged for the following specific uses: (1) given the number of a particular frame, find its location in the sequence of lunar surface activity, the station from which it was taken and the subject matter of the picture; (2) given a particular location or activity within the sequence of lunar surface activity, find the pictures taken at that time and their subject matter; and (3) given a sample number from the voice transcript listed, find the designation assigned to the same sample by the lunar receiving laboratory.

Batson, R. M.↗

Origin of amphiphilic molecules and their role in primary structure formation

Attempts to solve two fundamental questions are described: the first concerns which mechanisms were responsible for the self-assembly of membrane structures on the prebiotic Earth, and the second concerns the routes by which considerable amounts of membrane amphiphiles formed from simpler hydrocarbons. The physicochemical properties of several amphiphilic compounds extracted from the Murchison carbonaceous chondrite were studied, using infra-red and fluorescent spectroscopy, measurements of surface activity, chromato-mass spectrometry, and polarization and electron microscopy. The results supported previous observations that amphiphilic and aromatic hydrocarbons were present in significant quantities, and the first demonstration of surface activity among a number of acidic derivatives of hydrocarbons is reported. In addition, one fraction of the surface-active compounds can form bilayer structures, showing that membranes could have self-assembled on the prebiotic Earth. Photochemical oxidation of hydrocarbons is shown to be a likely source of the amphiphilic molecules required for the self-assembly of primary membrane structures.

NASA Discipline Number 52-20↗

Discovery and observation of BY Draconis variables

The discovery of BY Draconis variables was efficiently accomplished by a spectroscopic survey of dK-M stars for weak H-alpha emissions, using 1-2 A resolution. The four BY Dra variables discovered are all spectroscopic binaries with P values lower than about 10 d, in light of which, it is noted that the onset of high surface activity and appearance of H-alpha emission occur sharply at v(equator) of approximately 5 km/sec. At v(equator) of about 3 km/sec, dK-M stars have low levels of surface activity. It is found that while there is a range of Ca II emission strength, and only the strongest emitters of this line are BY Dra and/or flare stars, the H-alpha feature changes abruptly to an emission feature signaling the onset of flaring and/or the BY Dra syndrome. An increase of the rotation rate above v(equator) 5 km/sec does not appear to increase the level of surface activity.

Bopp, B. W.↗

An H-alpha survey of southern hemisphere active chromosphere stars

Because of the variety of extraordinary phenomena exhibited by active chromosphere objects, discovery of new, bright surface-active stars is of considerable importance. Ca II emission is a well-known signature of chromospheric activity, serving even as one of the points of definition of the class of RS CVn binary stars. In connection with the present investigation, spectroscopic observations of 27 Ca II emission stars have been conducted. The observations make it possible to identify unambiguously the most chromospherically active stars in the sample. By observing the H-alpha line, rather than H and K, it is possible to distinguish nine of these stars which are likely to be observational targets as interesting as the extremely surface active objects V711 Tau or FK Com. Of the 27 stars surveyed, two (HD 86005, HD 204128) showed H-alpha as an emission feature above continuum, with estimated equivalent width 1-2 A.

Bopp, B. W.↗

Characterization of atrial natriuretic peptide degradation by cell-surface peptidase activity on endothelial cells

Atrial natriuretic peptide (ANP) is a fluid-regulating peptide hormone that promotes vasorelaxation, natriuresis, and diuresis. The mechanisms for the release of ANP and for its clearance from the circulation play important roles in modulating its biological effects. Recently, we have reported that the cell surface of an endothelial cell line, CPA47, could degrade 125I-ANP in the presence of EDTA. In this study, we have characterized this degradation of 125I-ANP. The kinetics of ANP degradation by the surface of CPA47 cells were first order, with a Km of 320 +/- 60 nM and Vmax of 35 +/- 14 pmol of ANP degraded/10 min/10(5) cells at pH 7.4. ANP is degraded by the surface of CPA47 cells over a broad pH range from 7.0-8.5. Potato carboxypeptidase inhibitor and bestatin inhibited 125I-ANP degradation, suggesting that this degradative activity on the surface of CPA47 cells has exopeptidase characteristics. The selectivity of CPA47 cell-surface degradation of ANP was demonstrated when 125I-ANP degradation was inhibited in the presence of neuropeptide Y and angiotensin I and II but not bradykinin, bombesin, endothelin-1, or substance P. The C-terminal amino acids phe26 and tyr28 were deduced to be important for ANP interaction with the cell-surface peptidase(s) based on comparison of the IC50 of various ANP analogues and other natriuretic peptides for the inhibition of ANP degradation. These data suggest that a newly characterized divalent cation-independent exopeptidase(s) that selectively recognizes ANP and some other vasoactive peptides exists on the surface of endothelial cells.

NASA Discipline Regulatory Physiology↗

Computational Study of Oxidative Etch Pitting in FiberForm and the Effect on Its Material Properties

Erosion of carbon due to oxidation does not occur uniformly but through the formation of localized etch pits because of active surface sites. These active sites are formed due to the presence of atomic defects on the carbon surface, and have much higher reactivity compared to average non-defective sites. Thus, these active sites are first to react during ablation, resulting in their removal. This causes all the neighboring atoms to be defective and increase their reactivity, thus leading to the localized carbon removal around these “active” sites. In this manner, these highly reactive defective sites serve as nucleation sites for the formation and growth of etch pits with potentially detrimental effects on the structural integrity. In order to understand the influence of these etch pits on the material properties of carbon fiber microstructures, we have developed a new capability within direct simulation Monte Carlo (DSMC) to capture the etch pit formation process. This capability is developed within the DSMC code SPARTA (Stochastic PArallel Rarefied-gas Time-accurate Analyzer) and can model the material removal in presence of active sites leading to the formation of etch pits. The focus of the current work will be to study the effect of etch pits on the material properties of FiberForm, a commonly used base material within many thermal protection system materials (TPS). The microstructure of virgin FiberForm obtained directly from X-ray microtomography experiments is used within SPARTA to obtain the ablated geometries with etch pits. These pitted microstructures are then imported within the Porous Microstructure Analysis (PuMA) software and various material properties such as elasticity, thermal conductivity, and permeability are computed. The variation of these properties as a result of the complex evolution of the surface topology due to etch pit formation is studied and analyzed. Furthermore, the effect of pitting is compared to the case of shrinking fibers, which has been the standard for modelling ablation of carbon structures; and significant differences are observed. Thus, such a physically realistic modeling of material removal through the formation of etch pits will be helpful in predicting the degradation of carbon-based TPS more accurately during oxidation; as well as other mechanisms such as spallation, which involves the removal of chunks of material into the flow due to etch pit growth. This will ultimately improve our understanding of the failure modes in these materials due to ablation.

Carbon Ablators↗

Computational Study of Oxidative Etch Pitting in FiberForm and the Effect on Its Material Properties

Erosion of carbon due to oxidation does not occur uniformly but through the formation of localized etch pits because of active surface sites. These active sites are formed due to the presence of atomic defects on the carbon surface, and have much higher reactivity compared to average non-defective sites. Thus, these active sites are first to react during ablation, resulting in their removal. This causes all the neighboring atoms to be defective and increase their reactivity, thus leading to the localized carbon removal around these “active” sites. In this manner, these highly reactive defective sites serve as nucleation sites for the formation and growth of etch pits with potentially detrimental effects on the structural integrity. In order to understand the influence of these etch pits on the material properties of carbon fiber microstructures, we have developed a new capability within direct simulation Monte Carlo (DSMC) to capture the etch pit formation process. This capability is developed within the DSMC code SPARTA (Stochastic PArallel Rarefied-gas Time-accurate Analyzer) and can model the material removal in presence of active sites leading to the formation of etch pits. The focus of the current work will be to study the effect of etch pits on the material properties of FiberForm, a commonly used base material within many thermal protection system materials (TPS). The microstructure of virgin FiberForm obtained directly from X-ray microtomography experiments is used within SPARTA to obtain the ablated geometries with etch pits. These pitted microstructures are then imported within the Porous Microstructure Analysis (PuMA) software and various material properties such as elasticity, thermal conductivity, and permeability are computed. The variation of these properties as a result of the complex evolution of the surface topology due to etch pit formation is studied and analyzed. Furthermore, the effect of pitting is compared to the case of shrinking fibers, which has been the standard for modelling ablation of carbon structures; and significant differences are observed. Thus, such a physically realistic modeling of material removal through the formation of etch pits will be helpful in predicting the degradation of carbon-based TPS more accurately during oxidation; as well as other mechanisms such as spallation, which involves the removal of chunks of material into the flow due to etch pit growth. This will ultimately improve our understanding of the failure modes in these materials due to ablation.

Carbon Ablators↗

Computational Investigation of Oxidative Etch Pitting in FiberForm and Its Impact on Material Properties

Oxidation-driven carbon erosion does not occur uniformly but rather through the development of localized etch pits at active surface sites. These active sites form due to atomic defects on the carbon surface, making them significantly more reactive than the surrounding, non-defective areas. As a result, these sites are the first to react during ablation, leading to their removal. This process creates new defects in neighboring atoms, increasing their reactivity and causing localized carbon removal around these active sites. In this way, the highly reactive defective areas serve as nucleation points for the formation and growth of etch pits, which can have adverse effects on structural integrity of FiberForm. To better understand how these etch pits impact the material properties of carbon fiber microstructures, we have developed a new capability within the direct simulation Monte Carlo (DSMC) framework to capture the etch pit formation process. This capability, integrated into the DSMC code SPARTA (Stochastic Parallel Rarefied-gas Time-accurate Analyzer), models material removal in the presence of active sites, leading to the formation of etch pits. The current work focuses on studying the effects of these etch pits on the material properties of FiberForm, a widely used base material in thermal protection systems (TPS). The microstructure of virgin FiberForm, obtained via X-ray microtomography, is imported into SPARTA to generate the ablated geometries with etch pits. These modified microstructures are then analyzed using the Porous Microstructure Analysis (PuMA) software to compute various material properties, including elasticity, thermal conductivity, and permeability. We investigate the variation of these properties due to the complex surface topology changes caused by etch pit formation. Additionally, we compare the effects of pitting with the conventional model of shrinking fibers, traditionally used to simulate the ablation of carbon structures. Significant differences emerge between the two approaches. Consequently, this physically realistic model of material removal through etch pit formation offers improved accuracy in predicting the degradation of carbon-based TPS during oxidation. It also provides insights into other mechanisms, such as spallation, where chunks of material are removed into the flow due to etch pit growth. Ultimately, this model enhances our understanding of failure modes in these materials during ablation.

PuMA↗

Solar cell module

An improved solar cell module for use in terrestrial environments is disclosed. It is characterized by: (1) an internally reflective plate having a planar surface of incidence and an opposed textured surface (2) a plurality of uniformly spaced silicon solar cells having the active surfaces thereof bonded to portions of the textured surface, and (3) a layer of diffusely reflective matter applied to the textured surface in surrounding relation with the solar cells for reflecting solar energy. The solar energy then strikes the surface of incidence at such angles as to be internally re-reflected and caused to progress toward the active surfaces of the solar cells, whereby concentration of incident flux on the solar cell is achieved without increased module depth.

Shepard, N. F., Jr.↗

Surface-Normal Active Flow Control for Lift Enhancement and Separation Mitigation for High-Lift Common Research Model

This study explores the feasibility of using small surface-normal jets near the flap trailing edge as active aerodynamic load control on the high-lift Common Research Model wing/-body configuration. Chimera Grid Tools are utilized to generate structured curvilinear overset grids, and the Reynolds-averaged Navier-Stokes solver OVERFLOW is employed to solve for the flow-field around the geometry. The so-called microjet is initially employed across both the inboard and the outboard flaps on the pressure-side near the trailing edge. It is shown that implementing the microjet on the inboard flap is more effective compared to implementing it on the outboard flap. This is because, prior to microjet implementation, the flow on the outboard flap exhibits extensive separation, while the flow on the inboard flap exhibits moderate separation. For microjet implementation across the inboard flap only, the relationship between momentum coefficient of the microjet and lift-enhancement is found to be∆CL'1.66√Cμfor the rangeCμ= 0.00−0.012. We show that implementing a microjet with a jet velocity ratio of one, which corresponds toCμ= 0.003, can shift the linear region of the lift curve by ∆CL= 0.08. The linear shift in the lift curve is significant for enhancing airplane performance such as increasing its payload. Microjet implementation effects on the drag coefficient are also investigated through a drag decomposition analysis. Further, we employ an induced drag analysis based on the spanwise load distribution and show that the microjet-related increase in pressure drag coefficient is dominated by the increase in the induced drag while microjet implementation reduces the form drag. These preliminary results show that favorable changes in aerodynamic performance can be achieved by using the surface-normal jets presented in this study.

ARMD↗

Starspots as the cause of the intrinsic light variations in RS Canum Venaticorum type stars

A starspot model is proposed to interpret the light curves of three RS CVn type binary systems. Two of the systems are RS CVn and SZ Psc, which are detached, while the third system, RT Lac, is semidetached. Solar activity and the surface activity of the RS CVn type stars are compared. It is found that the spot model permits the detailed fitting of both the out-of-eclipse complications and the distorted shapes of the secondary eclipses in the light curves of these stars.

Eaton, J. A.↗

ARES Biennial Report 2012 Final

Since the return of the first lunar samples, what is now the Astromaterials Research and Exploration Science (ARES) Directorate has had curatorial responsibility for all NASA-held extraterrestrial materials. Originating during the Apollo Program (1960s), this capability at Johnson Space Center (JSC) included scientists who were responsible for the science planning and training of astronauts for lunar surface activities as well as experts in the analysis and preservation of the precious returned samples. Today, ARES conducts research in basic and applied space and planetary science, and its scientific staff represents a broad diversity of expertise in the physical sciences (physics, chemistry, geology, astronomy), mathematics, and engineering organized into three offices (figure 1): Astromaterials Research (KR), Astromaterials Acquisition and Curation (KT), and Human Exploration Science (KX). Scientists within the Astromaterials Acquisition and Curation Office preserve, protect, document, and distribute samples of the current astromaterials collections. Since the return of the first lunar samples, ARES has been assigned curatorial responsibility for all NASA-held extraterrestrial materials (Apollo lunar samples, Antarctic meteorites - some of which have been confirmed to have originated on the Moon and on Mars - cosmic dust, solar wind samples, comet and interstellar dust particles, and space-exposed hardware). The responsibilities of curation consist not only of the longterm care of the samples, but also the support and planning for future sample collection missions and research and technology to enable new sample types. Curation provides the foundation for research into the samples. The Lunar Sample Facility and other curation clean rooms, the data center, laboratories, and associated instrumentation are unique NASA resources that, together with our staff's fundamental understanding of the entire collection, provide a service to the external research community, which relies on access to the samples. The curation efforts are greatly enhanced by a strong group of planetary scientists who conduct peerreviewed astromaterials research. Astromaterials Research Office scientists conduct peer-reviewed research as Principal or Co-Investigators in planetary science (e. g., cosmochemistry, origins of solar systems, Mars fundamental research, planetary geology and geophysics) and participate as Co-Investigators or Participating Scientists in many of NASA's robotic planetary missions. Since the last report, ARES has achieved several noteworthy milestones, some of which are documented in detail in the sections that follow. Within the Human Exploration Science Office, ARES is a world leader in orbital debris research, modeling and monitoring the debris environment, designing debris shielding, and developing policy to control and mitigate the orbital debris population. ARES has aggressively pursued refinements in knowledge of the debris environment and the hazard it presents to spacecraft. Additionally, the ARES Image Science and Analysis Group has been recognized as world class as a result of the high quality of near-real-time analysis of ascent and on-orbit inspection imagery to identify debris shedding, anomalies, and associated potential damage during Space Shuttle missions. ARES Earth scientists manage and continuously update the database of astronaut photography that is predominantly from Shuttle and ISS missions, but also includes the results of 40 years of human spaceflight. The Crew Earth Observations Web site (http://eol.jsc.nasa.gov/Education/ESS/crew.htm) continues to receive several million hits per month. ARES scientists are also influencing decisions in the development of the next generation of human and robotic spacecraft and missions through laboratory tests on the optical qualities of materials for windows, micrometeoroid/orbital debris shielding technology, and analog activities to assess surface science operations. ARES serves as host to numerous students and visiting scientists as part of the services provided to the research community and conducts a robust education and outreach program. ARES scientists are recognized nationally and internationally by virtue of their success in publishing in peer-reviewed journals and winning competitive research proposals. ARES scientists have won every major award presented by the Meteoritical Society, including the Leonard Medal, the most prestigious award in planetary science and cosmochemistry; the Barringer Medal, recognizing outstanding work in the field of impact cratering; the Nier Prize for outstanding research by a young scientist; and several recipients of the Nininger Meteorite Award. One of our scientists received the Department of Defense (DoD) Joint Meritorious Civilian Service Award (the highest civilian honor given by the DoD). ARES has established numerous partnerships with other NASA Centers, universities, and national laboratories. ARES scientists serve as journal editors, members of advisory panels and review committees, and society officers, and several scientists have been elected as Fellows in their professional societies. This biennial report summarizes a subset of the accomplishments made by each of the ARES offices and highlights participation in ongoing human and robotic missions, development of new missions, and planning for future human and robotic exploration of the solar system beyond low Earth orbit.

Stansbery, Eileen↗

X-ray Activity in Pre-main Sequence Stars

X-ray findings and their interpretation with respect to winds and surface activity of pre-main sequence stars are summarized. Some recent optical and radio observations supporting the X-ray evidence for giant flares on PMS stars are discussed. The unusual properties of PMS/T Tauri stars were for many years primarily attributed to their strong winds. Numerous lines of evidence are outlined herein indicating that PMS stars also have enhanced surface activity, including extremely strong individual flares.

Feigelson, E. D.↗

Aerodynamic Assessment of Surface-Normal Active Flow Control for Lift Enhancement on the High-Lift Common Research Model

This study explores aerodynamic feasibility of small surface-normal pneumatic jets (micro-jets) for lift enhancement on the high-lift Common Research Model. To date, lift enhancement studies using microjets have been conducted at wind tunnel Reynolds numbers less than three and half million. This paper computationally investigates microjet effects at a flight Reynolds number of24.6million. Prior to microjet activation, it is shown that flow features such as trailing edge (TE) flow separation on both inboard and outboard flaps have noticeable sensitivity to Reynolds number. At the flight Reynolds number, the onset of TE flow separation shifts downstream resulting in less flow separation compared to at the wind tunnel Reynolds numberof3.26million. The effects are insignificant for lift enhancement due to microjet on the inboard flap. However, the effects are significant for lift enhancement on the outboard flap. Microjets are shown to be more effective in circulation control on the outboard flap at the higher Reynolds number. For a microjet with velocity ratio of one, lift enhancement is increased by17%at the flight Reynolds number. This highlights the sensitivity of microjet performance to the flow features of the configuration it is implemented on. Microjet lift enhancement trends at both Reynolds numbers are found to be consistent in their ability to move the lift curve upwards in the linear regime, with the lift enhancement related to microjet momentum coefficient throughΔ𝐶𝐿=𝐾√︁𝐶𝜇. Analysis of the impact microjets have on drag shows that microjets improve the configuration’s Oswald efficiency by5.4%and2.5%at the wind tunnel and flight Reynolds numbers respectively, while providing lift enhancement. Microjet effects on the trim drag are found to be less than one percent of the total drag. The results of this study highlight the potential of small surface-normal pneumatic jets for improved performance at high-lift conditions.

ARMD↗