The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Katherine T Fountaine - One of the best experts on this subject based on the ideXlab platform.
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experimental methods for efficient solar hydrogen production in Microgravity Environment
Journal of Visualized Experiments, 2019Co-Authors: Katharina Brinkert, Matthias H Richter, Omer Akay, Janine Liedtke, Katherine T Fountaine, Hansjoachim Lewerenz, Michael GiersigAbstract:Long-term space flights and cis-lunar research platforms require a sustainable and light life-support hardware which can be reliably employed outside the Earth's atmosphere. So-called 'solar fuel' devices, currently developed for terrestrial applications in the quest for realizing a sustainable energy economy on Earth, provide promising alternative systems to existing air-revitalization units employed on the International Space Station (ISS) through photoelectrochemical water-splitting and hydrogen production. One obstacle for water (photo-) electrolysis in reduced gravity Environments is the absence of buoyancy and the consequential, hindered gas bubble release from the electrode surface. This causes the formation of gas bubble froth layers in proximity to the electrode surface, leading to an increase in ohmic resistance and cell-efficiency loss due to reduced mass transfer of substrates and products to and from the electrode. Recently, we have demonstrated efficient solar hydrogen production in Microgravity Environment, using an integrated semiconductor-electrocatalyst system with p-type indium phosphide as the light-absorber and a rhodium electrocatalyst. By nanostructuring the electrocatalyst using shadow nanosphere lithography and thereby creating catalytic 'hot spots' on the photoelectrode surface, we could overcome gas bubble coalescence and mass transfer limitations and demonstrated efficient hydrogen production at high current densities in reduced gravitation. Here, the experimental details are described for the preparations of these nanostructured devices and further on, the procedure for their testing in Microgravity Environment, realized at the Bremen Drop Tower during 9.3 s of free fall.
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efficient solar hydrogen generation in Microgravity Environment
Nature Communications, 2018Co-Authors: Katharina Brinkert, Matthias H Richter, Omer Akay, Janine Liedtke, Michael Giersig, Katherine T FountaineAbstract:Long-term space missions require extra-terrestrial production of storable, renewable energy. Hydrogen is ascribed a crucial role for transportation, electrical power and oxygen generation. We demonstrate in a series of drop tower experiments that efficient direct hydrogen production can be realized photoelectrochemically in Microgravity Environment, providing an alternative route to existing life support technologies for space travel. The photoelectrochemical cell consists of an integrated catalyst-functionalized semiconductor system that generates hydrogen with current densities >15 mA/cm^2 in the absence of buoyancy. Conditions are described adverting the resulting formation of ion transport blocking froth layers on the photoelectrodes. The current limiting factors were overcome by controlling the micro- and nanotopography of the Rh electrocatalyst using shadow nanosphere lithography. The behaviour of the applied system in terrestrial and Microgravity Environment is simulated using a kinetic transport model. Differences observed for varied catalyst topography are elucidated, enabling future photoelectrode designs for use in reduced gravity Environments.
Richard Delombard - One of the best experts on this subject based on the ideXlab platform.
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Interpreting the International Space Station Microgravity Environment
43rd AIAA Aerospace Sciences Meeting and Exhibit, 2005Co-Authors: Richard Delombard, Kenneth Hrovat, Eric Kelly, Brad HumphreysAbstract:*† ‡ § The International Space Station (ISS) serves as a platform for Microgravity research for the foreseeable future. A Microgravity Environment is one in which the effects of gravity are drastically reduced which then allows physical experiments to be conducted without the overpowering effects of gravity. A physical Environment with very low-levels of acceleration and vibration has been accomplished by both the free fall associated with orbital flight and the design of the International Space Station. The International Space Station design has been driven by a long-standing, high-level requirement for a Microgravity mode of operation. The Space Acceleration Measurement System has been in operation for nearly four years on the ISS measuring the Microgravity Environment in support of principal investigators and to characterize the ISS Microgravity Environment. The Principal Investigator Microgravity Services project functions as a detective to ascertain the source of disturbances seen in the ISS Microgravity Environment to allow correlation between that Environment and experimental data. Payload developers need to predict the Microgravity Environment that will be imposed upon an experiment and ensure that the science and engineering requirements will be met. The Principal Investigator Microgravity Services project is developing an interactive tool to predict the Microgravity Environment at science payloads based on user defined operational scenarios. These operations (predictions and post-analyses) allow a researcher to examine the Microgravity acceleration levels expected to exist when their experiment is operated and then receive an analysis of the Environment which existed during their experiment operations. Presented in this paper will be descriptions of the Environment predictive tool and an investigation into a previously unknown disturbance in the ISS Microgravity Environment.
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Microgravity Environment on the international space station
42nd AIAA Aerospace Sciences Meeting and Exhibit, 2004Co-Authors: Richard Delombard, Kenneth Hrovat, Eric Kelly, Kevin McphersonAbstract:ABSTRACT The International Space Station is being assembledon-orbit to serve as a research platform for the nexttwenty years. A primary feature of this research platformwill be its Microgravity Environment – an Environment inwhich the effects of gravity are drastically reduced. Aphysical Environment with very low-levels ofacceleration and vibration has been accomplished byboth the free fall associated with orbital flight and thedesign of the International Space Station. TheInternational Space Station design has been driven by along-standing, high-level requirement for a Microgravitymode of operation. Various types of data are gathered when scienceexperiments are conducted, with common variablesbeing temperature, pressure, voltage, and power. Theacceleration levels experienced during operation shouldbe factored into the analysis of the experiment results ofmost Microgravity experiments. To this end, the NASAFundamental Microgravity Research in the PhysicalSciences program has had the Space AccelerationMeasurement System recording the acceleration levelsto support Microgravity researchers for over twelve yearsof Shuttle missions, three years on Mir, and now nearlythree years of International Space Station operations. The Fundamental Microgravity Research in thePhysical Sciences program also supports the PrincipalInvestigator Microgravity Services project to assist theprincipal investigators with their analysis of theacceleration (Microgravity) Environment. The PrincipalInvestigator Microgravity Services project providescataloged data, periodic analysis summary reports,specialized reports for experiment teams, and real-timedata in a variety of user-defined formats.Characterization of the various Microgravity carriers(e.g. Shuttle and International Space Station) is alsoaccomplished for the experiment teams. In the future, the Principal Investigator MicrogravityServices project will provide a detailed predictiveanalysis of the Microgravity Environment for particularpayloads in specified locations. This will assist greatly inthe operational payload planning process. In addition, aneural-network-based system is planned which willautomatically interpret the Environment in real-time andpresent the results to users in an easily understoodformat. Presented in this paper will be a short description ofhow Microgravity disturbances may affect someexperiment classes, a snapshot of the MicrogravityEnvironment, and a view into how well the space stationis expected to meet the user requirements. ABBREVIATIONS AND ACRONYMS
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Disturbance of the Microgravity Environment by experiments
AIP Conference Proceedings, 2001Co-Authors: Richard DelombardAbstract:The NASA Headquarters Microgravity Research Division sponsors the Microgravity Research Program with science disciplines of biotechnology, combustion science, fluid physics, fundamental physics, and materials science. Two supporting disciplines are multi-discipline science experiments conducted in a glovebox and Microgravity acceleration measurement. Microgravity science experiments are conducted in a variety of ground based and flight facilities, such as, drop towers, parabolic flight aircraft, sounding rockets, the space shuttle, and, in the very near future, the International Space Station. The Microgravity acceleration measurement activities allow the scientist to know the low-gravity conditions under which an experiment was conducted. For most Microgravity science experiments, the ideal Microgravity Environment is comprised of zero acceleration; this “weightless” condition is difficult if not impossible to achieve with real facilities. An experiment is subject to accelerations from (for example) equi...
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comparison tools for assessing the Microgravity Environment of space missions carriers and conditions
Visual Information Processing Conference, 1998Co-Authors: Richard Delombard, Kenneth Hrovat, Milton E Moskowitz, Kevin McphersonAbstract:The Microgravity Environment of the NASA Shuttles and Russia's Mir space station have been measured by specially designed accelerometer systems. The need for comparisons between different missions, vehicles, conditions, etc. has been addressed by the two new processes described in this paper. The Principal Component Spectral Analysis (PCSA) and Quasi- steady Three-dimensional Histogram (QTH) techniques provide the means to describe the Microgravity acceleration Environment of a long time span of data on a single plot. As described in this paper, the PCSA and QTH techniques allow both the range and the median of the Microgravity Environment to be represented graphically on a single page. A variety of operating conditions may be made evident by using PCSA or QTH plots. The PCSA plot can help to distinguish between equipment operating full time or part time, as well as show the variability of the magnitude and/or frequency of an acceleration source. A QTH plot summarizes the magnitude and orientation of the low-frequency acceleration vector. This type of plot can show the Microgravity effects of attitude, altitude, venting, etc.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
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Microgravity Environment description handbook
1997Co-Authors: Richard Delombard, Kevin Mcpherson, Kenneth Hrovat, Milton E Moskowitz, Melissa J B Rogers, Timothy ReckartAbstract:The Microgravity Measurement and Analysis Project (MMAP) at the NASA Lewis Research Center (LeRC) manages the Space Acceleration Measurement System (SAMS) and the Orbital Acceleration Research Experiment (OARE) instruments to measure the Microgravity Environment on orbiting space laboratories. These laboratories include the Spacelab payloads on the shuttle, the SPACEHAB module on the shuttle, the middeck area of the shuttle, and Russia's Mir space station. Experiments are performed in these laboratories to investigate scientific principles in the near-absence of gravity. The Microgravity Environment desired for most experiments would have zero acceleration across all frequency bands or a true weightless condition. This is not possible due to the nature of spaceflight where there are numerous factors which introduce accelerations to the Environment. This handbook presents an overview of the major Microgravity Environment disturbances of these laboratories. These disturbances are characterized by their source (where known), their magnitude, frequency and duration, and their effect on the Microgravity Environment. Each disturbance is characterized on a single page for ease in understanding the effect of a particular disturbance. The handbook also contains a brief description of each laboratory.
Katharina Brinkert - One of the best experts on this subject based on the ideXlab platform.
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experimental methods for efficient solar hydrogen production in Microgravity Environment
Journal of Visualized Experiments, 2019Co-Authors: Katharina Brinkert, Matthias H Richter, Omer Akay, Janine Liedtke, Katherine T Fountaine, Hansjoachim Lewerenz, Michael GiersigAbstract:Long-term space flights and cis-lunar research platforms require a sustainable and light life-support hardware which can be reliably employed outside the Earth's atmosphere. So-called 'solar fuel' devices, currently developed for terrestrial applications in the quest for realizing a sustainable energy economy on Earth, provide promising alternative systems to existing air-revitalization units employed on the International Space Station (ISS) through photoelectrochemical water-splitting and hydrogen production. One obstacle for water (photo-) electrolysis in reduced gravity Environments is the absence of buoyancy and the consequential, hindered gas bubble release from the electrode surface. This causes the formation of gas bubble froth layers in proximity to the electrode surface, leading to an increase in ohmic resistance and cell-efficiency loss due to reduced mass transfer of substrates and products to and from the electrode. Recently, we have demonstrated efficient solar hydrogen production in Microgravity Environment, using an integrated semiconductor-electrocatalyst system with p-type indium phosphide as the light-absorber and a rhodium electrocatalyst. By nanostructuring the electrocatalyst using shadow nanosphere lithography and thereby creating catalytic 'hot spots' on the photoelectrode surface, we could overcome gas bubble coalescence and mass transfer limitations and demonstrated efficient hydrogen production at high current densities in reduced gravitation. Here, the experimental details are described for the preparations of these nanostructured devices and further on, the procedure for their testing in Microgravity Environment, realized at the Bremen Drop Tower during 9.3 s of free fall.
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efficient solar hydrogen generation in Microgravity Environment
Nature Communications, 2018Co-Authors: Katharina Brinkert, Matthias H Richter, Omer Akay, Janine Liedtke, Michael Giersig, Katherine T FountaineAbstract:Long-term space missions require extra-terrestrial production of storable, renewable energy. Hydrogen is ascribed a crucial role for transportation, electrical power and oxygen generation. We demonstrate in a series of drop tower experiments that efficient direct hydrogen production can be realized photoelectrochemically in Microgravity Environment, providing an alternative route to existing life support technologies for space travel. The photoelectrochemical cell consists of an integrated catalyst-functionalized semiconductor system that generates hydrogen with current densities >15 mA/cm^2 in the absence of buoyancy. Conditions are described adverting the resulting formation of ion transport blocking froth layers on the photoelectrodes. The current limiting factors were overcome by controlling the micro- and nanotopography of the Rh electrocatalyst using shadow nanosphere lithography. The behaviour of the applied system in terrestrial and Microgravity Environment is simulated using a kinetic transport model. Differences observed for varied catalyst topography are elucidated, enabling future photoelectrode designs for use in reduced gravity Environments.
W R Hu - One of the best experts on this subject based on the ideXlab platform.
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planar thermocapillary migration of two bubbles in Microgravity Environment
Physics of Fluids, 2003Co-Authors: W R HuAbstract:A theoretical investigation is performed on the thermocapillary motion of two bubbles in arbitrary configuration in Microgravity Environment under the assumption that the surface tension is high enough to keep the bubbles spherical. The two bubbles are driven by the surface tension gradient due to temperature nonuniformity on the surfaces. The bubble interaction is considered for the limit of small Marangoni and Reynolds numbers in the present paper. In order to solve the problem analytically, the method of successive reflections is employed, and then accurate migration velocities of two arbitrarily oriented bubbles in the planar thermocapillary motions are derived. The results demonstrate that two equal-size bubbles exert no influence on the thermocapillary migration of each other at any separation because of the thorough cancellation of the thermal and fluid mechanical interaction effects, and the effect of the large bubble on the motion of the smaller one becomes significant with the two bubbles approaching each other, while the effect of the smaller one on the large remains weak. Moreover, three typical kinds of trajectories of the smaller bubble are identified.
G Kushida - One of the best experts on this subject based on the ideXlab platform.
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ignition and transition to flame spread over a thermally thin cellulosic sheet in a Microgravity Environment
Combustion and Flame, 1994Co-Authors: K Nakabe, Takashi Kashiwagi, Kevin B Mcgrattan, Howard R Baum, H Yamashita, G KushidaAbstract:Abstract An axisymmetric, time-dependent model is developed describing auto-ignition and subsequent transition to flame spread over a thermally-thin cellulosic sheet heated by external radiation in a quiescent Microgravity Environment. Due to the unique combination of a Microgravity Environment and low Reynolds number associated with the slow, thermally induced flow, the resulting velocity is taken as a potential flow. A one-step global gas phase oxidation reaction and three global degradation reactions for the condensed phase are used in the model. A maximum external radiant flux of 5 W/cm 2 (Gaussian distribution) with 21%, 30%, and 50% oxygen concentrations is used in the calculations. The results indicate that autoignition is observed for 30% oxygen concentrations but the transition to the flame spread does not occur. For 50% oxygen the transition is achieved. A detailed discussion of the transition from ignition to flame spread is given as an aid to understanding this process. Also, a comparison is made between the axisymmetric configuration and a two-dimensional (line source) configuration.
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heat and mass transport from thermally degrading thin cellulosic materials in a Microgravity Environment
Journal of Heat Transfer-transactions of The Asme, 1992Co-Authors: G Kushida, H R Baum, Takashi Kashiwagi, C Di BlasiAbstract:A theoretical model describing the behavior of a thermally thin cellulosic sheet heated by external thermal radiation in a quiescent Microgravity Environment is developed. This model describes thermal and oxidative degradation of the sheet and the heat and mass transfer of evolved degradation products from the heated cellulosic surface into the gas phase. At present, gas phase oxidation reactions are not included. Without buoyancy, the dominant vorticity creation mechanism in the bulk of the gas is absent except at the material surface by the requirement of the no-slip condition. The no-slip condition is relaxed, permitting the flow to be represented by a velocity potential. This approximation is permissible due to the combination of a Microgravity Environment and low Reynolds number associated with slow small-area heating by external radiation. Two calculations are carried out: heating without thermal degradation, and heating with thermal degradation of the sheet with endothermic char oxidation. The results show that pyrolysis is the main degradation reaction. Moreover, self-sustained propagation of smoldering for cellulosic materials is very difficult due to the lack of sufficient oxygen supply in a quiescent Environment.