The Experts below are selected from a list of 95748 Experts worldwide ranked by ideXlab platform
M. Raja Reddy - One of the best experts on this subject based on the ideXlab platform.
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Effect of low earth orbit atomic oxygen on spacecraft materials
Journal of Materials Science, 1995Co-Authors: M. Raja ReddyAbstract:This review attempts to bring together the published data and analysis related to the effect of low earth orbit (LEO) atomic oxygen (AO) interaction with spacecraft materials. The basic interaction mechanism of AO with spacecraft materials and quantification of its effect on materials performance are briefly discussed. After providing a list of materials susceptible to the LEO environment, the paper focuses on the degradation mechanism of various spacecraft materials. Particular emphasis is given to the protective mechanisms for AO-susceptible materials and development of AO-resistant materials for long-term LEO spacecraft applications. Ground-Simulation testing requirements and their present status are reviewed briefly. The need for further research is emphasized.
Ti Yuk - One of the best experts on this subject based on the ideXlab platform.
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Compact MIMO Antenna for Portable Devices in UWB Applications
IEEE Transactions on Antennas and Propagation, 2013Co-Authors: L. Liu, Sing Wai Cheung, Ti YukAbstract:A compact multiple-input-multiple-output (MIMO) antenna with a small size of 26× 40mm2 is proposed for portable ultrawideband (UWB) applications. The antenna consists of two planar-monopole (PM) antenna elements with microstrip-fed printed on one side of the substrate and placed perpendicularly to each other to achieve good isolation. To enhance isolation and increase impedance bandwidth, two long protruding Ground stubs are added to the Ground plane on the other side and a short Ground strip is used to connect the Ground planes of the two PMs together to form a common Ground. Simulation and measurement are used to study the antenna performance in terms of reflection coefficients at the two input ports, coupling between the two input ports, radiation pattern, realized peak gain, efficiency and envelope correlation coefficient for pattern diversity. Results show that the MIMO antenna has an impedance bandwidth of larger than 3.1-10.6 GHz, low mutual coupling of less than-15 dB, and a low envelope correlation coefficient of less than 0.2 across the frequency band, making it a good candidate for portable UWB applications. © 2013 IEEE.published_or_final_versio
E Grossman - One of the best experts on this subject based on the ideXlab platform.
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debris micrometeoroid impacts and synergistic effects on spacecraft materials
Mrs Bulletin, 2010Co-Authors: E Grossman, I Gouzman, R VerkerAbstract:In the last 40 years, the increased space activity created a new form of space environment of hypervelocity objects—space debris—that have no functional use. The space debris, together with naturally occurring ultrahigh velocity meteoroids, presents a significant hazard to spacecraft. Collision with space debris or meteoroids might result in disfunction of external units such as solar cells, affecting materials properties, contaminating optical devices, or destroying satellites. The collision normally results in the formation of additional debris, increasing the hazard for future missions. The hypervelocity debris effect is studied by retrieving materials from space or by using Ground Simulation facilities. Simulation facilities, which include the light gas gun and Laser Driven Flyer methods, are used for studying the materials degradation due to debris impact. The impact effect could be accelerated when occurring simultaneously with other space environment components, such as atomic oxygen, ultraviolet, or x-ray radiation. Understanding the degradation mechanism might help in developing materials that will withstand the increasing hazard from the space debris, allowing for longer space missions. The large increase in space debris population and the associated risk to space activity requires significant measures to mitigate this hazard. Most current efforts are being devoted to prevention of collisions by keeping track of the larger debris and avoiding formation of new debris.
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kapton as a standard for atomic oxygen flux measurement in leo Ground Simulation facilities how good is it
2004Co-Authors: E Grossman, Irina Gouzman, Y. Noter, G D Lempert, Y LifshitzAbstract:A common method for assessing the Atomic Oxygen (AO) flux in LEO Ground Simulation facilities is measuring the mass loss of attached Kapton coupon and assuming a known erosion yield of 3×10−24 cm3/O atom. However, in most Ground Simulation facilities additional components, e.g., UV radiation, excited and ionized oxygen atoms and molecules or reactive volatile products of degraded samples might be involved in Kapton-AO interaction. The present work studies the effect of simultaneous irradiation of AO and other reactive species on the Kapton etching rate. The Kapton mass loss was measured in-situ using Quartz Crystal Microbalanace (QCM). The etching rate was assessed as a function of AO and either VUV radiation, ions, various feed gases, sample temperature or reactive volatile products. X-ray photoelectron spectroscopy (XPS) and Atomic Force Microscopy (AFM) were also applied in order to understand the erosion mechanism involved in the etching rate alteration. The study shows that reactive species (other than AO) present in the Ground Simulation facilities could lead to substantial errors in the AO flux evaluation. The validity of the use of Kapton as a reference material for Ground Simulation testing (of spacecraft candidate materials for LEO applications) should be critically reassessed in the context of the present findings.
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space environment effects on polymers in low earth orbit
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2003Co-Authors: E Grossman, I GouzmanAbstract:Abstract Polymers are widely used in space vehicles and systems as structural materials, thermal blankets, thermal control coatings, conformal coatings, adhesives, lubricants, etc. The low earth orbit (LEO) space environment includes hazards such as atomic oxygen, UV radiation, ionizing radiation (electrons, protons), high vacuum, plasma, micrometeoroids and debris, as well as severe temperature cycles. Exposure of polymers and composites to the space environment may result in different detrimental effects via modification of their chemical, electrical, thermal, optical and mechanical properties as well as surface erosion. The high vacuum induces material outgassing (e.g. low-molecular weight residues, plasticizers and additives) and consequent contamination of nearby surfaces. The present work reviews the LEO space environment constituents and their interactions with polymers. Examples of degradation of materials exposed in Ground Simulation facilities are presented. The issues discussed include the erosion mechanisms of polymers, formation of contaminants and their interaction with the space environment, and protection of materials from the harsh space environment.
Christoph Borst - One of the best experts on this subject based on the ideXlab platform.
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the oos sim an on Ground Simulation facility for on orbit servicing robotic operations
International Conference on Robotics and Automation, 2015Co-Authors: Jordi Artigas, Marco De Stefano, Wolfgang Rackl, Roberto Lampariello, Bernhard Brunner, Wieland Bertleff, Robert Burger, Oliver Porges, Alessandro Massimo Giordano, Christoph BorstAbstract:On-orbit servicing involves a new class of space missions in which a servicer spacecraft is launched into the orbit of a target spacecraft, the client. The servicer navigates to the client with the intention of manipulating it, using a robotic arm. Within this framework, this work presents a new robotic experimental facility which was recently built at the DLR to support the development and experimental validation of such orbital servicing robots. The facility allows reproducing a close-proximity scenario under realistic three-dimensional orbital dynamics conditions. Its salient features are described here, to include a fully actuated macro-micro system with multiple sensing capabilities, and analyses on its performance including the amount of space environment volume that can be simulated.
L. Liu - One of the best experts on this subject based on the ideXlab platform.
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Compact MIMO Antenna for Portable Devices in UWB Applications
IEEE Transactions on Antennas and Propagation, 2013Co-Authors: L. Liu, Sing Wai Cheung, Ti YukAbstract:A compact multiple-input-multiple-output (MIMO) antenna with a small size of 26× 40mm2 is proposed for portable ultrawideband (UWB) applications. The antenna consists of two planar-monopole (PM) antenna elements with microstrip-fed printed on one side of the substrate and placed perpendicularly to each other to achieve good isolation. To enhance isolation and increase impedance bandwidth, two long protruding Ground stubs are added to the Ground plane on the other side and a short Ground strip is used to connect the Ground planes of the two PMs together to form a common Ground. Simulation and measurement are used to study the antenna performance in terms of reflection coefficients at the two input ports, coupling between the two input ports, radiation pattern, realized peak gain, efficiency and envelope correlation coefficient for pattern diversity. Results show that the MIMO antenna has an impedance bandwidth of larger than 3.1-10.6 GHz, low mutual coupling of less than-15 dB, and a low envelope correlation coefficient of less than 0.2 across the frequency band, making it a good candidate for portable UWB applications. © 2013 IEEE.published_or_final_versio
