Future space missions demand operations on large flexible structures,for example,space webs,the lightweight cable nets deployable in space,which can serve as platforms for very large structures or be used to capture o...Future space missions demand operations on large flexible structures,for example,space webs,the lightweight cable nets deployable in space,which can serve as platforms for very large structures or be used to capture orbital objects.The interest in research on space webs is likely to increase in the future with the development of promising applications such as Furoshiki sat-ellite of JAXA,Robotic Geostationary Orbit Restorer (ROGER) of ESA and Grapple,Retrieve And Secure Payload (GRASP) of NASA.Unlike high-tensioned nets in civil engineering,space webs may be low-tensioned or tensionless,and extremely flexible,owing to the microgravity in the orbit and the lack of support components,which may cause computational difficulties.Mathematical models are necessary in the analysis of space webs,especially in the conceptual design and evaluation for prototypes.A full three-dimensional finite element (FE) model was developed in this work.Trivial truss elements were adopted to reduce the computational complexity.Considering cable is a compression-free material and its tensile stiffness is also variable,we introduced the cable material constitutive relationship to work out an accurate and feasible model for prototype analysis and design.In the static analysis,the stress distribution and global deformation of the webs were discussed to get access to the knowledge of strength of webs with different types of meshes.In the dynamic analysis,special attention was paid to the impact problem.The max stress and global deformation were investigated.The simulation results indicate the interesting phenomenon which may be worth further research.展开更多
在过去的几十年里,系外行星研究发生了革命性的变化。三十年前,我们只知道太阳系外有少数几颗系外行星。今天,我们已经知道了超过5000个这样的遥远世界的存在,其中一些与地球大小相似,一些绕着与太阳类似的恒星运行。在这场系外行星革命...在过去的几十年里,系外行星研究发生了革命性的变化。三十年前,我们只知道太阳系外有少数几颗系外行星。今天,我们已经知道了超过5000个这样的遥远世界的存在,其中一些与地球大小相似,一些绕着与太阳类似的恒星运行。在这场系外行星革命中,一个重要的参与者是美国航天局(National Aeronautics and Space Administration,NASA)的开普勒空间望远镜,它已于2018年退役。迄今为止发现的所有系外行星中,有超过50%是通过搜索开普勒数据来寻找凌星信号而发现的。展开更多
Delay/Disruption-Tolerant Networking(DTN) originated from research on Interplanetary Internet and still today space applications are the most important application field and research stimulus. This paper investigates ...Delay/Disruption-Tolerant Networking(DTN) originated from research on Interplanetary Internet and still today space applications are the most important application field and research stimulus. This paper investigates DTN communications between the Earth and the far side of the Moon, by means of a lunar orbiter acting as relay. After an introductory part, the paper presents a comprehensive analysis of the DTN performance that can be achieved on the identified communication scenario. The focus is on the evaluation of the stateof-the-art ability of Interplanetary Overlay Network(ION), the NASA DTN implementation of Bundle Protocol(BP) and Contact Graph Routing(CGR), to meet the many challenges of the space communication scenario investigated(and more generally of a future interplaynetary Internet): intermittent links, network partitioning, scarce bandwidth, long delays, dynamic routing, handling of high priority and emergency traffic, interoperability issues. A study of security threats and Bundle Security Protocol(BSP) countermeasures complete the work.The many results provided, confirm the essential role of DTN in future space communications.展开更多
文摘Future space missions demand operations on large flexible structures,for example,space webs,the lightweight cable nets deployable in space,which can serve as platforms for very large structures or be used to capture orbital objects.The interest in research on space webs is likely to increase in the future with the development of promising applications such as Furoshiki sat-ellite of JAXA,Robotic Geostationary Orbit Restorer (ROGER) of ESA and Grapple,Retrieve And Secure Payload (GRASP) of NASA.Unlike high-tensioned nets in civil engineering,space webs may be low-tensioned or tensionless,and extremely flexible,owing to the microgravity in the orbit and the lack of support components,which may cause computational difficulties.Mathematical models are necessary in the analysis of space webs,especially in the conceptual design and evaluation for prototypes.A full three-dimensional finite element (FE) model was developed in this work.Trivial truss elements were adopted to reduce the computational complexity.Considering cable is a compression-free material and its tensile stiffness is also variable,we introduced the cable material constitutive relationship to work out an accurate and feasible model for prototype analysis and design.In the static analysis,the stress distribution and global deformation of the webs were discussed to get access to the knowledge of strength of webs with different types of meshes.In the dynamic analysis,special attention was paid to the impact problem.The max stress and global deformation were investigated.The simulation results indicate the interesting phenomenon which may be worth further research.
文摘在过去的几十年里,系外行星研究发生了革命性的变化。三十年前,我们只知道太阳系外有少数几颗系外行星。今天,我们已经知道了超过5000个这样的遥远世界的存在,其中一些与地球大小相似,一些绕着与太阳类似的恒星运行。在这场系外行星革命中,一个重要的参与者是美国航天局(National Aeronautics and Space Administration,NASA)的开普勒空间望远镜,它已于2018年退役。迄今为止发现的所有系外行星中,有超过50%是通过搜索开普勒数据来寻找凌星信号而发现的。
文摘Delay/Disruption-Tolerant Networking(DTN) originated from research on Interplanetary Internet and still today space applications are the most important application field and research stimulus. This paper investigates DTN communications between the Earth and the far side of the Moon, by means of a lunar orbiter acting as relay. After an introductory part, the paper presents a comprehensive analysis of the DTN performance that can be achieved on the identified communication scenario. The focus is on the evaluation of the stateof-the-art ability of Interplanetary Overlay Network(ION), the NASA DTN implementation of Bundle Protocol(BP) and Contact Graph Routing(CGR), to meet the many challenges of the space communication scenario investigated(and more generally of a future interplaynetary Internet): intermittent links, network partitioning, scarce bandwidth, long delays, dynamic routing, handling of high priority and emergency traffic, interoperability issues. A study of security threats and Bundle Security Protocol(BSP) countermeasures complete the work.The many results provided, confirm the essential role of DTN in future space communications.
