Magnetospheric Boundary Layer Structure and Dynamics as Seen From Cluster and Double Star Measurements

In this review, we discuss the structure and dynamics of the magnetospheric Low-Latitude Boundary Layer (LLBL) based on recent results from multi-satellite missions Cluster and Double Star. This boundary layer, adjacent to the magnetopause on the magnetospheric side, usually consists of a mixture of plasma of magnetospheric and magnetosheath origins, and plays an important role in the transfer of mass and energy from the solar wind into the magnetosphere and subsequent magnetospheric dynamics. During southward Interplanetary Magnetic Field (IMF) conditions, this boundary layer is generally considered to be formed as a result of the reconnection process between the IMF and magnetospheric magnetic field lines at the dayside magnetopause, and the structure and plasma properties inside the LLBL can be understood in terms of the time history since the reconnection process. During northward IMF conditions, the LLBL is usually thicker, and has more complex structure and topology. Recent observations confirm that the LLBL observed at the dayside can be formed by single lobe reconnection, dual lobe reconnection, or by sequential dual lobe reconnection, as well as partially by localized cross-field diffusion. The LLBL magnetic topology and plasma signatures inside the different sub-layers formed by these processes are discussed in this review. The role of the Kelvin-Helmholtz instability in the formation of the LLBL at the flank magnetopause is also discussed. Overall, we conclude that the LLBL observed at the flanks can be formed by the combination of processes, (dual) lobe reconnection and plasma mixing due to non-linear Kelvin-Helmholtz waves.      

Astrobiology through the ages of Mars: the study of terrestrial analogues to understand the habitability of Mars

Mars has undergone three main climatic stages throughout its geological history, beginning with a water-rich epoch, followed by a cold and semi-arid era, and transitioning into present-day arid and very cold desert conditions. These global climatic eras also represent three different stages of planetary habitability: an early, potentially habitable stage when the basic requisites for life as we know it were present (liquid water and energy); an intermediate extreme stage, when liquid solutions became scarce or very challenging for life; and the most recent stage during which conditions on the surface have been largely uninhabitable, except perhaps in some isolated niches. Our understanding of the evolution of Mars is now sufficient to assign specific terrestrial environments to each of these periods. Through the study of Mars terrestrial analogues, we have assessed and constrained the habitability conditions for each of these stages, the geochemistry of the surface, and the likelihood for the preservation of organic and inorganic biosignatures. The study of these analog environments provides important information to better understand past and current mission results as well as to support the design and selection of instruments and the planning for future exploratory missions to Mars.     

An Event Horizon Imager(EHI) Mission Concept Utilizing Medium Earth Orbit Sub-mm Interferometry

Submillimeter interferometry has the potential to image supermassive black holes on event horizon scales, providing tests of the theory of general relativity and increasing our understanding of black hole accretion processes. The Event Horizon Telescope (EHT) performs these observations from the ground, and its main imaging targets are Sagittarius A* in the Galactic Center and the black hole at the center of the M87 galaxy. However, the EHT is fundamentally limited in its performance by atmospheric effects and sparse terrestrial (u,v)-coverage (Fourier sampling of the image). The scientific interest in quantitative studies of the horizon size and shape of these black holes has motivated studies into using space interferometry which is free of these limitations. Angular resolution considerations and interstellar scattering effects push the desired observing frequency to bands above 500 GHz.
This paper presents the requirements for meeting these science goals, describes the concept of interferometry from Polar or Equatorial Medium Earth Orbits (PECMEO) which we dub the Event Horizon Imager (EHI), and utilizes suitable space technology heritage. In this concept, two or three satellites orbit at slightly different orbital radii, resulting in a dense and uniform spiral-shaped (u,v)-coverage over time. The local oscillator signals are shared via an inter-satellite link, and the data streams are correlated on-board before final processing on the ground. Inter-satellite metrology and satellite positioning are extensively employed to facilitate the knowledge of the instrument position vector, and its time derivative. The European space heritage usable for both the front ends and the antenna technology of such an instrument is investigated. Current and future sensors for the required inter-satellite metrology are listed. Intended performance estimates and simulation results are given.      

基于图像的测量方法在工业风洞跨声速流测量中的最新进展

风洞中非定常复杂流场的实验研究要求先进的测量技术.基于图像的测量技术中最重要的是测量平面流速度场、平面压强分布、模型位置和变形、模型温度以及定量的高速流可视化等技术.DLR(德国宇航研究院)对这些技术的应用包括从低速流到跨声速流、从增升装置到螺旋桨和旋翼、从弹射装置和水塔储水罐尾迹流旋涡到三角翼上涡破裂现象等的研究.由于跨声速风洞的特殊环境,将基于图像的测量技术用于跨声速流要求专门的技术开发和有经验的科学家.给出了DLR空气动力学和流动技术研究所将基于图像的测量技术应用于跨声速流研究的最新进展.     

Mission to Mars using integrated propulsion concepts: considerations, opportunities, and strategies

The aim of this paper is to evaluate the feasibility of a mission to Mars using the Integrated Propulsion Systems (IPS) which means to couple Nuclear-MPD-ISPU propulsion systems. In particular both mission analysis and propulsion aspects are analyzed together with technological aspects. Identifying possible mission scenarios will lead to the study of possible strategies for Mars Exploration and also of methods for reducing cost. As regard to IPS, the coupling between Nuclear Propulsion (Rubbia's engine) and Superconductive MPD propulsion is considered for the Earth-Mars trajectories: major emphasis is given to the advantages of such a system. The In Situ Resource Utilization (ISRU) concerns on-Mars operations; In Situ Propellant Utilization (ISPU) is foreseen particularly for LOX-CH4 engines for Mars Ascent Vehicles and this possibility is analyzed from a technological point of view. Tether Systems are also considered during interplanetary trajectories and as space elevators on Mars orbit. Finally strategic considerations associated to this mission are considered also.     

超声疲劳试样设计

介绍了超声疲劳试样的设计计算方法,给出了谐振状态下不同形式、尺寸试样中沿其谐振长度方向的位移、应力分布。结果表明:狗骨形试样中,中间等截面段尺寸对试样中应力的大小、分布影响很大。分析狗骨形试样应力放大系数表明,应力放大系数随着试样中间等截面段直径的减少会有显著增加,随着试样中间段长度的增加,应力放大系数也相应降低。     

未来的小型机动式GPS靶场测量设备

技术的迅速发展将有可能研制出一种小型的靶场跟踪和遥测系统。这种系统将装在拖车上,能够跟踪3个飞行器并显示其空间位置及遥测数据。     

选用最佳遥测跟踪天线接收转发的GPS信号

本文给出了对三种波束扫瞄原理相差甚远的遥测跟踪天线进行测量所得的性能数据。在S波段测量了天线馈源引起的相位噪声,并做了比较。     

DAIS航空电子软件研制技术

软件研制技术的主要目的是产生正确的工作软件.把本文提供的技术应用于一个完整的软件工程研制计划时,可降低产品的价格和寿命期费用,同时保持了高可靠性。空军 DAIS 计划担负着降低军用航空电子系统的研制、维护和寿命期费用的任务.DAIS 系统提供了一种硬件配置,该配置便于硬件维修、更换和增长.高级软件(HOS)提供一种产生高可靠性软件的方法,此软件是建立在一种高级的设计和开发基础上的.HOS 原理应用于 DAIS 系统,产生了标准的航空电子软件设计和管理方法,该设计方法建立了一个与 DAIS 目标相一致的软件结构标准;该管理方法提供了一种严格受控的、安排很好的软件开发过程,该过程受配置管理方案、开发和验证方法及自动生成文件支持。这里没有给出另一些软件费用因素是:软件的获得过程、人力的安排和组织、航空电子系统方案和支援软件的可移植性。这些费用因素是重要的,因为处理得不合理时,有时会发挥不出好的开发技术的益处。本文假定这些因素不影响 DAIS 航空电子软件所使用的技术。     

Conversations: with Carl Pilcher [interview by Johan Benson

An interview with Carl Pilcher, science program director for solar system exploration at NASA, examines NASA's past, present, and planned missions to explore the solar system. Specific questions relate to the status of current and planned missions, science results of the Pathfinder mission to Mars, cooperation with the Japanese space agency, the status of the search for extraterrestrial life in solar system meteoroids and asteroids, mission size for more in-depth exploration, reports of water on the moon, and the exploration of near-Earth objects.