前仆后继的火星"探测者"正在揭开面纱的"维多利亚"火星陨石坑

在过去的21个月中,"机遇"号火星车在火星表面以非常缓慢的速度走完了约9千米的路程,最终于9月27日到达了火星上"维多利亚"陨石坑的边缘,开始执行整个耗资8亿美元的火星表面双火星车探索计划中最为复杂、危险,同时也是最有价值的任务.三个美国火星轨道器也将相继在火星上继续它们的探险历程.     

探测器"排队"探火星美国和欧洲再次掀起火星探测热潮

近几年美国和欧洲对火星探测工作给予了高度重视，并将实施多项研究计划，其目标是通过找水源来探索火星是否存在生命。据美国ＮＡＳＡ估计，今后 １０年各参加国在火星取样回送工作上将花约２０亿美元     

火星探测新发现

<正>10月底,\"好奇\"号首次用自带的化学矿物仪器对摄人的土壤样本进行了矿物学鉴定,结果显示,火星部分土壤与夏威夷火山周围土壤相似,这一发现或许将成为探寻火星是否有支持微生物存活条件的重要线索。同时,这也是X射线衍射技术第1次用于分析地外星体的土壤。11月初,\"好奇\"号火星车又首次分析了火星大气的成分,未发现其中含有甲烷。由于地球大气中90%     

火星探测的新纪元

去年是掀起火星探测热潮的一年。先是美国航空航天局宣布在火星的一块陨石中发现了生命的证据,此事在全球引起很大的争议;接着英国科学家宣布了同样的发现,更是掀起轩然大波。于是人们都把目光集中在1996年11～12月美、俄两国发射的三个火星探测器上,希望它们能有助于解决这个世纪之谜。打头阵的“火星环球勘探者”11月7日,美国率先用德尔它-2火箭一举把“火星环球勘探者”送上太空。它将经10个月的飞行于1997年9月12日到达火星轨     

加拿大航天局计划探测火星

加拿大航天局近日宣布,将对加拿大研制火星探测器的可行性进行研究。探测器必须完全由加拿大研发,虽然加拿大没有运载火箭或发射台,但可以付费给其他国家发射自己的火星探测器。加拿大航天局表示,将授出为期6个月、价值25万美元的着陆或绕轨火星探测技术研发合同。加拿大航天局     

火星探测着陆器气动布局研究

火星探测活动是当前深空探测领域发展的热点,火星探测着陆器进入过程的气动布局问题是火星探测器设计的关键之一。根据国外火星探测器气动布局及地球轨道再入返回舱气动布局,从大气环境和布局形式两个方面出发研究火星探测器的主要气动特点,基于工程算法讨论了探测器所处大气环境及其布局形式对其高超声速升阻特性、配平特性及静稳定性的影响规律。大气环境分析表明,在高超声速进入条件下,火星大气热力学性质的改变,会改变高超声速气动力的大小和分布,会增加探测器的升阻力系数,对探测器的升阻比和配平特性影响很小,略提高飞行静稳定性。布局形式分析认为,球锥布局的防热大底较球冠布局具有更大的气动阻力,有利于着陆器减速,且较小的法向偏移量可实现足够的配平需求;球锥布局俯仰静稳定度对轴向的敏感度较低,也是探测器从气动考虑选用球锥布局的原因。相关研究结论可为火星探测着陆器的气动布局设计提供理论参考和技术支持。     

Biological implications of the Viking mission to Mars

A central purpose of Viking was to search for evidence that life exists on Mars or may have existed in the past. The missions carried three biology experiments the prime purpose of which was to seek for existing microbial life. In addition the results of a number of the other experiments have biological implications: (1) The elemental analyses of the atmosphere and the regolith showed or implied that the elements generally considered essential to terrestrial biology are present. (2) But unexpectedly, no organic compounds were detected in Martian samples by an instrument that easily detected organic materials in the most barren of terrestrial soils. (3) Liquid water is believed to be an absolute requisite for life. Viking obtained direct evidence for the presence of water vapor and water ice, and it obtained strong inferential evidence for the existence of large amounts of subsurface permafrost now and in the Martain past. However it obtained no evidence for the current existence of liquid water possessing the high chemical potential required for at least terrestrial life, a result that is consistent with the known pressure-temperature relations on the planet's surface. On the other hand, the mission did obtain strong indications from both atmospheric analyses and orbital photographs that large quantities of liquid water flowed episodically on the Martian surface 0.5 to 2.5 G years ago.The three biology experiments produced clear evidence of chemical reactivity in soil samples, but it is becoming increasingly clear that the chemical reactions were nonbiological in origin. The unexpected release of oxygen by soil moistened with water vapor in the Gas Exchange experiment together with the negative findings of the organic analysis experiment lead to the conclusion that the surface contains powerful oxidants. This conclusion is consistent with models of the atmosphere. The oxidants appear also to have been responsible for the decarboxylation of the organic nutrients that were introduced in the Label Release experiment. The major results of the GEX and LR experiments have been simulated at least qualitatively on Earth. The third, Pyrolytic Release, experiment obtained evidence for organic synthesis by soil samples. Although the mechanism of the synthesis is obscure, the thermal stability of the reaction makes a biological explanation most unlikely. Furthermore, the response of soil samples in all three experiments to the addition of water is not consistent with a biological interpretation.The conditions now known to exist at and below the Martian surface are such that no known terrestrial organism could grow and function. Although the evidence does not absolutely rule out the existence of favourable oases, it renders their existence extremely unlikely. The limiting conditions for the functioning of terrestrial organisms are not the limits for conceivable life elsewhere, and accordingly one cannot exclude the possibility that indigenous life forms may currently exist somewhere on Mars or may have existed sometime in the past. Nevertheless, the available information about the present Martian environment puts severe constraints and presents formidable challenges to any putative Martian organisms. The Martian environment in the past, on the other hand, appears to have been considerably less hostile biologically, and it might possibly have permitted the origin and transient establishment of a biota.     

湛蓝印象——中国航海博物馆札记

很喜欢海,深邃湛蓝,像美丽矢车菊的花瓣。赤脚漫步在洁白细软的沙滩上,眺望着大海的那边,想着人鱼公主美丽的传说,心里就有了浪花的低语轻吟,快乐就像展翅翱翔的海鸥,轻盈起落。     

硬镀铬的代用计划

介绍了美国在飞机、涡轮发动机制造以及维修上所用的热喷涂法代替硬镀铬的必要性、可行性和一些应用情况。     

X-Rays From Mars

X-rays from Mars were first detected in July 2001 with the satellite Chandra. The main source of this radiation was fluorescent scattering of solar X-rays in its upper atmosphere. In addition, the presence of an extended X-ray halo was indicated, probably resulting from charge exchange interactions between highly charged heavy ions in the solar wind and neutrals in the Martian exosphere. The statistical significance of the X-ray halo, however, was very low. In November 2003, Mars was observed again in X-rays, this time with the satellite XMM-Newton. This observation, characterized by a considerably higher sensitivity, confirmed the presence of the X-ray halo and proved that charge exchange is indeed the origin of the emission. This was the first definite detection of charge exchange induced X-ray emission from the exosphere of another planet. Previously, this kind of emission had been detected from comets (which are largely exospheres) and from the terrestrial exosphere. Because charge exchange interactions between atmospheric constituents and solar wind ions are considered as an important nonthermal escape mechanism, probably responsible for a significant loss of the Martian atmosphere, X-ray observations may lead to a better understanding of the present state of the Martian atmosphere and its evolution. X-ray images of the Martian exosphere in specific emission lines exhibited a highly anisotropic morphology, varying with individual ions and ionization states. With its capability to trace the X-ray emission out to at least 8 Mars radii, XMM-Newton can explore exospheric regions far beyond those that have been observationally explored to date. Thus, X-ray observations provide a novel method for studying processes in the Martian exosphere on a global scale.     

The Noise Model of the SEIS Seismometer of the InSight Mission to Mars

The SEIS (Seismic Experiment for Interior Structures) instrument on board the InSight mission to Mars is the critical instrument for determining the interior structure of Mars, the current level of tectonic activity and the meteorite flux. Meeting the performance requirements of the SEIS instrument is vital to successfully achieve these mission objectives. The InSight noise model is a key tool for the InSight mission and SEIS instrument requirement setup. It will also be used for future operation planning. This paper presents the analyses made to build a model of the Martian seismic noise as measured by the SEIS seismometer, around the seismic bandwidth of the instrument (from 0.01 Hz to 1 Hz). It includes the instrument self-noise, but also the environment parameters that impact the measurements. We present the general approach for the model determination, the environment assumptions, and we analyze the major and minor contributors to the noise model.     

The Rotation and Interior Structure Experiment on the InSight Mission to Mars

The Rotation and Interior Structure Experiment (RISE) on-board the InSight mission will use the lander’s X-band (8 GHz) radio system in combination with tracking stations of the NASA Deep Space Network (DSN) to determine the rotation of Mars. RISE will measure the nutation of the Martian spin axis, detecting for the first time the effect of the liquid core of Mars and providing in turn new constraints on the core radius and density. RISE will also measure changes in the rotation rate of Mars on seasonal time-scales thereby constraining the atmospheric angular momentum budget. Finally, RISE will provide a superb tie between the cartographic and inertial reference frames. This paper describes the RISE scientific objectives and measurements, and provides the expected results of the experiment.     

Pseudotransfer Function to Characterize a Hard Limiter

Results are reported on the attempt to define a pseudotransfer funtion of a circuit composed of a 2-pulse canceler and hard limiter.