Lichens survive in space: results from the 2005 LICHENS experiment

This experiment was aimed at establishing, for the first time, the survival capability of lichens exposed to space conditions. In particular, the damaging effect of various wavelengths of extraterrestrial solar UV radiation was studied. The lichens used were the bipolar species Rhizocarpon geographicum and Xanthoria elegans, which were collected above 2000 m in the mountains of central Spain and as endolithic communities inhabiting granites in the Antarctic Dry Valleys. Lichens were exposed to space in the BIOPAN-5 facility of the European Space Agency; BIOPAN-5 is located on the outer shell of the Earth-orbiting FOTON-M2 Russian satellite. The lichen samples were launched from Baikonur by a Soyuz rocket on May 31, 2005, and were returned to Earth after 16 days in space, at which time they were tested for survival. Chlorophyll fluorescence was used for the measurement of photosynthetic parameters. Scanning electron microscopy in back-scattered mode, low temperature scanning electron microscopy, and transmission electron microscopy were used to study the organization and composition of both symbionts. Confocal laser scanning microscopy, in combination with the use of specific fluorescent probes, allowed for the assessment of the physiological state of the cells. All exposed lichens, regardless of the optical filters used, showed nearly the same photosynthetic activity after the flight as measured before the flight. Likewise, the multimicroscopy approach revealed no detectable ultrastructural changes in most of the algal and fungal cells of the lichen thalli, though a greater proportion of cells in the flight samples had compromised membranes, as revealed by the LIVE/DEAD BacLight Bacterial Viability Kit. These findings indicate that most lichenized fungal and algal cells can survive in space after full exposure to massive UV and cosmic radiation, conditions proven to be lethal to bacteria and other microorganisms. The lichen upper cortex seems to provide adequate protection against solar radiation. Moreover, after extreme dehydration induced by high vacuum, the lichens proved to be able to recover, in full, their metabolic activity within 24 hours.     

欧洲空间操作中心的精密轨道确定

目前,欧洲空间操作中心正在进行着一项需4年时间的开发计划,以支持未来的需要高精度轨道确定的ESA近地飞行任务。该工作是围绕着欧洲空间操作中心已开发的供轨道确定和误差分析用的一个软件系统进行的,该软件含有适合于各种轨道摄动和测量类型的先进模型。除了卫星轨道参数外,它还能对地球物理参数和测地参数进行估计和误差分析。     

利用比力多重积分作为输入信号的捷联导航算法

本论文提出了异于传统的推导捷联导航算法的方法,现在常用的仍然是传统的推导方法,且不久前Paul Savage做过总结(Savage,P．G,“Strapdown Inertial Navigation Integration Algorithm Design Part2：Velocity and Position Algorithms”,Journal of Guidance,Control,and Dynamics,V01．21,No．2,1998,PP．208—221．)。新方法的要点是利用了额外的加速度计的输出信号,它是比力多重积分在迭代周期的增量。由此产生了比力转换算法新的家族,它有效地消弱所谓的假振摆效应(它在线性振动和高频陀螺仪误差存在时产生),以较低的速度计算且无须采用抗混叠预滤波。     

航天指控中心的发展

本文介绍航天飞机的航天指控中心的功能和历史,阐述了通信和数据处理设施,重点则在显示系统的变迁。作为航天指控中心改造的一部分,将用新技术成果取代现有的显示系统。这种更新改造将构成一套高性能局网(LAN),向各工程工作站发送实时和历史数据,在工作站上处理和显示。这种结构的好处是:软件开发环境更灵活,更加模块化,因而有利于今后的改造更新。探讨了建议的新结构以及这一改造的工程和计划管理问题,重点在各局网的任务。     

航天飞机时频传递实验

一、引言 1.背景美国航空航天局(NASA)的空间和地面应用处正在考虑一项航天飞机实验,用来验证几种比对全球高精密时钟和原始频标的技术。该实验准备在航天飞机上装一台氢脉泽时钟,利用微波和激光脉冲信号比对航天飞机上的空间时钟与地面站上的时钟。提出该项实验的目的是验证几种时间传递技术,这些技术能以1毫微秒以上的精度比对时钟时间,以10~(-14)以上的精度比对时钟频率。能以10~(-14)的精度比对频率这种能力是本项实验的独到之处。目     

关于无源铷频标中光漂移和缓冲气体漂移问题

本文报道了无源铷频标中光漂移和缓冲气体漂移的计算和测量结果。光漂移是以两种接法,即分立滤光器法和集成滤光器法进行测量的。文章介绍一种能够恰如其份地描述所得结果的唯象分析方法,报道了不同的纯净缓冲气体或混合缓冲气体引起的频率漂移的测量结果,评述了频率与温度的非线性关系,将所得结果跟从前发表的数据做了比较,并且利用二次温度方程式进行简明分析,以进一步对这些结果加以说明。