Human spaceflight and an asteroid redirect mission: Why?

The planning of human spaceflight programmes is an exercise in careful rationing of a scarce and expensive resource. Current NASA plans are to develop the new capability for human-rated launch into space to replace the Space Transportation System (STS), more commonly known as the Space Shuttle, combined with a heavy lift capability, and followed by an eventual Mars mission. As an intermediate step towards Mars, NASA proposes to venture beyond Low Earth Orbit to cis-lunar space to visit a small asteroid which will be captured and moved to lunar orbit by a separate robotic mission. The rationale for this and how to garner support from the scientific community for such an asteroid mission are discussed. Key points that emerge are that a programme usually has greater legitimacy when it emerges from public debate, mostly via a Presidential Commission, a report by the National Research Council or a Decadal Review of science goals etc. Also, human spaceflight missions need to have support from a wide range of interested communities. Accordingly, an outline scientific case for a human visit to an asteroid is made. Further, it is argued here that the scientific interest in an asteroid mission needs to be included early in the planning stages, so that the appropriate capabilities (here the need for drilling cores and carrying equipment to, and returning samples from, the asteroid) can be included.     

Comparison of the roles of nucleotide synthesis, polymerization, and recombination in the origin of autocatalytic sets of RNAs

Ribozymes that act as polymerases and nucleotide synthases are known experimentally, even though no fully self-replicating system has yet been found. If the RNA World hypothesis is true, ribozymes must have arisen initially from within a random abiotic polymerization system. To investigate the origin of the RNA world, we studied a mathematical model of a chemical reaction system describing RNA polymerization. It is supposed that, in absence of ribozymes, polymerization occurs at a small spontaneous rate, and that in the presence of polymerase ribozymes, polymerization occurs at a faster rate that is proportional to the ribozyme concentration. Chains must be longer than a minimum threshold length in order to have the possibility of acting as ribozymes. The reaction system has two stable states that we term dead and living. The dead state is controlled by the small spontaneous rate and has negligible concentration of ribozymes. The living state has high concentration of ribozymes, and the reaction rates are determined by the ribozymes; thus, the system is autocatalytic. Concentration fluctuations in a finite volume can cause a transition to occur from the dead to the living state, that is, an origin of life occurs within this model. We also consider ribozymes that catalyze nucleotide synthesis. We show that living and dead states arise in the presence of synthase ribozymes in the same way as for polymerases. It has been proposed that recombination reactions are a way of generating long RNA chains in the early stages of life. We show that if the possibility of random reversible recombination reactions is added to our model, this does not lead to an increase in long polymer concentration. Thus, if recombination is fully reversible, there is no autocatalytic state controlled by recombination. Nevertheless, recombination can play an important role in ribozyme synthesis if there is an additional process that keeps the recombination reactions out of equilibrium. We modeled a case studied experimentally in which building block strands of moderate length associate due to RNA secondary structure formation. A recombination reaction then occurs between these strands to form a longer sequence that catalyzes its own formation via the recombination reaction. This system has an autocatalytic state, and it is possible for it to arise within our random polymerization system. If complexes formed by associations of shorter strands can act as catalysts without the requirement that the strands be covalently linked, this would alleviate the need for synthesis of very long strands; hence, it makes the emergence of an autocatalytic system from an abiotic random polymerization system much more likely.     

Biological and cognitive determination of the gravitational reference frame

It is argued that space sickness is not so much a physiological problem, but a psychological one, having its roots in the perception of the environment, and its associated cognitive processing. This cognitive processing is argued to be that of field dependence and field independence, for which exist psychobiological and cognitive assessment tests. Since there is an obvious economic advantage in the use of cognite testing, it is recommended that this could be used as an initial screening when selecting for astronauts.     

Development of a scheduling algorithm and GUI for autonomous satellite missions

In this paper, a scheduling optimization algorithm is developed and verified for autonomous satellite mission operations. As satellite control and operational techniques continue to develop, satellite missions become more complicated and the overall quantity of tasks within the missions also increases. These changes require more specific consideration and a huge amount of computational resources, for scheduling the satellite missions. In addition, there is a certain level of repetition in satellite mission scheduling activities, and hence it is highly recommended that the operation manager carefully considers and builds some appropriate strategy for performing the operations autonomously. A good strategy to adopt is to develop scheduling optimization algorithms, because it is difficult for humans to consider the many mission parameters and constraints simultaneously. In this paper, a new genetic algorithm is applied to simulations of an actual satellite mission scheduling problem, and an appropriate GUI design is considered for an autonomous satellite mission operation. It is expected that the scheduling optimization algorithm and the GUI can improve the overall efficiency in practical satellite mission operations.     

真空热试验中红外笼对伞状天线非稳态加热过程数值仿真

文章针对真空热试验红外加热装置计算机辅助设计中的非稳态过程模拟问题,以一种较为复杂的伞状天线结构为例,以红外笼作为加热装置,对真空热试验环境下的加热过程进行数值仿真研究。采用红外笼的等效加热面模型简化仿真模型,使计算负荷可以达到工程应用的水平,同时满足模拟精度的要求。数值仿真与试验数据对比证明,所采用的计算方法可以为红外笼等红外加热装置的设计提供准确的非稳态加热过程模拟。     

基于TDRSS的高速数传信号载波捕获及跟踪算法研究

以TDRSS数传系统为研究背景,针对TDRSS数传信号的特点,以实现高速8PSK调制信号的载波同步与跟踪为研究前提。提出了一种采用二叉树(BinarySearchTree)频率搜索方法实现捕获及采用平均"滑动窗"递推最小二乘(RLS)一步预测方法实现频率跟踪的算法,并针对此方法进行了理论推导和蒙特卡洛(MonteCarlo)仿真。结果表明:该方法适用于全数字高速数传8PSK调制信号接收系统,同时也可移植、推广至全数字雷达接收机中。     

Soyuz in French Guiana: A strategic perspective

After a proposition from Russia to France, ESA agreed to see Soyuz rockets take off from French Guiana. From industry, to governments and agencies, many Russian and European actors were involved in this project and they all had different motives. It is therefore relevant to try to discern them so as to understand the rationale behind this cooperative endeavor. Soyuz's primary role is to consolidate Arianespace commercial position in the launching market and to bring activity and founding to a stagnating Russian space sector. With this decision Arianespace will have a full range of commercially available launchers with Soyuz completing the two European rockets Vega and Ariane V. But since Vega and Ariane must have the priority, there is a risk to see an insufficient launch rate for Soyuz, which would not satisfy the Russian partners. Commercial elements alone cannot justify the agreement. There is a larger strategic ambition behind. What is at stake is the future development of innovative launch systems. It is important for ESA to maintain an autonomous access to space and to maintain a dynamic and strong European propulsion industry. Cooperation with Russia can offer an increase of expandable rockets capabilities and can pave for the next generation of launch vehicles. Moreover, we can detect an interest in acquiring a system that has the potential for human space flight capacity. Finally, the decision to launch Soyuz from French Guiana was the conjunction of Russian and French national interests, which led to a complete redefinition of the relations between Europe and Russia. It is of strategic importance that we, Europeans, adapt to this evolution and understand the new place that Russia takes in our space sector.     

Divergence and phylogeny of firmicutes from the cuatro ciénegas basin, Mexico: a window to an ancient ocean

Abstract The Cuatro Ciénegas Basin (CCB) has been identified as a center of endemism for many life-forms. Nearly half the bacterial species found in the spring systems have their closest relatives in the ocean. This raises the question of whether the high diversity observed today is the product of an adaptive radiation similar to that of the Galapagos Islands or whether the bacterial groups are "survivors" of an ancient sea, which would be of interest for astrobiology. To help answer this question, we focused on Firmicutes from Cuatro Ciénegas (mainly Bacillus and Exiguobacterium). We reconstructed the phylogenetic relationships of Firmicutes with 28 housekeeping genes and dated the resulting tree using geological events as calibration points. Our results show that marine Bacillus diverged from other Bacillus strains 838?Ma, while Bacillus from Cuatro Ciénegas have divergence dates that range from 770 to 202?Ma. The members of Exiguobacterium from the CCB conform to a much younger group that diverged from the Andes strain 60?Ma and from the one in Yellowstone 183?Ma. Therefore, the diversity of Firmicutes in Cuatro Ciénegas is not the product of a recent radiation but the product of the isolation of lineages from an ancient ocean. Hence, Cuatro Ciénegas is not a Galapagos Archipelago for bacteria but is more like an astrobiological "time machine" in which bacterial lineages survived in an oligotrophic environment that may be very similar to that of the Precambrian. Key Words: Firmicutes-Cuatro Ciénegas-Precambrian-Molecular dating-Western Interior Seaway. Astrobiology 12, 674-684.     

On hydromagnetic flow of an Oldroyd-B fluid near a pulsating plate

An initial value investigation is made of the motion of an incompressible, viscoelastic, conducting Oldroyd-B fluid bounded by an infinite rigid non-conducting plate. The unsteady flow is generated from rest in the fluid due to velocity tooth pulses subjected on the plate in presence of an external magnetic field. It is assumed that no external electric field is acting on the system and the magnetic Reynolds number is very small. The operational method is used to obtain exact solutions for the fluid velocity and the shear stress on the plate. Quantitative analysis of the results are presented with a view to disclose the simultaneous effects of the magnetic field and the fluid elasticity on the flow and the wall shear stress for different periods of pulsation of the plate. It is shown that the classical and hydromagnetic Rayleigh solutions are limiting cases of the present analysis.     

Resources of free space vs. flags and footprints on Mars

Human space exploration since Apollo appears to lack an overall context. There has been an overall context for the world's space efforts. But it is an unofficial one and it is outmoded, because it was based on a false assumption. This is the space exploration plan articulated by Von Braun in the 1950s and restated as the Integrated Space Program - 1970–1990, whose principal aim is to send humans to explore Mars. The critical underlying assumption of this plan was that Mars is a planet much like Earth, with an active biosphere. This Program has persisted nearly two decades after this underlying assumption has been shown to be false. There is a competing context re-emerging for human space exploration and development which is better fitted to the needs of human society in the post-Cold War era than the Mars program embraced by NASA and, to a large extent, the USSR during the period of US-Russian competition. The original space program uses the resources of free space and provides an economic rationale for human space activity.     

VLSI processors for signal detection in SETI

The objective of the Search for Extraterrestrial Intelligence (SETI) is to locate an artificially created signal coming from a distant star. This is done in two steps: (1) spectral analysis of an incoming radio frequency band, and (2) pattern detection for narrow-band signals. Both steps are computationally expensive and require the development of specially designed computer architectures. To reduce the size and cost of the SETI signal detection machine, two custom VLSI chips are under development. The first chip, the SETI DSP Engine, is used in the spectrum analyzer and is specially designed to compute Discrete Fourier Transforms (DFTs). It is a high-speed arithmetic processor that has two adders, one multiplier-accumulator, and three four-port memories. The second chip is a new type of Content-Addressable Memory. It is the heart of an associative processor that is used for pattern detection. Both chips incorporate many innovative circuits and architectural features.     

A survey of algorithms for star identification with low-cost star trackers

This paper aims to present a set of lost-in-space star identification algorithms that works effectively for small satellites. Several algorithms are investigated for both phases of star identification: feature extraction and catalogue search. For feature extraction, it is shown that an algorithm using extended images with combined images works best, and for catalogue search, the Group Catalogue is shown to be most efficient. Therefore, this paper proposes an algorithm combining these three. Simulation results show the effectiveness of this algorithm for its robustness to various errors, and an application of this algorithm, “unequal” star trackers, is introduced.     

面向降落伞高空开伞的充气式钝锥阻力体气动构型仿真研究

针对钝锥阻力体航天器降落伞高空开伞试验采用低成本小直径火箭外形包络受限问题,提出在箭体上安装柔性充气环和充气裙锥两种变构型方案,用于模拟降落伞开伞过程真实流场环境。采用三维雷诺时均N-S（Reynolds Averaged Navier-Stokes, RANS）方程方法分别对某钝锥构型返回舱、某小型火箭以及火箭尾部加装充气环和充气锥裙4种构型进行流场数值模拟,并对比各种构型的尾流流场特征。计算结果表明,箭体上加装充气环和充气裙锥都可从一定程度上改善尾流特性;相比之下,采用充气裙锥方案更接近返回舱真实尾流流场。     

一种用于空间群目标分辨的滑动窗轨迹跟踪算法

针对大多数现有的微多普勒分析理论难以解决空间群目标的监测与识别问题,本文提出一种基于提取目标运动特征的弹道中段群目标分辨方法。首先建立了多个具有滑动散射中心的旋转对称目标模型并得到其m-D曲线,在此基础上,利用形态学图像处理方法抑制一维距离像旁瓣,然后提出了一种滑动窗轨迹跟踪的方法分离出各散射点相互交叉的m-D曲线,再对分离结果进行经验模式分解(Empirical-Mode Decomposition, EMD),最后通过提取能够反映目标运动特征的固有模态函数(Intrinsic Mode Function ,IMF),实现了群目标分辨。仿真实验校验了所提方法的可行性和鲁棒性。     

Roadmap to a star

NASA is currently constructing an Interstellar Roadmap that will outline a progressive series of phased technology efforts over several decades that would enable new science beyond the solar system, leading to and culminating in robotics exploration of nearby stars. The Roadmap is structured around a decadal progression of science missions and enabling technologies in which each decadal cycle has an intrinsic value in itself. The Roadmap serves at least 5 functions: 1) it lays the foundation for the development of a broad new strategic thrust of space exploration and development; 2) it outlines a long term progressive program for which each phase has an intrinsic value and can be argued independently of a Star Mission itself; 3) it defines a phased approach that would culminate in a large- scale breakthrough beamed energy capability that would have broad planetary and terrestrial applicability; 4) it describes an endeavor that could provide the technological basis of a U.S. economic engine for the first half of the 21st century; and 5) it provides a focus and a structure around which new government/industry economic relationships may be established. This paper outlines the process for constructing the Roadmap which is due to be completed in Fall 1998. It also poses questions raised by a mission of such scale and suggests some of the strategic value of such a Roadmap.     

A security space capability for Europe? Implications for US policy

As the European Union takes tentative steps towards creating a “rapid reaction force” able to operate independently of NATO, an important question is what capabilities that force must have in order to operate effectively. Among those capabilities is the use of space systems for communications and intelligence applications. This article examines the prospects for an independent security space capability in Europe, and the implications of the emerging European interest in space autonomy for US policy.     

一种GPS快速定位技术研究

用LAMBDA方法确定GPS载波相位测量的整周模糊度,需要较高精度的浮点解。但用短时间GPS观测值构建的法方程容易出现病态,以致法方程的解很不稳定。本文使用谱修正迭代法,消除法方程病态,进而用LAMBDA方法确定整周模糊度。我们的实验结果表明,对于1min左右的单频GPS载波相位测量,利用本文方法即可正确地解算出它的整周模糊度,从而实现厘米级定位。     

典型装配工艺模块化的应用研究

航天器类产品具有派生型号多、生产批量小等特点,因而存在工艺设计重复工作量大、效率低等问题。研究了基于典型工艺模块化的参数化工艺设计方法。通过合理选择装配单元划分特征,给出了有效的典型装配单元划分及鉴别方案,提出了基于典型工艺应用规划装配流程的方法,并以“天宫一号”热控多层组件制作为实例进行了应用过程分析。在“天宫一号”总装工艺设计过程应用的实际效果证明该方法切实可行,能够提高工艺设计效率。     

基于神经网络在线建模的非线性动态系统中传感器故障检测方法

本文提出一种基于神经网络在线建模的动态非线性系统中传感器故障检测方法，它首先利用神经网络在线建立动态非线性系统的超前一步预测模型，然后利用神经网络对传感器的预测输出和传感器实际输出之差与一预定阈值比较以检测传感器故障。本文的优点是可以检测多个传感器故障，同时由于采用在线学习方式，非常适于航天器自主系统传感器故障检测的需要。此外，故障检测阈值的选取也比较简单。为了验证本文方法，仿真了一控制系统中同时发生漂移故障的两个传感器故障检测过程。结果表明，方法十分有效。