Physiological and biomechanical considerations for a human Mars mission

Evolving on Earth has made humans perfectly adapted, both physiologically and biomechanically, to its gravity and atmospheric conditions. Leaving the Earth and its protective environment, therefore, results in the degradation of a number of human systems. Long-duration stays on the International Space Station (ISS) are accompanied by significant effects on crew's cardiovascular, vestibular and musculoskeletal systems. Bone loss and muscle atrophy are experienced at a rate of 1-3% and 5% per month respectively, while VO2 (oxygen consumption) measurements are reduced by approximately 25% after a few weeks in space. If these figures are simply extrapolated, a future human mission to Mars will be seriously jeopardised and crews may find they cross the threshold of bone and muscle loss and aerobic fitness--ultimately with them being unable to return to Earth. When arriving on Mars, considerable biomechanical alterations will also occur. Optimum walking speeds will be approximately 30% lower and transitioning from a walk to a run will occur at a speed 25% slower. Peak vertical forces will be reduced by as much as 50%, while stride length, stride time and airborne time will all increase. On Mars, half as much energy will be required to travel the equivalent distance on Earth and it will be 65% more economical to run rather than to walk.     

Small step or giant leap? Human locomotion on Mars

Human locomotion on Mars will be considerably different from on Earth. Optimum walking speeds will be approximately 30% lower and transitioning from a walk to a run will occur at a speed 25% slower. Peak vertical forces will be reduced by as much as 50%, and although ground contact time will remain constant with locomotion in 1 g, stride length and stride time will increase. During running on Mars airborne time will increase by approximately 80% in comparison to running on the Earth. On Mars, half as much energy will be required to travel the equivalent distance on Earth and it will be 65% more economical to run rather than to walk. Crews will, therefore, find themselves using a loping gait--a running-like action, with a slight upper body lean and an extended aerial phase, an unfamiliar gait in terrestrial locomotion.     

嫦娥五号探测器多圈调相地月转移应急轨道设计与分析

针对嫦娥五号任务上升段末期火箭二级发动机可能出现的提前关机故障造成入轨半长轴偏差较大和中途修正速度增量超限问题,提出了多圈调相地月转移轨道应急控制策略.首先,分析了不同入轨半长轴偏差、中途修正时刻与中途修正速度增量消耗之间的关系;其次,针对半长轴偏差较大问题,基于微分改正算法与B平面参数,设计了解析窗口搜索与多圈调相地...     

水下航行体空泡发展及出水溃灭特性实验研究

针对水下航行体出水过程中的空泡发展及溃灭特性问题,基于新型实验平台,即减压水下航行体运动平台,进行了垂直约束式发射实验,探究了傅汝德数和空化数对空泡发展和溃灭过程的影响。对空泡出水溃灭过程进行描述,并定义了空泡溃灭数Fc,用以衡量空泡溃灭速度。结果表明,傅汝德数主要影响空泡形状,空化数主要影响空泡的尺寸。此外,水下航行体出水时空泡溃灭向下推进速度与傅汝德数呈负相关关系,与空化数呈正相关关系。     

From Earth's orbit to the outer planets and beyond: Psychological issues in space

Current planning for the first interplanetary expedition to Mars envisions a crew of 6 or 7 people and a mission duration of around 2.5 years. However, this time frame is much less than that expected on expeditions to the outer solar system, where total mission durations of 10 years or more are likely. Although future technological breakthroughs in propulsion systems and space vehicle construction may speed up transit times, for now we must realistically consider the psychological impact of missions lasting for one or more decades.Available information largely deals with on-orbit missions. In research that involved Mir and ISS missions lasting up to 7 months, our group and others have studied the effects of psychological and interpersonal issues on crewmembers and on the crew-ground relationship. We also studied the positive effects of being in space. However, human expeditions to the outer planets and beyond will introduce a number of new psychological and interpersonal stressors that have not been experienced before. There will be unprecedented levels of isolation and monotony, real-time communication with the Earth will not be possible, the crew will have to work autonomously, there will be great dependence on computers and other technical resources located on board, and the Earth will become an insignificant dot in space or will even disappear from view entirely.Strategies for dealing with psychological issues involving missions to the outer solar system and beyond will be considered and discussed, including those related to new technologies being considered for interstellar missions, such as traveling at a significant fraction of the speed of light, putting crewmembers in suspended animation, or creating giant self-contained generation ships of colonists who will not return to Earth.     

Progress in multilateral Earth observation cooperation: CEOS, IGOS and the ad hoc Group on Earth Observations

The Committee on Earth Observation Satellites (CEOS) coordinates international civil space-borne missions designed to observe and study planet Earth. With over 100 Earth observation satellites expected to be launched during the next 10 years, it is clear that collaborative opportunities have not been fully maximized. In 2003 CEOS has been focusing on articulating a more comprehensive satellite data utilization approach and in following up on its significant involvement in the World Summit on Sustainable Development. The CEOS Chair also serves as Co-Chair of the Integrated Global Observing Strategy (IGOS) Partnership, which seeks to reduce observation gaps and unnecessary overlaps and to harmonize and integrate common interests of space-based and in situ systems. IGOS focused in 2003 on development of a number of themes, including Carbon Cycle, Water Cycle and GeoHazards. The IGOS Ocean Theme is now in its implementation phase. NOAA, while chairing CEOS and co-chairing IGOS, has also been actively involved in organizing and hosting a ministerial-level Earth Observation Summit with a follow-on Group on Earth Observations (GEO) charged with developing the framework for a comprehensive global Earth observation system(s). All these activities demonstrate the commitment to developing more coherent and sustained Earth observation strategies for the good of the planet.     

Planetary Defense From Space: Part 2 (Simple) Asteroid Deflection Law

A system of two space bases housing missiles for an efficient Planetary Defense of the Earth from asteroids and comets was firstly proposed by this author in 2002. It was then shown that the five Lagrangian points of the Earth–Moon system lead naturally to only two unmistakable locations of these two space bases within the sphere of influence of the Earth. These locations are the two Lagrangian points L1 (in between the Earth and the Moon) and L3 (in the direction opposite to the Moon from the Earth). In fact, placing missiles based at L1 and L3 would enable the missiles to deflect the trajectory of incoming asteroids by hitting them orthogonally to their impact trajectory toward the Earth, thus maximizing the deflection at best. It was also shown that confocal conics are the only class of missile trajectories fulfilling this “best orthogonal deflection” requirement.The mathematical theory developed by the author in the years 2002–2004 was just the beginning of a more expanded research program about the Planetary Defense. In fact, while those papers developed the formal Keplerian theory of the Optimal Planetary Defense achievable from the Earth–Moon Lagrangian points L1 and L3, this paper is devoted to the proof of a simple “(small) asteroid deflection law” relating directly the following variables to each other:

(1) the speed of the arriving asteroid with respect to the Earth (known from the astrometric observations);

(2) the asteroid's size and density (also supposed to be known from astronomical observations of various types);

(3) the “security radius” of the Earth, that is, the minimal sphere around the Earth outside which we must force the asteroid to fly if we want to be safe on Earth. Typically, we assume the security radius to equal about 10,000 km from the Earth center, but this number might be changed by more refined analyses, especially in the case of “rubble pile” asteroids;

(4) the distance from the Earth of the two Lagrangian points L1 and L3 where the defense missiles are to be housed;

(5) the deflecting missile's data, namely its mass and especially its “extra-boost”, that is, the extra-energy by which the missile must hit the asteroid to achieve the requested minimal deflection outside the security radius around the Earth.

This discovery of the simple “asteroid deflection law” presented in this paper was possible because:

(1) In the vicinity of the Earth, the hyperbola of the arriving asteroid is nearly the same as its own asymptote, namely, the asteroid's hyperbola is very much like a straight line. We call this approximation the line/circle approximation. Although “rough” compared to the ordinary Keplerian theory, this approximation simplifies the mathematical problem to such an extent that two simple, final equations can be derived.

(2) The confocal missile trajectory, orthogonal to this straight line, ceases then to be an ellipse to become just a circle centered at the Earth. This fact also simplifies things greatly. Our results are thus to be regarded as a good engineering approximation, valid for a preliminary astronautical design of the missiles and bases at L1 and L3.

Still, many more sophisticated refinements would be needed for a complete Planetary Defense System:

(1) taking into account many perturbation forces of all kinds acting on both the asteroids and missiles shot from L1 and L3;

(2) adding more (non-optimal) trajectories of missiles shot from either the Lagrangian points L4 and L5 of the Earth–Moon system or from the surface of the Moon itself;

(3) encompassing the full range of missiles currently available to the USA (and possibly other countries) so as to really see “which missiles could divert which asteroids”, even just within the very simplified scheme proposed in this paper.

In summary: outlined for the first time in February 2002, our Confocal Planetary Defense concept is a simplified Keplerian Theory that already proved simple enough to catch the attention of scholars, popular writers, and representatives of the US Military. These developments would hopefully mark the beginning of a general mathematical vision for building an efficient Planetary Defense System in space and in the vicinity of the Earth, although not on the surface of the Earth itself!We must make a real progress beyond academic papers, Hollywood movies and secret military plans, before asteroids like 99942 Apophis get close enough to destroy us in 2029 or a little later.     

The AURORA Project: Removal of plastic substrate to obtain an all-metal solar sail

The Orbital Angular Momentum Reversal (H-Reversal mode), is a new class of trajectories to get a cruise speed ranging from 12 to 20 AU/yr. To accomplish the H-reversal mode, a sailcraft needs of all metal solar sail. The solar sail envisaged by the “AURORA Project” is composed of two metallic layers (AI and Cr) deposited on plastic substrate. To obtain an all metal solar sail, required by the Project, the substrate must be removed in orbit. In order to accomplish that, two possible methods are described in this paper. The first one is based on the UV degradation of a buffer layer located between the substrate and the metallic layers. The UV degradation would be the starting mechanism that causes the interface weakness. The Diamond Like Carbon has been used as buffer layer and preliminary experimental results on its UV degradation are reported. The second method exploits the characteristic of most plastics to be etched (ashing process) by the atomic oxygen. The number density of atomic oxygen in Low Earth Orbit could be enough to remove a properly-selected plastic substrate in Short time.     

Impact seeding and reseeding in the inner solar system

Assuming that asteroidal and cometary impacts onto Earth can liberate material containing viable microorganisms, we studied the subsequent distribution of the escaping impact ejecta throughout the inner Solar System on time scales of 30,000 years. Our calculations of the delivery rates of this terrestrial material to Mars and Venus, as well as back to Earth, indicate that transport to great heliocentric distances may occur in just a few years and that the departure speed is significant. This material would have been efficiently and quickly dispersed throughout the Solar System. Our study considers the fate of all the ejected mass (not just the slowly moving material), and tabulates impact rates onto Venus and Mars in addition to Earth itself. Expressed as a fraction of the ejected particles, roughly 0.1% and 0.001% of the ejecta particles would have reached Venus and Mars, respectively, in 30,000 years, making the biological seeding of those planets viable if the target planet supported a receptive environment at the time. In terms of possibly safeguarding terrestrial life by allowing its survival in space while our planet cools after a major killing thermal pulse, we show via our 30,000- year integrations that efficient return to Earth continues for this duration. Our calculations indicate that roughly 1% of the launched mass returns to Earth after a major impact regardless of the impactor speed; although a larger mass is ejected following impacts at higher speeds, a smaller fraction of these ejecta is returned. Early bacterial life on Earth could have been safeguarded from any purported impact-induced extinction by temporary refuge in space.     

Does life's rapid appearance imply a Martian origin?

The hypothesis that life's rapid appearance on Earth justifies the belief that life is widespread in the universe has been investigated mathematically by Lineweaver and Davis (Astrobiology 2002;2:293-304). However, a rapid appearance could also be interpreted as evidence for a nonterrestrial origin. I attempt to quantify the relative probabilities for a non-indigenous versus indigenous origin, on the assumption that biogenesis involves one or more highly improbable steps, using a generalization of Carter's well-known observer-selection argument. The analysis is specifically applied to a Martian origin of life, with subsequent transfer to Earth within impact ejecta. My main result is that the relatively greater probability of a Martian origin rises sharply as a function of the number of difficult steps involved in biogenesis. The actual numerical factor depends on what is assumed about conditions on early Mars, but for a wide range of assumptions a Martian origin of life is decisively favored. By contrast, an extrasolar origin seems unlikely using the same analysis. These results complement those of Lineweaver and Davis.     

The mass and speed dependence of meteor air plasma temperatures

The speed and mass dependence of meteor air plasma temperatures is perhaps the most important data needed to understand how small meteoroids chemically change the ambient atmosphere in their path and enrich the ablated meteoric organic matter with oxygen. Such chemistry can play an important role in creating prebiotic compounds. The excitation conditions in various air plasma emissions were measured from high-resolution optical spectra of Leonid storm meteors during NASA's Leonid Multi-Instrument Aircraft Campaign. This was the first time a sufficient number and range of temperature measurements were obtained to search for meteoroid mass and speed dependencies. We found slight increases in temperature with decreasing altitude, but otherwise nearly constant values for meteoroids with speeds between 35 and 72 km/s and masses between 10(-5) g and 1 g. We conclude that faster and more massive meteoroids produce a larger emission volume, but not a higher air plasma temperature. We speculate that the meteoric plasma may be in multiphase equilibrium with the ambient atmosphere, which could mean lower plasma temperatures in a CO(2)-rich early Earth atmosphere.     

European perspectives on trends in public sector Earth observation data policies

The growing number of Earth observation satellites are producing ever increasing amounts of data. These data sets require adequate management to be widely exploited and to ensure preservation of what is a valuable information resource. Many Earth observation organisations have formulated or are developing policies related to how data are managed and distributed which encompass issues such as property rights, access and price of the data, exclusive data use and data archiving. European Earth observation is gaining more prominence in these developing policy issues. This paper is a review, from a largely European perspective, of current Earth observation data policies in operation by various public sector international, regional and national organisations in both the data providing and data user sectors. It will be demonstrated that certain trends exist between the various data policies but that differences in position are present in some key areas which may need to be reconciled in order for the Earth observation sector to reach maturity.     

地球自转对光机扫描仪摆扫成像的影响分析

地球自转会影响地物相对光机扫描仪的运动。不同纬度的地速不同,地速的变化会造成扫描条带畸变、相邻条带错动和重叠率的变化。文章研究了地球自转的变化规律,从扫描条带畸变、相邻条带错动和重叠率变化3方面因素研究了地速对光机扫描仪成像的影响。最后,针对这些影响提出了校正建议。     

基于深度学习的多步预测方法在太阳风速度预测上的应用

为对近地环境太阳风状况进行可靠预测,引入基于深度学习的多步预测方法来预测在太阳与地球之间的拉格朗日点1(L1)处距离输入观测数据序列未来24、48、72、96 h的太阳风速度.采用SDO的图像数据提取冕洞面积等特征信息,并从NASA OMNIWEB数据集提取其他输入特征,形成多变量的时序数据作为太阳风速度预测的输入信息...     

Implications of an anthropic model of evolution for emergence of complex life and intelligence

Structurally complex life and intelligence evolved late on Earth; models for the evolution of global temperature suggest that, due to the increasing solar luminosity, the future life span of the (eukaryote) biosphere will be "only" about another billion years, a short time compared to the approximately 4 Ga since life began. A simple stochastic model (Carter, 1983) suggests that this timing might be governed by the necessity to pass a small number, n, of very difficult evolutionary steps, with n < 10 and a best guess of n = 4, in order for intelligent observers like ourselves to evolve. Here I extend the model analysis to derive probability distributions for each step. Past steps should tend to be evenly spaced through Earth's history, and this is consistent with identification of the steps with some of the major transitions in the evolution of life on Earth. A complementary approach, identifying the critical steps with major reorganizations in Earth's biogeochemical cycles, suggests that the Archean-Proterozoic and Proterozoic-Phanerozoic transitions might be identified with critical steps. The success of the model lends support to a "Rare Earth" hypothesis (Ward and Brownlee, 2000): structurally complex life is separated from prokaryotes by several very unlikely steps and, hence, will be much less common than prokaryotes. Intelligence is one further unlikely step, so it is much less common still.     

Influence on photosynthesis of starlight, moonlight, planetlight, and light pollution (reflections on photosynthetically active radiation in the universe)

Photosynthesis on Earth can occur in a diversity of organisms in the photosynthetically active radiation (PAR) range of 10 nmol of photons m(-2) s(-1) to 8 mmol of photons m(-2) s(-1). Similar considerations would probably apply to photosynthetic organisms on Earth-like planets (ELPs) in the continuously habitable zone of other stars. On Earth, starlight PAR is inadequate for photosynthetically supported growth. An increase in starlight even to reach the minimum theoretical levels to allow for photosynthesis would require a universe that was approximately ten million times older, or with a ten million times greater density of stars, than is the case for the present universe. Photosynthesis on an ELP using PAR reflected from a natural satellite with the same size as our Moon, but at the Roche limit, could support a low rate of photosynthesis at full Moon. Photosynthesis on an ELP-like satellite of a Jupiter-sized planet using light reflected from the planet could be almost 1% of the rate in full sunlight on Earth when the planet was full. These potential contributions to photosynthesis require that the contribution is compared with the rate of photosynthesis driven by direct radiation from the star. Light pollution on Earth only energizes photosynthesis by organisms that are very close to the light source. However, effects of light pollution on photosynthesis can be more widespread if the photosynthetic canopy is retained for more of the year, caused by effects on photoperiodism, with implications for the influence of civilizations on photosynthesis.     

基于变体积力的跨水气界面多相流及流固耦合问题实验方法研究

航行体跨水气界面过程物理现象复杂并且多种力学效应耦合,相关研究往往需要利用缩比模型实验开展。已有缩比模型实验体积力保持不变,主要考虑弗劳德数和空化数相似,难以分析其他相似参数影响。利用离心机形成可变体积力环境,增加了实验可控参数,提高了实验模拟参数的完备性。通过流动和结构形变理论分析,形成了基于变体积力的跨水气界面多相流及流固耦合问题研究方案,可在考虑弗劳德数和空化数影响条件下,进一步考察雷诺数或结构形变的影响。针对上述研究方案,分析了缩比模型实验模拟条件并开展了仿真计算,验证了所提出实验方案的可行性,为跨介质问题研究丰富了探索途径。     

太赫兹通信技术研究进展及空间应用展望

太赫兹波具有频带宽、传榆速率高、方向性好、安全性高、散射小及高穿透性等特性。近些年天体物理学,行星和地球科学研究的任务增多促进了太赫兹源和系统的不断发展。文章介绍和分析了太赫兹通信的一些关键技术和最新研究成果;同时,对太赫兹的技术发展趋势和应用前景做了展望。     

A two-dimensional approach to multibody free dynamics in space environment

The equation of motion of a multibody system, described here as a chain of rigid bars and revolute joints orbiting around the Earth, is derived.

For each bar two translational and one rotational equilibrium equations are written. The forces acting on each body are the gravitational forces and the reaction forces (unknown) acting on it's end joints. The complete set of equilibrium equations consists of N_X differential equations, where N_X is the order of the state vector. The total number of unknowns is N_X+N_R where N_R=2N_J and N_J is the number of joints. The N_R additional equations, to make the system determinate, are provided by the nondifferential compatibility equations.

The resulting system is a set of differential algebraic equations (DAE) for which the well-known method of reducing the system to ordinary differential equations (ODE) is applied.

Since the internal forces are associated with the relative displacements between the bodies, which are small fractions of the distance of the multibody spacecraft from the center of the Earth, the task of obtaining these forces from inertial coordinates, from a numerical viewpoint, could be impossible. So the problem is reformulated in such a way that the equation of motion of the system, contains global quantities where no internal forces appear, and local equations where internal forces do appear. In the latter one, only quantities of the same order of the spacecraft dimensions are present. Numerical results complete the work.