排序方式: 共有70条查询结果,搜索用时 15 毫秒
51.
Pullan D Westall F Hofmann BA Parnell J Cockell CS Edwards HG Villar SE Schröder C Cressey G Marinangeli L Richter L Klingelhöfer G 《Astrobiology》2008,8(1):119-156
We have investigated how morphological biosignatures (i.e., features related to life) might be identified with an array of viable instruments within the framework of robotic planetary surface operations at Mars. This is the first time such an integrated lab-based study has been conducted that incorporates space-qualified instrumentation designed for combined in situ imaging, analysis, and geotechnics (sampling). Specimens were selected on the basis of feature morphology, scale, and analogy to Mars rocks. Two types of morphological criteria were considered: potential signatures of extinct life (fossilized microbial filaments) and of extant life (crypto-chasmoendolithic microorganisms). The materials originated from a variety of topical martian analogue localities on Earth, including impact craters, high-latitude deserts, and hydrothermal deposits. Our in situ payload included a stereo camera, microscope, M?ssbauer spectrometer, and sampling device (all space-qualified units from Beagle 2), and an array of commercial instruments, including a multi-spectral imager, an X-ray spectrometer (calibrated to the Beagle 2 instrument), a micro-Raman spectrometer, and a bespoke (custom-designed) X-ray diffractometer. All experiments were conducted within the engineering constraints of in situ operations to generate realistic data and address the practical challenges of measurement. Our results demonstrate the importance of an integrated approach for this type of work. Each technique made a proportionate contribution to the overall effectiveness of our "pseudopayload" for biogenic assessment of samples yet highlighted a number of limitations of current space instrument technology for in situ astrobiology. 相似文献
52.
Andrea Bolle Christian Circi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
The aim of the present paper is to propose a hybrid, self adjusting, search algorithm for space trajectory optimization. By taking advantage of both direct and indirect methods, the present algorithm allows the finding of the optimal solution through the introduction of some new control parameters, whose number is smaller than that of the Lagrange multipliers, and whose range is bounded. Eventually, the optimal solution is determined by means of an iterative self-adjustment of the search domain occurring at “runtime”, without any correction by an external user. This new set of parameters can be found through a reduction process of the degrees of freedom, obtained through the transversality conditions before entering the search loop. Furthermore, such a process shows that Lagrange multipliers are subject to a deep symmetry mirroring the features of the state vector. The algorithm reliability and efficiency is assessed through some test cases, and by reproducing some optimal transfer trajectories: a full three-dimensional, minimum time Mars mission, an optimal transfer to Jupiter, and finally an injection into a circular Moon orbit. 相似文献
53.
Joshua Poganski Norbert I. Kömle Günter Kargl Helmut F. Schweiger Matthias Grott Tilman Spohn Olaf Krömer Christian Krause Torben Wippermann Georgios Tsakyridis Mark Fittock Roy Lichtenheldt Christos Vrettos José E. Andrade 《Space Science Reviews》2017,211(1-4):217-236
The NASA InSight mission will provide an opportunity for soil investigations using the penetration data of the heat flow probe built by the German Aerospace Center DLR. The Heat flow and Physical Properties Probe (HP3) will penetrate 3 to 5 meter into the Martian subsurface to investigate the planetary heat flow. The measurement of the penetration rate during the insertion of the HP3 will be used to determine the physical properties of the soil at the landing site. For this purpose, numerical simulations of the penetration process were performed to get a better understanding of the soil properties influencing the penetration performance of HP3. A pile driving model has been developed considering all masses of the hammering mechanism of HP3. By cumulative application of individual stroke cycles it is now able to describe the penetration of the Mole into the Martian soil as a function of time, assuming that the soil parameters of the material through which it penetrates are known. We are using calibrated materials similar to those expected to be encountered by the InSight/HP3 Mole when it will be operated on the surface of Mars after the landing of the InSight spacecraft. We consider various possible scenarios, among them a more or less homogeneous material down to a depth of 3–5 m as well as a layered ground, consisting of layers with different soil parameters. Finally we describe some experimental tests performed with the latest prototype of the InSight Mole at DLR Bremen and compare the measured penetration performance in sand with our modeling results. Furthermore, results from a 3D DEM simulation are presented to get a better understanding of the soil response. 相似文献
54.
Resolution Needed for an Adequate Determination of the Mean Ocean Circulation from Altimetry and an Improved Geoid 总被引:4,自引:0,他引:4
The sea surface topography observed by satellite altimetry is a combination of the geoid and of the ocean dynamic topography.
Satellite altimetry has thus the potential to supply quasi-global maps of mean sea surface heights from which the mean geostrophic
surface ocean currents can be derived, provided that the geoid is known with a sufficient absolute accuracy. At present, however,
given the limited accuracy of the best available geoid, altimetric mean sea surface topographies have been derived only up
to degree 15 or so, i.e. for wavelengths of approximately 2000 km and larger. CHAMP, GRACE, and the future GOCE missions are
dedicated to the improvement of the Earth's gravity field from space. Several studies have recently investigated the impact
of these improvements for oceanography, concluding to reductions of uncertainties on the oceanic flux estimates as large as
a factor of 2 in the regions of intense an narrow currents. The aim of this paper is to focus on what are the typical horizontal
scales of the mean dynamic topography of the ocean, and to compare their characteristics to the error estimates expected from
altimetry and these future geoids. It gives also an illustration of the oceanic features that will be resolved by the combination
of altimetry and the GRACE and GOCE geoids. It further reassesses the very demanding requirements in term of accuracy and
resolution agreed in the design of these new gravity missions for ocean science applications. The present study relies on
recent very high-resolution numerical Ocean General Circulation Model simulations.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
55.
R.A. Mewaldt N.E. Yanasak M.E. Wiedenbeck A.J. Davis W.R. Binns E.R. Christian A.C. Cummings P.L. Hink R.A. Leske S.M. Niebur E.C. Stone T.T. Von Rosenvinge 《Space Science Reviews》2001,99(1-4):27-39
There are a number of radioactive clocks in the cosmic radiation that can be used to measure the time scales for cosmic ray processes in the Galaxy. With high-resolution isotope measurements available from ACE it is now possible to read these clocks with greatly improved accuracy and address key questions about the origin and lifetime of cosmic rays. This paper discusses the status of three such investigations. 相似文献
56.
Groemer GE Hauth S Luger U Bickert K Sattler B Hauth E Föger D Schildhammer D Agerer C Ragonig C Sams S Kaineder F Knoflach M 《Astrobiology》2012,12(2):125-134
We have developed the space suit simulator Aouda.X, which is capable of reproducing the physical and sensory limitations a flight-worthy suit would have on Mars. Based upon a Hard-Upper-Torso design, it has an advanced human-machine interface and a sensory network connected to an On-Board Data Handling system to increase the situational awareness in the field. Although the suit simulator is not pressurized, the physical forces that lead to a reduced working envelope and physical performance are reproduced with a calibrated exoskeleton. This allows us to simulate various pressure regimes from 0.3-1 bar. Aouda.X has been tested in several laboratory and field settings, including sterile sampling at 2800 m altitude inside a glacial ice cave and a cryochamber at -110°C, and subsurface tests in connection with geophysical instrumentation relevant to astrobiology, including ground-penetrating radar, geoacoustics, and drilling. The communication subsystem allows for a direct interaction with remote science teams via telemetry from a mission control center. Aouda.X as such is a versatile experimental platform for studying Mars exploration activities in a high-fidelity Mars analog environment with a focus on astrobiology and operations research that has been optimized to reduce the amount of biological cross contamination. We report on the performance envelope of the Aouda.X system and its operational limitations. 相似文献
57.
Christian Cochand 《航空制造技术》2005,(6):110
机床制造者在制造机器时,总离不开一个极敏感的因素,即定位精度。在考虑整个实体的精度时,它是一个复杂的问题,涉及各个工作轴和参考点距离等问题。为了用激光检测加工中心的真实定位精度和重复精度,DIXI公司生产了DHP80系列和最新坐标镗加工中心JIG1200。按照VDI3441标准,实现恒温控制,机床无论是空载还是加工状态,都要有效地达到双向测量定位精度小于或等于3μm,在整个加工区域1m3的范围内均可达到精度要求,即实体精度。下面通过所采用的方法来证明这个精度的真实性。误差的放大。首先,应注意机床上可能安放几个测量位置,如果测量点… 相似文献
58.
Christian Vocks 《Space Science Reviews》2012,172(1-4):303-314
Kinetic models are necessary to describe the physical processes associated with non-Maxwellian velocity distribution functions (VDFs) of electrons or ions in the solar corona and wind. It is shown that pitch-angle scattering of electrons in the solar wind needs to be considered in kinetic solar wind models. Coulomb collisions are not efficient enough to provide this scattering, but resonant interaction with whistler waves is. A solar wind model for undisturbed fast wind is presented, and the influence of scattering on flare electron propagation is investigated. Furthermore, it is found that resonant interaction of electrons with whistler waves is capable of producing suprathermal tails of electron distributions even under quiet conditions without flare activity. 相似文献
59.
Eliot Christian 《Space Policy》2005,21(2):274-109
The Group on Earth Observations was established to promote comprehensive, coordinated, and sustained Earth observations. Its mandate is to implement the Global Earth Observation System of Systems (GEOSS) in accord with the GEOSS 10-Year Implementation Plan and Reference Document. During the months over which the GEOSS Implementation Plan was developed, many issues surfaced and were addressed. This article discusses several of the more interesting or challenging of those issues—e.g. fitting in with existing organizations and securing stable funding—some of which have yet to be resolved fully as of this writing. Despite the relatively short period over which the Implementation Plan had to be developed, there is a good chance that the work undertaken will be influential for decades to come. 相似文献
60.
Christian Knuchel 《航空制造技术》2004,(1):100-101
在过去的几年里,米克朗公司不断为高速加工行业开发出性能优异的加工中心,并且成功地将其推向了市场。他们优质工作的新成果就是XSM 400U型机床。这台五轴联动超高速加工中心,在其所有的5个轴上都具有最高的动态特性,以及最短的过程控制时间。 相似文献