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71.
In this paper we revisit the topic of how to formulate error terms for estimation problems that involve rotational state variables. We present a first-principles linearization approach that yields multiplicative error terms for unit-length quaternion representations of rotations, as well as for canonical rotation matrices. Quaternion algebra is employed throughout our derivations. We show the utility of our approach through two examples: (i) linearizing a sun sensor measurement error term, and (ii) weighted-least-squares point-cloud alignment. 相似文献
72.
Paul Brooks 《Acta Astronautica》2003,52(9-12):905-914
73.
The authors present proposals for establishing an international environmental resources satellite consortium. All countries share a need for data on the Earth and its resources, and economies of scale could be achieved through an international system. The formation of Inmarsat could serve as a model for setting up Envirosat. The role of Envirosat could expand as international confidence in it grows. 相似文献
74.
Paul S. Butterworth 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(9):177-184
In April 1972 OAO-2 obtained broadband filter measurements of the Galilean satellites from 2100 to 4300 Å. All four bodies were shown to have low albedos declining towards shorter wavelengths, thus constraining the proportions of their surfaces that could be covered by reflective frosts. Although the vast data return from Voyager spacecraft has for the first time permitted a detailed comparison of Galilean satellites with terrestrial planets, it has not removed the need for continuing long time-base observations of the former. Since January 1978, IUE has repeatedly obtained Galilean spectra within the range 1150 to 3200 Å. Observations of Io have placed an upper limit on the global abundance of SO2 in its atmosphere. Spectral variations with phase have allowed spatial mapping of surface reflectance in the case of Io, and may enable volcanic activity to be monitored. 相似文献
75.
Paul S. Wesson 《Space Science Reviews》1980,27(2):109-153
Cosmology as it is usually studied suffers from the problem that no criterion is known which isolates from the large class of models allowed by the equations of physics those few which are realized in Nature. To provide such a criterion, it is proposed that cosmology should be based on the study of models which are free of arbitrary scales or units, this condition being compatible with (but not identical with) the Cosmological Principle. Formally, the basis for scale-free cosmology can be expressed in a dimensional Conspiracy Hypothesis: The material parameters of a system (mass, density, pressure etc.), the constants of physics and the coordinates have realizable physical meanings only when they occur together in dimensionless combinations (-numbers) in which the components may vary with time or place but in such a manner that the variations conspire to keep the -numbers constant. The Conspiracy Hypothesis (CH) streamlines cosmology, simplifying it to the finding of a few dimensionless numbers. Applied to Einstein's general relativity, the CH yields a simple cosmological model consisting of static clusters of galaxies with inverse-square density profiles embedded in an expanding, homogeneous background. This model agrees well with the observed Universe insofar as the latter can be described by general relativity. The CH can also be applied to other theories of gravity, especially those in which the gravitational parameter G is variable, and can also in itself be taken as a basis for gravitational theory. 相似文献
76.
在北美,波音747-400运营商到海外进行机体的重维修似乎成为其唯一的选择。根据《航空周刊》5月1日的数据,美国有10家公司运营着125架波音747飞机,其中93架为波音747-400。在这些飞机中,有51架从事客运服务,主要由美联航和达美航空公司运营,其余42架用作货机。北美其他国家不运营波音747。 相似文献
77.
Gerda Horneck Angioletta Coradini Gerhard Haerendel May-Britt Kallenrode Paul Kamoun Jean Pierre Swings Alberto Tobias Jean-Jacques Tortora 《Space Policy》2010
As a result of increasing public and political interest in ‘space’ (i.e. solar system) exploration at the global scale, the Space Advisory Group of the European Commission has evaluated the situation in Europe with regard to its potential to participate in this ambitious global enterprise. Aspects of science, technology, environment and safety, society, spin-offs and international cooperation were all considered. The group concluded that Europe possesses sufficient key technologies and scientific expertise to play a major role in international space exploration and has recommended that the EU take a central role to ensure the success of future European space exploration, not only to give a clear political signal for the way forward but also to ensure an appropriate financial framework. In this way Europe would embrace the spirit of the European Space Policy and contribute to the knowledge-based society by investing significantly in space-based science and technology, thereby playing a strong role in international space exploration. 相似文献
78.
The objective of the 2009 Mars Science Laboratory (MSL), which is planned to follow the Mars Exploration Rovers and the Phoenix lander to the surface of Mars, is to explore and assess quantitatively a site on Mars as a potential habitat for present or past life. Specific goals include an assessment of the past or present biological potential of the target environment and a characterization of its geology and geochemistry. Included in the 10 investigations of the MSL rover is the Sample Analysis at Mars (SAM) instrument suite, which is designed to obtain trace organic measurements, measure water and other volatiles, and measure several light isotopes with experiment sequences designed for both atmospheric and solid-phase samples. SAM integrates a gas chromatograph, a mass spectrometer, and a tunable laser spectrometer supported by sample manipulation tools both within and external to the suite. The sub-part-per-billion sensitivity of the suite for trace species, particularly organic molecules, along with a mobile platform that will contain many kilograms of organic materials, presents a considerable challenge due to the potential for terrestrial contamination to mask the signal of martian organics. We describe the effort presently underway to understand and mitigate, wherever possible within the resource constraints of the mission, terrestrial contamination in MSL and SAM measurements. 相似文献
79.
应用多体动力学理论研究了一种新的辊轴型摩擦摆隔振系统。基于该系统的运动学规律,将其简化为一个单自由度多体系统。应用非惯性系中微分形式的质点系相对动能定理,推导出该系统的非线性运动微分方程。通过讨论与小角位移无阻尼情形对应的线性无阻尼自由振动微分方程,得到了相应的固有频率,与实验结果一致。直接求解该运动方程可有效准确地研究摩擦摆隔振系统的动力学行为,并给包含该系统的半主动控制的仿真和实现带来便利。 相似文献
80.