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排序方式: 共有318条查询结果,搜索用时 46 毫秒
291.
292.
Tetrahedral Robotics for Space Exploration 总被引:2,自引:0,他引:2
Curtis S. Brandt M. Bowers G. Brown G. Cheung C. Cooperider C. Desch M. Desch N. Dorband J. Gregory K. Lee K. Lunsford A. Minetto F. Truszkowski W. Wesenberg R. Vranish J. Abrahantes M. Clark P. Capon T. Weaker M. Watson R. Olivier P. Rilee M.L. 《Aerospace and Electronic Systems Magazine, IEEE》2007,22(6):22-30
A reconfigurable space filling robotic architecture has a wide range of possible applications. One of the more intriguing possibilities is mobility in very irregular and otherwise impassable terrain. NASA Goddard Space Flight Center is developing the third generation of its addressable reconfigurable technology (ART) tetrahedral robotics architecture. An ART-based variable geometry truss consisting of 12 tetrahedral elements made from 26 smart struts on a wireless network has been developed. The primary goal of this development is the demonstration of a new kind of robotic mobility that can provide access and articulation that complement existing capabilities. An initial set of gaits and other behaviors are being tested, and accommodations for payloads such as sensor and telemetry packages are being studied. Herein, we describe our experience with the ART tetrahedral robotics architecture and the improvements implemented in the third generation of this technology. Applications of these robots to space exploration and the tradeoffs involved with this architecture will be discussed. 相似文献
293.
应用多重网格MacCormack显式格式对不同矢量角下二元喷管的内部流动进行了模拟分析。计算时, 在细网格上采用了雷诺平均N-S方程与k-ε湍流模型方程;在粗网格上则采用Euler方程。数值计算给出了较清晰的流谱, 壁面压力分布的计算也与实验结果相吻合。通过计算结果分析了矢量喷管几何参数对流场的影响, 并对矢量喷管的推力特性进行了数值研究。 相似文献
294.
Jen King Jao Lee C.E. Ayasli S. 《IEEE transactions on aerospace and electronic systems》1999,35(2):614-626
Analysis of UHF synthetic aperture radar (SAR) images has revealed a spatially correlated phase structure over a resolved target such as a long wire or a large truck. This phase variation, approximated by a simple, range-dependent factor 4πr/λ, results in a line-shaped image spatial spectrum. Such image phase and spectral features can be exploited by coherent spatial filtering to improve target-to-clutter ratios of large targets and stationary target detectability in a strong clutter environment 相似文献
295.
The interaction between the input filter and the control loop of switching regulators often results in detrimental effects, such as loop instability, degradation of transient response, and audiosusceptibility, etc. The concept of pole-zero cancellation is employed to mitigate some of these detrimental effects and is implemented using a novel feedforward loop, in addition to existing feedback loops of a buck regulator. Experimental results are presented which show excellent correlation with theory. 相似文献
296.
V Andersen F Ballarini G Battistoni M Campanella M Carboni F Cerutti A Empl A Fassò A Ferrari E Gadioli M V Garzelli K Lee A Ottolenghi M Pelliccioni L S Pinsky J Ranft S Roesler P R Sala T L Wilson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(6):1302-1310
The FLUKA Monte Carlo transport code is widely used for fundamental research, radioprotection and dosimetry, hybrid nuclear energy system and cosmic ray calculations. The validity of its physical models has been benchmarked against a variety of experimental data over a wide range of energies, ranging from accelerator data to cosmic ray showers in the earth atmosphere. The code is presently undergoing several developments in order to better fit the needs of space applications. The generation of particle spectra according to up-to-date cosmic ray data as well as the effect of the solar and geomagnetic modulation have been implemented and already successfully applied to a variety of problems. The implementation of suitable models for heavy ion nuclear interactions has reached an operational stage. At medium/high energy FLUKA is using the DPMJET model. The major task of incorporating heavy ion interactions from a few GeV/n down to the threshold for inelastic collisions is also progressing and promising results have been obtained using a modified version of the RQMD-2.4 code. This interim solution is now fully operational, while waiting for the development of new models based on the FLUKA hadron-nucleus interaction code, a newly developed QMD code, and the implementation of the Boltzmann master equation theory for low energy ion interactions. 相似文献
297.
The function of the receiver in a binary digital communication system is to make a binary (?space?, ?mark? or ?"0?, ?1?) decision by comparing the signal values from the mark and space filters (or correlators) at known successive time intervals (?bit? or ?baud? time intervals). When the signal value out of the mark filter is greater than that out of the space filter, it is decided that mark or 1 is transmitted, and vice versa. It is of fundamental importance to know the exact instant of time at which the two filter outputs are to be compared. This is the problem of synchronization between the transmitter and the receiver. In this paper, we assume a system that is perfectly synchronized. In a practical system, the difference between the two filter outputs must differ from a threshold by some finite amount in order to cause the device to respond reliably. The examination of the effects of this dead zone (finite-width decision threshold) on digital transmission systems is of important practical interest. Its effects on binary differentially coherent phase-shift-keying, and m-level phase-shift-keying systems have been investigated previously. In this paper we consider its effects on binary coherent phase-shift-keying (CPSK), coherent orthogonal (CFSK), and noncoherent orthogonal (NCFSK) systems. The probability of bit error and the channel capacity of each system is obtained in terms of the dead zone threshold. 相似文献
298.
VEGA Balloon Science Team Lee S. Elson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1987,7(12):337-342
Instruments aboard the gondolas of the two VEGA balloons obtained in situ measurements of pressure, temperature, vertical velocity relative to the balloon, cloud particle backscatter, lightning and the ambient light level. Atmospheric motions at the balloon float altitudes were also determined from Earth-based tracking results. To illustrate the history of the balloon flights and to facilitate comparisons between some of the different observed quantities, measurements of pressure, temperature and backscatter are presented as time series for the entire lifetime of each balloon. Both long and short period variations have been detected. In addition, the environmental entropy encountered by each balloon will be discussed. 相似文献
299.
300.
Lee B. Holcomb Montemerlo Melvin D. 《Aerospace and Electronic Systems Magazine, IEEE》1987,2(4):19-26
This paper presents an overview of NASA's Automation and Robotics (A&R) technology development program, covering its history, objectives, organization and content. This program is being carried out by the Office of Aeronautics and Space Technology (OAST) which has the responsibility to provide long range, high risk aerospace technology. 相似文献