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701.
702.
Sensitivity analyses of satellite propulsion components with their thermal modelling 总被引:1,自引:0,他引:1
Cho Young Han Jae Ho You Kyun Ho Lee Hui Kyung Kim Sung Nam Lee 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Performing the sensitivity analyses of the contact conduction and the position of thermostat on the basis of the thermal model established, the study of thermal design is accomplished for the preparation of possible mechanical interface change of the satellite propulsion system depending on the satellite system design. A relatively simple thermal model is taken into consideration for the convenience of the analysis. A variety of the spacecraft bus voltages and the contact resistances are examined as well as the position of thermostat on propulsion components. As a consequence, even though the mechanical interface condition is changed on the same module, the successful thermal design could be achieved if we design the heater to have sufficiently large power with reference to the heritage value of contact resistance. Besides the reasonable performance on the thermal control is assured with the thermostat location errors, if the uncertainty in the position of thermostat is not quite large when assembling tank module. 相似文献
703.
Seung-Woo Lee Jeongrae Kim Myeong-Sook Jeong Young Jae Lee 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
A method for monitoring atomic clocks on board Global Navigation Satellites System (GNSS) satellites is described to address the issue of clock related signal integrity in safety–critical applications of GNSS. The carrier-phase time transfer is employed in the clock monitoring method which enables tight tracking of the satellite onboard clocks and thus improves detectability of clock anomalies. Detecting onboard clock anomalies requires the ability to monitor clocks in real time, and a Kalman filter can then be utilized to estimate the phase offsets between the satellite clocks and ground clocks. This study, using the difference between the measured and predicted phase offset as a test statistic, sets a threshold for clock anomalies based on the prediction interval approach. Finally the validity of the monitoring method is examined by processing a set of real GNSS data that includes two recent incidents of clock anomalies in GNSS satellites. 相似文献
704.
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706.
Hsuan Ren Qian Du Jing Wang Chein-I Chang Jensen J.O. Jensen J.L. 《IEEE transactions on aerospace and electronic systems》2006,42(4):1372-1385
Due to recent advances in hyperspectral imaging sensors many subtle unknown signal sources that cannot be resolved by multispectral sensors can be now uncovered for target detection, discrimination, and identification. Because the information about such sources is generally not available, automatic target recognition (ATR) presents a great challenge to hyperspectral image analysts. Many approaches developed for ATR are based on second-order statistics in the past years. This paper investigates ATR techniques using high order statistics. For ATR in hyperspectral imagery, most interesting targets usually occur with low probabilities and small population and they generally cannot be described by second-order statistics. Under such circumstances, using high-order statistics to perform target detection have been shown by experiments in this paper to be more effective than using second order statistics. In order to further address a challenging issue in determining the number of signal sources needed to be detected, a recently developed concept of virtual dimensionality (VD) is used to estimate this number. The experiments demonstrate that using high-order statistics-based techniques in conjunction with the VD to perform ATR are indeed very effective 相似文献
707.
Korea has participated in space development only since the 1990s. Despite its short history, Korea has been increasing its technological capabilities with the successful experience of several national projects. The Korean government established a long-term space development plan in 1996, which suggests a clear way forward for space development up to 2015. Space activities in Korea will grow continuously. The direction of future space activities will be decided by the national space development plan. This paper discusses Korea's past and present space activities and future development projects. 相似文献
708.
Jin Young Choi Dongkyoung Chwa 《IEEE transactions on aerospace and electronic systems》2006,42(2):659-669
An adaptive control against uncertainties in tail-controlled STT (skid-to-turn) missiles is presented. First, we derive an analytic uncertainty model from a parametric affine missile model developed by the authors. Based on this analytic model, an adaptive feedback linearizing control law accompanied by a sliding mode control law is proposed. We provide analyses of stability and output tracking performance of the overall adaptive missile system. The performance and validity of the proposed adaptive control scheme are demonstrated by simulation. 相似文献
709.
Efficiency improvements using predictive and adaptive methods over satellite channels with weather-induced impairments are presented. Scintillation and rain attenuation are the two dominant factors for signal fading over satellite-Earth paths at operating frequencies over 10 GHz. We develop statistical and spectral analyses of these processes, and obtain simple linear predictors for received signal attenuation using autoregressive (AR) models. For adaptation, we propose changing signal transmission power, modulation symbol size, and/or code rate as the state of the channel changes. In particular, we introduce a continuous power control and discrete rate control strategy. Quantitative analyses of power consumption and channel capacity indicate that there can be a substantial gain in performance with such adaptive schemes. 相似文献
710.
在装备论证过程中,由可靠性目标值合理确定门限值是在整个可靠性要求论证中,十分关键的部分。本文论述的是基于Duane模型,在装备目标值明确的前提下,利用综合评判法确定装备可靠性可能的增长潜力,科学、合理地确定门限值。 相似文献