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81.
Yongqiang Qi Yingmin Jia 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
A new switching control algorithm under constant thrust is designed for the chaser fast flying around the target spacecraft along a specified fly-around trajectory. The switching control laws are obtained based on the acceleration sequences and the on time of thrusters which can be computed by the time series analysis method. The perturbations and fuel consumptions are addressed during the computation of the on time of thrusters. Furthermore, the relative position parameters of the target spacecraft are obtained by using the vision measurement and the target fly-around positions are calculated through the isochronous interpolation method. The change of the relative position and the relative velocity of the chaser during the constant thrust fast fly-around are presented through simulation example. It is proved that, with the switching control laws, the chaser will fast fly around the target spacecraft along the specified fly-around trajectory. 相似文献
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对力反馈在航空中的应用进行综述,主要涉及无人机遥操作和飞行安全性两大领域。首先,为了解决无人机所捕获的图像信息在分辨率、动态范围、视野等方面的不足,力反馈技术逐渐被引入,并得到了初步应用。起初没有考虑地面控制站与无人机之间的通讯时延问题,力反馈与小波变量的结合能有效地解决时延问题,但操纵负荷仍然很大,继而力刚度反馈技术被提出。其次,飞机执行器速率的限制易导致飞行员诱发的震荡危及飞行安全,为了有效地抑制这类震荡,智能提示和智能增益技术被提出。通过上述的分析和探讨,说明力反馈技术在航空中的研究与应用具有重要的意义。 相似文献
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光学基片表面软质抛光胶体粒子的激光清洗 总被引:1,自引:0,他引:1
介绍了光学基片表面软质抛光胶体粒子激光清洗的基本方法、原理和实验装置,并通过对含有污染微粒的基片表面进行激光清洗,获得了高洁净表面的光学基片. 相似文献
86.
Qile Zhao Jing Guo Zhigang Hu Chuang Shi Jingnan Liu Hua Cai Xianglin Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The GRACE (Gravity Recovery And Climate Experiment) monthly gravity models have been independently produced and published by several research institutions, such as Center for Space Research (CSR), GeoForschungsZentrum (GFZ), Jet Propulsion Laboratory (JPL), Centre National d’Etudes Spatiales (CNES) and Delft Institute of Earth Observation and Space Systems (DEOS). According to their processing standards, above institutions use the traditional variational approach except that the DEOS exploits the acceleration approach. The background force models employed are rather similar. The produced gravity field models generally agree with one another in the spatial pattern. However, there are some discrepancies in the gravity signal amplitude between solutions produced by different institutions. In particular, 10%–30% signal amplitude differences in some river basins can be observed. In this paper, we implemented a variant of the traditional variational approach and computed two sets of monthly gravity field solutions using the data from January 2005 to December 2006. The input data are K-band range-rates (KBRR) and kinematic orbits of GRACE satellites. The main difference in the production of our two types of models is how to deal with nuisance parameters. This type of parameters is necessary to absorb low-frequency errors in the data, which are mainly the aliasing and instrument errors. One way is to remove the nuisance parameters before estimating the geopotential coefficients, called NPARB approach in the paper. The other way is to estimate the nuisance parameters and geopotential coefficients simultaneously, called NPESS approach. These two types of solutions mainly differ in geopotential coefficients from degree 2 to 5. This can be explained by the fact that the nuisance parameters and the gravity field coefficients are highly correlated, particularly at low degrees. We compare these solutions with the official and published ones by means of spectral analysis. It is found that our solutions are, in general, consistent with others in the spatial pattern. The water storage variations of the Amazon, Chari and Ganges river basins have also been computed. The variations computed with the NPARB approach are closer to those produced by JPL and DEOS solutions, while the variations produced with the NPESS approach are in good agreement with those produced by the CSR and GFZ solutions. A simulation study is implemented with considering realistic noise and low-frequency error. The two approaches are used to recover the true model. The NPESS solution appears closer to the true one. Therefore we are inclined to estimate the nuisance parameters simultaneously with the geopential coefficients. 相似文献
87.
采用恒载荷拉伸实验技术,研究了镀锌30GrMnSiA锡螺栓干涉配合连接LY12-CZ铝合金构件在3.5%NaCal+0.5%H2O2溶液中的应力腐蚀开裂特性。结果表明,随干涉量的增加,应力腐蚀敏感性有所下降,基材与紧固件的电偶效应对应力腐蚀繁感性有重大影响。 相似文献
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89.
X. Wang J.K. Shi G.J. Wang G.A. Zherebtsov O.M. Pirog 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(4):556-561
Responses of low-latitude ionospheric critical frequency of F2 layer to geomagnetic activities in different seasons and under different levels of solar activity are investigated by analyzing the ionospheric foF2 data from DPS-4 Digisonde in Hainan Observatory during 2002–2005. The results are as follows: (1) the response of foF2 to geomagnetic activity in Hainan shows obvious diurnal variation except for the summer in low solar activity period. Generally, geomagnetic activity will cause foF2 to increase at daytime and decrease at nighttime. The intensity of response of foF2 is stronger at nighttime than that at daytime; (2) seasonal dependence of the response of foF2 to geomagnetic activity is very obvious. The negative ionospheric storm effect is the strongest in summer and the positive ionospheric storm effect is the strongest in winter; (3) the solar cycle has important effect on the response of foF2 to geomagnetic activity in Hainan. In high solar activity period, the diurnal variation of the response of foF2 is very pronounced in each season, and the strong ionospheric response can last several days. In low solar activity period, ionospheric response has very pronounced diurnal variation in winter only; (4) the local time of geomagnetic activities occurring also has important effect on the responses of foF2 in Hainan. Generally, geomagnetic activities occurred at nighttime can cause stronger and longer responses of foF2 in Hainan. 相似文献
90.