Impact of covariance information of kinematic positions on orbit reconstruction and gravity field recovery

Gravity missions are equipped with onboard Global Positioning System (GPS) receivers for precise orbit determination (POD) and for the extraction of the long wavelength part of the Earth’s gravity field. As positions of low Earth orbiters (LEOs) may be determined from GPS measurements at each observation epoch by geometric means only, it is attractive to derive such kinematic positions in a first step and to use them in a second step as pseudo-observations for gravity field determination. The drawback of not directly using the original GPS measurements is, however, that kinematic positions are correlated due to the ambiguities in the GPS carrier phase observations, which in principle requires covariance information be taken into account. We use GRACE data to show that dynamic or reduced-dynamic orbit parameters are not optimally reconstructed from kinematic positions when only taking epoch-wise covariance information into account, but that essentially the same orbit quality can be achieved as when directly using the GPS measurements, if correlations in time are taken into account over sufficiently long intervals. For orbit reconstruction covariances have to be considered up to one revolution period to avoid ambiguity-induced variations of kinematic positions being erroneously interpreted as orbital variations. For gravity field recovery the advantage is, however, not very pronounced.     

直升机低速飞行特性与意外右偏航

根据国外有关参考资料，对直升机丧尾桨推力导致意想不右偏航进行了讨论分析，简单介绍了直升机飞行时的四种飞行特性，（风标稳定性、尾桨涡环状态、主旋翼桨盘旋涡影响，丧失前飞升力）在意外右偏航中的作用和特点，以及改出方法和实施改出的应急措施，为飞行人员保证飞行安全提供了参考依据。     

用DFT计算立方氮化硼的状态方程及体积模量

立方氮化硼的高硬度起因于硼原子和氮原子形成的B-N sp3键很强。为获得对B-Nsp3键的定量认识,用DFT计算了它在常压到百万大气压(0-100GPa)范围内的状态方程(EOS)及体积模量。采用保模赝势模拟硼原子和氮原子,分别根据GGA、LDA进行相关计算。计算结果表明,立方氮化硼的体积模量B0为372.8±2.2GPa~395.8±0.2GPa,GGA对B-N sp3键的计算偏弱。     

导弹复合控制系统的模糊逻辑控制分配

针对空空导弹复合控制系统中的控制分配问题,提出了一种模糊逻辑控制分配算法。采用动态面控制方法设计了复合控制量的控制律。在设计过程中,利用扩张状态观测器估计汇总不确定项,并采用光滑二阶滑模控制算法设计了控制律,达到了提高鲁棒性和削弱抖振现象的目的。应用模糊逻辑控制分配算法将复合控制量分解为直接力控制指令和舵偏角控制指令。为了检验所设计的复合控制系统的控制效果,对采用基于模糊逻辑控制分配算法的复合控制系统和传统的气动力控制系统进行了对比仿真实验。仿真结果表明,所设计的复合控制系统具有更好的控制效果。     

ESO-based event-triggered attitude control of spacecraft with unknown actuator faults

An event-triggered control strategy based on extended state observer (ESO) is proposed for the attitude tracking problem of small plug-and-play spacecraft with uncertain inertia parameters, external disturbances, and actuator faults. A simplified controller is developed based on the angular velocity and the general disturbances estimated by the provided ESO using the information of the system inputs and the angular velocities. In the designed event-triggered sampling mechanism, a state-dependent event-triggered strategy determines the triggering instant of the controller to reduce the frequency of information transmission between the controller and the actuator. In comparison with the previous literature, this paper considers uncertain inertia parameters, external disturbances, and actuator faults as general disturbances estimated by ESO, especially for the actuator faults. The inputs of ESO are the error of the angular velocities, which can simplify the controller design. Moreover, the designed ESO can effectively attenuate the influence of measured noises generated by the gyroscopes. The proposed event-triggered policy balances the performance of event-triggering and the control stability performance, which reduces the final state convergence regions without increasing more triggering times compared to existing studies. Furthermore, the investigated policy achieves Zeno-free triggering. Numerical simulations verify theoretical results.     

一种基于链路状态的舱内环境自适应干扰消除算法

针对舱内无线光传输系统多种干扰问题,比如多径损耗和突发干扰等,提出一种基于链路状态的自适应干扰消除技术,该方法分析舱内链路状态,完成链路状态估计,采用环境自适应的变遗忘因子RLS（recursive least squares）算法,针对不同链路状态采取差异化的干扰消除策略,以提高舱内通信质量。仿真结果表明：该算法在尽力避免增加算法复杂度的条件下,相对于传统固定遗忘因子算法,在平稳状态下优先保证传输的误码性能,在链路状态变化时具有更好的收敛性能,灵活适应了舱内多种传输情况。     

基于实验室定标和均匀景统计的相对辐射定标方法

提出了一种基于实验室定标和均匀景统计的定标方法,并应用于CBERS-02卫星遥感图像相对辐射校正。首先分析宽视场成像仪(Wide Field Imager,WFI)实验室基础定标系数;然后结合均匀景的定标方法,生成一组新的相对辐射定标系数;最后评价WFI图像相对辐射校正的效果。结果表明:文章提出的定标方法有效,可以较好地解决宽幅遥感图像辐射校正问题,同时为遥感卫星相对辐射校正提供了一种新的途径。     

高阶带谐摄动下卫星相对运动精确动力学模型

在考虑J 2 项摄动的卫星相对运动精确动力学模型基础上,推导了可以精确到任意阶带谐非球形引力摄动的卫星相对运动精确动力学模型,还给出了一组简洁的基于参考卫星轨道要素（Reference Satellite Variables）的微分方程,能够描述精确到任意阶带谐非球形引力的卫星地球轨道运动。由于在模型推导过程中没有引入任何简化,新推导的结果适用于任意偏心率的地球轨道。