Fixed-time adaptive model reference sliding mode control for an air-to-ground missile

This paper addresses the fixed-time adaptive model reference sliding mode control for an air-to-ground missile associated with large speed ranges, mismatched disturbances and un-modeled dynamics. Firstly, a sliding mode surface is developed by the tracking error of the state equation and the model reference state equation with respect to the air-to-ground missile. More specifically,a novel fixed-time adaptive reaching law is presented. Subsequently, the mismatched disturbances and the un-modeled dynamics are treated as the model errors of the state equation. These model errors are estimated by means of a fixed-time disturbance observer, and they are also utilized to compensate the proposed controller. Therefore, the fixed-time controller is obtained by an adaptive reaching law and a fixed-time disturbance observer. Closed-loop stability of the proposed controller is established. Finally, simulation results including Monte Carlo simulations, nonlinear six-DegreeOf-Freedom(6-DOF) simulations and different ranges are presented to demonstrate the efficacy of the proposed control scheme.     

小数偏差产品质量评估及固定性能分析

为了评估不同小数偏差产品的数据质量和模糊度固定效果，比较了2016年全年的SGG FCB产品和CNES产品，结果表明两种产品具有很高的一致性，SGG FCB产品的数据完整性更好。应用两种产品进行精密单点定位(PPP)固定解的静态结果平面位置精度可以达到1 cm以内，高程位置精度可以达到1~2 cm，采用两种产品获得的PPP模糊度固定率十分接近，动态模式下处理静态数据的位置结果可以达到平面2~3 cm，高程5 cm以内的精度，两组固定解的位置误差结果差异不超过5 mm，模糊度固定成功率分别为92.37%和92.14%，两种小数偏差产品在23分钟左右完成首次固定，能够有效提高PPP的收敛速度。使用两种小数偏差产品得到的机载动态数据结果也非常相近。     

Single photon laser altimeter simulator and statistical signal processing

Spaceborne altimeters are common instruments onboard the deep space rendezvous spacecrafts. They provide range and topographic measurements critical in spacecraft navigation. Simultaneously, the receiver part may be utilized for Earth-to-satellite link, one way time transfer, and precise optical radiometry. The main advantage of single photon counting approach is the ability of processing signals with very low signal-to-noise ratio eliminating the need of large telescopes and high power laser source. Extremely small, rugged and compact microchip lasers can be employed. The major limiting factor, on the other hand, is the acquisition time needed to gather sufficient volume of data in repetitive measurements in order to process and evaluate the data appropriately. Statistical signal processing is adopted to detect signals with average strength much lower than one photon per measurement. A comprehensive simulator design and range signal processing algorithm are presented to identify a mission specific altimeter configuration. Typical mission scenarios (celestial body surface landing and topographical mapping) are simulated and evaluated. The high interest and promising single photon altimeter applications are low-orbit (∼10 km) and low-radial velocity (several m/s) topographical mapping (asteroids, Phobos and Deimos) and landing altimetry (∼10 km) where range evaluation repetition rates of ∼100 Hz and 0.1 m precision may be achieved. Moon landing and asteroid Itokawa topographical mapping scenario simulations are discussed in more detail.     

Spiking-free HGO-based DSC for flexible joint manipulator

The tracking control problem for Flexible Joint Manipulator Control System(FJMCS)with unmeasurable states is addressed in this paper. Firstly, a High-Gain Observer(HGO) is constructed to estimate the unmeasurable states and the uncertainties. Then, a Dynamic Surface Control(DSC) scheme is developed by using the estimation of HGO. The newly proposed controller has two advantages over the existing methods:(A) a novel Spike Suppression Function(SSF) is developed to avoid the estimation spike proble...     

卫星变轨初探

为了推算卫星变轨时刻和研究变轨过程中轨道变化规律,在仿真计算检验方案可行性的基础上,对有实际背景的某类卫星变轨进行了计算,大致复现了整个变轨过程。仿真和实例结果可为研究非合作目标的卫星轨道改变和变轨后再次捕获提供相关信息和参考依据。     

一类有限时间观测器设计及其在飞控系统中的应用

文章针对强可观系统提出了一种有限时间全阶未知输入观测器(Unknown Input Observer,UIO)。首先,设计2个独立的全阶UIO,其特征值满足一定的要求;其次,合并这2个观测器得到新的有限时间观测器,并且能够在预先设定的时间内准确估计出系统状态和未知输入,并借助超螺旋微分器重构了未知输入;最后,用一个飞控系统例子诠释了算法的有效性。     

Validation of space-born Moderate Resolution Imaging Spectroradiometer remote sensors aerosol products using application of ground-based Multi-wavelength Radiometer

The measurements of aerosol optical properties were carried out during April 2006 to March 2011 over Mohal (31.9°N, 77.12°E) in the northwestern Indian Himalaya, using the application of ground-based Multi-wavelength Radiometer (MWR) and space-born Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensors. The average (±standard deviation) values of aerosol optical depth (AOD) at 500 nm, Ångström exponent and turbidity coefficient during the entire measurement period were 0.25 ± 0.09, 1.15 ± 0.42 and 0.12 ± 0.06 respectively. About 86% AOD values retrieved from MODIS remote sensor were found within an uncertainty limit (Δτ_pλ = ±0.05 ± 0.15τ_pλ). In general, the MWR derived AOD values were higher than that of MODIS retrieval with absolute difference ∼0.02. During the entire period of measurement space-born MODIS remote sensor and ground-based MWR observation showed good correspondence with significant correlation coefficient ∼0.78 and root mean square difference ∼0.06. For daily observations the relative difference between these two estimates stood less than 9%. However, satellite-based and ground-based observation showed good correspondence, but further efforts still needed to eliminate systematic errors in the existing MODIS algorithm.     

新型快速Terminal滑模及其在近空间飞行器上的应用

为加快Terminal滑模收敛速度,并避免控制器奇异,首先分析了Terminal滑模产生奇异的原因,基于李代数给出Terminal滑模控制器非奇异判据.然后,设计了两种新型非奇异快速Terminal滑模,其收敛速度在任意点均快于现有标准快速Terminal滑模;给出了收敛时间公式.将新型快速Terminal滑模与动态滑...     

基于神经网络干扰观测器的柔性航天器姿态稳定控制

本文针对柔性航天器在惯性参数未知、外界干扰、输入饱和等复杂条件下的姿态控制问题,提出了1种基于神经网络干扰观测器的柔性航天器姿态稳定控制方法。首先,基于包含压电振动抑制输入的柔性航天器姿态动力学模型,构建了包含外界干扰、惯性参数不确定性的综合扰动项;其次,基于RBF神经网络设计干扰观测器与自适应参数调节律实时地估计综合扰动;再次,设计了1种固定时间收敛且有限时间稳定的非线性滑模控制器,并通过Lyapunov理论进行了稳定性分析;最后,利用航天器闭环姿态动力学系统进行数值仿真。结果表明:所设计的基于神经网络干扰观测器的控制方法可以有效实现航天器的姿态稳定、振动抑制与干扰估计,从而顺利完成航天器的高精高稳控制任务。     

导弹敏捷转弯段的新型非奇异终端滑模控制

针对具有快时变性、不确定性、强非线性和系统初始状态远离平衡点等特点的敏捷导弹的直接力/气动力复合控制律设计问题,提出了一种新型非奇异终端滑模控制方法。为缩短到达平衡态的时间,设计了一种组合非奇异终端滑模面,提高了系统状态在滑模面上的收敛速度,设计了改进的变系数双幂次趋近律,提高了系统状态到达滑模面的速度,并利用扩张状态观测器实时估计系统内外扰动,消除了观测误差对系统造成的干扰,抑制了抖振。最后,证明了所提方法的有限时间收敛特性,通过仿真对比校验了所提方法的有效性。