Multiple-constraint cooperative guidance based on two-stage sequential convex programming

An improved approach is presented in this paper to implement highly constrained cooperative guidance to attack a stationary target. The problem with time-varying Proportional Navigation (PN) gain is first formulated as a nonlinear optimal control problem, which is difficult to solve due to the existence of nonlinear kinematics and nonconvex constraints. After convexification treatments and discretization, the solution to the original problem can be approximately obtained by solving a sequence of Second-Order Cone Programming (SOCP) problems, which can be readily solved by state-of-the-art Interior-Point Methods (IPMs). To mitigate the sensibility of the algorithm on the user-provided initial profile, a Two-Stage Sequential Convex Programming (TSSCP) method is presented in detail. Furthermore, numerical simulations under different mission scenarios are conducted to show the superiority of the proposed method in solving the cooperative guidance problem. The research indicated that the TSSCP method is more tractable and reliable than the traditional methods and has great potential for real-time processing and on-board implementation.     

Hybrid method based on flame volume concept for lean blowout limits prediction of aero engine combustors

The Lean Blowout (LBO) limit is crucial for the aircraft engines. The semi-empirical (such as Lefebvre’s LBO model and Flame Volume (FV) model), numerical and hybrid methods are widely utilized for the LBO limit quick prediction. An innovative hybrid method based on the FV concept is proposed. This method can be classified as a semi-empirical/physical based hybrid prediction method. In this hybrid method, it is assumed that the flame volume varies nearly linearly with the fuel/air ratio near the LBO. The flame volume is obtained directly by the numerical simulation using the threshold value of the visible flame boundary as 900 K. Then the final LBO limits is determined by the FV model. On the premise of keeping the good generality of prediction, the hybrid method based on the FV concept can further improve the prediction accuracy. The comparison with the prediction of the existing available methods on fifteen combustors shows that the hybrid method based on the FV concept achieves better prediction accuracy. The prediction uncertainties between the experimental results and the predicted values by the hybrid method based on the FV concept are within about ±10%.     

Integrated cooperative guidance framework and cooperative guidance law for multi-missile

An integrated cooperative guidance framework for multi-missile cooperatively attacking a single stationary target is proposed in this paper by combining both the centralized and decentralized communication topologies. Once missiles are distributed into several groups, missiles within a single group communicate with the centralized leader-follower framework, while the leaders from different groups communicate using the nearest-neighbor topology. To implement the integrated cooperative guidance framework, a group of Finite-Time Cooperative Guidance (FTCG) laws considering the saturation constraint on FOV (FTCG-FOV) are firstly derived within the centralized leader-follower framework to satisfy the communication topology of missiles in a single group. Then, an improved sequential approach is developed to adapt the FTCG-FOV to satisfy the communication topology between groups. The numerical simulations demonstrate the effectiveness and high efficiency of the integrated cooperative guidance framework and the cooperative guidance laws, as well as the superiority of the developed sequential approach.     

GNSS global real-time augmentation positioning: Real-time precise satellite clock estimation,prototype system construction and performance analysis

Lots of ambiguities in un-differenced (UD) model lead to lower calculation efficiency, which isn’t appropriate for the high-frequency real-time GNSS clock estimation, like 1 Hz. Mixed differenced model fusing UD pseudo-range and epoch-differenced (ED) phase observations has been introduced into real-time clock estimation. In this contribution, we extend the mixed differenced model for realizing multi-GNSS real-time clock high-frequency updating and a rigorous comparison and analysis on same conditions are performed to achieve the best real-time clock estimation performance taking the efficiency, accuracy, consistency and reliability into consideration. Based on the multi-GNSS real-time data streams provided by multi-GNSS Experiment (MGEX) and Wuhan University, GPS + BeiDou + Galileo global real-time augmentation positioning prototype system is designed and constructed, including real-time precise orbit determination, real-time precise clock estimation, real-time Precise Point Positioning (RT-PPP) and real-time Standard Point Positioning (RT-SPP). The statistical analysis of the 6 h-predicted real-time orbits shows that the root mean square (RMS) in radial direction is about 1–5 cm for GPS, Beidou MEO and Galileo satellites and about 10 cm for Beidou GEO and IGSO satellites. Using the mixed differenced estimation model, the prototype system can realize high-efficient real-time satellite absolute clock estimation with no constant clock-bias and can be used for high-frequency augmentation message updating (such as 1 Hz). The real-time augmentation message signal-in-space ranging error (SISRE), a comprehensive accuracy of orbit and clock and effecting the users’ actual positioning performance, is introduced to evaluate and analyze the performance of GPS + BeiDou + Galileo global real-time augmentation positioning system. The statistical analysis of real-time augmentation message SISRE is about 4–7 cm for GPS, whlile 10 cm for Beidou IGSO/MEO, Galileo and about 30 cm for BeiDou GEO satellites. The real-time positioning results prove that the GPS + BeiDou + Galileo RT-PPP comparing to GPS-only can effectively accelerate convergence time by about 60%, improve the positioning accuracy by about 30% and obtain averaged RMS 4 cm in horizontal and 6 cm in vertical; additionally RT-SPP accuracy in the prototype system can realize positioning accuracy with about averaged RMS 1 m in horizontal and 1.5–2 m in vertical, which are improved by 60% and 70% to SPP based on broadcast ephemeris, respectively.     

Attitude control without angular velocity measurement for flexible satellites

In this paper, by using quaternion models, the problem of attitude control is investigated for a class of flexible satellites. Two control laws are presented for the considered flexible satellite models to guarantee convergence of the closed-loop systems without using angular velocity measurement. One is in the form of a partial state feedback for the case where the modal variable is available, and the other is in the form of an observer-based partial state feedback for the case where the modal variable cannot be measured. Finally, an example is employed to illustrate the effectiveness of the proposed control laws.     

基于LADRC的无人直升机轨迹跟踪

无人直升机轨迹控制系统是对多输入/多输出强耦合非线性系统进行解耦控制的系统。为解决无人直升机轨迹控制效果依赖于直升机物理参数的测量和辨识精度以及外部扰动大小问题,提出了一种基于线性自抗扰控制(LADRC)的多回路无人直升机轨迹控制系统。首先建立无人直升机X-Cell的飞行动力学模型,并引入风切变、大气紊流和突风模型以更加准确模拟真实飞行环境;然后对X-Cell进行配平计算以验证动力学模型和配平算法的准确性,并选取一组配平值作为轨迹控制仿真的初始状态和操纵量;随后根据被控量的动力学方程阶次选取对应的一阶和二阶LADRC基本控制器,并结合时间尺度原理,自内向外依次构建无人直升机的姿态、速度和位置控制回路,将三回路串联从而建立了无人直升机轨迹控制系统;而后进行了稳定性分析,特征根计算结果表明轨迹控制系统镇定了X-Cell开环系统不稳定的动态特性;最后将该控制系统应用于各种扰动下直升机轨迹跟踪仿真,结果表明本文无人直升机轨迹控制系统能很好地实现带爬升率的"8"字形轨迹跟踪,且相比于基于比例积分和微分(PID)控制的轨迹控制系统,该控制系统具有更优的鲁棒性和抗扰性。     

等离子体气动激励控制超声速边界层分离的实验研究

等离子体气动激励与超声速气流相互作用已成为高速流动控制领域的研究热点。激波与边界层相互作用现象广泛存在于超声速飞行器之中。本文进行了等离子体气动激励控制压缩角区和激波诱导边界层分离的实验,通过流场纹影显示和壁面静压测量,研究等离子体气动激励如何影响激波、激波如何影响边界层特性的科学问题。实验结果表明:施加毫秒量级表面电弧放电能够前移压缩角区的诱导斜激波,使分离区后移,分离区域增加,但激波强度减弱,流场总压增加;施加微秒量级表面电弧放电能够抑制激波诱导边界层分离,使分离区减小,流场总压减小。基于实验结果,认为毫秒量级表面电弧放电激励控制超声速气流的主要机理为放电过程的焦耳热效应;微秒量级表面电弧放电激励控制超声速气流的主要机理为焦耳热效应和冲击波效应共同作用。     

深空探测器自主技术发展现状与趋势简

 深空探测器距离地球远、所处环境复杂、苛刻,利用地面测控站进行深空探测器的遥测和遥控已经很难满足探测器控制的实时性和安全性要求。深空探测器自主技术即通过在探测器上构建一个智能自主管理软件系统,自主地进行工程任务与科学任务的规划调度、命令执行、星上状态的监测与故障时的系统重构,完成无人参与情况下的探测器长时间自主安全运行,自主技术已经逐渐成为深空探测领域未来发展的一项关键技术。本文首先分析了传统测控模式对深空探测的约束,回顾了深空探测器自主技术发展的现状,分析了实现深空探测器自主运行的关键技术,包括在轨自主管理系统设计技术、自主任务规划技术、自主导航与控制技术、自主故障处理技术和自主科学任务操作技术。然后结合深空探测工程实施和技术发展需求,提出未来深空探测器自主技术发展的趋势和重点。     

Optimal guidance of extended trajectory shaping

To control missile＇s miss distance as well as terminal impact angle, by involving the timeto-go-nth power in the cost function, an extended optimal guidance law against a constant maneuvering target or a stationary target is proposed using the linear quadratic optimal control theory.An extended trajectory shaping guidance（ETSG） law is then proposed under the assumption that the missile-target relative velocity is constant and the line of sight angle is small. For a lag-free ETSG system, closed-form solutions for the missile＇s acceleration command are derived by the method of Schwartz inequality and linear simulations are performed to verify the closed-form results. Normalized adjoint systems for miss distance and terminal impact angle error are presented independently for stationary targets and constant maneuvering targets, respectively. Detailed discussions about the terminal misses and impact angle errors induced by terminal impact angle constraint, initial heading error, seeker zero position errors and target maneuvering, are performed.     

The art and science of interstellar message composition: a report on international workshops to encourage multidisciplinary discussion

Throughout the history of the Search for Extraterrestrial Intelligence (SETI), there has been widespread recognition of the profound societal implications of detecting intelligence beyond Earth. At the SETI Institute, interstellar message construction serves as the focus of a multidisciplinary attempt to prepare for the cultural impact of signal detection and the critical events that would follow. Interstellar message construction at the SETI Institute builds upon the recommendations of the 1991–1992 Workshops on the Cultural Aspects of SETI, while also exploring opportunities for multidisciplinary contributions on new topics. Through a series of international workshops in Toulouse, Paris, Zagreb, Washington, and Bremen, the SETI Institute and partner organizations have fostered broad-based discussion about some of the most important decisions that would follow detection of extraterrestrial intelligence, including “should we reply?” and if so, “what should we say, and how might we say it?”. Several of the themes addressed at these workshops will be highlighted, including the relationship between art and science in designing messages, the value of interactive messages, and the importance of better understanding the nature of language.