箔条质心干扰中的发射和机动决策仿真研究

针对反舰导弹的来袭方位、作战海域的海况,如何确定干扰弹的发射方案和舰艇的规避机动方案是箔条质心干扰战术运用需要解决的关键问题。采用动态仿真的方法,分析了箔条质心干扰的效果与反舰导弹威胁方向、干扰弹发射舷角、舰艇规避机动方向、作战海域的风速风向等要素的关系,得出了质心干扰时干扰弹发射和舰艇机动的一些原则。     

星载SAR的多普勒中心频率估计的新探索

本文对几种经典的多普勒中心频率估计算法的从滤波的角度加以分析，分析了符号相关算法的实质，并提出一种了简单适用的非线性滤波方法，对雷达回波方位功率谱周期图进行平滑，在满足成象要求下，可以快速估计出多普勒中心频率。     

Cost Engineering – The new paradigm for space launch vehicle design

The paper describes the basic definition and application of 'Cost Engineering' which means to design a vehicle system for minimum development cost and/or for minimum operations cost. This is important now and for the future since space transportation has become primarily a commercial business in contrast to the past where it has been mainly a subject of military power and national prestige. Several examples are presented for minimum-cost space launch vehicle configurations, such as increasing vehicle size and/or the use of less efficient rocket engines in order to reduce development and operations cost. Further a cost comparison is presented on single-stage (SSTO)-vehicles vs. two-stage launchers which shows that SSTOs have lower development and operations cost although they are larger, respectively have a higher lift-off mass than two-stage vehicles with the same performance. The design of a space tourism-dedicated launch vehicle is an extreme challenge for a cost-engineered vehicle design in order to achieve cost per seat not higher than $50,000. Finally an outlook is presented on the different options for manned Earth-to-Moon transportation modes and vehicles – another most important application of 'cost engineering', taking into account the large cost of such a future venture.     

Fault-tolerant control with mixed aerodynamic surfaces and RCS jets for hypersonic reentry vehicles

This paper proposes a fault-tolerant strategy for hypersonic reentry vehicles with mixed aerodynamic surfaces and reaction control systems (RCS) under external disturbances and subject to actuator faults. Aerodynamic surfaces are treated as the primary actuator in normal situations, and they are driven by a continuous quadratic programming (QP) allocator to generate torque com-manded by a nonlinear adaptive feedback control law. When aerodynamic surfaces encounter faults, they may not be able to provide sufficient torque as commanded, and RCS jets are activated to augment the aerodynamic surfaces to compensate for insufficient torque. Partial loss of effective-ness and stuck faults are considered in this paper, and observers are designed to detect and identify the faults. Based on the fault identification results, an RCS control allocator using integer linear programming (ILP) techniques is designed to determine the optimal combination of activated RCS jets. By treating the RCS control allocator as a quantization element, closed-loop stability with both continuous and quantized inputs is analyzed. Simulation results verify the effectiveness of the proposed method.     

Real-time trajectory planning for UCAV air-to-surface attack using inverse dynamics optimization method and receding horizon control

This paper presents a computationally efficient real-time trajectory planning framework for typical unmanned combat aerial vehicle (UCAV) performing autonomous air-to-surface (A/S) attack. It combines the benefits of inverse dynamics optimization method and receding horizon optimal control technique. Firstly, the ground attack trajectory planning problem is mathematically formulated as a receding horizon optimal control problem (RHC-OCP). In particular, an approximate elliptic launch acceptable region (LAR) model is proposed to model the critical weapon delivery constraints. Secondly, a planning algorithm based on inverse dynamics optimization, which has high computational efficiency and good convergence properties, is developed to solve the RHCOCP in real-time. Thirdly, in order to improve robustness and adaptivity in a dynamic and uncer- tain environment, a two-degree-of-freedom (2-DOF) receding horizon control architecture is introduced and a regular real-time update strategy is proposed as well, and the real-time feedback can be achieved and the not-converged situations can be handled. Finally, numerical simulations demon- strate the efficiency of this framework, and the results also show that the presented technique is well suited for real-time implementation in dynamic and uncertain environment.     

Star visibility and tracking from the Space Station

Purpose of the present study is to provide algorithms for and examples of how to simulate star visibility and tracking by a Telescope attached to the main truss of the International Space Station (ISS).     

Friction Stir Welding of Metal Matrix Composites for use in aerospace structures

Friction Stir Welding (FSW) is a relatively nascent solid state joining technique developed at The Welding Institute (TWI) in 1991. The process was first used at NASA to weld the super lightweight external tank for the Space Shuttle. Today FSW is used to join structural components of the Delta IV, Atlas V, and Falcon IX rockets as well as the Orion Crew Exploration Vehicle. A current focus of FSW research is to extend the process to new materials which are difficult to weld using conventional fusion techniques. Metal Matrix Composites (MMCs) consist of a metal alloy reinforced with ceramics and have a very high strength to weight ratio, a property which makes them attractive for use in aerospace and defense applications. MMCs have found use in the space shuttle orbiter's structural tubing, the Hubble Space Telescope's antenna mast, control surfaces and propulsion systems for aircraft, and tank armors. The size of MMC components is severely limited by difficulties encountered in joining these materials using fusion welding. Melting of the material results in formation of an undesirable phase (formed when molten Aluminum reacts with the reinforcement) which leaves a strength depleted region along the joint line. Since FSW occurs below the melting point of the workpiece material, this deleterious phase is absent in FSW-ed MMC joints. FSW of MMCs is, however, plagued by rapid wear of the welding tool, a consequence of the large discrepancy in hardness between the steel tool and the reinforcement material. This work characterizes the effect of process parameters (spindle speed, traverse rate, and length of joint) on the wear process. Based on the results of these experiments, a phenomenological model of the wear process was constructed based on the rotating plug model for FSW. The effectiveness of harder tool materials (such as Tungsten Carbide, high speed steel, and tools with diamond coatings) to combat abrasive wear is explored. In-process force, torque, and vibration signals are analyzed to assess the feasibility of on-line monitoring of tool shape changes as a result of wear (an advancement which would eliminate the need for off-line evaluation of tool condition during joining). Monitoring, controlling, and reducing tool wear in FSW of MMCs is essential to the implementation of these materials in structures (such as launch vehicles) where they would be of maximum benefit.     

带弹性元件扑翼机构的动力学分析及实验

为研究扑翼飞行器传动机构的能量特性，以特拉华大学机械系统实验室所研制样机为原型进行了建模。引入气动项和拉力弹簧建立了完整的动力学模型。分析发现，气动项的力矩峰值为惯性项的4.8倍，对电机的转矩峰值的影响起主要作用。运用正交法进行仿真发现，引入拉力弹簧可以使电机转矩峰值最大降低77.5%，与理论分析相符合。进一步的物理实验验证了理论分析和仿真结果的正确性，并得到了当弹簧的连接点位置为185 mm、原长为200 mm及刚度为0.1 N/mm时实验结果取得最优值，可为扑翼机传动机构的优化设计提供依据。此外，引入弹性元件也可有效降低电机的转速波动，进而为仿生扑翼飞行器的生产和实践应用提供理论指导。     

A parameterized geometry design method for inward turning inlet compatible waverider

Intensive studies have been carried out on generations of waverider geometry and hypersonic inlet geometry. However, integration efforts of waverider and related air-intake system are restricted majorly around the X43A-like or conical flow field induced configuration, which adopts mainly the two-dimensional air-breathing technology and limits the judicious visions of developing new aerodynamic profiles for hypersonic designers. A novel design approach for integrating the inward turning inlet with the traditional parameterized waverider is proposed. The proposed method is an alternative means to produce a compatible configuration by linking the off-the-shelf results on both traditional waverider techniques and inward turning inlet techniques. A series of geometry generations and optimization solutions is proposed to enhance the lift-to-drag ratio. A quantitative but efficient aerodynamic performance evaluation approach （the hypersonic flow panel method） with lower computational cost is employed to play the role of objective function for opti- mization purpose. The produced geometry compatibility with a computational fluid dynamics （CFD） solver is also verified for detailed flow field investigation. Optimization results and other numerical validations are obtained for the feasibility demonstration of the proposed method.     

A Detailed Analysis of the Operational Orbit of the Hipparcos Satellite

An analysis of the orbital evolution of the ESA's Hipparcos satellite is presented. Hipparcos operated between August 1989 and March 1993 in a highly elliptical orbit: a geostationary transfer orbit with increased perigee height. The requirements of the scientific mission included high accuracy knowledge of the position and velocity vectors of the spacecraft as a function of time. Through a study of the variations in the total orbital energy, the loss of energy during the mission as a result of non-conservative forces is recovered. These are explained as largely due to atmospheric drag during perigee passages. Apparent variations in the drag coefficient are in agreement with orientation variations of the satellite during those perigee passages. Two different models used for calculating the atmospheric drag give significantly different results, confirming earlier findings by other users of those models. This revised version was published online in August 2006 with corrections to the Cover Date.