Guidance law with impact time and impact angle constraints

A novel closed-form guidance law with impact time and impact angle constraints is pro- posed for salvo attack of anti-ship missiles, which employs missile’s normal acceleration (not jerk) as the control command directly. Firstly, the impact time control problem is formulated as tracking the designated time-to-go (the difference between the designated impact time and the current flight time) for the actual time-to-go of missile, and the impact angle control problem is formulated as tracking the designated heading angle for the actual heading angle of missile. Secondly, a biased proportional navigation guidance (BPNG) law with designated heading angle constraint is constructed, and the actual time-to-go estimation for this BPNG is derived analytically by solving the system differential equations. Thirdly, by adding a feedback control to this constructed BPNG to eliminate the time-to-go errorthe difference between the standard time-to-go and the actual time-to-go, a guidance law with adjustable coefficients to control the impact time and impact angle simultaneously is developed. Finally, simulation results demonstrate the performance and feasibility of the proposed approach.     

Decision program on asteroid threat mitigation

The Association of Space Explorers Committee on Near-Earth Objects (NEOs) and its Panel on Asteroid Threat Mitigation have prepared a decision program to aid the international community in organizing a coordinated response to asteroid impact threats. The program is described in the ASE's report, Asteroid Threats: A Call for Global Response, which will be considered by the United Nations Committee on the Peaceful Uses of Outer Space in its 2009 sessions. The findings and recommendations of this report are presented here as well as some of the major implications of the complex decision-making involved in developing a coordinated international response to the challenge of protecting the Earth from NEO impacts.     

带末端攻击角约束连续有限时间稳定制导律

针对制导武器末端攻击角约束与末端弹道尽可能平直的要求,应用有限时间控制方法,设计了具有末端攻击角约束的连续有限时间稳定制导律,使闭环制导系统在有限时间内视线角速度收敛到零和视线角收敛到期望值。通过非线性控制系统的有限时间稳定齐次性理论对该制导律进行了分析,证明了闭环制导系统的视线角速度和视线角全局有限时间稳定特性,并基于有限时间Lyapunov稳定性理论给出了闭环制导系统有限停息时间的表达式。在实例应用仿真中,比较了该制导律与最优制导律的制导性能,检验了该制导律在不同作战任务下的制导效果。仿真结果证实了该制导律的有效性和鲁棒性。     

捕获目标后组合体航天器抗干扰自适应控制

针对空间机器人系统捕获非合作目标后由于质量特性参数和动量突变影响导致的组合体系统失稳问题,提出了一种基于系统动力学模型的抗干扰自适应控制方法。利用拉格朗日方法对系统进行动力学建模,通过冲击动力学建模分析得到了捕获目标后组合体系统的初始状态;基于系统动力学模型设计了线性反馈控制方法,考虑组合体质量特性参数不确定性以及外在干扰不确定性,对组合体系统动力学模型进行了不确定参数线性化,设计了参数自适应线性反馈控制方法;最后以平面三关节机械臂系统捕获旋转目标为例进行了仿真计算。组合体系统的运动状态量趋于期望值,速度级状态变量误差量级控制在10-4以下,位置级状态变量误差量级控制在10-3以下,说明该控制方法可以很好地保持捕获目标后组合体系统的稳定。     

Failure mechanisms of bolted flanges in aero-engine casings subjected to impact loading

In this paper, a failure evaluation criterion was proposed for the bolted casing-flange structure under impact loading. Subsequently, ballistic tests with eighteen bolted casing-flange structure specimens were conducted to validate the failure evaluation criterion. Parameter studies were then carried out using the validated FE models. Both the experimental and numerical results demonstrated the accuracy of the failure evaluation criterion. The failure evaluation criterion provided a quick and easy way to determine the failure mode of the casing connection area by using the materials and dimensions of the structure. Based on the failure evaluation criterion, designing the structural failure mode of the bolted casing-flange structure to be between flange failure and bolt failure can improve the impact resistance of the connection area of the aero-engine casings. This investigation revealed that the impact failure is not the unique criterion in evaluating the containment of the casing connection area, structural failure should also be involved in the evaluation criteria.     

Meteoroid bombardment as a source of the lunar exosphere

The column densities of impact-produced metal atoms in the exosphere during the peaks of activity of the main meteor showers – Geminids, Quadrantids and Perseids – and during quiet periods are estimated. The Na supply rate is estimated to be 2 × 10⁴, 3 × 10³, 10⁴, and 2 × 10⁴ atoms cm⁻² s⁻¹ for sporadic meteoroids, Perseid, Geminid, and Quadrantid meteor showers, respectively. A low upper limit on Ca in the lunar exosphere is explained by the condensation of Ca into dust grains during expansion of the cooling impact-produced vapor cloud. The chemical composition of gas-phase species released to the lunar exosphere during meteoroid impacts has been estimated. Most impact-produced molecules that contain metals are destroyed by solar photons while on ballistic trajectories. Energies of Na, K, Ca, and Mg atoms produced via photolysis of the respective monoxides are estimated to be 0.4, 0.35, 0.6, and 0.45 eV, respectively. The relative content of impact-produced Na and K atoms is maximal at altitudes of about 1000–2000 km and during the main meteor showers, lunar eclipses, and passages of the Moon through the Earth’s magnetosphere.     

带隔热层蜂窝夹层结构的超高速撞击特性研究

带隔热层的蜂窝夹层结构是航天器常用的结构材料。针对带隔热层蜂窝夹层结构开展了超高速撞击试验研究和数值模拟。通过试验获得了带隔热层蜂窝夹层结构的弹道极限方程,并利用该方程计算了带隔热层前板的等效厚度;同时采用光滑质点流体动力学(SPH)和有限元(FE)耦合的方法,对蜂窝夹层结构的超高速撞击过程进行了数值模拟,模拟结果表明:蜂窝芯限制了碎片云的径向膨胀,碎片云轴向流的导流和分流作用。     

Vectran织物复合材料冲击响应与失效模式分析

文章以Vectran纤维织物与涂覆低温硅胶的Vectran织物复合材料为研究对象,通过低速冲击实验研究了材料的冲击响应与破坏模式,分析了冲击速率、冲头尺寸与冲头形状对材料冲击特性的影响。实验结果表明:Vectran纤维织物冲击破坏模式主要为主纱线的拉伸破坏,以及冲头非接触区域纱线的弹塑性变形与滑移;涂覆硅胶的Vectran织物复合材料冲击破坏模式主要为纤维断裂和拔出;织物复合材料具有明显的应变速率效应。     

Debris area distribution of spacecraft under hypervelocity impact

Cross-sectional area is an important parameter for spacecraft breakup debris as it is the directly measured data in space observation. It is significant for observing and analysing the spacecraft breakup event to accurately modelling the area distribution of the breakup debris. In this paper, experimental study has been performed on debris area distribution characteristics of spacecraft under hypervelocity impact. The tests are carried out at the ballistic ranges of CARDC. Aluminium projectiles are launched to normally impact the simulated spacecrafts at about 3.0 km/s. The simulated spacecrafts are made up of aluminium plates, filled with some simulated electronics boxes, each of which was installed with a circuit board. “Soft-catch” devices are used to recover the breakup fragments. The test results show that: 1) the relationship between the cross-sectional area and the characteristic length of debris, which can be obtained in the logarithmic coordinates by linear fitting, represents the debris shape characteristic in a certain extent; 2) the area-to-mass ratios of fragments show normal distributions in the logarithmic coordinates; 3) debris made of different materials can be distinguished by different peaks on the distribution curves; 4) the area-to-mass ratio distributions can be expressed by a linear superimposition of several normal functions which represent the main materials of the spacecraft.     

两种命中误差指标之间关系的研究

针对两种命中误差指标在轴向偏差独立同分布情形下的关系进行了推导,并运用仿真试验进行验证,说明了推导的正确性。对独立非同分布以及非独立非同分布的一般情形进行了进一步的拟合分析,得到了两种命中误差指标关系的拟合多项式。