An analysis of the flexibility modeling of a net for space debris removal

Operational spacecraft are facing a risk of collision with space debris objects. The net capturing method has been proposed to mitigate this risk on spacecraft. The mass-spring model is usually applied for net modeling by discretizing a cable into one or several mass-spring-damper elements in simulation. The absolute nodal coordinates formulation (ANCF) has also been applied to model the net, and this model is able to describe the flexibility of a net using less elements. However, the influence on the net behavior in simulation by the flexibility modeling of a net is not well understood and barely discussed. In this paper, flexibility models of a net are established based on the mass-spring model and the ANCF model,respectively. The influence on the net behavior by the flexibility modeling is, for the first time, analyzed via simulations. Two case studies of capturing a ball and a cube shaped targets are performed. It is found that the flexibility modeling has little influence on the net dynamics in simulation. Finally, the characteristics and benefits of the ANCF model are described and analyzed. A drawback of the ANCF model was found to be its inferior computational performance.     

Dynamic modeling and multi-stage integrated control method of ultra-quiet spacecraft

Space telescope ultrahigh precision pointing control requires the spacecraft platform to provide an ultra-quiet working environment. Vibration isolator rejection control and the multi-stage integrated control method is believed to be one of the best methods to improve the space telescope attitude control performance. In this paper, the fine dynamics model of multi-stage spacecraft systems is presented and the multi-stage integrated controller design techniques are provided. Effectiveness of the multi-stage integrated control approach is demonstrated by both the numerical simulation and experiment results. An integrated design and demonstrated experimental environment is developed for high-fidelity control performance assessment. The verification experiments for the space telescope attitude control and vibration control are carried out. The results show that the pointing accuracy and stability of the line-of-sight (LOS) for space telescope are improved at least one order by the multi-stage integrated control method.     

Analysis of spatiotemporal trajectories for stops along taxi paths

Stops along taxi trajectories, such as picking up and dropping off passengers, are spatially clustered and related to certain attributes of places where stops are made. To detect the hidden knowledge regarding these places, this article examines the semantics of massive taxi stops in a large city. Each taxi trajectory is modeled as a series of sequential semantic stops labeled by street names. All the trajectories can be examined as a document corpus, from which the hidden themes of the stops are identified through Latent Dirichlet Allocation model. Conventional GIS tools are coupled with topic modeling toolkit to visualize and analyze potential information of stop topics for understanding intra-city dynamics. The effectiveness of this approach is illustrated by a case study using a large dataset of taxi trajectories including approximately 4,000 taxis in Wuhan, China.     

影响环形微阴极电弧推力器寿命的因素研究

为了研究影响环形微阴极电弧推力器寿命的因素，首先分析了可能的因素，接着通过试验研究了电流参数对阴阳极间电阻的影响，不同功率下的推力器热性能以及功率大小对绝缘体腐蚀的影响。试验结果表明，为了延长推力器的寿命，需要控制推力器较大的放电电流，使得阴阳极间电阻动态平衡，维持在0.5~10 kΩ；需要选择合适的放电功率，功率阈值应考虑各部件材料的高温承受能力；另外，绝缘体的腐蚀是制约推力器寿命的主要因素，降低放电功率有助于减缓该腐蚀。     

薄板光学反射面面形变形驱动器集成设计

针对某光学载荷薄板反射面面形调整需求,对一种新型精密微调驱动器开展了集成设计研究。分析了柔性太阳翼冷热交变对敏感载荷的影响,设计了一种基于巨磁致伸缩材料(GMM)的主动补偿驱动器,对驱动器关键部件进行了优化。建立了驱动器的动力学模型,并利用模糊自适应PID算法对其进行闭环控制。仿真结果表明:设计的驱动器能实现较大的行程、较高的定位精度,可用于面形变形补偿。     

Improvement and application of Y2O3 directional solidification crucible

In order to satisfy the drastic temperature change and high chemical activity in directional solidification of Nb–Si based alloys, Y_2O_3 crucible is demanded to possess high thermal shock resistance and erosion resistance. This paper improved the sintering degree and density of Y_2O_3 crucible by optimizing the sintering temperature and time, and its practical application performance was investigated. Y_2O_3 grains gathered with the increase of sintering temperature and time, and the contact area enlarged, resulting in the open pores being changed into closed pores.The higher density caused the improvement of erosion resistance of Y_2O_3 crucibles. However, excessive density weakened the thermal shock resistance. Considering high-temperature strength, erosion resistance, thermal shock resistance and costs, optimum sintering temperature and time of Y_2O_3 directional solidification crucible were 1800 °C and 120 min, respectively, and the porosity was20%. Improved Y_2O_3 crucible has been successfully applied to directional solidification of Nb–Si based alloys, and significantly reduced the oxygen contamination. Slight interaction occurred between Hf and Y_2O_3, but no obvious dissolution, penetration or erosion was found, showing good erosion resistance and thermal shock resistance.     

基于Markov的察打无人机数据链时延建模与补偿研究

为了改善在数据链时延情况下察打无人机的性能,对造成时延的因素及影响进行了分析,在此基础上对数据链时延进行了合理的假设和简化。并对无人机整个控制回路的各个节点的响应方式,提出了一种时间-事件-事件-时间驱动方式,使得无人机数据链的时延序列具有Markov性,同时给出了状态转移矩阵的求取方法。为了改善无人机的响应特性,采用最优控制的方法对时延进行了补偿,并基于某无人机平台验证了补偿方法的有效性。仿真结果表明,该方法的引入使得无人机的动态响应特性有了显著提高。     

针对多机型多基地执管结构下的航材布局优化研究

从航材备件保障效能出发,综合考虑多种因素,建立了一个航材保障体系的配置-调配模型,科学量化地确定配属和流动的平衡点,从而定量评价航材保障系统的效率,并通过部件实测结果证明了这个模型的有效性和实用价值.     

一类需求不确定闭环物流系统的模糊规划模型与仿真

考虑了一类需求不确定闭环物流系统的运作过程。该系统由多个供应商、多个制造商、多个分销商和多个顾客组成,并且顾客的需求是不确定的。基于早期的研究结果,考虑正向物流和逆向物流的集成运作,采用模糊集描述需求的不确定性,建立了该系统的模糊规划模型并进行了仿真。仿真结果表明,虽然需求的波动会使系统的总成本较需求确定时的值有不同程度的增加,但决策者仍可以根据顾客需求的不确定性程度做出最佳决策方案。