Scientific objectives and payloads of Tianwen-1, China’s first Mars exploration mission

This paper describes the scientific objectives and payloads of Tianwen-1, China’s first exploration mission to Mars. An orbiter, carrying a lander and a rover, lifted-off in July 2020 for a journey to Mars where it should arrive in February 2021. A suite of 13 scientific payloads, for in-situ and remote sensing, autonomously commanded by integrated payload controllers and mounted on the orbiter and the rover will study the magnetosphere and ionosphere of Mars and the relation with the solar wind, the atmosphere, surface and subsurface of the planet, looking at the topography, composition and structure and in particular for subsurface ice. The mission will also investigate Mars climate history. It is expected that Tianwen-1 will contribute significantly to advance our scientific knowledge of Mars.     

宽带高集成多级射频互连技术

针对微波电路三维集成结构的迫切需求,开展宽带高集成多级射频互连技术研究。主要设计了两种电路结构,多级水平互连电路与多级垂直互连电路。多级水平互连电路中,通过优化同轴-微带线的水平过渡以及倒角过渡方式,得到在DC～30GHz内的仿真结果,回波损耗优于21dB,插入损耗优于0.16dB;多级垂直互连电路中,通过优化BGA板间互连结构,得到在DC～30GHz内的仿真结果,信号的回波损耗优于13dB,插入损耗优于0.57dB。在小型化、高集成的需求下,宽带高集成多级射频互连技术是解决宽带射频信号传输问题的关键技术路径,可以广泛应用在微波电路三维集成结构中,具有重大的应用前景。     

A New D-GCL for Unidirectional Motion with Large Displacement

Numerical simulations of unsteady flow problems with moving boundaries commonly require the use of geometric conservation law(GCL).However,in cases of unidirectional large mesh deformation,the cumulative error caused by the discrete procedure in GCL can significantly increase,and a direct consequence is that the calculated cell volume may become negative.To control the cumulative error,a new discrete GCL(D-GCL)is proposed.Unlike the original D-GCL,the proposed method uses the control volume analytically evaluated according to the grid motion at the time level n,instead of using the calculated value from the D-GCL itself.Error analysis indicates that the truncation error of the numerical scheme is guaranteed to be the same order as that obtained from the original D-GCL,while the accumulated error is greatly reduced.For validation,two challenging large deformation cases including a rotating circular cylinder case and a descending GAW-(1)two-element airfoil case are selected to be investigated.Good agreements are found between the calculated results and some other literature data,demonstrating the feasibility of the proposed D-GCL for unidirectional motions with large displacements.     

Simulation analysis for effects of bone loss on acceleration tolerance of human lumbar vertebra

The purpose of the present study was to analyze and predict the changes in acceleration tolerance of human vertebra as a result of bone loss caused by long-term space flight. A human L3–L4 vertebra FEM model was constructed, in which the cancellous bone was separated, and surrounding ligaments were also taken into account. The simulation results demonstrated that bone loss has more of an effect on the acceleration tolerance in x-direction. The results serve to aid in the creation of new acceleration tolerance standards, ensuring astronauts return home safely after long-term space flight. This study shows that more attention should be focused on the bone degradation of crew members and to create new protective designs for space capsules in the future.     

Stability of relative equilibria of the full spacecraft dynamics around an asteroid with orbit–attitude coupling

The full dynamics of spacecraft around an asteroid, in which the spacecraft is considered as a rigid body and the gravitational orbit–attitude coupling is taken into account, is of great value and interest in the precise theories of the motion. The spectral stability of the classical relative equilibria of the full spacecraft dynamics around an asteroid is studied with the method of geometric mechanics. The stability conditions are given explicitly based on the characteristic equation of the linear system matrix. It is found that the linearized system decouples into two entirely independent subsystems, which correspond to the motions within and outside the equatorial plane of the asteroid respectively. The system parameters are divided into three groups that describe the traditional stationary orbit stability, the significance of the orbit–attitude coupling and the mass distribution of the spacecraft respectively. The spectral stability of the relative equilibria is investigated numerically with respect to the three groups of system parameters. The relations between the full spacecraft dynamics and the traditional spacecraft dynamics, as well as the effect of the orbit–attitude coupling, are assessed. We find that when the orbit–attitude coupling is strong, the mass distribution of the spacecraft dominates the stability of the relative equilibria; whereas when the orbit–attitude coupling is weak, both the mass distribution and the traditional stationary orbit stability have significant effects on the stability. We also give a criterion to determine whether the orbit–attitude coupling needs to be considered.     

基于流形结构重建的多目标气动优化算法

在多目标优化中，Pareto解集是一个分段连续的k维流形，这一规律被传统进化算法所忽略。本文提出了一种基于流形结构重建的多目标优化算法，首先利用流形结构重建方法完成解集分布从目标空间到设计空间的映射，建立解集的概率分布，并在目标空间中扩展流形结构，从而借助解集在目标空间的推进来指导优化算法的快速演化。数值算例表明本文算法对于具有不同特征的Pareto前沿具有很好的适应性，能够极大提高算法的收敛效率。多目标气动优化算例验证，本文算法相比于常规多目标进化算法能够减少约80%的计算量，极大程度缩短了气动设计的周期。     

SSPS-OMEGA超大型球形聚光器结构拓扑构型与设计

为同时兼顾千米量级尺度空间太阳能电站聚光系统的在轨发射安装难度、光学收集效率、稳定性及结构工艺等多方面的因素，提出采用基于球面正多面体的经纬线划分法模块化构建球形聚光器。该方法不仅可实现基础划分单元分布均匀、规格种类少，降低在轨构建与运载发射难度。而且只要合理控制弧高等分数和基础划分单元的口径就可以同时保证聚光系统的光学收集效率。理论与仿真结果显示，当弧高等分数为24时，该划分法共有25种基础单元件，整个球面被分成5762块。并且此时模块化构建的实际球形聚光器的光学收集效率与理想球面相比基本保持不变，解决了太阳能电站聚光系统设计中存在的关键问题。     

基于子阵级非周期的有限扫描阵列研究

对基于子阵级非周期的有限扫描阵列进行研究,采用数值仿真和遗传算法对基于不同子阵规模的非周期阵列进行优化设计,分析4?4和2?2两种子阵规模对接收多波束应用中伴随波束方向图的影响,研究表明子阵规模过大会引起伴随波束方向图的旁瓣抬升,通过减小子阵规模可以避免该问题,论证了设计的基于2?2子阵的非周期八角阵可应用于有限视场扫描相控阵中。     

涡扇发动机地面起动过程性能模拟

用积分方法建立了混合排气加力涡扇发动机起动过程模拟模型并用该模型进行了仿真计算,模型基于气动热力学方程、各部件特性以及经验关系式,根据给出的发动机起动过程初始条件、燃烧室供油规律等进行计算.为说明所建立的起动性能模型的模拟效果,将程序计算结果与试验结果进行了比较,结果表明该起动仿真模型能较准确地模拟混排加力涡扇发动机的地面起动过程.还分析了计算过程中对起动过程有比较大影响的因素,包括计算时间步长,起动机脱开转速,燃烧室总压恢复系数的经验系数,大气温度、压力以及海拔高度等.了解这些因素对起动过程及模拟结果的影响,便于通过修正的途径将该计算方法用于发动机地面起动性能的准确模拟.     

非对称偏差下质量特性值分布评价

传统的统计过程控制以公差中心为基准研究质量问题,对基本尺寸未给予足够重视,导致公差为非对称偏差时产品质量测度方法缺乏完善性.对此,以基本尺寸为基准,对非对称偏差下基于正态分布和切段正态分布假设的产品质量水平进行了分析,运用Taguchi质量损失函数对两类分布下产品价值的期望进行比较.结果表明,质量特性值服从切段正态分布的产品质量水平较优,产品价值的期望较高.