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.     

中国月球探测进展（2011-2020年）

回顾2011至2020年10年来中国月球探测的进展，重点介绍嫦娥三号和嫦娥四号任务工程实施情况以及取得的主要科学探测成果，展望中国月球和行星探测的未来发展.      

涡轮基组合循环发动机分布式控制系统通信网络混合拓扑结构优化方法

涡轮机组合循环(Turbine based combined cycle,TBCC)发动机控制系统通信网络拓扑结构是其分布式控制系统方案设计的重要部分,优化网络拓扑结构可提高发动机推重比和控制系统可靠性。本文基于智能优化算法提出TBCC分布式控制系统网络拓扑结构优化方法。基于图论建立TBCC几何模型和网格模型,以重量和可靠性为优化性能指标,同时考虑发动机表面高温区域以及控制节点的工作可靠性,分别采用粒子群算法和遗传算法优化星形结构中智能中央节点位置、中央节点的环形拓扑结构,获得星形-环形混合拓扑结构。仿真实例表明,基于本文方法优化所得的混合拓扑结构相较于星形集中式控制结构,系统重量降低了51.9%。     

PBT弹性体微相分离及对其力学性能的影响研究

为了获得微相分离对宽温PBT叠氮聚醚弹性体力学性能的影响规律,用红外光谱分析法(FT-IR)和动态热力学分析法(DMA)研究了PBT叠氮聚醚弹性体产生微相分离的机理和影响因素。用调节硬段含量、交联参数的方法调控其微相分离,控制适当的微相分离程度可显著改善推进剂的力学性能。研究结果表明:在二元醇扩链的弹性体体系中,当硬段含量约为15%时,弹性体发生相对最大比例的微相分离,体现出较佳的综合力学性能。通过微相分离的调控可获得宽温范围内综合力学性能较好的叠氮聚醚推进剂用粘合剂基体材料。     

Early analysis of precise orbit and clock offset determination for the satellites of the global BeiDou-3 system

Eight new-generation BeiDou satellites (BeiDou-3) have been launched into Medium Earth Orbit (MEO), allowing for global coverage since March 2018, and they are equipped with new hydrogen atomic clocks and updated rubidium clocks. Firstly, we analyzed the signals for the carrier-to-noise-density ratio (C/N0) and pseudorange multipath (MP) by using international GNSS (Global Navigation Satellite System) Monitoring and Assessment System (iGMAS) station data, and found that B1C has a lower C/N0, and B2a has the same level of C/N0 as the B1I and B3I signals. For pseudorange multipath, compared with the BeiDou-2 satellites, the obvious systematic variation of MP scatters related to the elevation angle is greatly improved for the BeiDou-3 and BeiDou-3e satellites signals. For the signals of the BeiDou-3 satellites, the order of the Root Mean Square (RMS) values of multipath and noise is B3I?<?B1I?<?B2a?<?B1C. Then, the comparison of the precise orbit determination and clock offset determination for the BeiDou-2, BeiDou-3, and BeiDou-3 experimental (BeiDou-3e) satellites was done by using 10 stations from iGMAS. The 3D precision of the 24?h orbit overlap is 24.55, 25.61, and 23.35?cm for the BeiDou-3, BeiDou-3e, and BeiDou-2 satellites, respectively. BeiDou-3 satellite has a comparable precision to that of the BeiDou-2 satellite. For the precision of clock offset estimation, the Standard Deviation (STD) of the BeiDou-3 MEO satellite is 0.350?ns, which is an improvement of 0.042?ns over that of the BeiDou-2 MEO satellite. The stabilities of the BeiDou-3 and BeiDou-3e onboard clocks are better than those of BeiDou-2 by factors of 2.84 and 1.61 at an averaging time of 1000 and 10,000?s, respectively.     

低温推进剂空间管理技术研究进展与展望

本文介绍了低温推进剂的性能优势与空间管理挑战，梳理了低温流体空间管理(CFM)技术特征及其研究现状，建议按照重力依赖型与重力无关型分类开展技术成熟度提升研究。调研了美国逾半个世纪的CFM技术搭载实验研究历程，分析了各类平台的工作特性与性能优势。基于我国航天发展现状与未来需求，探析了我国开展CFM技术攻关、飞行搭载实验的可行方案。建议在我国载人空间站规划舱内低温技术实验柜与舱外暴露平台实验模块，加速我国CFM技术向工程应用的转化。     

RTK model and positioning performance analysis using Galileo four-frequency observations

This paper proposes a real-time kinematic (RTK) model that uses one common reference satellite for the Galileo system with four frequency observations. In the proposed model, the double-differenced (DD) pseudorange and carrier phase biases among the different frequencies are estimated as unknown parameters to recover the integer features of the DD ambiguities among the different frequencies for ambiguity resolution and precise positioning. Analysis results show that the E5a, E5b, and E5 frequencies have virtually the same performance in terms of the positioning accuracy, observation residuals, and ratio values of ambiguity resolution. However, the E1 frequency performs worse than the E5a, E5b, and E5 frequencies. The RTK results for the combination of multiple frequencies are much better than those for a single-frequency observation, the coordinates’ standard deviation is improved about 20–30%, and the ambiguity fix time is improved about 10%.     

Interference torque of a three-floated gyroscope with gas-lubricated bearings subject to a sudden change of the specific force

A numerical study is carried out to investigate the influence of a sudden change of the specific force on a three-floated gyroscope with a rotor supported on gas-lubricated bearings.The interference torque is calculated to evaluate the influence by modeling the transient behavior of the rotor-bearing system. In combination with dynamic equations of the rotor displacement,the Reynolds equation is solved on the surface of spiral-grooved conical bearings. It is assumed that a steady state has been obtained with a constant specific force, and then the specific force is suddenly changed and maintained constant after that. Responses of the sudden change are obtained by solving the equations. Numerical results show that the direction of the sudden change of the specific force is the main factor which influences the interference torque curve. With a sudden change along the input direction, the interference torque fluctuation has a constant frequency and a decreasing amplitude. With a sudden change along the output direction, the interference torque fluctuates in a small range. With a sudden change along the spin direction, the change of the interference torque combines a fluctuation and a gradually-changing quasi-equilibrium value. This study provides a supplement to the steady-state error model of the three-floated gyroscope.     

全柔性空间机器人基于虚拟力的输出反馈有限维重复学习控制及振动抑制

探讨了基座、关节、臂均存在柔性情况下，空间机器人关节轨迹运动及多重柔性振动的主动控制和主动抑制问题.结合线性弹簧、扭转弹簧、简支梁及假设模态法，利用拉格朗日方程建立了基座、关节、臂全柔性影响下的空间机器人系统动力学模型，利用奇异摄动法，将模型分解为关节运动慢变子系统与关节柔性振动快变子系统.为控制慢变子系统中载体姿态、关节刚性运动并且抑制臂的柔性振动，依据虚拟控制力的概念，设计了基于有限维傅里叶级数解析周期信号的输出反馈重复学习算法.李雅普诺夫直接法证实了上述控制器的稳定性.为了抑制快变子系统中基座和关节的柔性振动，分别采用线性二次最优控制方法以及引入关节柔性补偿器间接增大关节等效刚度的方式，使控制算法不局限于求解弱非线性问题.系统数值仿真结果表明，所提出的控制器能够有效抑制机器人多重柔性构件的振动，实现对期望信号的高品质追踪.      

弹载变转速定量泵高动态压力控制特性分析

传统弹载电液伺服系统的液压能源采用有刷直流电机驱动恒压变量泵的方式，泵源压力在导弹飞行过程中设定值恒定，但在平飞段过程长、负载小，对能源压力需求低，造成弹上能源总利用率不高的问题，提出无刷直流电机驱动小排量液压泵的压力控制泵源的设计，在低气动负载阶段适当降低系统压力，进而降低节流损失与泄漏量，提高能量利用率。分析了变转速定量泵的流量压力特性曲线，通过建立基于变转速压力控制泵源的位置电液伺服系统数学模型与仿真模型，分析了变转速定量泵压力控制系统在典型工况下的位置跟踪、系统压力变化与能量利用效率，验证了压力控制系统能够在导弹平飞段保证位置伺服系统跟踪正常的前提下，能有效提高系统效率，证明了变转速定量泵压力控制系统的有效性与可行性。