载人月球科研试验站建设规划及设想

进入21世纪以来，月球再次成为太空探索的焦点，许多国家提出各自的探月计划。区别于在美国60年前完成的阿波罗工程，未来月球探测的重点聚焦月球的长期建设与开发。如何充分利用当前的技术积累，在有限的运载能力和合理的发射运营成本条件下，建设载人月球科研试验站，实现月球极端环境下的长期运行是一个值得关注和研究的课题。结合当前国内外载人航天与探月工程发展情况，提出我国载人月球科研试验站人货分落、分段建设的规划设想。通过对安全性设计、乘组规模、环控生保需求、选址等展开分析，明确初步月球科研试验站建设需求，并提出满足2人长期月面驻留“2+1”构型月球科研试验站方案。     

机器人动态受力感知及零重力运动模拟技术

针对航天器在轨服务任务的地面零重力模拟需求，研究基于工业机器人的零重力运动模拟技术。建立基于BP神经网络的受力感知预测模型，该模型采用机器人末端姿态、加速度、角速度和角加速度作为输入层参数，采用机器人末端六维力传感器数据作为输出层参数，实现了对机器人末端负载的高精度动态受力感知。设计正交试验方法确定机器人的运动路径点进行样本数据采集，实现了受力感知预测模型对机器人全工作空间的覆盖。进一步，基于对机器人末端负载的受力感知数据，应用动力学理论计算负载在失重状态下的运动速度，并控制机器人执行相应的运动，实现了对机器人末端负载的零重力运动模拟。     

Finite time non-singular sliding mode control for spinning tether system with prescribed performance under artificial gravity mission

In this paper, the spinning tether system (STS) is applied to produce the artificial gravity overload with a proposed spin-up scheme in elliptical transfer orbits. To improve the comfort of the astronauts during spinning, the combined control scheme with tension and thrust is designed for spin-up. Then, based on the novel performance function and sliding mode technology, a finite time prescribed performance controller is proposed to track angular velocity for the desired artificial gravity overload. Compared with the existing works, the tracking error is controlled within the preset transient performance and converged to the origin within finite time even in the presence of unknown external disturbance. The stability of closed-loop tracking system is proved by Lyapunov theorem. Finally, the numerical simulations are given to demonstrate the effectiveness and robustness of the proposed controllers in the artificial gravity mission.     

An improved altimeter-derived gravity anomaly from shipborne gravity based on the mean sea surface height constraint factors method

Coastal marine gravity modeling faces challenges due to the degradation of the quality and poor coverage of altimeter data in coastal regions. The effective fusion of shipborne gravity data and altimeter-derived marine gravity data can make shipborne gravity data more useful for the accurate estimation of altimeter-derived coastal marine gravity. A mean sea surface height constraint factor (MSSHCF) method based on the ordinary kriging method and the remove-restore technique is proposed to fuse altimeter-derived gravity model with shipborne gravity data. In this method, all data are standardized during the interpolation process to reduce the error and mean sea surface as a vertical variable is added to the semi-variance function in ordinary kriging to obtain the residual shipborne gravity as corrected data source. The coastal marine gravity models V2.1 and V3.1 which fused altimeter-derived gravity data with shipborne gravity data and V1.1 without shipborne gravity data at a spatial resolution of 1′×1′ can be obtained. Validation experiments show that the accuracy of the gravity model V3.1 obtained by the MSSHCF method more closely agrees with the validated gravity model DTU17 and SS V31 than the model V2.1 obtained by the ordinary kriging interpolation method and the V1.1 model. Our results were validated against shipborne gravity data; the accuracy of model V3.1 was 4.95 % higher than the model V1.1 in South China Sea area A and 2.48 % higher in South China Sea area B. Meanwhile, the accuracy of model V3.1 was 2.07 % higher than model V2.1 in South China Sea area A and 2.42 % higher in South China Sea area B. The effects of distance from the coast and sea depth on the marine gravity model were also evaluated. The results show that the gravity model V3.1 has higher accuracy with the change in ocean distance and depth than the V2.1 and V1.1 gravity models. Thus, our study shows that the MSSHCF method effectively refines coastal altimeter-derived gravity using shipborne gravity data.     

Four-body cislunar quasi-periodic orbits and their application to ballistic lunar transfer design

Examining the properties of quasi-periodic orbits provides insight into the Sun-perturbed environment in cislunar space. In this investigation, quasi-periodic trajectories and their properties are explored in the Sun-Earth-Moon four-body problem. Computation and the stability characteristics of families of invariant tori are detailed. Furthermore, this investigation offers a framework for construction of ballistic lunar transfer trajectories in the four-body problem. The framework leverages manifold trajectories to supply a set of initial conditions for construction of periapsis Poincaré maps. Periapsis maps reduce the dimensionality of the space and illuminate solutions of interest as a basis to produce feasible families of transfers. Through a continuation process, families of ballistic transfers and families of transfers that include powered lunar flybys are constructed. Ultimately, these solutions supply an initial guess for transition to the Sun-Earth-Moon ephemeris model.     

Autonomous navigation for lunar final approach based on gravity gradient measurements

Lunar final approach navigation is critical for pin-point lunar landing in future missions. This study investigates the use of lunar gravity gradient measurements for autonomous navigation of a lunar probe during the final approach phase. As the spacecraft approaches the Moon, the strength of gravity gradient signals improves. A spaceborne gravity gradiometer can precisely measure local gravity gradients, and the latest lunar gravity model GL1500E is used to provide reference values. The employed truncation degree and order of the gravity model are increased stepwise considering the decreasing altitude of the spacecraft in order to reach a compromise between computational costs and model accuracy. An iterative Kalman filter is developed for coupled orbit and attitude estimation using gravity gradient measurements and attitude quaternions obtained from star sensors. A simulated spacecraft with a gradiometer noise level of 0.01 E is considered. Simulation results show that the spacecraft’s position converges rapidly and achieves an accuracy of less than 100 m at the last epoch.     

量子重力梯度仪研究进展

重力梯度是重力位的二阶微分,对地球密度扰动具有更高的分辨率,能够更加精细、全面地反映重力位在空间上的变化。高精度重力梯度测量在地质调查、地球重力场测绘、惯性导航以及基础科学研究等方面发挥着重要作用。量子重力梯度仪是近年来快速发展的一种基于激光操控原子技术的新型高精度重力梯度测量设备,具有测量精度高、长期稳定性好等特点,尤其是对振动噪声具有良好的抑制效果。目前,量子重力梯度仪的最佳灵敏度可达4E/√Hz,与最先进的旋转加速度计式重力梯度仪灵敏度3E/√Hz的水平相当。本文介绍了量子重力梯度仪的基本原理和应用,并分析了其国内外研究现状,最后讨论了目前限制量子重力梯度仪灵敏度的主要因素以及未来发展方向。     

FY-3(05)星主动对月定标控制技术研究

月球是低轨气象卫星载荷进行外定标的一个理想目标,不同载荷通过观测月球可以建立统一的参考基准,提高相互之间的数据匹配性。对于低轨卫星,月球一般每月一次进入载荷的视场,但停留时间只有几秒钟。为进一步提高对月定标的观测时长,积累更多的观测数据,本文针对低轨偏置动量卫星提出了一种主动对月定标控制方案,通过卫星平台的姿态控制,使月球在载荷视场中停留30 min以上。仿真结果表明:对月定标过程中卫星姿态控制精度满足指标要求,具备工程应用条件。