Influence of the gravitational vertical on geometric visual illusions

The occurrence of geometric orientation illusions and the perception of ambiguous figures were analyzed in 24 subjects during static body tilt relative to gravity on Earth. Results showed that illusions such as the Rock's diamond/square, the Ponzo illusion, and orientation contrast illusions occurred less frequently, and that depth reversal of ambiguous figures took more time when subjects were lying on their side or supine compared to upright, thus suggesting that the gravitational reference plays a significant role in these “visual” illusions. The structure of images, our representation of the environment, and orientation relative to gravity are all integral parts in interpreting visual images. In a weightless environment where no gravitational reference can be used, it is expected that similar alterations in visual perception will occur.     

一种液体火箭发动机试验台螺纹拧紧力矩量化控制方法

针对液体火箭发动机试验台工艺装配可靠性提升的需求,提出一种螺纹拧紧力矩量化控制方法。利用非试验和试验环境的力矩值统计与分析,确定液体火箭发动机试验台螺纹拧紧力矩值区间;通过拧紧力矩强度理论计算,验证力矩值区间的合理性;结合试验台螺纹空间位置的具体特点,确定适用不同空间位置的力矩量化控制方法和流程,并在试验中进行了应用。应用结果表明,本文提出的方法可有效提高发动机试验工艺的可靠性。     

Modeling irregular small bodies gravity field via extreme learning machines and Bayesian optimization

Close proximity operations around small bodies are extremely challenging due to their uncertain dynamical environment. Autonomous guidance and navigation around small bodies require fast and accurate modeling of the gravitational field for potential on-board computation. In this paper, we investigate a model-based, data-driven approach to compute and predict the gravitational acceleration around irregular small bodies. More specifically, we employ Extreme Learning Machine (ELM) theories to design, train and validate Single-Layer Feedforward Networks (SLFN) capable of learning the relationship between the spacecraft position and the gravitational acceleration. ELM-base neural networks are trained without iterative tuning therefore dramatically reducing the training time. Analysis of performance in constant density models for asteroid 25143 Itokawa and comet 67/P Churyumov-Gerasimenko show that ELM-based SLFN are able learn the desired functional relationship both globally and in selected localized areas near the surface. The latter results in a robust neural algorithm for on-board, real-time calculation of the gravity field needed for guidance and control in close-proximity operations near the asteroid surface.     

基于决策树的涡轴发动机气路健康评估方法

为解决涡轴发动机退化模式多、故障样本大、分类困难的问题,将梯度提升决策树(GB?DT)算法应用于涡轴发动机气路健康评估.首先对涡轴发动机故障标签进行了拆解,针对每一类标签设计了一个分类器.通过特征重要度排序筛选了6个分类标签的输入特征,有效降低模型复杂度.通过遍历确定树的最优数量和深度,确保了分类的准确性.仿真结果表明...     

Relevant experience learning: A deep reinforcement learning method for UAV autonomous motion planning in complex unknown environments

Unmanned Aerial Vehicles (UAVs) play a vital role in military warfare. In a variety of battlefield mission scenarios, UAVs are required to safely fly to designated locations without human intervention. Therefore, finding a suitable method to solve the UAV Autonomous Motion Planning (AMP) problem can improve the success rate of UAV missions to a certain extent. In recent years, many studies have used Deep Reinforcement Learning (DRL) methods to address the AMP problem and have achieved good results. From the perspective of sampling, this paper designs a sampling method with double-screening, combines it with the Deep Deterministic Policy Gradient (DDPG) algorithm, and proposes the Relevant Experience Learning-DDPG (REL-DDPG) algorithm. The REL-DDPG algorithm uses a Prioritized Experience Replay (PER) mechanism to break the correlation of continuous experiences in the experience pool, finds the experiences most similar to the current state to learn according to the theory in human education, and expands the influence of the learning process on action selection at the current state. All experiments are applied in a complex unknown simulation environment constructed based on the parameters of a real UAV. The training experiments show that REL-DDPG improves the convergence speed and the convergence result compared to the state-of-the-art DDPG algorithm, while the testing experiments show the applicability of the algorithm and investigate the performance under different parameter conditions.     

重力梯度对自由漂浮空间机器人姿态扰动分析

分析重力梯度对在轨运行的自由漂浮空间机器人姿态运动影响。由Lagrange方法建立自由漂浮空间机器人受重力梯度扰动的非线性动力学模型。首先,考虑无控关节自由状态,分析重力梯度对关节运动的影响。其次,利用相平面轨迹分析重力梯度对自由漂浮系统姿态运动影响。最后,由速度偏差曲线分析重力梯度对机械臂的影响。结果表明,当作用时间接近轨道周期或更长时,重力梯度引起的关节偏差已十分显著,且这种扰动作用主要由轨道偏心率决定;关节锁定时俯仰姿态受扰运动有周期振动与翻滚两种形式,若初始角速度满足一定限值可以保证俯仰运动不发生翻滚;当机械臂长时间工作时,忽略重力梯度将产生明显的末端定位误差。     

载人火星探测任务方案构想

提出了一种我国2030年代载人火星探测任务实施方案的构想。通过分批式提前部署方式,分别按货运、载人两个阶段实施对我国载人登火并对火星探测。其中,载人阶段在返回地球时可利用金星借力的方式以缩短整个载人任务周期。利用重型运载和长征五号运载火箭,分别在海南文昌和西昌卫星发射中心发射,实现2030年代的我国载人火星探测。     

Polyhedron tracking and gravity tractor asteroid deflection

In the wake of the Chelyabinsk airburst, the defense against hazardous asteroids is becoming a topic of high interest. This work improves the gravity tractor asteroid deflection approach by tracking realistic small body shapes with tilted ion engines. An algorithm for polyhedron tracking was evaluated in a fictitious impact scenario. The simulations suggest a capability increase up to 38.2% with such improved tilting strategies. The long- and short-term effects within polyhedron tracking are illustrated. In particular, the orbital reorientation effect is influential when realistic asteroid shapes and rotations are accounted for. Also analyzed is the subject of altitude profiles, a way to tailor the gravity tractor performance, and to achieve a steering ability within the B-plane. A novel analytical solution for the classic gravity tractor is derived. It removes the simulation need for classic tractor designs to obtain comparable two body model Δv$\mathrm{\Delta }v$ figures. This paper corroborates that the asteroid shape can be exploited for maximum performance. Even a single engine tilt adjustment at the beginning of deflection operations yields more deflection than a fixed preset tilt.     

影响环月飞行器定轨精度的误差源分析

以我国正在实施的探月计划“嫦娥1号”工程为背案,在现有测控网分布、观测弧段以及尽可能接近真实情况的误差源等前提下,利用仿真模拟的方法对影响环月飞行器定轨精度的误差源进行了初步探讨和分析。重点考察了月球重力场误差、观测量精度、初始时刻的先验轨道误差以及观测资料类型等对环月飞行器定轨精度的影响。     

基于多源卫星融合资料的中国近海海洋锋检测研究

海洋锋是海洋动力学中重要的研究对象.目前主要利用卫星遥感海面温度数据分析海洋锋.由于夏季中国近海海域海面温度趋同特性,无法利用海面温度数据分析海洋锋,而卫星遥感海色数据可以有效弥补海面温度检测海洋锋的不足,提高海洋锋检测的准确性.基于多源卫星融合数据,利用梯度检测算法对中国近海海域进行海洋锋研究,结合海面温度和蓝绿波段...