地外天体着陆巡视探测自主智能技术进展

以月球、火星和小行星等地外天体着陆巡视探测任务为背景，对自主智能技术的发展现状、应用情况与未来趋势进行了分析研究。回顾了目前国内外地外天体着陆巡视探测任务的实施情况；从导航定位与环境感知、轨迹优化与制导控制、自主探测与路径规划、故障诊断与自主处理等四个方面，阐述了该领域自主智能技术的研究现状，并对未来发展态势进行了展望。     

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.     

1-D dusty photo-ionization models of WR planetary nebulae NGC 2452 and IC 2003

We report dusty photo-ionization models for two Planetary Nebulae NGC 2452 and IC 2003, which have [WR] type central stars, using 1D photo-ionization code Cloudy17.02. We used the medium resolution optical spectra and archival IRAS photometry to constrain our models. The physical size of the ionized nebula derived using accurate distance measurements and absolute H$\beta$ flux available in the literature were used as additional constrains. We examine the importance of photo-electric heating and found that models with and without considering photo-electric heating do not make significant difference for both PNe for the MRN grain size distribution considered in this study. We derive the nebular elemental abundances of these PNe by the empirical method as well as by making dusty photo-ionization models. The values of N/O ratios for both PNe obtained from our models are lower than their respective values arrived using empirical methods. The central stars are assumed to be black bodies and the photospheric temperatures derived respectively for NGC 2452 and IC 2003 from their best fit models are 182 kK and 155 kK and their respective luminosities are 630$L_{\odot }$ and 1015$L_{\odot }$. We propose that both the PNe were resulted from low-mass progenitors of mass $?$2.8 M_⊙.     

Ground-based investigations on phase-moving phenomenon with space sublimation cooling for lunar exploration missions

The lunar surface is a typical vacuum environment, and its harsh heat rejection conditions bring great challenges to the thermal control technology of the exploration mission. In addition to the radiator, the sublimator is recommended as one of the promising options for heat rejection. The sublimator makes use of water to freeze and sublimate in a porous medium, rejecting heat to the vacuum environment. The complex heat and mass transfer process involves many physical phenomena such as the freezing and sublimation phase change of water in the porous medium and the movement of the phase-change interface. In this paper, the visualized ground-based experimental approaches of space sublimation cooling were presented to reveal the moving law of three-phase point and the growth phenomenon of ice-peak and icicle in microchannels under vacuum conditions. The visualized experiments and results prove that the freezing ice is divided into the porous ice-peak and the transparent icicle. As the sublimation progresses, the phase-change interface moves downward steadily, the length of the ice-peak increases, but the icicle decreases. The visualized experiments of space sublimation cooling in the capillary have guiding significance to reveal the sublimation cooling mechanism of water in the sublimator for lunar exploration missions.     

弱全局信息下月面超远距离保通行性移动规划

针对月面超远距离移动规划任务因缺乏精确全局信息而导致的规划路径可通行性不足问题，提出了月面道路拓扑网的构建设想及相应路径规划技术，凭借复杂道路网络的连通能力确保巡视器超远距离规划路径的可通行性。首先进行月面道路拓扑网的设计方法研究，分别提出了基于滑动最优泊松采样算法的网络节点设计方法和基于均匀领邻网络拓扑模型网络结构设计方法，使月面道路网网络节点分布均匀、密度适中且覆盖完整，网络连接合理且各路径尽量远离障碍区域。然后进行基于月面道路拓扑网的超远距离移动规划研究，分析了基于月面道路拓扑网路径规划技术的概率完备性和整体可通行概率，并提出了基于月面道路拓扑网的K优路径规划方法，通过道路网的连通性来提高超远距离移动探测任务的整体可通行概率。最后以阿波罗两次登月任务的着陆点之间进行超远距离转移任务为仿真场景，验证了本方法的有效性。