May 2022, Volume 4 Issue 2
    

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  • Survey of Two Classes of Continuation Methods for Solving Optimal Bang-Bang Control of Low-Thrust Space Trajectories
    ZHU Zhengfan, GAO Yang
    2017, 4(2): 101-110. https://doi.org/10.15982/j.issn.2095-7777.2017.02.001
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    The optimal Bang-Bang control problem of low-thrust space trajectories is introduced. Two classes of continuation methods are described：the first solves the energy-optimal solution，and subsequently employs the energy-fuel homotopy to obtain the optimal Bang-Bang control；the second introduces a switching principle，and obtains the optimal Bang-Bang control through parameter continuation starting from a two-impulse solution. The two continuation methods are compared，and the advantages and characteristics of the two methods are discussed. The prospects of the continuation methods applying to more complicated low-thrust trajectory designs are proposed. The concept of artificial intelligence trajectory optimization is presented，which contains three aspects：initial solution，continuation，and patching.
  • Design of Chang’e-4 Lunar Farside Soft-Landing Mission
    WU Weiren, WANG Qiong, TANG Yuhua, YU Guobin, LIU Jizhong, ZHANG Wei, NING Yuanming, LU Liangliang
    2017, 4(2): 111-117. https://doi.org/10.15982/j.issn.2095-7777.2017.02.002
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    The design of the Chang’E-4 lunar farside soft-landing mission is introduced in this paper. The landing area is initially selected as the Von Kármán crater inside the South Pole-Aitken basin on the lunar farside. A relay satellite is used to realize the lander and rover to the ground communication, and a Halo orbit around the second Earth-Moon Lagrangian point is chosen as its mission orbit. The relay satellite and the lander-rover combination are launched by a CZ-4C rocket and a CZ-3B rocket respectively. The lander, rover and relay satellite containing six domestic scientific payloads and three international scientific payloads, have carried out scientific exploration focusing on VLF radio astronomical observation, roving area topography survey, mineral composition and shallow structure investigation. In addition, two formation flying microsatellites on lunar orbit, lunar micro-ecosphere and large-aperture laser angle reflector are launched to carry out ultra-long-wave astronomical interferometry test, lunar surface ecosystem test and laser ranging test over the Earth-Moon distance respectively. By innovatively designing the top-level tasks, adequately inheriting mature technology and products, adding the function module of relay communication, and opening some resources to introduce high-performance payloads and test projects, a low-cost, short-duration, great-openness and high-efficiency lunar exploration mission would be achieved.
  • A Design Method of Multi-Window Launch Trajectories Design for Lunar Exploration Mission
    TANG Mingliang, WANG Ying, ZHANG Xuegong, GU Yanfeng, LU Liangliang
    2017, 4(2): 118-121. https://doi.org/10.15982/j.issn.2095-7777.2017.02.003
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    Aiming at multi-window launch requirements as well as the target orbit’s property of strong lunar perturbation in lunar exploration mission，a quick and efficient design method of launch trajectory is presented in this paper. During the launch phase before Spacecraft/Launch Vehicle（SC/LV）separation，each launch window has the same trajectory in the first and second stage flight sections，only the program angles of third stage work sections and the durations of coast sections need to be adjusted to satisfy injection requirements. During the orbital stage passivation phase，in order to raise the perigee altitude of orbital stage above GEO protected region，its velocity direction is properly modified with the help of lunar perturbation. This method can consolidate LV’s status in first and second stage fight sections，reduce sub-stages’ impact zones，strengthen the flexibility of injection parameter design，enhance the effieciency of injection parameter iteration and relative analyses，obviously improve the de-orbit effect of orbital stage，meet the requirements of space safety. This method can be applied to multi-window launch trajectory design for other deep space missions.
  • Trajectory Analysis and Design for Relay Satellite at Lagrange L2 Point of Earth-Moon System
    GAO Shan, ZHOU Wenyan, LIANG Weiguang, LIU Decheng, TANG Yuhua, YANG Weilian
    2017, 4(2): 122-129. https://doi.org/10.15982/j.issn.2095-7777.2017.02.004
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    The Earth-Moon L2 point plays a significant role in the far-side lunar landing mission due to its special location. Orbits about the L2 point could provide continuous communications link between the Earth and the lunar far-side lander. Transfer trajectories using lunar gravity assisted to L2 point and libration point trajectories are studied in this paper. Considering mission requirements，the trajectory characteristics and influence factors are analyzed，including launch window，transfer duration，amplitude of halo orbit，attitude and inclination of periselene. Through the analysis of influence factors，the paper provides several conclusions of trajectory characteristics，which could offer references for relay satellite trajectory design and optimization.
  • Study on Laser Ranging for Satellite on the Second Lagrange Point of Earth-Moon System
    He Yun, Liu Qi, Tian Wei, Duan Huizong, Yeh Hsienchi, Fan Shuhua, Li Yuqiang
    2017, 4(2): 130-137. https://doi.org/10.15982/j.issn.2095-7777.2017.02.005
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    The background and scientific goals of lunar/relay-satellite laser ranging is introduced. The current status and development trends of laser ranging is presented. The mission design is discussed，mainly including the manufacture of a single 170-mm-aperture Corner-Cube Retroreflector（CCR）a the laser ranging system based on a 1.2-m telescope installed at the Kunming station of Yunnan Observatory. A pulse laser with pulse width of 10ns and pulse energy of 3 J is used. The received photon number of 0.74 is expected，and the ranging precision is better than 1 meter.
  • Environment Testing Technology of Radioisotope Heat Source for Deep Space Exploration
    HU Yupeng, LU Liang, XIANG Yanhua, LI Sizhong, HU Wenjun, HU Shaoquan
    2017, 4(2): 138-142. https://doi.org/10.15982/j.issn.2095-7777.2017.02.006
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    In order to ensure security and reliability of the radioisotope heat source for deep space exploration，the research on the environment testing technology of the radioisotope heat source is conducted. The test items are concluded by analyzing the mission profile during the whole life of the radioisotope heat source for deep space exploration. The high temperature-centrifuge，high temperature-impact，high temperature-vibration compound environment testing technologies are studied，and the technologies of ground simulation test for launch site fire accident，aerodynamic heating and thermal shock is also discussed in detail. The capacity of the environment reliability test and abnormal condition security test for the radioisotope heat source has been set up. Then，the environment test is performed which can provide support for the research of radioisotope heat source for deep space exploration.
  • Influence Analysis of Terrain of the Farside of the Moon on Soft-Landing
    LI Fei, ZHANG He, WU Xueying, MA Jinan, LU Liangliang
    2017, 4(2): 143-149. https://doi.org/10.15982/j.issn.2095-7777.2017.02.007
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    Chang’e-4 probe is planned to land on the farside of the moon for the first time of the human being. Compared to the nearside of the moon, the terrain on the farside of the moon is rugged and complex, and there is no large flat area, so the change of the terrain will affect the soft-landing of Chang’e-4. The Chang’e-4 landing site on the South-Pole Aitken Basin is analyzed and compared wth the landing area of Chang’e-3 mission, considering the influences ofthe mission design, the lander design and the lunar working procedure. The main conclusions are as follows: 1) The latitude and longitude range of the landing area is reduced from 16.4° and 3° for Chang’e-3 mission to about 4° and 2° for Chang’e-4 mission; 2) During the power descent phase, the strategy after the main deceleration phase is changed from the oblique forward motion trajectory to the vertical down trajectory, and the operation time of the distance measuring sensor is also changed; 3) The signal transmission powers and signal to noise ratios of the microwave ranging and velocity sensor will be improved; 4) The lighting of the lander and the communication by the terrain occlusion will be prediected, and the design operation strategies such as sleep mode or eclipse mode will be established. Through the modification, Chang’e-4 mission can be adapted to the changes in the topography of the farside of the moon to reduce the risk of landing and lunar mission.
  • Key Technologies of Very Low Frequency Radio Observations on the Lunar Far-Side
    JI Yicai, ZHAO Bo, FANG Guangyou, PING Jinsong, WU Weiren, NING Yuanming, LU Wei, ZHOU Bin
    2017, 4(2): 150-157. https://doi.org/10.15982/j.issn.2095-7777.2017.02.008
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    The Moon has a large size，which can effectively block the low-frequency electromagnetic interference from the Earth，so the lunar far-side is the best place for low-frequency radio astronomical observation. In this paper，the significance of using a very low frequency radio spectrometer（VLFRS）for the low frequency radio astronomical observation on the back of the moon is discussed. And the goals，as well as the basic principles，design，composition and achievements of the VLFRS are described. Finally，experiments on the radiation spectrum of low frequency electromagnetic wave in Zhongguancun area，Beijing are analyzed. The results show that the low frequency radio signals in the 0.1~40MHz band, which are emitted by the radio stations and the time-service centers, can be clearly detected by the VLFRS.
  • Formation Flying Around Lunar for Ultra-Long Wave Radio Interferometer Mission
    ZHANG Jinxiu, CHEN Xuelei, CAO Xibin, AN Junshe
    2017, 4(2): 158-165. https://doi.org/10.15982/j.issn.2095-7777.2017.02.009
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    The farside of the Moon can effectively block the radio interference from the Earth and the Sun，which provides almost the quietest electromagnetic environment within the solar system. Hence，it would be the best place to make astronomical super-long wavelength observation in the space. In this mission，we will realize the basic mission goal of conducting interferometry experiment，and will also try to make important scientific discoveries. Two micro satellites will be manufactured and launched into space by piggybacking on the CHANG’E-4 mission. The two satellites will be detached from the rocket at the start of the earth-moon transfer orbit and conduct orbit transfer autonomously，and make a brake as closing to the moon. Due to limited fuel supply，the orbit is a large ellipse orbit. They are to fly in formation and perform super long wave interferometry at the lunar farside of the orbit. In this paper the work modes of the system is presented，and the data processing and analysis methods are discussed，including the data pre-processing，the interference imaging and global spectrum measurement. The micro-satellite supporting services model and the scientific payload model are also described. The key technology problems are summarized. With this project，the first formation flying microsatellite system in lunar orbit is realized，and the first star-star interferometry astronomical observation is conducted.
  • Earth-Moon L2 Libation Point Orbit Long Term Station Keeping
    LIANG Weiguang, ZHOU Wenyan, ZHOU Jianliang, YANG Weilian
    2017, 4(2): 166-170. https://doi.org/10.15982/j.issn.2095-7777.2017.02.010
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    Earth-Moon L2 libration point is unstable. The necessary orbit station keeping operations are required for spacecraft in order to maintain around Earth-Moon L2 libration point for a long time. Long term station keeping operations fortwo types of orbits, quasi-Halo orbit and Lissajous orbit, are studied. Control once per cycle when crossing the xz plane is used as the control strategy. Control values are chosen by single step prediction. One year trajectories of quasi-Halo orbit and Lissajous orbit with station keeping are simulated in the real celestial mechanics model respectively. Comparison of simulation results shows that the cost of station keeping for Lissajous orbit is lower than that of the quasi-Halo orbit. This can be explained from orbit topological configuration. Corresponding contrast experiment is designed to verify the inference. Research results have engineering reference for Earth-Moon L2 libration point selection, station keeping control strategy design, long term trajectory and effect analysis.
  • Preliminary Study of Illumination Characteristics of Aristarchus Plateau Using LOLA Data
    ZHANG Jidong, MENG Zhiguo, PING Jinsong, LI Wenxiao, WANG Mingyuan, ZHAO Rui
    2017, 4(2): 171-177. https://doi.org/10.15982/j.issn.2095-7777.2017.02.011
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    The illumination analysis algorithm at mid-low latitudes is improved. Taking Aristarchus plateau （AP） as an example，the high resolution and high accuracy LOLA data from the LRO satellite and DE/LE430 lunar planetary ephemeris are used to quantitatively calculate and analyze the illumination characteristics of AP based on the Moon’s libration model. The results show that the illumination rates of AP area are all over 0.35，and the illumination condition of flat area is good. The illumination rates vary greatly in different regions because of the influence of terrain. The maximum illumination rate is higher than the minimum above 30%. Considering the typical long term libration effects，the results of 18.6 years show that the change of illumination rate is small and stable，which is an important reference for the research on the evolution of the lunar surface.
  • Design of Lunar Free-Return Trajectories Based on UKF Parameter Estimation
    ZHANG Hongli, HAN Chao, HU Wenting
    2017, 4(2): 178-183. https://doi.org/10.15982/j.issn.2095-7777.2017.02.012
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    A fast and convenient design-method based on UKF parameter estimation is proposed for lunar free-return trajectories. The method proposed avoids calculating the Jacobian matrix and obtains large convergence ability compared with the common differential-correction method. Given that the initial estimate of the free-return trajectory is generated under the two-body Earth-spacecraft model, the difficulty of guessing a good initial estimate is greatly reduced. Through solving the converted parameter estimation problem using the method proposed, the converged final solution can be found under a high-fidelity gravitational model by a few iterations. Despite its simplicity, the method is proves to be quite effective in finding the solution of lunar free-return trajectories with great numerical accuracy.
  • On Guidance Algorithm for Martian Atmospheric Entry in Nonconforming Terminal Constraints
    Guo Minwen, Li Maodeng, Huang Xiangyu, Wang Dayi
    2017, 4(2): 184-189. https://doi.org/10.15982/j.issn.2095-7777.2017.02.013
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    A method for Martian atmospheric entry guidance is researched in this paper，regarding the problems faced by Mars exploration vehicle with low lift-to-drag ratios. Firstly，with a certain ballistic coefficient and lift-to-drag ratios，the initial reentry angle is designed considering the process variable constrains and the parachute deployment constrains. Then the reference trajectory is developed for providing the sufficient margin to overcome the parameter uncertainties considering the nonconforming terminal constrains and the low control authority. Finally, the tracking guidance law is presented. The six degree of freedom simulation demonstrates the effectiveness of the approach，which provides references to the Mars exploration project.
  • Calculation and Analysis of the Impact Defense to the Potentially Hazardous Asteroids
    JIANG Yu, CHEN Bin, BAOYIN Hexi, LI Hengnian
    2017, 4(2): 190-195. https://doi.org/10.15982/j.issn.2095-7777.2017.02.014
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    The dynamical problems of the asteroid defense are investigated by using the impact method. The polyhedron model isused to build the shape model of the asteroids, and the rubble-pile model is used to build the structure model of the asteroids. A sphere which has the same dense and material quality with the asteroid is assumed to impact to the asteroid, and the high velocity impact and the distribution of the rocks and rubbles after the impact are computed. Considering the contact deformation between the asteroid and the impact sphere, and the contact deformation inside the body of the asteroid among the rocks and rubbles which comprise the structure of the asteroid, the mutual gravitational force, the normal contact force, the tangential static frictional force, the tangential kinetic friction force, and the moment of rolling friction are calculated. Asteroid 101955 Bennu is used to calculate the dynamical behaviors of the impact defense of the potentially hazardous asteroids. The results show that the method of high velocity impact is useful for the defense of potentially hazardous asteroids, the asteroids can be crashed into a large number of rocks and rubble. The presented methodhas no pollution to the space environment. In this sense, the method is much better than the nuclear explosion method.
  • Research on a Potential Stability Form of Doubly Synchronous Binary System Based on Triaxial Ellipsoids Model
    LAN Lei, YANG Mo
    2017, 4(2): 196-200. https://doi.org/10.15982/j.issn.2095-7777.2017.02.015
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    There are numerous binary systems in solar system. The research on binary systems is important for understanding the origin and evolution of asteroids. A two-triaxial-ellipsoid system is used to model the binary asteroids. Combining with Joshua’s research in fourth-order mutual gravitational torque of two bodies, the stability of the binary system is proved by KTC theorem. Thus, the results verify a potential form of the doubly synchronous binary asteroids system where there is a roll angular velocity between the primary and moonlet.