Overview of China Chang'e-3 Mission and Development of Follow-on Mission

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1 Overview of China Chang'e-3 Mission and Development of Follow-on Mission Ming Li, Zezhou Sun, He Zhang, Xueying Wu, Fei Li, Leyang Zou, Ke Wu China Academy of Space Technology (CAST), Beijing , China Abstract The Chinese Lunar Exploration Program is putting forward and has already achieved great progress. The Chang'E-3, launched on December 14th, 2013, has landed successfully near the Rainbow Bay on the Moon. Then on December 15th, the Lunar Rover named Yutu left her footprints on the surface of the Moon. After 40 years of silence, the human being gave the Moon a warm embrace. Soft landing and rover exploration of Chang'E-3 spacecraft is the second step in Chinese Lunar Exploration Program which includes orbiting, landing and sample returning to the Earth. The China Academy of Space Technology (CAST) takes in charge of the overall development of the Chang'E-3 spacecraft. This paper introduces the mission characteristics and its achievements, specifically the results of the flight procedure, the soft landing procedure, the separation between the Lander and the Rover, the sleeping and waking up procedure, the working state of the Lander and the Rover exploration on the surface of the Moon. This paper also summarizes the technical innovations of the Chang'E-3 spacecraft. Some progress and status of Chang'E follow-on mission development is also introduced. China will take responsibility for the space exploration and play an important role in making the space development beneficial for all humankind. Keywords: Chang e-3, Chang e-5, probe, Lunar 1 Introduction The moon is the nearest celestial body to the Earth and contains rich natural resources and energy. It has been the beginning and basis in the Deep Space Exploration Program of many countries, and is also the most understood celestial body besides the Earth. The Chinese Deep Space Exploration activity starts with the lunar exploration and is divided into three main operational phases, which are orbiting, landing and sample returning and collectively referred to as Lunar Exploration Program. Chang e-1 satellite, the first Chinese lunar probe successfully completed the orbiting exploration of the moon and accomplished the orbiting goal in the first phase of the Chinese Lunar Exploration Program. As the vanguard of the second phase of the Chinese Lunar Exploration Program, the Chang e-2 satellite successfully completed the orbiting exploration of the moon and perfectly achieved the multiple phases of stretch assignments. Through a single launch, it 1

2 completes the explorations of multiple targets, including the moon, the L2 point of the Sun-Earth system and the asteroid Toutatis. On December 14 th, 2013, the Chang e-3 probe successfully landed in the Sinus Iridum area of the moon. On December 15 th, the track of the Yutu lunar rover was left on the lunar surface. After the silence of almost 40 years, the moon again greeted the regards of the human being. The success of the Chang e-3 lunar probe realized the soft-landing and roving of the Chinese spacecraft on the celestial body other than the Earth for the first time, and marked the fully implementation of the second phase of the Chinese Lunar Exploration Program. 2 Overview of the Chang e-3 probe The Chang e-3 mission is one of the most complicated and difficult mission in the field of the Chinese Aerospace. The Chang e-3 probe is the core part in the second phase of the Chinese Lunar Exploration Program, and it breaks through key technologies such as the autonomous guidance, navigation & control technology in moon landing, the variable-thrust propulsion technology, the landing cushion technology, the lunar surface locomotion technology, and the lunar survival technology. 2.1 Mission features The Chang e-3 lunar probe is designed to achieve soft-landing and roving exploration on the lunar surface. The corresponding mission profile is significantly different from the spacecraft orbiting the Earth and other celestial bodies. Moreover, the complicated lunar environment is never experienced by any other Chinese spacecraft. For the soft-landing objective, the velocity increment required in the powered descent phase is much larger than the other spacecraft. Additionally, the objective requires the autonomous navigation and control with non-cooperative targets measurement and also the precision of the attitude of the probe after soft landing. The system and subsystem design and realization of the Lander faces new and higher requirements in satisfying the demands brought by the mission profile, which is meanly reflected in the innovation and application of new technologies in the subsystems including the Guidance, Navigation and Control (GNC) subsystem, the 2

3 Propulsion subsystem, the Landing Cushion subsystem and the Structure and Mechanism subsystem. The requirement of the roving exploration objective includes the locomotion of the Rover on the unstructured terrain of lunar surface, and the realization of lunar surface environment perception, the obstacle recognition, the local path planning and the coordinated control of multi-wheel motion. The system and subsystem design and realization of the Rover faces new and higher requirements in satisfying the demands brought by the mission profile, which is mainly reflected in the innovation and application of new technologies in the subsystems such as the Guidance, Navigation and Control (GNC) subsystem and the Locomotion subsystem. Chang e-3 lunar probe also faces the complicated environment such as the space particles radiation, the lunar infrared radiation, the lunar topography, the lunar soil, the lunar dust, the landing impact and the thruster plumes. These new environment brought tremendous difficulties and risks for the design and experimental verification of the probe. 2.2 System composition The Chang e-3 lunar probe consists of the lunar soft-landing probe (referred as the Lander) and the lunar roving probe (referred as the Rover). The Lander is composed of 11 subsystems and the engineering parameter measurement devices. The Lander carries 4 types of scientific instrument such as the landing camera, the topography camera, the lunar-based optical telescope and the extreme ultraviolet camera. 2 types of engineering measurement devices such as the lunar dust measurement device and the surveillance camera are also installed on the Lander. The Rover is composed of 9 subsystems. It brings 4 types of scientific instrument including the panorama camera, the lunar measurement radar, the infrared spectrometer and the particle induced X-ray spectrometer. 2.3 Mission profile The probe was launched by the CZ-3B/G2 launch vehicle in the Xi Chang Satellite Launch Center. After the separation from the launch vehicle, the probe performed the mid-course corrections with the support of the ground TT&C, 3

4 IAC-14.A3.2A.6 x26702 implemented the first brake in the perilune point with an altitude of 100km, and directly inserted into the 100km circular orbit around the moon. During the orbiting in the circular orbit, the probe carried out orbit maneuver in the selected time to insert into the 100km 15km elliptical orbit. The probe then performed the powered descent in the perigee of the elliptical orbit and accomplished soft landing on the Sinus Iridum area of the moon. The flight and soft landing process is shown in figure 1. After the soft landing, the Lander released the Rover and became two independent probes. During the lunar day, the Lander and the Rover carried out scientific exploration on the lunar surface with the support of energy, thermal control and telecommunication. During the lunar night, both probes entered the lunar night sleep mode, and survived the harsh lunar night with the support of radioisotope heater unit (RHU) and the two-phase fluid circuits. Figure 1 The flight and the soft-landing process of the Chang e-3 probe 4

5 2.4 The mean result of the on-orbit flight Precise orbit maneuver At 01:30:00 on December 2 nd, 2013, the Chang e-3 probe was launched by the CZ-3B/G2 launch vehicle in the Xi Chang Satellite Launch Center. After approximately 1139s flight time, the probe separated from the launch vehicle and directly inserted into the trans-lunar trajectory with the perigee altitude of about 200km, the apogee altitude of about 370,000km and the inclination angle of In the trans-lunar process, the probe twice performed the mid-course correction. On December 6 th, 2013, the probe successfully entered the lunar orbit through a brake in the perilune point. The orbit maneuver control achieved extraordinary precision, which laid a solid foundation for the following powered descent Perfect landing At 20:59:52 on December 14 th, 2013, the 7500N thruster of the Chang e-3 probe was turned on, and the probe started powered descent from the scheduled point. At 21:11:19, the probe landed on the lunar surface safely and steadily. The entire powered descent process took 687s, and perfectly realized the soft landing on celestial body for the first time of China. In the process of powered descent, all GNC navigation sensors operated smoothly, successfully realized obstacle avoidance and precisely landed on the scheduled area. The location of the landing point was ( W, N), and the landing attitude was in rolling angle, 1.50 in pitch angle and 1.48 in yaw angle. During landing, the landing camera installed on the Lander recorded the process of the probe gradually approaching the lunar surface. The typical picture of the lunar surface is shown in Figure 2. 5

6 (a) (b) (c) (d) Figure 2 The picture of the powered descent process (taken by the landing camera) Successful separation At 04:35 on December 15 th, 2013, after the probe had completed the solar array deployment, the propellant passivation and the Earth-capture of the directional antenna of the Lander, and the lunar surface initialization mission of the Rover, the Rover was released and separated from the Lander through the transfer mechanism under the ground control. The detail is shown in Figure 3. Figure 3 The Rover moved to the lunar surface (taken by the surveillance camera C) Splendidly interactive imaging The full view picture of the Lander taken by the panorama camera of the Rover 6

7 is shown in Figure 4, and the full view picture of the Rover taken by the topography camera of the Lander is shown in Figure 5. Figure 4 The full view picture of the Lander taken by the Rover (the panorama camera) Figure 5 The full view picture of the Rover taken by the Lander (the topography camera) Effective exploration According to the three scientific goals of The investigation of the topography and the geological structure of the lunar surface, The investigation of the material composition and the available resources of the lunar surface, and The exploration of the space environment of the Sun, the Earth and the Moon, and the lunar-based optical astronomical observation, the probe applied scientific payload to carried out a great amount of scientific explorations on the lunar surface and acquired numerous scientific and engineering data of the moon. 3 The technological achievements of the Chang e-3 probe The Chang e-3 probe is a totally new spacecraft. The percentage of the new technologies and the new products is over 80%. The Chang e-3 probe acquires a series of independent and innovative scientific and engineering achievements in the design of spacecraft system, the guidance, navigation and control system, the 7

8 propulsion system and the thermal control system. The Chang e-3 probe effectively promotes the development of the aerospace technology and the progress of multidisciplinary technology, and also elevates the technologically independent innovation capability of China. 1) The soft landing autonomous guidance, navigation and control technology Many technical difficulties have been broken through in conceptual design and technical design of GNC subsystem. There are a large number of individual technical innovations and integrated innovations throughout the entire development process of the subsystem. A lot of novel control methods and strategies have been applied in the field of navigation, guidance, obstacle avoidance and attitude control. It promotes the developments of spacecraft guidance, navigation and control technology. In term of technical design, high-precision large-dynamic-range laser ranging technique and microwave range and velocity measurement technique are broken through; meanwhile, bringing non-cooperative targets measurement technique, by means of laser and microwave navigation sensors, into engineering application in the field of aerospace, bringing along the development of laser and microwave measurement techniques. 2) Complicated propulsion subsystem design and variable-thrust engine technology By use of system flow resistance matching technique, anti-oscillation and antispin techniques, pressure reducing regulation technique, a series of design challenge for the propulsion subsystem have been overcame, such as the system parallel balanced emission, liquid anti-oscillation, and system stability in large-flow variablecondition, etc. The Chinese first spacecraft-use high-specific-impulse and highprecision variable-thrust engine is developed, which adopts the pintle-type flow rate regulating device, precisely controlling the flow rate of oxygen circuit, fuel circuit and cooling circuit, respectively. Continuously variable thrust is realized, with the thrust varying from 1500N to 7500N and a control precision of 6.25N. 3) Soft landing cushion technology The cantilever-type configuration design is adopted for the landing cushion 8

9 mechanism. Through the integrated design of main devices and auxiliary bumpers, the problems of hold-down-to-release and deploy-to-latch are solved. By means of developing new normal-temperature superplastic materials, with an elongation of more than 70%, the challenge of tensile energy-absorption cushion is addressed, and then the development of materials science is propelled. 4) Lunar surface locomotion technology In the aspect of locomotion design, multiple innovative movement methods are proposed and optimized according to the locomotion requirement under the lunar surface environment. As for the optimization design of wheels, wheel-dust dynamic model is built according to the related theories of ground mechanics. The performance and lunar surface environmental adaptability of various wheel configurations are compared via testing, combined with the Rover traveling performance, such as power performance, trafficability, stability, and other analysis, to determine the configuration of wheels. 5) Lunar surface survival technology Gravity-assisted two-phase fluid loops are applied on Chang e-3 probe to introduce radioisotope heater to solve the difficulty of lunar-night survival. Also, variable-conductance heat pipes and other thermal control hardware are used on the Lander to enrich the thermal control hardware products used in spacecraft. Meanwhile, the illumination-based autonomous awaken scheme is innovatively designed. 6) The lunar surface autonomous navigation and teleoperation control technology By applying the stereo vision-based technique, the three-dimensional recovery and reconstruction of the unknown lunar surface environment is achieved. Multiple heuristic-based path algorithms, which are accommodated with the topography of the lunar surface, are proposed and completed the path planning. By innovatively applying the stereo vision-based local autonomous obstacle-avoidance algorithm, the autonomous local path planning of the Rover is accomplished, and the adaptability of 9

10 the probe for the complicated terrain of the lunar surface is enhanced. 7) The realization of the in-situ and roving scientific exploration on the lunar surface Lunar radars, lunar-based optical telescopes, extreme ultraviolet cameras and other scientific instruments are developed to achieve lunar shallow structure profiling, lunar-based long period observation of astronomical variable-source brightness, Earth plasma detection and other scientific tasks. A great quantity of firsthand scientific exploration data is acquired. 4 The future development of the Chinese Lunar Exploration Program The second phase of the Chinese Lunar Exploration Program has been completed, and the third phase is in progress. The engineering goal of the third phase is to realize unmanned sample return from the lunar surface. The probe system consists of 15 subsystems including structure, mechanism, TT&C and data transmission, antenna, data management, power distribution, thermal control, sample and capsulation, engineering parameter measurement, GNC, propulsion, reclaim, docking and sample transfer, separation mechanism and payload. The configuration of the probe at launch is shown in figure 6. Ascender Lander Re-entry module Orbital module X -Y -Z Figure 6 The configuration of the Chang e-5 probe at launch 10

11 4.1 Mission profile After the separation between the probe and the launch vehicle, the probe will spend about 5 days in the trans-lunar trajectory. At the time of arriving the perilune point, the probe will brake and enter the circular orbit around the moon with an altitude of 200km. Then the probe will be divided into the Orbital module/re-entry module combination and the Lander/Ascender combination. The Orbital module/reentry module combination will stay in the 200km circular orbit, while the Lander/Ascender combination will decelerate and enter the 15km 200km elliptical orbit, and choose a time to perform powered descent and soft landing on the lunar surface. After landing, the Lander/Ascender combination will perform scientific exploration, the gathering and capsulation of the lunar sample, and the preparation of taking off. Meanwhile, the in-orbit Orbital module/re-entry module combination will execute the necessary phase adjustment maneuver. After the unlock and separation between the Lander and the Ascender, the thruster of the Ascender will start working and send the Ascender to the 15km 180km target orbit. Then the autonomous rendezvous and docking procedure will begin. The Orbital module/reentry module combination and the Ascender will autonomously set up the initial condition of the rendezvous and docking, then the driving part of the docking and sample transfer subsystem will complete the rendezvous and docking procedure and transfer the capsulation device from the Ascender to the sample capsule inside the Re-entry module. The Ascender and the Orbital module/re-entry module combination will safely separate after the completion of the sample transfer process. After separation, the Orbital module/re-entry module combination will stay in the lunar orbit for about 10 days and choose the appropriate time to accelerate and enter the Moon-Earth transfer orbit. It will take about 5 days for the Orbital module/re-entry module combination to get close enough to the Earth. At an altitude of about 5000km, the Orbital module and the Re-entry module will separate and the Orbital module perform avoidance maneuver, then the Re-entry module will start individual flight, perform half-ballistic re-entry while entering the atmosphere and complete the return mission. 11

12 4.2 Expected achievement Through the accomplishment of the return goal of the third phase of the Chinese Lunar Exploration Program, key technologies such as the autonomous sampling on the lunar surface, the capsulation and preservation of the sample, taking off from the lunar surface, the design of the sample and return orbit, high-speed reentry into the atmosphere of the Earth, the rendezvous and docking on lunar orbit, the multi-target high-precision telecommunication, the preservation of the lunar sample and the ground laboratory analysis. Meanwhile, the scientific research of the moon will be promoted by carrying out the topography exploration and geological background investment of the landing area, acquiring on-scene analyzed data related to the returned sample, and constructing the relationship between the on-scene analyzed data and the laboratory analyzed data. The lunar sample will be studied in the laboratory to analyze the structure, composition and physical properties of the lunar surface material in the landing site, and deepen the research on the cause of formation and the evolution history of the moon. 5 Conclusion The Chang e-1 satellite and Chang e-3 probe successively achieved the lunar orbiting exploration and the lunar landing and roving exploration. Meanwhile, the Chang e-2 satellite opens the door of asteroid exploration. Along with the progress of the third phase in the Chinese Lunar Exploration Program, the elevation of the capability of the launch vehicle, the improvement of the launch site system, the construction of the deep space TT&C station and the formation of the scientific application system, indicate that China has preliminarily acquired the deep space exploration ability for those more distant objectives. China will subsequently carry out the terrestrial planet exploration, the giant planet exploration, the asteroid exploration and other deep space exploration activities and head to the deeper space. Reference 1 Ye P J. The technological advancements of the Chang e-1 satellite. Chinese Aerospace, 2008: Ye P J, Huang J C, Zhang T X. The technological achievements of the Chang e-2 satellite and the expectations of Chinese deep space exploration. Sci China: Tech Sci, 2013, 43:

13 3 Sun Z Z, Zhang T X, Zhang H, et al. The technological design and achievements of the Chang e-3 probe. Sci China: Tech Sci, 2014, 44: Sun Z Z, Jia Y, Zhang H. Technological advancements and promotion roles of Chang e-3 lunar probe mission. Sci China: Tech Sci, 2013, 11: