Chang 'e-2 satellite is the second lunar exploration satellite in China, the second artificial solar system asteroid, and the technical pilot star of the second phase of China's lunar exploration project. Chang 'e-2 satellite developed by China Academy of Space Technology is the backup satellite of Chang 'e-1, China's first lunar exploration satellite. Following the platform of Dongfanghong-3 satellite, the cost is about 600 million yuan.
Chang 'e-2 satellite was successfully launched by the Long March-3 C carrier rocket in xichang satellite launch center at10/018: 59 57 seconds, and successfully entered the earth-moon transfer orbit.
Chang 'e-2 completed a series of engineering and scientific goals, and obtained three-dimensional images of the lunar surface with a resolution better than 10 meter, the distribution map of lunar material composition and other materials. On 20 11April1day, Chang 'e II launched an experiment, and completed experiments such as entering the orbit around the L2 point of Lagrange of the sun and the earth for deep space exploration. Since then, Chang 'e II has successfully carried out the re-expansion test by flying over asteroid 4 179 (Tutatis), and the Chang 'e II project ended.
I. Development history
On June 5438+February 65438+February 7, 2007, after the successful completion of the Chang 'e-1 satellite mission, the Center for Lunar Exploration and Space Engineering organized various systems to carry out the preliminary scheme demonstration of the backup star mission, and named the backup star Chang 'e-2 according to the principle of sequential naming.
On June 24, 2008, the symposium on Chang 'e-2 satellite was held.
In July 2008, China Academy of Space Technology, as a satellite development unit, completed the second round of overall scheme demonstration and reported it to the Center for Lunar Exploration and Aerospace Engineering. Chang' e-2 satellite was finally determined to be based on Chang' e-1 satellite, and after technical improvement according to the mission requirements, it was used as the "pilot star of the second phase of lunar exploration project" to carry out the preliminary flight test.
In 2008, 10 menstrual period was approved by the State Council.
Chang 'e-2 satellite has gone through the stages of scheme, initial sample, prototype and launch implementation since its mission design. It only took more than two years to complete the development and online implementation tasks. In 2008, the whole satellite design was mainly completed, and top-level planning, technical status cleaning and review, and overall specification formulation were carried out. Research on new product technologies such as mission trajectory design, interface coordination among large-scale systems, formulation of technical specifications for subsystems, X-band transponders, and special tests for mission requirements and environmental changes has been carried out.
In the top-level planning, technical processes, special tests, quality assurance and risk control at all stages and levels have been completed. The satellite system directly enters the prototype development stage; The newly developed stand-alone and technical test subsystem has gone through the complete stages of scheme, initial sample and normal sample; Because most stand-alone machines are modified or newly developed products to improve performance, the payload subsystem starts with the initial samples. At the same time of tackling key technical problems, special tests such as design and verification of propulsion gas path and 490 N engine life extension, adaptability of solar wing to high temperature in recent months, and compensation of speed-height ratio of TDI-CCD camera were designed and carried out.
In 2009, product development, system integration and test verification were comprehensively promoted. Single machine, technical test and preliminary prototype development of payload subsystem were completed, speed-height ratio compensation of orbit determination accuracy and special coordination of 15 km orbital flight system support were completed, and all special tests were completed. The prototype product development, final assembly, electrical performance test in AIT stage and software /FPGA welding were completed. In parallel, the quality review and recalculation of orbit design and space single event effect protection were carried out, which supplemented the technical research and coordination of "orbit design, flight procedures, rainbow bay imaging, surveillance camera/ultraviolet imaging". In August 2009, it passed the review of prototype design. In 20 10, the research group completed large-scale experiments such as EMC, mechanics and thermal vacuum. On the basis of fully verifying the satellite system itself, the docking tests of large-scale systems such as carrier docking, TT&C docking and wireless joint test of large-scale systems are completed, which verifies the correctness and matching of the interfaces between systems. Quality review and ex-factory review were completed on June 20 10.
On July 20 10/0, Chang 'e II satellite entered xichang satellite launch center.
Second, the bearing capacity
Chang 'e-2 satellite system consists of 13 subsystems, including overall and comprehensive test subsystem and structure, thermal control, guidance/navigation and control (GNC), propulsion, power supply and distribution, data management, measurement and control data transmission, directional antenna, technical test (engineering load) and payload. The launch mass of the satellite is 2480 kg, the dry weight is 1 169 kg, and the load is 166 kg (including the payload 136 kg and the engineering load is 30 kg). [6]
New performance
According to the launch capability, the launch weight of Chang 'e-2 satellite is increased by 130 kg compared with Chang 'e-1, and the fuel can provide a total speed increase of about 2.3 km/s; In the aspect of measurement and control data transmission ability, LDPC coding function is adopted to improve the gain by about 2.5 dB compared with convolutional coding. The data transmission channel of engineering load is increased, and the minimum multi-file bit rate of 23.4375kbps is designed, which can support data transmission as far as 20 million kilometers from the ground. In the aspect of maneuvering flight capability, on the basis of orbit control technology based on high-precision accelerometer, the measurement range of accelerometer, attitude control compensation, fuel quantity prediction and other aspects are improved to improve the accuracy of orbit control; Real-time and delayed forced unloading methods are adopted to realize the coupling control of attitude and orbit; Autonomous inertial alignment function is used to improve the autonomy of track control; The design adds the maintenance function of large thrust track, which improves the control accuracy and autonomy on the premise of ensuring reliability. In addition, the working life of the propulsion system will be increased from 3 months to more than 6 months.
Third, the solar high-energy particle detector
During the on-orbit operation of Chang 'e-2 satellite, which coincides with the peak of solar activity, it is the best detection period to detect and study solar high-energy particle events, CME (Coronal Mass Ejection), solar wind and its impact on the lunar environment. Using solar high-energy particle detector and solar wind ion detector, the flux, composition and energy spectrum of interplanetary solar high-energy particles and solar wind ions and their temporal and spatial variation characteristics can be obtained, which can be used to study the interaction between solar activities and the space environment of the earth, moon and near moon. Provide environmental scientific data for the follow-up lunar exploration project.
On Chang 'e-2 satellite, there is also a management system to command, control and manage these seven instruments and collect data. Among them, mass storage is a newly developed device. Its storage capacity is increased from 48GB of Chang 'e-1 to 128GB, with higher throughput and faster processing speed. This makes the seven payloads more efficient and the data more reliable.
Fourth, the propulsion system
Chang 'e II propulsion system adopts high-performance two-component propulsion system, and Chang 'e II propulsion system is equipped with 1 490N engine, which is used for the orbital maneuver of Chang 'e II satellite. Configuration 12 thruster 10 N, divided into two paths for mutual backup, used for attitude control and orbit adjustment of Chang 'e-2 satellite; Equipped with two propellant tanks-oxidant tank and combustion agent tank, which are respectively filled with oxidant (dinitrogen tetroxide) and combustion agent (methylhydrazine) to provide the required propellant for the 490 N engine and 10 N thruster; The 1 gas path system is provided to provide helium with stable pressure for the propellant tank during the ignition of the 490 N engine. The two helium bottles are containers for storing high-pressure helium, and the high-pressure helium is depressurized and stabilized to the pressure required for tank operation through the pressure reducer. Two check valves are used to prevent the propellant vapor in the tank from diffusing to the pressure reducer, thus avoiding the danger of explosion caused by the contact of two propellant vapors downstream of the pressure reducer.
Verb (abbreviation of verb) flight control support system
According to the characteristics of the mission, the overall framework and design idea of the satellite flight control support system are put forward systematically for the first time: based on digital simulation technology, the modeling of related key components is solved, the unified satellite attitude and orbit dynamics model is used to drive, and the independent modules such as mathematical simulation subsystem, flight control drill subsystem and visual simulation tool are organically combined, and a comprehensive and practical flight control support system is realized through system integration and innovation. Task-aided design of key flight events through auxiliary analysis tools and mathematical simulation can realize real-time strategy generation, and effectively predict the execution effect of flight control tasks through the effective combination of 1: 1 flight control process drills oriented to execution level.
Main functions:
1) satellite attitude and orbit dynamics model function: the dynamics software environment of flight control support system has high accuracy and self-selection ability, which can be driven according to the orbit position, that is, the main orbit power can be selected independently according to the orbit characteristics, so as to realize the self-adaptation ability of dynamic model adjustment.
2) Functions of auxiliary analysis tools: Based on digital simulation, attitude control strategies in key tasks are generated, and related simulation calculations are completed by using mathematical modules such as astronomical vector calculation, directional antenna pointing calculation, solar wing pointing calculation, orbit disturbance calculation of attitude maneuver, engine thrust calculation and stray light suppression calculation of camera/star sensor.
3) Function of mathematical simulation subsystem: Different from physical/semi-physical simulation system, the design of mathematical simulation subsystem is completely based on software, which has the characteristics of good system stability, fast execution speed and high consistency of simulation results. The design scheme of normal mode and the strategy scheme of fault mode can be simulated and verified for many times to obtain the optimal design, and the correctness of satellite dynamic model modeling in different flight States can be verified in time. It is an effective CAD tool for forming flight control strategy.
4) Flight control drill subsystem: Flight control drill subsystem is a simulation of task execution. Its simulation environment includes "soft" and "hard" aspects, and the core is the satellite-ground docking system composed of on-board computer and dynamic model. The system can directly receive satellite data blocks, simulate flight control process in real time at any time, predict flight control execution process, verify the correctness of flight control strategy and check the effectiveness of airborne command module. [ 12]
5) Visual simulation tool: The visual simulation tool mainly completes the expected imaging effect of the imaging task, especially for the imaging task of asteroid flying over. Driven by the dynamic model, the visual simulation tool can directly predict the size, brightness, distortion, apparent motion, background starry sky and other effects of the target in the field of view during the task, and support scheme selection and simulation verification. The sub-modules of flight control support system can be used jointly to simulate and verify important strategies, or independently to optimize mission parameters. Taking the flying over Tutatis asteroid as an example, the workflow of ground simulation verification of flight control support system is given.
actual load
Note: The payload of a satellite is an instrument, equipment or subsystem that directly performs a specific satellite mission.
Chang 'e-2 satellite is equipped with seven scientific detection instruments in five categories. Use high-resolution CCD stereo camera. The spatial resolution and data updating frequency of the laser altimeter are improved. By increasing the calibration source and replacing the detection crystal, the detection accuracy of γ/X-ray spectrometer is improved and the detection types are expanded.
Tasks and requirements of intransitive verbs
The scheduled mission orbits of Chang 'e-2 satellite include the direct transfer orbit from the earth to the moon, the capture orbit in recent months, 100km and 100km× 15 km mission orbits. The extended mission includes lunar escape orbit (phase modulation orbit), transfer orbit, solar-terrestrial L2 orbit and asteroid rendezvous orbit.
In addition to the unique time window, Chang 'e-2 satellite needs to complete other scheduled tasks of the project, including all orbit maneuver tests before power reduction in the subsequent landing mission; The extended tasks include flying around L2 point and 4 179 asteroid rendezvous control. In lunar exploration, from the circular orbit of 100km to the elliptical orbit of 100km* 15 km, it is necessary to arrange two orbital descent maneuvers in the unmeasurable arc.
Task characteristics
The whole mission of the satellite can be divided into seven relatively independent stages: pre-launch preparation stage, activity stage, phase-modulated orbit stage, earth-moon transfer stage, moon capture stage, moon-orbiting working state establishment stage and moon-orbiting operation stage.
1) The flight process control is complicated. Chang 'e I needs to fly 380000km to capture the moon, while Chang 'e II needs to pass 100km× 100km and 100km× 15km to test its orbit around the moon. It needs to go through many complicated orbit and attitude maneuvers, which requires high satellite orbit control.
2) The space environment is complex. Outstanding performance in the issue of eclipses, Chang 'e-1 satellite needs to experience two eclipses in its lifetime, and the effective shadow time of each eclipse is about 3 hours. During this period, the satellite can't get light energy, and the temperature of the satellite will drop rapidly. Therefore, the requirements for satellite energy, temperature and working mode of the whole satellite are higher.
3) The three-body joint control mode is complicated. During the satellite's orbit around the moon, the star should face the moon, the solar wing should face the sun, and the directional antenna should face the ground. Therefore, the attitude control requirements of satellite body, solar wing and antenna are higher.
4) There are many newly developed and improved equipments. Chang 'e-2 satellite not only contains six payloads in Chang 'e-1 satellite, but also adds a technical test subsystem, including X-band transponder, landing camera and other engineering loads. Therefore, the types of intelligent terminals in satellite systems are complex, and there are special requirements for the collection, storage, compression and coding of satellite information.
technical requirement
In order to avoid collision (the highest altitude of the Moon Mountain exceeds 10km), the stable flight of 15km in recent months also depends on autonomous, reliable and high-precision orbit control. The realization of the extended mission also needs high-precision orbit control, such as the transfer orbit from the lunar orbit to the L2 point, which is highly sensitive to speed control. The control of near-earth asteroids requires not only high-precision orbit control, but also high-reliability orbit control strategy.
One of the mission orbits of Chang 'e-2 satellite is the elliptical orbit of 100km* 15 km. Due to the low altitude and high speed of the satellite in the near moon, if the orbit control error is large, the near moon position will change and deviate from the target area of interest, which will also affect the continuous measurement and control conditions. If it is too big, there is even the risk of a satellite hitting the moon. Therefore, the orbit control of Chang 'e II must be accurate enough. The braking of the first 1 recent month is unique, so it is necessary to slow down near the recent month, otherwise the satellite will fly away from the moon, and it will take a lot of fuel and time to reach the moon again, which is even impossible. Moreover, reliable control and stable operation can save fuel budget margin and reduce fuel consumption, which is the basis for carrying out extended tasks. Therefore, high reliability requirements are put forward for satellites. In order to ensure the timely implementation of orbit transfer as planned, considering the bad situation, the satellite should also have certain autonomous orbit transfer ability without the support of ground measurement and control. Especially for the interstellar flight in the extended mission, it is impossible to get the ground support thousands of kilometers away from the earth in real time, so the ability of autonomous fault tolerance and fault handling is put forward.
Seven. Engineering significance
1, technical breakthrough
(1) In the subsequent landing mission, all the orbit and maneuvering flight control technologies before power descent were designed and verified, and they directly entered the Earth-Moon transfer orbit, using X-band measurement and control for the first time, and imaging the Chang 'e III landing area with high resolution.
(2) In view of the uneven gravity field of the moon and the rugged terrain, the key technologies such as lunar quasi-freezing orbit design, satellite autonomous inertial alignment, and maneuvering orbit splicing have been broken through, and the circular orbit of 100km and the orbit of 100km× 15km have been successfully realized for the first time, and the ignition orbit change of the main engine on the back of the moon without measurement and control has been realized. The accuracy of satellite orbit control reaches 0.02%.
(3) In the international lunar exploration, the time delay integration (TDI) imaging technology was adopted for the first time, and two imaging methods, namely, ground line frequency data injection and altimetry data-assisted speed-height ratio compensation, were designed, and a full moon stereoscopic image with 7m resolution was obtained. A local image with the resolution of 1.3 m was obtained, reaching the international advanced level.
(4) Innovate and develop the first X-band high-sensitivity digital TT&C transponder based on unified carrier system, and realize many breakthroughs in TT&C technology on board in the field of deep space exploration. In-orbit test verified the X-band TT&C system and technology in deep space. Breakthrough the key technologies such as differential one-way ranging (DOR) interferometry, X-band digital transponder, and ground S/X dual-band measurement and control equipment development. The speed measurement accuracy reaches 1 mm/s, and the distance measurement accuracy reaches 1m, and the very low bit rate remote control of 7.8 125 bps is realized.
(5) Break through the micro-intelligent design technology, and realize the monitoring and imaging of the Earth-Moon space flight process for the first time. For the first time, the dynamic images of key links such as solar wing deployment, antenna deployment/rotation and main engine ignition are obtained in real time, which provides a visual means for subsequent important flight events.
(6) LDPC coding and decoding is applied to space segment for the first time in aerospace engineering, and the main indexes such as coding gain and efficiency are superior to international (CCSDS) standards, which improves China's position and voice in the field of international deep space channel coding and decoding.
(7) The long-life technology of the high-pressure gas path of the propulsion system was verified in orbit for the first time, which laid a dynamic foundation for high-intensity (time span more than half a year, times 10) orbital maneuver and subsequent L2 point and asteroid detection tests.
(8) Break through the integration technology of detection sensor and load for the first time, and use imaging sensor to complete the navigation test of satellite-ground loop.
(9) In the complex environment of the Earth-Moon and Sun-Earth satellites, aiming at the complex perturbation of the moving point of the gravity balance of the Sun-Earth, the lack of analytical solution in orbit design, and the long TT&C distance, the technologies such as manifold design of nonlinear system and low-energy transfer orbit control are overcome to realize the orbit design, flight control and long-distance TT&C communication from the lunar orbit to L2 point. It is the first time in the world to fly from the lunar orbit to the L2 point of Lagrange. The energy spectra of the earth's far magnetic tail ions, solar flare bursts and cosmic gamma bursts were scientifically detected. China has become the third country to conduct space exploration in L2 after the United States and Europe.
(10) broke through the deep space orbit and TT&C communication technology with a distance of100000 kilometers from the ground, and realized interstellar flight for the first time. Based on the strong constraints of energy, distance and time, combined with the physical characteristics of the target, the selection strategy of potential asteroid targets is put forward, and the approach flight detection method and gaze imaging technology based on the fading point of high-speed rendezvous are designed and realized for the first time in the world. The asteroid Tutatis, which flew over 4 179, was successfully approached for the first time in the world, and an optical color image with 3m resolution was obtained.
(1 1) innovatively uses the characteristics of Lagrange point orbiting the sun, and under the constraints of satellite propellant, satellite-ground communication distance and ground large antenna progress, it is the first time in the world to transfer from Lagrange point to fly over small celestial bodies.
(12) Through innovative design, comprehensive verification and careful implementation, the satellite's surplus resources are fully utilized, and the satellite's potential is brought into play. The multi-objective and multi-task exploration with international characteristics and standards has been realized, and the outstanding effect of "good, fast and economical" has been achieved.
(13) Through the transformation and application of the previous research results, the multi-station special observation at home and abroad was carried out, and the orbit determination prediction of the target asteroid was realized, with the accuracy reaching the international advanced level.
2. Scientific achievements
Chang 'e II was equipped with seven kinds of scientific payloads, such as CCD stereo camera, γ spectrometer, solar wind ion detector and high-energy particle detector, and obtained about 6 TB of original data, such as high-resolution full moon image, local image of Hongwan area and Earth-Moon space. According to the release policy of scientific data of lunar exploration project in China, it has been released to relevant universities and research institutes in China, including Hong Kong and Macao, which will drive the analysis and research of scientific data of lunar and space science in China. At present, many important scientific achievements have been made, such as the full moon image with a spatial resolution of 7 m and the distribution map of various elements on the moon surface. The analysis and research of scientific data is a long-term process. After a period of research, based on the data obtained by Chang 'e II, scientists will further deepen their knowledge and understanding of lunar science and space science, and obtain more innovative results to answer scientific questions such as the origin of the moon and the solar system.
At 2012121316: 30, Chang' e-2 satellite passed Tutatis at close range after 200 days' trek and five corrections, and successfully obtained a complete high-resolution image. The successful implementation of this mission has created a number of records: the first asteroid exploration from Lagrange point; The first close-range detection of Tutatis; A high-resolution optical image of Tutatis was obtained for the first time.
Through the mission and extended experiment of Chang 'e-2, the high-resolution image of Hongwan area in the pre-selected landing area of Chang 'e-3 was obtained. It is verified that the main engine maneuver technology of high thrust autonomous orbit is adopted under the condition that the back of the moon is invisible, which has carried out technical verification for the soft landing of Chang 'e-3 and laid a good foundation.
CCD stereo camera has obtained 35-track local stereo images with a spatial resolution of about 1.3m and a full-moon stereo image with a spatial resolution of 7m and a coverage of 100, which is the highest and clearest full-moon stereo image in the world so far.