Chang'e 2 is the second moon orbiting satellite in China's lunar exploration programChina Lunar Exploration ProjectThe technology leader star of Phase II was originallyChang'e-1The backup star is named after Chang'e, a mythical figure in ancient China.
On October 1, 2010, Chang'e-2 was launched from Xichang Satellite Launch Center[1-2]；On October 6, 2010, Chang'e-2 was captured by the moon and entered the lunar orbit[3]；On August 25, 2011, Chang'e-2 entered the Lagrange L2 point orbit[4]；On December 15, 2012, the Chang'e-2 project was declared closed[4]。
The complete success of Chang'e-2 mission marks that China has made breakthroughs in the field of deep space exploration and mastered a large number of new core technologies and key technologies with independent intellectual property rights, laying a solid technical foundation for the follow-up implementation of the second phase of the lunar exploration project and the further development of deep space exploration such as Mars,China has taken another important step in the process of moving from a space power to a space power[5]。
On December 17, 2007, Chang'e-1 backup star was named Chang'e-2[7]。
On June 24, 2008, the symposium on Chang'e-2 satellite was held;In July, the second round of overall plan demonstration of Chang'e-2 was completed;In October, Chang'e-2 was approved by the State Council.In 2008, the design of the whole Chang'e-2 satellite program was completed. It mainly carried out research and development work such as top-level planning, technical status clearing and review, and overall specification formulation, as well as mission orbit design, interface coordination between large systems, subsystem technical specification formulation, and technical breakthrough and special testing of new products such as X-band transponders[7]。
In 2009, the prototype development of Chang'e-2 single machine, technical test and payload subsystems was completed;Special coordination and all special tests such as the requirements of speed height ratio compensation on track determination accuracy and the guarantee of 15 km orbit flight large system have been completed;The electrical performance test and software/FPGA drop welding in the development, final assembly and AIT stages of the prototype products have been completed;It also carried out quality review and recheck recalculation of orbit design and space single event effect protection, and supplemented technical monographic studies such as "orbit design, flight procedures, rainbow bay imaging, surveillance camera/ultraviolet imaging".
In June 2010, the quality review and factory review of Chang'e-2 were completed;On July 10, Chang'e-2 arrivedXichang Satellite Launch Center[8]。
Chang'e-2 Launch
Operation history
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Launch
date
time
flight time
event
October 1, 2010
11:00
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Officially enter the launch procedure and hold the last weather "conference"
13:30
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The weather report was released, and the rocket was filled with liquid hydrogen at low temperature
17:00
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Enter the pre launch system, and the ground starts to power up the system
18:20
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The slewing platform of No. 2 tower unfolds step by step from top to bottom
18:45
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The last group of attendants left tower 2
18:58:27
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The rocket is powered from the ground to the internal battery of the system
18:58:57
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Count down to 60 seconds and prepare for ignition and launch
18:59:57
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ignition
19:00:00
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take off
19:02:07
127.4992 seconds
booster separation
19:02:23
143.4972 seconds
Primary and secondary separation
19:04:15
255.4117 seconds
Throw down the fairing
19:05:24
324.7087 seconds
Secondary and tertiary separation
Three level one-time shutdown
Three stage secondary ignition
Level 3 secondary shutdown
Final speed correction shutdown
19:25:33
1533 seconds
Separation of star and arrow
reference material:[1-2]
On orbit operation
On October 2, 2010, Chang'e-2 completed its first missionEarth Moon imaging[9]。
On October 6, 2010, Chang'e-2 was captured by the moonNear lunar braking, entering the elliptical lunar orbit with a period of about 12 hours[3]。
In April 2011, the design life of Chang'e-2 has expired, and the established engineering goals and scientific tasks have been completed[4]。
Expand operation
Photo 1 of asteroid 4179 (exposure time: 7 ms)[10]
On June 9, 2011, Chang'e-2 officially flew away from the moon to the L2 point of the solar terrestrial Lagrange, starting a new journey of deep space exploration in China[4]。
On August 25, 2011, Chang'e-2 entered the Lagrange L2 point orbit[4]。
On June 1, 2012, Chang'e-2 entered the transfer orbit to an asteroid after a controlled orbit change[4]。
On December 13, 2012, Chang'e-2 met with the 4179 asteroid (Toutatis) and captured the asteroid image, completing the first close range optical exploration of the 4179 asteroid.
On December 15, 2012, Chang'e-2 flew into the deep space about 7 million kilometers away from the earth, passing by the asteroid Tutatis, marking the success of Chang'e-2's further expansion experiment and the closure of Chang'e-2 project[4]。
On January 5, 2013, the distance between Chang'e-2 and the earth exceeded 10 million kilometers.
On February 28, 2013, the distance between Chang'e-2 and the earth exceeded 20 million kilometers.
On July 14, 2013, the distance between Chang'e-2 and the earth exceeded 50 million kilometers[11]。
On November 26, 2013, the distance between Chang'e-2 and the earth exceeded 61 million kilometers[12]。
In the middle of 2014, the distance between Chang'e-2 and the earth exceeded 100 million kilometers[13]。
flying commission
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Flight plan
The Chang'e-2 mission is divided into seven phases: pre launch preparation phase, active phase, phase modulation orbit phase, earth moon transfer phase, moon capture phase, moon working state establishment phase and moon operation phase.
S/N
start time
Flight plan
one
October 1, 2010
Launch
two
October 2, 2010
Earth moon transfer
three
October 6, 2010
Lunar capture
four
October 6, 2010
Circumlunar exploration
five
April 14, 2011
Lunar orbit deepening exploration
six
June 9, 2011
Lunar to Lagrange L2 point transfer
seven
August 25, 2011
Solar terrestrial Lagrange L2 point detection
Mission purpose
1. Obtain the three-dimensional image of the moon surface with a resolution better than 10 meters, providing the basis for the subsequent optimization of landing areas, and providing the original data for the division of the fine structure, fracture and annular structure of the lunar surface geomorphic units[14]。
2. Detect the lunar material composition, detect the content and distribution characteristics of silicon, magnesium, aluminum, calcium, titanium, potassium, thorium, uranium and other elements on the lunar surface, and obtain element distribution maps with higher spatial resolution and detection accuracy[14]。
3. To detect the characteristics of lunar soil.Using microwave detection technology, measure the microwave radiation characteristics of the moon surface, obtain the microwave radiation brightness temperature data, and estimate the thickness of the lunar soil[14]。
4. To explore the space environment of the Earth moon and near moon.Chang'e-2 in orbit is the peak year of solar activity, which is the best time to explore and study the solar high-energy particle events, solar wind and its impact on the lunar environment.The solar high-energy particle detector and solar wind ion detector are used to obtain the flux, composition, energy spectrum of interplanetary solar high-energy particles and solar wind ions, as well as their spatiotemporal variation characteristics, so as to study the interaction between solar activity and the Earth Moon space and near Moon space environment;Obtaining the earth moon space environmental data can provide environmental scientific data for the follow-up mission of China's lunar exploration project[14]。
Task characteristics
"Fast, near, refined and abundant"
key word
Characteristic description
fast
Chang'e-2 satellite is directly sent into the lunar orbit by the carrier rocket, without passing through the transition orbit, which is more efficient.
near
Chang'e-2's orbit around the moon is reduced to 100 kilometers, and the closest point is only 15 kilometers, so we can observe the moon at a closer distance.
essence
The measurement accuracy of Chang'e-2 is improved. The camera resolution is 10 meters at 100 km orbit and 1.5 meters at 15 km orbit, with high resolution.
many
Chang'e-2 carried out many experiments, such as deep space exploration, landing camera test and other projects.
reference material:[15]
Complex flight process control
Chang'e-2 needs to go through 100km × 100km and 100km × 15km test lunar orbit, needs to go through many complex orbit and attitude maneuvers, and has high requirements for satellite orbit control[16]。
Complex space environment
Chang'e-2 will experience two lunar eclipses during its lifetime, and the effective shadow time of each eclipse is about 3 hours.During this period, the satellite is unable to obtain light energy, and the satellite temperature will rapidly decrease, requiring high satellite energy, temperature, and the whole satellite working mode[16]。
Complex control mode of three body combination
During the lunar cycle of Chang'e-2, the stars should be oriented to the moon, the solar wing should be oriented to the sun, and the directional antenna should be oriented to the ground. Therefore, the attitude control requirements for the satellite body, solar wing, and antenna are high[16]。
Many newly developed and improved equipment
In addition to the six payloads of Chang'e-1, Chang'e-2 satellite has also added a technical test subsystem, including engineering loads such as X-band transponder and landing camera. Therefore, the types of intelligent terminals of the satellite system are complex, and there are special requirements for processing modes such as satellite information collection, storage, compression and coding[16]。
technical conditions
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technical requirement
project
technical requirement
Satellite weight
≤ 2480kg
Satellite dry weight
≤ 1175kg
Working track
100km × 100km
Test track
100km × 15km
Satellite lifetime
6 months
Structure body size
2000mm × 1720mm × 2200mm
Attitude control accuracy for lunar pointing
≤± 1 degree (3 σ)
Stability of lunar pointing attitude control
≤ 0.005 degrees/second
Promotion mode
Bipropellant unified propulsion system
Power supply output power
1466W
Angle of incidence
45 ° incidence angle
Measurement and control system
USB+VLBI
Telemetry code rate
512 bits per second/1024 bits per second (after encoding)
Remote control code rate
125 bits per second
Coding method
Convolutional coding/LDPC coding
Data transmission modulation mode
BPSK
Data transmission rate
6 megabits per second
reference material:[17]
Satellite composition
Chang'e-2 uses the Dongfanghong 3 satellite platform, with a total mass of 2350kg, a design life of one year, and a size of 2000mm × 1720mm × 2200mm. It inherits the mature technologies and products of Earth satellites such as Yuanzi 1 and Yuanzi 2 for adaptive transformation.
Chang'e-2 satellite has 10 subsystems, which can be divided into service system and payload.The service system includes: structure, thermal control, guidance/navigation and control (GNC), propulsion, power supply and distribution, data management, measurement and control data transmission, directional antenna, technical test, etc.The load subsystem is composed ofccd stereo camera 、Microwave detector、solar high energy particle detector And other loads.
TT&C communication
Use of Chang'e-2LDPCEncoding function, the gain is about 2.5 dB higher than convolutional encoding;The engineering load data transmission channel has been added, and a multi file code rate of at least 23.4375 kilobits per second has been designed, which can support data transmission 20 million kilometers away from the ground.
Flight carriage
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executive summary
Scientific instruments carried by Chang'e-2
Chang'e-2 satellite is equipped with 7 kinds of detection equipment, including CCD stereo camera, laser altimeter, gamma ray spectrometer, X-ray spectrometer, microwave detector, solar high-energy particle detector and solar wind ion detector. The total payload is about 140 kg.
APS camera
Chang'e-2 carried four APS cameras as the main equipment of the technical test subsystem, and carried out new technical test verification on the cameras.It mainly includes APS in orbit imaging technology, high system integration technology, automatic exposure technology, high magnification compression technology, space environment adaptive imaging design and other key technologies[10]。
ccd stereo camera
Chang'e-2 is equipped with a TDI-CCD camera, which uses the principle of multiple exposures of multiple linear array CCD to the same target. This can meet the requirements of improving the resolution for camera exposure control, and can obtain ultra-high resolution images with a resolution of more than 1.5 meters in the local area of the near lunar arc[18]。
solar high energy particle detector
Chang'e-2 is equipped with a solar high-energy particle detector, which can obtain the flux, composition, energy spectrum of interplanetary solar high-energy particles and solar wind ions, as well as the characteristics of their changes with time and space, to study the interaction between solar activity and the Earth Moon space and near Moon space environment, and provide environmental scientific data for subsequent lunar exploration projects[19]。
X-ray and gamma ray spectrometer
Chang'e-2Gamma ray spectrometer, its detection crystal is usedLanthanum bromideNew material, the detection sensitivity is more than doubled;The X-ray spectrometer carried by Chang'e-2 can detect the content and distribution characteristics of nine elements on the moon surface, including silicon, magnesium, aluminum, calcium, titanium, potassium, thorium and uranium, and obtain element distribution maps with higher spatial resolution and detection accuracy[19]。
technical support
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key technology
1. During the operation of Chang'e-2, all orbit and maneuver flight control technologies before power descent in the subsequent landing mission were designed and verified, and directly enteredEarth moon transfer orbitIt is the first time to use X-band measurement and control to conduct high-resolution imaging of Chang'e-3 landing area.
2. In view of the uneven gravity field of the moon and the high undulating terrain environment, the key technologies such as the design of the moon's quasi frozen orbit, autonomous inertial alignment of satellites, and the splicing of mobile orbits were broken through. For the first time, 100 km circular orbit and 100 km × 15 km orbit flights were successfully realized, and the ignition and orbit transfer of the main engine was realized for the first time without measurement and control on the back of the moon.The maximum accuracy of satellite orbit control is 0.02%.
3. Chang'e-2 first adopted time delay integration in international lunar exploration（TDI）Imaging technology: two kinds of velocity height ratio compensation imaging methods are designed, namely, ground traveling frequency data injection and altimetry data assistance, to obtain a 7-meter resolution three-dimensional image of the whole moon;Local images with a resolution of 1.3 meters were obtained, reaching the international advanced level.
4. The first X-band high-sensitivity digital TT&C transponder based on the unified carrier system has been innovatively developed, which has achieved many breakthroughs in spaceborne TT&C technology in the field of deep space exploration.The X-band deep space measurement and control system and technology are verified by the in orbit test.It has broken through 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 has reached 1 mm/s, the ranging accuracy has reached 1 m, and the remote control of 7.8125 bits per second at an extremely low code rate has been realized.
5. It broke through the micro and small intelligent design technology, and realized the monitoring and imaging of the earth moon space flight process for the first time.For the first time, dynamic images of key links such as solar wing deployment, antenna deployment/rotation and main engine ignition were obtained in real time.
6. For the first time, it is applied in space segment in aerospace engineeringLDPCThe main indicators such as coding and decoding, coding gain and efficiency are superior to the international (CCSDS) standards.
7. The long-life technology of the high-pressure gas path of the propulsion system was verified for the first time in orbit, laying a dynamic foundation for high-intensity (time span more than half a year, more than 10 times) orbital maneuvers and subsequent L2 point and asteroid detection tests.
8. It is the first time to break through the integrated technology of detection sensor and payload, and complete the satellite ground large loop navigation test by using the imaging sensor.
9. In the complex environment of the Earth Moon Star and the Sun Earth Star, aiming at the difficulties such as the complex perturbation of the libration points of the sun and the earth gravity, the lack of analytical solutions in the orbit design, and the long measurement and control distance, the nonlinear system manifold design, low energy transfer orbit control and other technologies were overcome, and the orbit design, flight control, and remote measurement and control communication from the lunar orbit to L2 point were realized.For the first time in the world, it has flown from the lunar orbit to the Japan Earth Lagrange L2 point for exploration, and carried out scientific exploration of the Earth's far magnetic tail ion spectrum, solar flare bursts and cosmic gamma bursts, making China the third country after the United States and Europe to achieve L2 point for space exploration.
10. It has broken through the deep space orbit and TT&C communication technology 10 million kilometers away from the earth, and achieved interplanetary flight for the first time.Based on strong constraints such as energy, distance, time and target physical characteristics, a strategy for selecting potential asteroid targets was proposed. For the first time in the world, an approach overflight detection method and a staring imaging technology based on high-speed rendezvous fading point were designed and realized.For the first time in the world, it successfully approached and flew over the asteroid 4179 Tuttis and obtained optical color images with a resolution of 3 meters.
11. Innovative utilizationLagrange pointWith the characteristics of circling the sun with the ground, under the constraints of satellite propellant, satellite ground communication distance, ground large antenna progress and other constraints, it is the first time in the world to realize the transfer from Lagrange point to fly over small objects.
12. Through innovative design, comprehensive verification, and careful implementation, we made full use of the satellite's remaining resources and gave full play to the potential of the satellite. From the moon to L2 and then to Tutatis, we achieved multi-target and multi mission exploration with international characteristics and standards, and achieved outstanding results of "good, fast, and economical".
13. Through the transformation and application of previous research achievements, we carried out multi station special observation at home and abroad, achieved the orbit determination and prediction of the target asteroid, and the accuracy reached the international advanced level[20]。
Space experiment
S/N
experiment
one
Breakthrough in launch technology of launch vehicle directly launching satellite into earth moon transfer orbit
two
Test X-band deep space TT&C technology and preliminarily verify the deep space TT&C system
three
Validate 100km lunar orbit capture technology and accumulate more near lunar space environment data
four
Verification of 100 km × 15 km lunar elliptical orbit maneuver and rapid orbit determination technology
five
Test low-density parity check code telemetry channel coding, high-speed data transmission, landing camera and other technologies
six
High resolution imaging test on the lunar rainbow bay landing area pre selected for Chang'e-3 mission
seven
Transfer and Test of Flying from Lunar Orbit to Solar Earth L2 Point
The complete success of Chang'e-2 mission marks that China has made breakthroughs in the field of deep space exploration and mastered a large number of new core technologies and key technologies with independent intellectual property rights, laying a solid technical foundation for the follow-up implementation of the second phase of the lunar exploration project and the further development of deep space exploration such as Mars,China has taken another important step in the process of moving from a space power to a space power[5]。(Academician of the Chinese Academy of Sciences, representative of Chang'e-2 mission project development unit, chief designer of launch vehicleJiang JieComment)
Hongwan
The mission and expansion experiments of Chang'e-2 have obtained high-resolution images of Hongwan area, the pre selected landing area of Chang'e-3;Verified the maneuverability technology of using the main engine for high thrust autonomous orbit when the back of the moon is not visible, which has carried out technical verification for the soft landing of Chang'e-3 and laid a good foundation[22]。(China News Online Review)
The controlled and accurate orbit of Chang'e-2 into the solar terrestrial Lagrange L2 point is the first time for China to carry out the design and control of the Lagrange point transfer orbit, and realize 1.5 million km long distance measurement and control communication.It marks that China has become the third country in the world to visit the L2 point of Lagrange, and also the first country in the world to reach this point from the lunar orbit[23]。(commented by People's Daily)
