The Beidou-3 global satellite navigation system, announced on July 31, 2020, is one of the most dazzling achievements of China's aerospace industry in the past decade. This global satellite navigation system, which is independently built and operated by China, has played an irreplaceable role in safeguarding national security and serving economic and social development. From its official launch in 1994 to its full completion in 2020, the Beidou satellite navigation system took 26 years, organized a total of 44 Beidou launch missions, and successively sent 59 Beidou satellites into predetermined orbits, with a mission success rate of 100%!
Behind the world's remarkable achievements, in addition to the outstanding performance of stars and arrows, there is also a mysterious "shepherd" team that guards the largest constellation system in China to date. Especially in the deployment mission of the Beidou-3 GEO-2 satellite network in March 2020, the team overcame various unfavorable factors such as the new crown epidemic, and in the face of satellite failure and out-of-control situation, with excellent skills and the spirit of responsibility, successfully rescued the satellite and sent it into the predetermined orbit to ensure that the Beidou-3 global satellite navigation system was successfully completed as scheduled in that year. As the guardian of China's space assets, this obscure team is also turning the tide again and again, practicing the great spirit of "integrating brilliance into the constellation of the motherland".
Schematic diagram of the Beidou-3 global satellite navigation system
Thrilling 5 minutes
At 19:55 on March 9, 2020, the mainland used the Long March 3B carrier rocket at the Xichang Satellite Launch Center to smoothly send the Beidou-3 GEO-2 satellite into a large elliptical orbit of more than 200 kilometers near the perigee and more than 36,000 kilometers from the apogee. As the 29th satellite of the Beidou-3 global satellite navigation system, the successful launch of the Beidou-3 GEO-2 satellite means that China's Beidou is only one step away from global networking. Next, as long as the Beidou-3 GEO-3 satellite is smoothly sent into the predetermined orbit in June of that year, the deployment of the Beidou-3 global satellite navigation system will be successfully concluded.
However, at the Xi'an Satellite Measurement and Control Center, the successful launch of the big red screen indicates the beginning of the follow-up more onerous tasks of China's "shepherds". According to the plan, after entering the large elliptical orbit, the Beidou-3 GEO-2 satellite will implement five orbit changes, gradually raising the height of the perigee of the satellite orbit and reducing the orbital inclination. The ultimate goal is to put satellites into geostationary orbit at a distance of more than 36,000 kilometers from Earth.
During the first orbit change that took place on the second day of launch, everything went as usual, but in the process of implementing the second orbit change, an accident occurred. After the satellite's main engine ignited for ten minutes, telemetry data showed that the satellite's attitude suddenly changed its attitude. "The screen in the command hall shows that there is an interference torque that causes the attitude of the satellite to be disturbed" Wang Xin, senior engineer of the Xi'an Satellite Measurement and Control Center, told the Global Times reporter, which is like a person who was originally standing in a correct posture, but suddenly an external force appeared, pushing the person to the left and then to the right.
Anomalies in satellite attitude often trigger a series of catastrophic consequences. Wang Xin said that the instability of the satellite attitude will cause the devices on the satellite to be damaged so that they cannot work at all, and more seriously, it may cause the communication between the satellite and the ground to be interrupted, resulting in the inability of ground personnel to monitor and control the satellite.
Beidou-3 GEO-2 satellite rescue mission site
In the face of sudden abnormal situations, the flight control personnel of the Xi'an Satellite Measurement and Control Center did not even have much time to be shocked and dazed. Although it was not clear at the first time why the attitude of the satellite suddenly changed, it was necessary to urgently formulate a disposal method to quickly control the attitude of the satellite.
Generally speaking, for each launch mission, in the command hall of the Xi'an Satellite Measurement and Control Center, there will be a flight control team of the center and the technical team of the satellite developer to jointly perform the early monitoring and control task in order to better grasp the relevant situation and status of the satellite. However, in March 2020, when the new crown epidemic was raging across the country, although the technical team of the satellite developer was also in the Xi'an Satellite Measurement and Control Center, due to the requirements of epidemic prevention and control, the two teams could only be scattered in two work halls to carry out this task, and they could not share data and exchange ideas face-to-face at the critical moment of satellite failure, and could only discuss solutions through telephone and dispatchers.
In the face of the dangerous situation that the satellite interference moment data on the big red screen continues to increase, the ground flight control personnel decide to set a critical parameter for the satellite after researching and judging, and once the parameters of the satellite attitude change reach this value, the ground personnel must immediately send instructions to urgently shut down the main engine of the satellite to ensure the safety of the satellite. "The situation at that time was that if the attitude change parameters of the satellite exceeded this critical point, the satellite might lose contact and lose control, and if we had not implemented the main engine shutdown before that, then the satellite would no longer be able to accept the instruction to shut down, and in the end we could not know what state the satellite was in and where it flew." Wang Xin said that because only the main engine was working in the power system of the satellite at that time, everyone initially judged that there should be a problem with the main engine of the satellite that led to the change of the satellite attitude, and once the main engine was turned off, the attitude of the satellite should be stable.
Finally, five minutes after the change in the attitude of the satellite, the abnormal parameters reached a critical point, and ground personnel urgently sent instructions to shut down the main engine of the satellite. After the shutdown, the large screen in the command hall soon showed that the trend of satellite attitude change was gradually slowing down. "That is to say, within about five minutes of the abnormal situation on the satellite, we have preliminarily judged the problem of the satellite, formulated and implemented the disposal measures, and ensured that the satellite is not completely out of control. Wang Xin recalled.
20 days of swinging gas back to the intestine
Rescuing satellites from the brink of runaway doesn't give ground flight controllers a sigh of relief. As a type of satellite with the most functions, the most signals, the largest size and the longest life in the Beidou-3 satellite system, the cost of the Beidou-3 GEO orbit satellite is naturally not cheap, and if the satellite cannot climb into the geostationary orbit due to the failure of the main engine, thus losing its due role, it will undoubtedly cause huge economic losses.
In addition, according to the overall planning of the Beidou-3 global satellite navigation system, since November 2017, the deployment of 30 Beidou-3 satellites will be completed through 18 high-density launches in more than two years, so as to realize the global networking of the Beidou-3 satellite. Wang Xin said that this networking plan is very full, and interlocking, for the major systems of the entire project, it is difficult to have a "margin" to reissue a satellite to fill the gap within the scheduled time. "As the penultimate networking satellite before the system is fully completed, if the Beidou-3 GEO-2 satellite fails to put into normal operation, it will take at least another year to complete the launch of the 'substitute' satellite, which means that the expected goal of completing the network in 2020 will be difficult to achieve, and the relevant plans for the full completion of the Beidou-3 global satellite navigation system will be postponed."
Beidou-3 GEO-3 satellite measurement and control mission site
In the face of such a non-fathomable satellite, these task personnel who followed the Beidou Project all the way were not willing to give up. After resolving the crisis of the satellite out of control, the ground flight controller immediately sent instructions to let the attitude of the satellite gradually return to normal, and entered the safe working mode, and then began to work with the technical team of the satellite developer to carry out a detailed analysis of the abnormal phenomenon and data of the satellite, trying to locate the fault point of the satellite as soon as possible.
Combined with the results of the analysis, the satellite developer applied the identification part of the satellite to conduct a test of the nature of "resuring" on the ground through simulation and other means, and found that the reason why the attitude of the satellite was out of control was because of the phenomenon of ablation in the throat of the main engine nozzle. "In layman's terms, the throat of the main engine nozzle of the satellite burns a hole, which will lead to the instability of the thrust of the engine, and the working fluid leaking from the burned place will cause disturbance to the attitude of the satellite, resulting in a change in the attitude of the satellite." Wang Xin said.
At that time, the satellite was stranded in a transition orbit of more than 6,000 kilometers at perigee altitude, and if it wanted to continue to climb to geostationary orbit, it must rely on the satellite's own power system to raise more than 30,000 kilometers near the site altitude. Since the previous orbit change plan is formulated around the normal operation of the satellite main engine, there is a voice proposition that since the attitude of the satellite has been stabilized, it is possible to try to re-ignite the main engine of the satellite and implement the orbit change as originally planned.
However, another voice believes that because the ablation point of the main engine nozzle of the satellite will always produce an interfering moment, affecting the stability of the satellite attitude, and the working fluid emitted may cause damage to the satellite components closer to the nozzle, this scheme is too risky. A more complex but safer solution won out: abandoning the satellite's main engine and instead using a possibility-controlled thruster with less on-satellite thrust to maintain the satellite's attitude stability to implement more orbital changes.
However, such a programme also faces a number of constraints in its implementation. Wang Xin said that in the process of satellite orbit change, it is particularly critical to grasp the status of the satellite at any time and send instructions in time to accurately implement the satellite thruster switch and switch, which requires ensuring the smooth flow of the satellite-to-ground measurement and control link between the ground and the satellite. However, due to the limited scale of the continental measurement and control network, it is impossible to realize the full arc measurement and control of the satellite in orbit, therefore, in the selection of the satellite orbit change point, in addition to being as close as possible to the most "time-saving and labor-saving" orbital apogee when changing orbit, the orbit change point must also be within our measurement and control range.
In addition, in this more complex orbit change process, it is necessary to save the fuel of the satellite as much as possible and reduce the impact on the life of the satellite's attitude and orbit control thruster. "This requires us to develop a reasonable ignition strategy, optimize satellite fuel consumption, ignition orbit position and ignition arc segment, and use different thruster combinations to implement ignition at different orbit change points, so as to avoid the over-life use of satellite attitude and orbit control thrusters because of the execution of emergency orbit change tasks." Wang Xin said.
After comprehensively considering various factors, after careful calculation by a group of "strongest brains" in the task team, three sets of posture and rail control thruster combinations with sufficient thrust were finally matched to formulate the reasonable working time of each group of thrusters and adjust the thruster jet direction. After a pilot fire that confirmed that each thruster combination would ensure the satellite's attitude stability, the exciting orbit change program finally began.
On March 28, after spending nearly 20 days and implementing nearly 20 precise orbit changes, the Beidou-3 GEO-2 satellite finally relied on more than ten posture-orbit control thrusters on the star to achieve continuous orbital altitude, gradually lower the orbital inclination, and successfully fixed the earth at rest of more than 36,000 kilometers above the ground. This satellite, which is related to the overall construction of the Beidou Project, was finally successfully rescued!
On June 30, 2020, the last networking satellite of the Beidou-3 system, the Beidou-3 GEO-3 satellite, was successfully fixed
What is even more valuable is that after the subsequent calculation of the technicians of the Xi'an Satellite Measurement and Control Center, the unexpected "savior" mission did not have a significant impact on the design and service life of the satellite. Wang Xin said that thanks to the redundant design of the satellite development team, the actual amount of fuel carried by the satellite, as well as the actual service life of the devices on the satellite, exceeded the design service life, "In this 'savior' mission, we have also formulated the most optimized orbit change strategy, as far as possible to shorten the ignition time of the satellite attitude orbit control thruster, the final fuel consumed, and the loss caused by the thruster is very small, and the remaining service life of the satellite can still be greater than the design service life." ”
A glorious decade
"Space assets are national strategic assets, which must be managed and used well, and even more must be well protected." In the past decade, the number of satellites in orbit on the mainland has become more and more, the functions are getting stronger and stronger, and the value is getting bigger and bigger, as the most solid guardian of China's space assets, the "Shepherd" team of the Xi'an Satellite Measurement and Control Center has also lived up to its mission and written more "hidden and great" in the vast universe.
"The growing number of Chinese satellites and the increasingly complex space environment mean that the tasks we are undertaking are becoming more and more arduous, but also more and more significant." Yang Yong'an, senior engineer of the Xi'an Satellite Measurement and Control Center, told the Global Times reporter that today, the number of various satellites managed by the Xi'an Satellite Measurement and Control Center has reached more than three hundred, of which more than one-third of the satellites are in overdue service, and these long-term satellites in orbit will inevitably fail due to equipment, device aging and other issues, but with excellent operation and maintenance, the satellite is still in good working condition, and it plays a residual heat in space to serve the national economy and people's livelihood.
The secret to making the "China Star" shine in space for a long time lies in excellent skills and the spirit of courage to take responsibility. Yang Yongan said that in the past decade, the Xi'an Satellite Measurement and Control Center has carried out a number of innovative explorations, and has formed a full-process fault diagnosis and maintenance capability for the "physical examination", "diagnosis" and "treatment" of satellites in orbit. Summarizing the experience of implementing measurement and control tasks over the years, the satellite failure analysis plan and rescue plan can deal with most of the current satellite failures, and it is precisely under the guarantee of this system that the "Shepherd" team of the Xi'an Satellite Measurement and Control Center has successfully completed many satellite rescue missions including Zhongxing 9A and Beidou-3 GEO-2 satellites in the past ten years, creating many space miracles.
Xi'an Satellite Measurement and Control Center Beidou Measurement and Control Team
However, the value created by "reborn" satellites is not always known. Like many other space systems, "doing earth-shattering things and burying celebrities in anonymity" is also a tradition and belief deeply rooted in the Xi'an Satellite Measurement and Control Center.
In the 1970s, China's aerospace monitoring and control network began to build, and a group of young scientific and technological personnel with superb knowledge participated in it and embarked on the vigorous construction of the mainland's aerospace measurement and control industry. They bent down to build the foundation of the country, cleverly weave constellations, pastoral stars, and the story of winning space was once a secret that must be hidden, unspeakable, so those who were infected by their dedication could only write this feeling into a song called "The Motherland Will Not Forget", the song that "I don't need you to praise me, I don't want you to repay me, I melt the glory into the constellation of the motherland." It is a true portrayal of the lives of many Chinese "shepherds".
Source: World Wide Web