Mars has always been a magical existence in many science fiction movies. There are strange-looking aliens and mysterious scientific research there. The base even has glowing gems that contain some kind of special energy. These all express human beings' strong thirst for knowledge in real life, eager to understand Mars and get closer to Mars.
"As we all know, there are eight planets in the solar system. From nearest to farthest from the sun, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Although Mars is in the above order It is right next to the Earth, but in fact, the distance between Mars and the Earth is very, very far away." Liu Zhanguo said that the distance between Mars and the Earth is not fixed data. They both orbit the sun, and due to their orbits. Depending on the period, the straight-line distance will always change. According to relevant data, Mars and the Earth are 56 million kilometers apart when they are closest, and more than 400 million kilometers apart when they are farthest. The farther away the ground fire is, the higher the requirements will not only be placed on the speed of the rocket carrying the detector, the detector's orbit technology, and information transmission capabilities, but it will also consume unpredictable manpower and material resources. This has set up many hurdles for mankind’s journey to explore Mars.
Since as mentioned above, the distance between ground and fire is always changing, then it is very important to choose when to detect fire. Liu Zhanguo said that there is a window period for fire detection every two years, so every two years, the world will usher in a small climax of Mars exploration. The opportunity for Mars to be closest to Earth every 26 months is the best time window to launch a Mars probe. According to accurate calculations by scientists, about one month in 2020 will be the best window period for detecting fires. During this period, the probe will arrive at Mars along the "Earth-Fire Main Road" Earth-Fire Hohmann Transfer Orbit, which will save fuel and shorten the arrival time.
Flying to Mars is not as "easy" as flying to the moon. The moon is only 380,000 kilometers away from the earth, but flying to Mars is really difficult to reach the sky. The voyage time of the "Tianwen-1" probe is more than 7 months, and the flight distance is about 400 million kilometers. This distance is about 10,000 times the distance between the earth and the moon, which is equivalent to about 8.3 million marathon races.
How to reach such a long distance? Liu Zhanguo explained that first of all, the rocket carrying the detector must reach the second cosmic speed of 11.2 Km/s so that the detector can escape the gravity of the earth and not run towards other celestial bodies. The emergence of the Long March 5 carrier rocket meets this condition.
Of course, the development of the Long March 5 launch vehicle did not happen overnight. The Sixth Academy of the Aerospace Science and Technology Group, which is responsible for the development of rocket power, has spent more than 20 years, and several generations of astronauts have overcome many difficulties and challenges. After many setbacks, a new generation of green, pollution-free liquid oxygen kerosene engines and hydrogen-oxygen engines were successfully developed. During this process, the space propulsion system developed by the Sixth Academy for the Long March 5 has been continuously upgraded and improved. The variable thrust engine has experienced the test of many missions such as Chang'e landing on the moon and soft landing on the back of the moon. Whether it is product quality or reliability, They are becoming more and more mature.
How can we ensure signal transmission between the ground and the detector at such a long distance? Liu Zhanguo said that signal strength is inversely proportional to the square of the distance. The farther the distance, the weaker the signal. Therefore, before launching the fire detection journey, China took the lead in launching the lunar exploration project and established a more complete deep space detection capability through this task. For ultra-long-distance measurement and control, China has built deep space measurement and control stations and achieved measurement and control of more than 100 million kilometers in the Chang'e-2 expansion mission.
In this fire detection mission, the signal delay caused by the distance between ground and fire is as high as 20 minutes. In other words, a round trip between ground and fire will take 40 minutes. During the critical period when the probe enters Mars orbit and lands, it can only rely on data input by researchers in advance and the probe can make independent judgments.
During this period, many unexpected situations may occur. How can the promotion subsystem prevent these problems in advance? The propulsion subsystem development team of the Sixth Institute of Aerospace Science and Technology Group has developed a variety of failure plans and autonomous management plans for the detector's propulsion subsystem, allowing the detector to judge emergencies by itself and take action to resolve them.