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Many people have played shui-bo in the pond when they were young. Provided the strength and technique are right, thrown pebbles can bounce off the surface of the water several times and draw a beautiful arc.
Today this interesting old game has been integrated into high altitude space missions. On December 17, 2020, the Chang’e-5 return capsule used the same principle to make a “water drift” on the surface of the atmosphere and return safely to Earth.
According to experts from China Fifth Academy Aerospace Science and Technology Corporation, Chang’e 5’s “space water drift” is called “semi-ballistic jump return” in terminology, that is, after the come back enter a certain depth of the atmosphere for the first time and glide a certain distance, adjust your attitude. Let it jump again under aerodynamic action, to reduce its flight speed from near the second cosmic speed (11.2 kilometers per second) to within the first cosmic speed (7.9 kilometers per second). The return process thereafter is similar to that of the Shenzhou spacecraft, so I am familiar with it.
Therefore, at 1:59 am on the 17th, the returner Chang’e-5 landed in the planned area of Siziwang Banner in Inner Mongolia.
There are many ways here.
When we were young, we fought in the water, but we were out of control when we dumped it. From the initial return to the atmosphere, the Chang’e-5 return module will eventually land at the preselected landing site, during which it must fly 6,000 to 7,000 kilometers in a state of rapid turbulence and great ups and downs.
How do you manage to “mean hitting”? It is due in large part to the guidance, navigation, and control system provided by Fifth Academy’s 502 Institute.
This system is known as “GNC”. G stands for Orientation. The returning computer will perform guidance processing based on current position and speed information, combined with the position of the landing point, and will automatically plan an optimal flight path to the parachute opening point; N stands for Navigation, high Precision navigation equipment can obtain its own position, speed and other information in real time in the vast universe; C is control (Control), sending instructions to the motor installed outside the returner to operate, thus adjusting the returner’s posture to make the returner fly along the planned trajectory. The three of them work together to help the returnee find his way home.
Of course, it is easier to talk than to do. To achieve a “smooth jump and precise landing”, the scientific research team completed countless simulated flight tests during the development of the return GNC system, simulating millions of flight paths. Perhaps the actual flight path of the returner is not exactly the same as that of either of them, but it certainly cannot exceed this category.
