2021February 10 19: 52, China's first Mars exploration mission? Tian Wen No.1? Mars capture braking was implemented on the probe. After the engine worked for about 15 minutes, the probe successfully entered a large elliptical ring fire orbit with a near fire point height of about 400 kilometers, a period of about 10 Earth days and an inclination of about 10, becoming the first artificial Mars satellite in China to realize this task? Round and round? The first step of the goal is to successfully start the orbit around Mars mode.

This trip to Mars has four highlights:

1, not to say that you can go;

(1) Traveling to Mars is not equal to walking. A trip to Mars often requires an escape speed as high as 70km/s, but at present, the maximum escape speed provided by human launch vehicles is only about15 km/s. ..

(2) In order to save energy as much as possible, we usually choose the Homan transfer method to realize the transfer from the Earth to Mars, which requires waiting until the Earth and Mars orbit to a specific relative position before launching the Mars probe. The period of revolution of the Earth is about 365.26 days, and the period of revolution of Mars is about 687.99 days. Therefore, the rendezvous period of ground fire is about 778 days (that is, about 26 months). In other words, the Earth and Mars will have an opportunity to meet in orbit by Hohmann transfer every 26 months. What do we call it? Launch window? (Each window lasts about 20 days). According to the launch window in 2020, the development team of the Eighth Academy of China Aerospace Science and Technology Corporation completed the transfer orbit design from the Earth to Mars, and customized an interstellar highway to Mars for our detector.

2. inseparable transfer trajectory design:? Pork chop? , that is? Pork chop? . ? Pork chop? When designers design interplanetary exploration orbits, they draw isoline maps of emission energy required for different launch dates and arrival dates. This contour map looks like two pork chops. Pork chop? This is called openness in the industry.

In order to bring more instruments and equipment to the Mars probe as much as possible and see enough Mars at one time, the orbit designer needs to find the most energy-saving ground fire transfer trajectory. Are you online? Pork chop? Taking the date selected on the map as the initial value, mathematical methods such as differential correction can be used. After iterative calculation in the dynamic model of Mars exploration orbit with certain accuracy, the design results of the ground fire transfer orbit for the mission can be obtained.

After eating the delicious fried pork chop, the designer is going to take our Mars probe along this underground fire road.

Do you have to succeed once? Space brakes? ：

After the launch of (1), China's Mars probe will fly forward along the underground fire expressway at a speed of nearly 65438+100000 km/h (about 30 km/s). At such a high speed, it will take the probe about seven months to reach Mars. At this time, the probe needs to complete key capture and brake control.

(2) The Mars orbiter will start its engine to decelerate the thrust, so that the speed will be captured by the gravity of Mars and become a satellite orbiting Mars, otherwise the detector will fly over Mars and continue to orbit the sun.

(3) In the critical braking section, the research team designed a reliable braking scheme, which can not only accurately judge whether to reduce to the target speed, but also independently judge the magnitude and direction of the engine thrust in real time during the engine thrust deceleration control process, and independently update the braking parameters and corresponding control algorithms to ensure reliable and accurate braking.

4. Is it difficult to balance accuracy and reliability? Diving? Pulled by the invisible hand of Mars gravity, after several months of careful observation and adjustment, the orbiter will separate another key actuator in the trip to Mars.

In about three hours, the orbiter needs to change its orbit to one that has a dangerous collision with Mars, and establish and maintain the attitude required for the lander to enter the Martian atmosphere. At the scheduled separation time, the orbiter and lander must be separated. After flying at a safe distance, the orbiter needs to accelerate its thrust quickly to return to a safe orbit around Mars. The circulator is like an excellent diver, completing a difficult somersault in the air and entering the water at a precise time.

Fall into the water? It is too early to ensure the accuracy of lander entry. Fall into the water? Too late will lead to the risk that the orbiter will hit Mars. Before entering the water, the air rolls, and the attitude rotation of the circulator is accompanied by its own speed change at all times. The angle and time of entering the water should be completely consistent, and this group of super actions needs the circulator to complete without the support of real-time measurement and control on the ground.

Designers carefully consider the potential risks in the separation process, and design an autonomous disposal scheme under the conditions of attitude measurement, speed calculation, thrust output and other factors. In this way, when some thrusters or sensors fail, the orbiter can not only ensure the accurate separation of the orbiter from the lander, but also ensure the safe return of the orbiter after separation. This exquisite difficulty? Diving? You must not miss it.