More than 50,000 welds! See how hard the "Fat Five" works to "run to fire"

On July 23, the Long March 5 Y4 carrier rocket, developed by the China Academy of Launch Vehicle Technology under the China Aerospace Science and Technology Corporation, successfully sent my country's first Mars probe "Tianwen-1" into the planned orbit, and the launch mission was a complete success. Let's look at this set of numbers to see how hard the "Fat Five" has worked to "go to Mars".

Screenshot of the simulated animation of the launch process of Tianwen-1 (provided by the Fifth Academy of China Aerospace Science and Technology Corporation)

"11.2" - the fastest speed of 11.2 km/s

According to the launch mission requirements, the Long March 5 Yao-4 rocket will lift the Tianwen-1 Mars probe and accelerate it to a speed of more than 11.2 kilometers per second, sending the probe directly into the Earth-Mars transfer orbit, starting its journey to Mars.

The speed of 11.2 km/s is the second cosmic velocity. When the speed of a spacecraft reaches this speed, it can completely escape the gravity of the earth and go to other planets or asteroids in the solar system. Therefore, it is also called the "escape velocity."

When the payload launched by a carrier rocket is a satellite or a spacecraft, they all make periodic motions around the earth. The maximum speed of the carrier rocket's last stage only needs to exceed the first cosmic velocity of 7.9 km/s. The first cosmic velocity is the launch speed required for the spacecraft to make circular motions along the surface of the earth. It is also called the "orbital velocity". If the launch speed is lower than this speed, the spacecraft will return to the surface of the earth under the influence of the earth's gravity.

Previously, when launching a lunar probe, the Long March 3B rocket had reached a launch speed of more than 10 kilometers per second. "This time, the Long March 5 Y4 rocket launched the Mars probe, which was the first time that a Chinese rocket reached and exceeded the second cosmic speed of 11.2 kilometers per second, and reached the fastest speed of a Chinese carrier rocket," said Li Dongjie, chief designer of the Long March 5 rocket.

"42" - 42 launch tracks

For general launch missions, a launch window only requires the design of a rocket launch trajectory. However, the launch of the Mars probe is different. If the launch is compared to target practice, the target practice when launching a deep space probe is to hit a "moving target" because the relative positions of the Earth and Mars are constantly changing. Only by constantly adjusting the launch trajectory can the probe enter the orbit more accurately and save its own fuel in the process of heading to Mars.

To this end, the development team has carried out a refined "narrow window multi-orbit" design for the rocket launch orbit. According to the calculation of the mission launch window, this launch has a continuous window period of 14 days, and the launch window width is 30 minutes per day. In order to be more precise and accurate, the developers subdivided the 30-minute launch window into three windows with a width of 10 minutes, and designed the launch orbits separately, that is, three launch orbits were designed for the rocket every day, and a total of 42 launch orbits were designed during the 14-day window period, controlling the orbit deviation within a very small range.

Wang Jue, chief commander of the Long March 5 rocket, said that designing so many launch orbits for one launch is unprecedented in the history of China's space launches. At the same time, this launch also realized the automatic switching of launch orbits for the first time, which can be realized through software.

"35" - 35 reliability improvements

The Long March 5 rocket system continues to carry out the "three re-analysis, re-design and re-verification" work, comprehensively reviewing the standardization and effectiveness of various work from the aspects of design plan, product manufacturing, operation and process control, etc. Through technical improvements, the inherent reliability of the rocket is further improved.

Based on the Long March 5 Yao-3 rocket and the Long March 5B Yao-1 rocket, the Long March 5 Yao-4 rocket has adopted a total of 35 technical improvements and reliability improvement change projects, involving multiple systems such as the onboard control system, measurement system, rocket body structure, pressurization and delivery system, power system, and ground launch support system. Through reliability improvement, the rocket is made more robust and reliable. For example, in order to improve the sealing of the product, gaskets are added to the installation interface of related products; in order to improve the working reliability of the product, filters are added between some valves; in order to ensure the reliability of the product, the fixing method of a sensor wire is improved, and so on.

Among these reliability improvement measures, some improvements are only "in the millimeter". For example, the capillary length of a thrust chamber of an auxiliary power system engine has been increased by 1 mm; the diameter of the charge hole of a certain igniter has been reduced by 1 mm. Behind these subtle changes is the attitude and pursuit of excellence of aerospace personnel.

"120+" - analysis and confirmation of more than 120 key flight action indicators

The Long March 5 rocket development team regards the rocket's "closure analysis and confirmation of key flight action indicators" as a special analysis work, and carries out closure inspection of product and system functions and performance indicators for key actions and important links that affect the success or failure of the flight, such as rocket ignition, booster separation, fairing separation, interstage separation, and rocket-craft separation.

The development team adopted the idea of ​​"flight event chain" and comprehensively sorted out the products involved according to the physical transmission link of the system function. For the sorted products, based on the functional failure analysis, the key design parameters of the products were identified, and the key design parameters were sorted out from the aspects of function, performance, installation and protection adaptability, etc. Taking environmental adaptability as an example, the specific installation location of the cables on the arrow, whether effective protection is carried out, whether the connectors will be abnormally disconnected in a vibration environment, etc., should be paid attention to, and specific indicators should be decomposed.

After entering the launch site, the development team reconfirmed the closure of key indicators based on the final status of the product and test results to ensure that each key link functions normally.

"50000+"——More than 50,000 weld quality reviews and confirmations

The quality of welds directly affects the realization of related product functions and performance, especially some key welds on the rocket body structure, pressurization delivery pipelines and various levels of rocket engines. These welds are not only huge in number, but also directly affect the success or failure of rocket launches. Weld quality control has always been one of the important links in the quality control of launch vehicle products.

As my country's largest and most complex launch vehicle, the Long March 5 has more than 50,000 welds of various types, most of which are Class I welds. The development team conducted a 100% inspection and confirmation of the weld quality through a variety of inspection methods, including X-ray transillumination, hydraulic airtightness test, weld helium mass spectrometry, fluorescence inspection, surface coloring inspection, ultrasonic inspection, kerosene penetration inspection, and test piece sectioning inspection. The welds of the engine products have also been assessed by calibration test runs. After inspection, the quality of all welds on the Long March 5 Yao-4 rocket is stable and reliable, and can meet the requirements for rocket flight.