Long March 5B rocket: The unique skills of the "big guy"

At 14:22 on July 24, the Long March 5B carrier rocket successfully launched the Chinese Space Station Wentian Laboratory, the world's largest single manned spacecraft, from the Wenchang Space Launch Center in China .

The Long March 5B carrier rocket launches the Wentian experimental module (Photo by Wang Lei, a reporter from China Aerospace News)

The Long March 5B carrier rocket, which successfully completed its maiden flight in 2020, is an improved version of the Long March 5 and is specially designed to launch large payloads into low-Earth orbit. Simply put, the two-and-a-half-stage configuration of the Long March 5 has been changed to a one-and-a-half-stage configuration, that is, the core stage and four boosters remain unchanged, and only the core stage 2 is removed. At present, its main task is to launch the various components of our country's Tiangong space station. The success or failure of the Long March 5B flight mission is directly related to the success or failure of the construction of my country's first space station.

Although the Long March 5B is about 3 meters shorter and 20 tons lighter than the Long March 5, it has inherited most of the excellent genes of the Long March 5. Like the Long March 5, the core stage of the Long March 5B is 5 meters in diameter and is bundled with four boosters with a diameter of 3.35 meters. Although the core stage is removed, the length of the fairing is increased to meet the envelope requirements of the space station compartment; the rocket is about 53.7 meters long, with a takeoff mass of about 849 tons, and a low-Earth orbit carrying capacity of 25 tons.

The Long March 5 carrier rocket launches the Wentian experimental module (Photo by Wang Lei, a reporter from China Aerospace News)

Unlike the Long March 5, which is good at long-distance transportation and focuses on geosynchronous orbit and beyond, the Long March 5B is more like a weightlifter, good at handling larger payloads. It focuses on the low-Earth orbit of 300 to 500 kilometers and serves the main battlefield of my country's space station construction. In order to complete the construction mission of my country's space station, the Long March 5B has also cultivated some unique skills.

Special skill 1: "Big head" fairing

my country's Tiangong space station consists of a core module and two experimental modules in a T-shaped layout. The three large modules, the Tianhe core module, the Wentian experimental module and the Mengtian experimental module, were successively sent into low-Earth orbit by the Long March 5B for on-orbit assembly and construction of the basic configuration of the space station. Although it has been disassembled, the size of each module is still amazing. The Tianhe core module is 16.6 meters long, 4.2 meters in diameter, and weighs 22.5 tons. The Wentian experimental module has a total axial length of 17.9 meters, which is 1.3 meters longer than the Tianhe core module, and has a similar diameter and weight. The Mengtian experimental module weighs slightly less, about 21 tons, but its length and diameter are basically the same as those of the Wentian experimental module.

In order to accommodate such a large-sized space station module, the Long March 5B is equipped with the longest and largest fairing in my country. The fairing is 20.5 meters long and 5.2 meters in diameter. The fairing is equivalent to the height of a 6-story building, and it is tailor-made to create a spacious space for launching the core module and experimental module of the space station. The fairing can ensure that the space station module will not be affected by harmful environments such as aerodynamics, aerodynamic heating and acoustic vibration during the journey from the surface of the earth to space.

Long March 5B carrier rocket fairing (Photo taken by Wang Lei, a reporter from China Aerospace News)

In order to make such a huge fairing both reduce the aerodynamic drag during the rocket's flight and have sufficient structural strength, the fairing also adopts a streamlined von Karman curve shape. Since the surface of the von Karman curve shape is not a plane after unfolding, the previous conical fairing manufacturing method cannot be simply used, and the manufacturing difficulty is increased by one level.

Special skill 2: Large diameter cabin-rocket separation capability

During the active phase of the launch vehicle's flight, huge vibrations and overloads will occur. In order to ensure the safety of the payload being transported, a stable and reliable connection needs to be made between the rocket and the payload, just like the "seat belt" on a car secures the "passenger" to ensure safety. However, the requirements are higher than the "seat belt" on a car. The launch vehicle also needs to release the payload neatly and quickly after entering orbit, without any delay, otherwise it may cause certain damage to the payload.

The most special thing about the "Long March 5B" is that the diameter of its connection interface with the space station module is more than 4 meters. With such a large diameter and complex load and environmental conditions, it is necessary to consider the reliability and safety of the connection, ensure the rapid and reliable separation, and minimize the adverse effects of the impact environment during the separation process. To this end, the "Long March 5B" adopts the "shock isolation frame + damping box" shock reduction solution, and applies "particle damping technology" to the damping box, which effectively improves the separation shock and vibration of the cabin-rocket separation interface.

"Particle damping technology" is a new type of passive vibration control technology. It fills a large number of tiny particles in the limited closed space of the vibrating body, and uses the friction and inelastic collision between the tiny particles during vibration to quickly dissipate the vibration energy and achieve the effect of reducing impact.

Special skill 3: High thrust direct orbital capability

In order to ensure that the payload can be released in place with precise position, attitude and speed, the launch vehicle generally uses a low-thrust rocket engine in the final stage of the rocket, and is also equipped with a terminal velocity correction and attitude adjustment power system. But we know that compared with the "Long March 5", the "Long March 5B" has removed the core second stage, so the low-thrust rocket engine, terminal velocity correction and attitude adjustment power system deployed on the core second stage have also been removed.

The Long March 5B uses a first-stage rocket to send the space station module directly into the predetermined orbit. When the first-stage rocket engine is shut down, about 140 tons of thrust will disappear within a few seconds, which is equivalent to a high-speed train suddenly "braking". So how does the Long March 5B ensure that the space station module can enter the orbit accurately and the rocket can be parked steadily at the designated location?

In order to achieve this function, the Long March 5B has improved the accuracy of the rocket's attitude control and reduced the impact of guidance errors on accuracy by adopting attitude control gain optimization and composite guidance methods. By adopting this control method, it is ensured that the rocket is in the best attitude and the most accurate position when separating. Furthermore, the Long March 5B is also equipped with two deorbiting rockets, so that the first-stage rocket body can perform on-orbit maneuvers in time after separating and releasing the space station module, avoiding the orbital plane where the space station module operates, avoiding possible collisions, and improving the safety margin of the separation of the module and rocket. By taking these measures, the Long March 5B has become the first rocket that can achieve precise orbital insertion of payloads only by boosting and first-stage flight.