China's aerospace enters the era of rocket recovery; experts analyze highlights of the first flight of Long March 10B.

On July 10, another historic moment for China's aerospace sector unfolded over the South China Sea. At 12:15 PM that day, the Long March 25k carrier rocket (hereinafter referred to as Long March 10B) launched from the Hainan Commercial Space Launch Site, successfully sending a satellite into its predetermined orbit, marking a complete success for its maiden flight. Six minutes after the first and second stages separated, the first stage vertically returned and was successfully recovered via a net capture system on an offshore recovery platform more than 300 kilometers from the launch site, marking a complete success for the first stage recovery mission.

According to a Global Times reporter, this mission marked China's first successful controlled recovery of a carrier rocket's first stage, and also the world's first net capture recovery of a carrier rocket. The Long March 10B became China's first recoverable and reusable carrier rocket to achieve successful recovery. This signifies a historic breakthrough for China in reusable rocket technology, laying a solid foundation for accelerating the enhancement of China's space access capabilities. With this, China's aerospace industry has entered the era of rocket recovery.

Nail-biting Recovery Process

Before the maiden flight mission, a Global Times reporter closely viewed the Long March 10B in its vertical erection state. The massive rocket body, about the height of a 20-story building, with seven high-thrust engines clustered together, highlighted the immense difficulty of achieving this first successful recovery.

It is understood that the Long March 10B was developed under the leadership of the China Academy of Launch Vehicle Technology (CALT), a subsidiary of the China Aerospace Science and Technology Corporation (CASC). This rocket type has a diameter of 5 meters and adopts a two-stage tandem configuration. The core first stage inherits the state of the Long March 10A carrier rocket's first sub-stage, using liquid oxygen and kerosene propellant. The core second stage uses liquid oxygen and methane propellant. The rocket's total liftoff thrust is approximately 890 tons, with a liftoff weight of about 760 tons. The maiden flight rocket is approximately 63 meters in total length, and in its reusable state, it has a low Earth orbit (LEO) payload capacity of 16 tons.

"A 5-meter diameter is the mainstream design for current large launch vehicles, allowing for larger thrust engines and more propellant to support high payload capacity requirements," Kan Lei, a rocket technology expert from CALT, told a Global Times reporter. Kan Lei stated that the Long March 10B can meet the requirements for various missions, including deploying low Earth orbit satellite internet constellations and launching large commercial satellites. In its reusable state, it can significantly reduce launch costs, offering advantages of high payload capacity and cost-effectiveness.

During the maiden flight mission, the Long March 10B continuously ascended for about 3,000 seconds after ignition. Kan Lei explained that during the ascent phase, the rocket's first stage's seven liquid oxygen/kerosene engines completed the acceleration flight. After stage separation, one liquid oxygen/methane engine on the second stage took over. Through phases including one burn, coasting and attitude adjustment, and a second ignition, the satellite was precisely inserted into its predetermined orbit, and the rocket body underwent passivation disposal.

The return and landing phase was the core validation content of this launch mission. According to a Global Times reporter, the first stage of the Long March 10B separated from the second stage about 150 seconds after liftoff. It then began its descent from an altitude of over 100 kilometers, entering the return flight phase at several times the speed of sound.

"The return process will go through four phases: coasting and attitude adjustment, powered deceleration, aerodynamic deceleration, and landing," Wang Cong, a rocket designer from CALT, told a Global Times reporter. During the coasting and attitude adjustment phase, the first stage's grid fin system deploys and completes the re-entry attitude adjustment. Additionally, the propellant settling management system operates simultaneously to settle and concentrate the propellant in the tank at the bottom, fully preparing for subsequent engine ignition. In the powered deceleration phase, the first stage's engines reignite, acting like a 'brake' before entering the dense atmosphere to reduce speed and prevent damage to the rocket body from adverse factors like heat flux. Then, the first stage enters the aerodynamic deceleration phase, a critical validation link for thermal protection design. In this phase, the rocket decelerates using the aerodynamic drag generated by the grid fins, and the bottom of the first stage body endures severe aerodynamic heating and loads. Finally, the first stage enters the landing phase, employing a 'quasi-hovering' control strategy. All control mechanisms are utilized; the grid fins and rocket engine work together for control, obtaining an optimal control sequence through online trajectory planning to bring both the altitude and velocity of the first stage to relative 'zero,' culminating in successful recovery via the net capture system on the offshore platform.

In the maiden flight mission on July 10, the Long March 10B's first stage was precisely captured by the offshore recovery platform about 8 minutes after launch, a process that was nail-biting. Reporters at the scene saw many Chinese aerospace engineers involved in the Long March 10B's development tearing up upon seeing the live footage of the first stage landing smoothly. China's aerospace industry had finally reached the historic moment of successful recovery, making China the second country in the world to master vertical rocket recovery technology.

World-First Net Capture Recovery

Currently, the vast majority of reusable rockets worldwide use landing leg recovery schemes. The Long March 10B development team devised a unique and innovative method: offshore platform net capture recovery technology. This provides a Chinese solution for large-scale rocket body recovery globally, showcasing Eastern wisdom.

On July 10, as the Long March 10B first stage descended 'from the sky,' a rocket net capture recovery platform named 'Pioneer' was already waiting in the South China Sea. This massive vessel, 144 meters long, 50 meters wide, with a draft of 5.5 meters and a full-load displacement of 25k tons, possesses DP2 dynamic positioning capability, allowing it to use its thrusters to counteract environmental disturbances like wind, waves, and currents to maintain a preset position or heading. Combined with the net capture device and other products, it functions as a stable, precise mobile landing pad on the vast ocean.

"As the Long March 10B first stage arrives above the offshore platform's net capture device and continues decelerating, the net device uses a trolley-driven rope system to engage the first stage. The navigation and positioning system on the first stage body obtains velocity and position information in real-time, transmitting it to the control system to adjust the stage's attitude and speed. Simultaneously, the offshore platform's net capture device monitors the stage's status in real-time, controlling the rope movements via the ground control system," Sun Zhenlian, a technical expert from CALT, described this process as a precise 'two-way rendezvous' between the rocket and the offshore recovery platform, working together to achieve precise net entry for the first stage.

Once the first stage body enters the net capture device, the hooking mechanism on the stage deploys in advance, subsequently making contact with four cross-shaped ('井' shape) ropes. Sun further explained that the stage body slowly descends and is precisely captured. The entire process is very brief, requiring close coordination between the stage, ropes, and hooking mechanism. The instantaneous load poses a significant challenge to the hooking mechanism, which must withstand complex forces during net contact, sliding, and pulling. "The hooking mechanism acts like a pair of powerful hands, firmly catching the rocket. Subsequently, under the action of the offshore platform's net capture device, the rocket achieves cushioning and deceleration."

After capturing the stage, the recovery system on the offshore platform must further secure it. "Affected by environmental factors like sea waves and wind, the stage might sway within the net platform. The recovery system secures the stage in two steps. First, auxiliary stabilization ropes provide initial fixation from around the stage. Second, an automatic locking platform moves beneath the stage to complete clamping, locking, and support. It's like fastening a seatbelt for the rocket, keeping it stable at sea. At this point, the rocket is fully secured," Sun stated.

Net capture recovery has its unique advantages. Chen Muye, a technical expert from CALT, explained that compared to current mainstream recovery schemes, net capture is more lenient towards the rocket's landing parameters. "Net capture recovery helps simplify the rocket's structure. The rocket doesn't need complex landing legs, thus reducing the stage's weight and increasing payload capacity and efficiency. Furthermore, this recovery method has strong adaptability to deviations in the rocket's landing point; the 'capture window' can be 'enlarged' through the coordination of the netting system. The net capture system can also be adapted to recover rockets of different scales through a series of designs," Chen said.

It is understood that the Long March 10B rocket development team will continue to optimize rocket performance and accelerate the iterative upgrade of reusable rocket technology. It is expected that a re-flight of the first sub-stage will be completed by the end of this year.

Building a New Space Transportation System for China

Against the backdrop of commercial aerospace, satellite internet, and deep space exploration being incorporated into the '15th Five-Year Plan' outline, China's significant breakthrough in reusable technology for its space transportation system is naturally of great importance.

"The technological maturity and industrialization level of recoverable and reusable rockets directly determine China's technical capability and cost for accessing space," Kan Lei explained. From the demand perspective, multiple giant satellite internet constellations in China have entered substantive launch phases. "The launch demand for these constellations is huge, showing explosive growth, characterized by highly concentrated launch windows and high launch frequency. This makes the 'constraints' of traditional expendable launch vehicles in terms of cost and production capacity increasingly prominent, making it difficult to keep up with the short-cycle, high-density network deployment launch demands."

He further stated that the significance of the Long March 10B's successful maiden flight and recovery for China's commercial space development lies in breaking through low-cost, high-capacity reusable rocket technology, filling a domestic gap in this field. In the future, it will be able to significantly reduce commercial launch costs and enhance the competitiveness of China's commercial space industry in the international market. "In the future, the Long March 10B will undertake low Earth orbit satellite network deployment and other commercial launch missions, supporting large-scale network deployment needs for low Earth orbit satellite internet and medium Earth orbit communication satellites."

It is understood that in the future, the Long March 10B can also utilize a recovered first sub-stage from the Long March 10A rocket to execute launch missions. This will also accumulate flight data for the Long March 10A rocket's crewed missions, further enhancing reliability. As China's next-generation low-Earth-orbit crewed rocket, the Long March 10A is primarily responsible for low-Earth-orbit crew and cargo transport missions, considered a 'comprehensive upgraded version' integrating features of the Long March 2F and Long March 7 carrier rockets. In the future, it will serve as the 'ladder of life' for astronauts traveling between Earth and space stations.

Furthermore, based on the Long March 10B's 5-meter diameter, China is developing a larger-scale liquid oxygen/methane first sub-stage. Combined with the liquid oxygen/methane module of the Long March 10B's second sub-stage, it will form the fully liquid-oxygen/methane Long March 10C carrier rocket. Wang Cong stated that this rocket is positioned as a main commercial rocket with stronger payload capacity, better meeting the needs of different commercial launch missions. "Currently, the Long March 10C carrier rocket is under intensive development and will strongly promote the industrialization of China's space transportation in the future."

"This successful flight test of the Long March 10B carrier rocket is a significant milestone," Kan Lei said. On one hand, as a full-profile flight validation for the Long March 10A carrier rocket, it will effectively advance the development process of China's next-generation crewed rocket. On the other hand, as China's first successfully recovered rocket, it marks the official entry of China's launch vehicles into a new era of reuse, significantly accelerating the formation of China's capability for routine reusable rocket launches. Additionally, this test validated the functionality and performance of the liquid oxygen/methane engine, providing solid support for overcoming key technical challenges for the Long March 10C carrier rocket.

Source: Global Times

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