The Chinese people have yearned for space for thousands of years, and many flying myths witness this dream. Nowadays, it has long been a reality for Chinese rockets to fly into space. However, these rockets that have flown into space have not yet had the experience of "flying home" - rocket recovery is still a hurdle in front of Chinese rocket enthusiasts. In fact, the exploration of recycling domestically produced large rockets has accelerated this year. Recently, a new technology validation rocket for reusable launch vehicles developed by the Eighth Academy of China Aerospace Science and Technology Corporation successfully conducted a 10 kilometer flight test at the Jiuquan Satellite Launch Center. Blue Arrow Aerospace is about to conduct a 10 kilometer vertical takeoff and landing flight test, and Deep Blue Aerospace is also about to welcome a 5-kilometer vertical takeoff and landing test for the first stage of the "Nebula 1" rocket... Almost every month, Chinese rockets have a "big move" in recovery. So, why recycle rockets like we recycle cola bottles? Where is the difficulty of rocket recovery? How many steps does a rocket take from "leaving home" to "returning home"? Why recycle rockets? With the command "3, 2, 1, ignite!", the rocket soared into the sky and soared into the clouds. This is the impression most people have of rocket launches. When a rocket flies into space, a beautiful parabolic curve is all that people remember, and few people care whether it can come back or not. On January 19, 2024, Blue Arrow Aerospace conducted a successful vertical takeoff and landing test of experimental arrows at the Jiuquan Satellite Launch Center. Indeed, before 2015, rockets were disposable consumables that never returned after launch. However, the successful recovery of Falcon 9 in 2015 made history: rockets could also be reused, and "flight based launch" was not impossible. In fact, Qian Xuesen, the "father of China's aerospace industry," envisioned in his 1963 book "Introduction to Interstellar Navigation" that "transport rockets, whether they are large first stage rockets or small second stage rockets, can fly back to the ground with wings, so transport rockets can be used many times. What are the benefits of letting rockets" fly home "? Three sentences - cost reduction, efficiency improvement, and quality enhancement. The most direct is cost control - recycling and reuse, which naturally dilutes costs. Rocket recycling is the best way to directly reduce launch costs. In the past, launching a rocket was a one-time use, just like wasting time on a disposable airplane. When a rocket is recycled, it can take off and land multiple times like an airplane, spreading the cost even thinner, "said Bai Guolong, a member of the China Aerospace Association and a space science blogger known as" Captain of the Shenzhou ". Secondly, rockets are recyclable, which means that the launch frequency has increased, which is the hope for industrial expansion. Traditional rocket launches require a preparation period of at least two months and a tight time window for observation. Unlike reusable rockets, which only require simple repair and maintenance to be launched again, the significant improvement in rocket utilization, launch frequency, and launch flexibility will greatly enhance the ability to quickly enter space, making large-scale space exploration and development possible, "said Huo Liang, founder of Deep Blue Aerospace. In addition, the upgrade of the transport capacity of reusable rockets helps to improve the overall quality of space exploration. "At present, large-scale constellation networking especially needs rocket launch with large capacity, low cost and high frequency. Large reusable rockets can support China's Internet constellation engineering strategy," said Dai Zheng, general manager of the Blue Arrow Space Rocket Research and Development Department and chief commander of Zhuque No. 3. How difficult is it to recycle rockets? The roadmap is concise and clear, but turning it into reality is extremely difficult. A traditional rocket consists of two stages, with the first stage at the bottom and the second stage at the top. The current rocket recovery refers to the process in which the first and second stages separate when the rocket reaches an altitude of over 100 kilometers, and the second stage enters the predetermined orbit. The first stage, which could only self destruct, returns to the launch site. In short, rocket "recovery" currently means the first stage of "returning home". Its' return home 'can be roughly divided into three steps. The first step is to separate the arrow body and adjust its posture. After the rocket is ignited and launched, it rises to an altitude of over 100 kilometers. The engine of the first stage is turned off, and the second stage separates from the first stage. To return to the ground, the first step is to "turn around", which means adjusting the posture. The second step is to slow down. After turning around, the rocket enters the return process at a fast speed. At this point, the engine needs to ignite again to reduce the speed. The third step is landing and hovering. As the ideal posture for the rocket to return to its original position is with the tail down and the head up, a third ignition of the engine is required to adjust the posture and give the rocket a counter thrust to reduce its acceleration and velocity to zero during landing. Why is it harder for a rocket to 'go home' than to launch a rocket? The most difficult thing is to 'get it right'. During the descent of a rocket, as fuel consumption and speed change, it is necessary to output thrust of different sizes to ensure smooth deceleration. This requires the rocket engine to accurately and dynamically adjust thrust and have the function of multiple starts. Huang Shuai, the chief designer of the Gravity II rocket of Dongfang Space Company, emphasized that the rocket must have a set of precise algorithms to carefully guide it to return smoothly. Being stable is not easy either. During the return of a rocket, the descent attitude and landing angle must be controlled with high precision. If the landing angle is incorrect, the rocket may capsize, causing fuel leakage and explosion. This difficulty is like throwing chopsticks into a bottle, let alone a giant "chopstick" that descends at a speed of over 1000 meters per second. In fact, even if effective deceleration is achieved before landing, the enormous inertia brought by rockets weighing tens of tons must be taken into account. You should know that there are a large number of precision electronic components in rockets, and to ensure that these "treasures" can be used again, their buffering skill values must be fully tapped. On July 21st, the Nebula 1 rocket independently developed by Deep Blue Aerospace completed a simulated high-altitude recovery flight test. Another challenge is' using it for a long time '. Zheng Ze, Deputy General Manager of Deep Blue Aerospace, introduced that reusable rockets need to withstand multiple repeated uses and atmospheric reentry tests, which requires the use of new composite materials with high strength, high temperature resistance, and ultra lightweight to overcome a series of material performance difficulties. The reliability requirements for engine and other components are particularly high. In addition, reusable rockets must be well maintained, and simple testing and maintenance after recycling can meet the requirements for re launch. There are also many technical gaps in this area that need to be filled for evaluation and testing. Exploration will not stop, what more needs to be done for China's rockets to achieve 'go and go'? On the one hand, optimize the management and approval process for rocket launches, balancing safety and efficiency. On the other hand, building more launch sites and stations, including land and sea recycling launch platforms, to meet the higher frequency launch needs Bai Guolong said that creating an environment of rapid technological iteration, continuous optimization of processes and costs is the key to making this mountain climbing path smoother. Rocket recovery is difficult, but the confidence of astronauts is not worn down. In the Qian Xuesen Library of Shanghai Jiao Tong University, there is an envelope displayed. In 1941, Qian Xuesen wrote "Final" in red pen on the envelope containing his famous paper "Axial Buckling of Column Shell". When he finished writing, he suddenly realized that "Final" was also "finished": "How can the pursuit of truth come to an end?" Qian Xuesen took the envelope and wrote in black, "Nothing is final". Huang Shuai said, "Our exploration of rocket recovery technology is also endless