In recent years, the development of reusable rocket technology has become a hot topic in the global aerospace field. Especially in the field of commercial aerospace, companies from various countries are rushing to develop reusable rockets that can take off and land vertically. In this process, the 10-kilometer altitude seems to have become an important "threshold" for verifying repeatable rocket technology. Whether it is SpaceX of the United States, the verification rocket of the Eighth Institute, or the VTVL-1 of Suzaku-3, the altitude of 10 kilometers always appears repeatedly in tests.
So why was this height chosen? What does it mean for the validation of repeatable rocket technology? After overcoming this hurdle, will the road ahead really be smooth? Today, we will spend some time talking about it.
The first thing that needs to be answered is - what does an altitude of 10 kilometers mean? In fact, during the rocket launch process, the height of 10 kilometers is not a particularly significant "milestone". It has not even broken through the atmosphere and is still within the earth's troposphere. However, for reusable rockets, this is a crucial height. First of all, the atmosphere below 10 kilometers is denser and the air resistance is strong. In such an environment, the rocket will experience tremendous pressure and air resistance during both its ascent and descent. This means that the rocket's attitude control system, stability control system, and auxiliary equipment such as grid rudders all need to withstand severe tests. In addition, the rocket will also experience "maximum dynamic pressure" at this altitude, which is the maximum pressure exerted on the rocket by aerodynamic forces. This is one of the most complex stages of rocket flight, and the rocket needs to remain stable during this stage to avoid structural damage or failure. Secondly, 10 kilometers is the height at which the rocket needs to experience changes in supersonic and subsonic speeds during flight. For repeatable rockets, this is also an opportunity to verify "transonic" control capabilities. Transonic speed refers to the process in which a rocket transitions from subsonic speed, which is less than the speed of sound, to supersonic speed, which exceeds the speed of sound. At this stage, changes in airflow will cause huge disturbances to the rocket's attitude and control system. Therefore, a flight altitude of 10 kilometers can not only test the endurance of the rocket, but also verify the stability and precise control capabilities of the rocket at transonic speeds. This altitude was chosen as a key test point precisely because it represents a test of the rocket's performance under extreme conditions.
So, what does it mean to complete this 10-kilometer flight? It can be said that it marks a major advancement in rocket technology. First of all, the rocket's return and successful landing at such an altitude means that it has basic reuse capabilities. As the design team of China's Zhuque-3 emphasized, this flight success shows that the rocket's core components such as the engine and grid rudder can accurately fit and remain stable during the return process. However, the successful completion of this high-level test does not mean that there are no obstacles ahead. Although the 10-kilometer flight verified the rocket's adaptability and control capabilities in some complex environments, it is still far from a true orbital-level flight. At higher altitudes, rockets need to face more severe challenges, especially the high temperatures and extremely high speeds during re-entry into the atmosphere. For China's repeatable rocket technology, the success of the 10-kilometer flight means more that the verification of the technology has entered a critical stage. The rocket's vertical takeoff and landing technology has already achieved preliminary results, but what needs to be solved in the future is how to achieve vertical recovery at a higher altitude and deal with the huge heat and kinetic energy generated during reentry. For example, how to effectively protect against the high temperature generated when re-entering the atmosphere; for example, how to further improve the rocket's landing accuracy and speed control; and for example, how to make the rocket's structure light enough but strong enough to cope with the fatigue loss of multiple uses, etc. We expect that as the technology matures and the number of flights increases, these problems will be gradually solved.
When it comes to the development and current situation of my country's repeatable rocket technology, one point that cannot be bypassed is the achievements of SpaceX. SpaceX has been committed to developing reusable rockets since the early 2000s, and successfully achieved vertical recovery of the rocket for the first time in 2015. Since then, SpaceX has completed the recovery and reuse of orbital-class rockets many times, completely changing the cost structure of the aerospace industry. In contrast, China's repeatable rocket technology started late. Although significant progress has been made in recent years, there is still a certain gap with SpaceX. Taking Zhuque-3 VTVL-1 as an example, China's current test is still in the vertical take-off and landing stage at an altitude of 10 kilometers, while SpaceX has already achieved maritime recovery and reuse of orbital-class rockets. However, this does not mean that China Aerospace has no possibility of catching up. China has invested a lot of resources in the research and development of aerospace technology in recent years and has achieved major breakthroughs in many tests. From a time perspective, the practical process of China's reusable rockets may take about 5-10 years to reach the current level of SpaceX. However, China's huge market demand and private enterprises' investment in technological innovation will further shorten this gap.
All in all, the 10-kilometer flight test is not only an important step in technical verification, but also the cornerstone of future aerospace exploration. Although my country started late in this field, with continued investment and technology accumulation, it is expected to catch up with SpaceX in the near future and start our own era of recyclable aerospace.