高超音速競賽2.0：中國用革命性技術測試下一代“乘波器”

China has successfully developed a new type of surface material for hypersonic vehicles, capable of withstanding the rigours of a long flight. This breakthrough was announced by the scientists involved in the project, marking a significant milestone in a field previously considered impossible to conquer. The Chinese military conducted a test where this thin material was applied to the surface of a 'waverider' aircraft. This unique aircraft utilises shock waves generated by its own flight to enhance lift. During the test, the air surrounding the hypersonic aircraft was heated to thousands of degrees Celsius. Despite these extreme conditions, the smooth, non-ablative surface of the material not only maintained the coolness of critical components inside the aircraft but also facilitated the free transmission of wireless signals. This allowed for target identification and communication throughout the flight, as evidenced by the analysis of telemetry data. The team of scientists declared the test flight a complete success in a paper published in the peer-reviewed journal Physics of Gases. However, they did not disclose the time and location of the test. This new thermal protection technology could potentially aid in the development of another generation of reusable hypersonic vehicles. These vehicles would be capable of longer range, faster speed, and constantly pushing the boundaries of flight. The team, led by Ai Bangcheng, deputy director of the China Academy of Aerospace Aerodynamics in Beijing, stated that the hypersonic race has entered a new phase, presenting enormous challenges and opportunities. Traditional ballistic missiles can achieve hypervelocity, or speeds more than five times the speed of sound, before they hit a target. Space shuttles and re-entry capsules utilise thermal tiles that can burn and dissipate heat. However, these hypersonic flights were short-lived, usually lasting just a few minutes. NASA and the US military have initiated numerous projects in the past to develop hypersonic vehicles capable of making long-distance flights regularly, akin to jet planes. However, these projects were eventually cancelled due to the inability to find a material that could withstand the rigours of a hypersonic flight lasting an hour or more. In recent years, the US government has revived its hypersonic programme but continues to face setbacks. A report to politicians by the US Congressional Budget Office in January highlighted thermal damage as the primary concern for American hypersonic weapon developers. The report stated that the fundamental challenge lies in managing the extreme heat that hypersonic missiles are exposed to by travelling at high speeds in the atmosphere for most of their flight. Shielding the sensitive electronics of hypersonic missiles, understanding the performance of various materials, and predicting aerodynamics at sustained temperatures as high as 3,000 degrees Fahrenheit (1,650 degrees Celsius) require extensive flight testing. Despite ongoing tests, failures in recent years have delayed progress. According to the Chinese researchers, the US appears to still be struggling at the first stage of the hypersonic race. China, on the other hand, has surpassed this stage. Many hypersonic missiles are already in use by China's military, with some designed to hit a moving target, such as an aircraft carrier, with unpredictable manoeuvring from a long distance. The second stage of the hypersonic race extends beyond missiles and focuses on the development of long-range, reusable platforms that will have both military and civilian applications. These hypersonic aircraft can carry out reconnaissance missions, drop bombs, intercept stealth aircraft such as the F-22, or transport a small group of special ops to any location on the planet in an hour or two. However, this would necessitate a fundamentally different approach to heat management. Some Chinese hypersonic platforms under development need to fly more than 3,000 seconds in the atmosphere with a surface temperature reaching as high as 3,000 degrees Celsius. In such an extreme environment, molecules in the air would break down and start chemical reactions with the surface material. The method employed by Ai's team to keep the waverider surface intact remains a secret. However, in their paper, the scientists listed several possible options such as polishing the surface to extremely smooth conditions; adding elements like niobium, molybdenum, and boron to resist ablation; redesigning the structure of the surface component completely to reduce weight; and converting the harmful heat to propulsion thrust with a liquid medium. These technologies are mostly still in the experimental stages in laboratories in other countries, including the United States. In China, some key methods have reached the technological readiness levels (TRLs) of up to 8, indicating that the system has been completed and qualified in an operational environment. This is just one step away from the final approval for field deployment. The term 'hypersonic flight' was first coined by Qian Xuesen, a founding scientist of the legendary Jet Propulsion Laboratory in the US, in a 1946 paper. After returning to his homeland and initiating China's rocket programme, Qian proposed a practical method to convert big engineering challenges in thermal barriers to scientific questions that can be solved by a large number of scientists from different academic backgrounds. Qian's idea is still being used in the design of active heat protection today. According to the Pentagon, China has conducted more hypersonic test flights in a year than the US did in a decade. In 2021, the Chinese military flew a hypersonic vehicle around the globe, surprising the US military with technology reportedly 'defying the laws of physics'. Meanwhile, in May, a suborbital space plane completed its second flight and landed in a military airport in the Gobi Desert. In response to public queries as to why no photos were available, the Chinese space authorities stated that the hypersonic vehicle had used some technology 'too advanced for public display'.