Original title: The development of hypersonic missiles has to pass three hurdles: boosters, gliders, and scramjets
[环球时报记者 魏 齐]According to a report by the Korean Central News Agency on the 12th, the North Korean Academy of National Defense Science successfully conducted a test launch of a hypersonic missile on January 11, hitting an established target in waters 1,000 kilometers away. The purpose of this test is to finally confirm the overall technical characteristics of the newly developed hypersonic missile weapon system. This is the second time North Korea has tested a hypersonic missile this year. At present, many countries around the world are paying close attention to the development and deployment of hypersonic missile weapons. So how many steps will the development of hypersonic missiles have to pass?
Level 1: Booster
A hypersonic missile in a broad sense refers to a missile with a maximum speed exceeding Mach 5. The maximum speed of most ballistic missiles also exceeds Mach 5, which is considered a hypersonic missile in a broad sense. However, when it comes to hypersonic missiles now, it is usually only a narrow hypersonic missile, that is, a missile with a ground strike as its main task, mainly flying in the atmosphere, with a maximum speed of more than Mach 5, and can implement large-scale maneuvering.
In the narrow sense, hypersonic missiles are mainly divided into two categories. One is a boost-glide hypersonic missile. This type of missile is roughly composed of a booster and a glider. The booster is a rocket engine. After it accelerates to a certain speed and altitude, it releases the unpowered glider. The glider is equipped with guidance, control devices and warheads. Its range is related to its maximum speed, the higher the maximum speed, the longer the range. When the United States tested the HTV-2 glider that year, it used a launch vehicle to accelerate the HTV-2 to Mach 22. This glider has an intercontinental range. The second category is hypersonic cruise missiles. The missile is first accelerated to a certain speed and altitude by a booster, then boosted to disengage, and the scramjet engine is activated. Overall, hypersonic cruise missiles require additional solutions to scramjets, which are more difficult to develop. Currently only the Russian “Zircon” will begin to equip troops. According to Zhang Xuefeng, a Chinese military expert, whether it is a boost-gliding hypersonic missile or a hypersonic cruise missile, the development of the booster needs to be solved first. Especially in the former, booster is the only source of power for the entire missile, and its performance is critical. However, in general, the technology of the booster is relatively traditional and belongs to the entry-level technology for the development of hypersonic missiles.
Zhang Xuefeng said that for a boost-gliding hypersonic missile, its booster is basically the same as the rocket engine of a ballistic missile. Many of these missiles, including the Russian “Dagger”, are not much different in shape from ballistic missiles. The engine is almost the same as using a ballistic missile engine. Such engines can be single-stage or multi-stage, solid rocket motors or liquid rocket motors. For example, the U.S. Air Force’s AGM-183A hypersonic missile (pictured) uses a new solid rocket motor with small size, high thrust and high energy, with a maximum range of more than 1,600 kilometers. However, the three test launches all ended in failure, indicating that the development of high-performance rocket engines is not straightforward. Of course, hypersonic cruise missiles also need boosters to accelerate the missile to the working speed of the scramjet. Overall, though, boosters for these types of missiles are relatively small.
Level 2: Glider
The development of boosters is only the first step in the development of hypersonic missiles. The second level – gliders are the core area of hypersonic missiles. Generally speaking, the warhead of a ballistic missile will fly in the atmosphere only in the terminal section, and at most the middle section near the terminal section. Although ballistic missiles can maneuver and change orbits in the middle section, they are mainly carried out by engines, and the range of maneuvering is small. Ballistic missile warheads can also maneuver in the final stage, but the range is small, and their maneuvers are mainly used to avoid interception. A major difference between boost-glide hypersonic missiles is that the warhead mainly flies in the atmosphere, and can rely on aerodynamic force to perform a wide range of lateral and vertical maneuvers in the atmosphere, making it difficult for the opponent to predict its strike point.
Zhang Xuefeng said that in order to efficiently glide in the atmosphere, the boost-gliding missile is required to have large lift, low resistance and long gliding distance during flight. At the same time, it is necessary to “can hold something in the stomach”. Among them, the waverider has the best lift-drag characteristics, but it is relatively difficult to develop. In addition, due to its flat shape and small volume, there is no practical model at present. The volume of the cone or cone-like body is larger, but the lift-to-drag ratio is relatively low. The earliest boost-gliding hypersonic missiles, such as the Russian “Dagger” glider, are mainly conical-like swirls, the shape of which is not much different from the warhead of a ballistic missile. It is mainly obtained by controlling its angle of attack when it flies in the atmosphere. A certain lift, the lift-drag is relatively small, and the overall development difficulty is relatively low.
The third level: scramjet
Hypersonic cruise missiles are widely considered to have advantages over boost-glide missiles. Because this missile can absorb oxygen in the air through the engine, the missile body can be made smaller for the same range and the same average speed. For example, the Russian “Zircon” hypersonic missile can be installed in the frigate’s vertical launch system. And hypersonic cruise missiles are generally cheaper, more economical, and easier to use in large numbers. Boost-gliding hypersonic missiles, due to the lack of power in the gliding phase, will fly lower and lower in speed. At the end, they will become “the end of the arrow”, and it is easy to provide an interception window for the opponent’s interception system. The hypersonic cruise missile can maintain a relatively balanced speed.
But the development of scramjet engine is a big difficulty. According to Zhang Xuefeng, the scramjet engine can be said to be the core technology of the hypersonic vehicle propulsion technology and even the entire hypersonic vehicle technology system. It involves the frontier issues of aerodynamics, aerodynamic thermodynamics, computational fluid dynamics, combustion, and materials science, as well as many interdisciplinary subjects. “Some people describe that the combustion chamber of a scramjet engine works like igniting a match in a hurricane, which shows the difficulty of its development.” In addition, in order to further improve the performance of hypersonic cruise missiles, it is necessary to solve the integration of aerodynamic thrust and so on. Technology. A large part of the reason why Russia’s “Zircon” has reached the state of being close to the armed forces is due to the accumulation of technology in the Soviet era, and Russia attaches great importance to the development of such strategically important technologies and weapons.
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