China is developing an anti-ship missile that turns into a torpedo during its terminal phase, combining airborne and underwater capabilities in a single weapon to increase the likelihood of a successful strike.
This week the The South China Morning Post reported that China’s new 5.4-meter hybrid weapon could reach Mach 2.5 at 10,000 meters for 200 kilometers before switching to a supersonic skimming mode for 20 kilometers. After reaching the last 10 kilometers to the target, it switches to supercavitating torpedo mode moving at 100 meters per second.
Senior scientist Li Pengfei and his team at Changsha National University of Defense Technology claimed that no existing onboard defense system can protect against this “cross-medium” attack, with the missile capable of changing course at will or to dive up to 100 meters to escape the defenses on board.
The article mentions that traditional boron-fueled engines are designed only to operate in the air, while supercavitation torpedoes use aluminum or magnesium-based fuels that react with water.
To overcome this challenge, Li and his team proposed a design for a boron-fired solid-fuel ramjet (SFRJ) that can operate both in air and underwater in the September 8 issue of the Journal of Solid Rocket Technology. .
An SFRJ consists of three main components, namely an air intake system, a combustion chamber and a nozzle, and is the easiest method to achieve supersonic flight. Since it relies only on its forward motion to compress intake air, it has no moving parts. And although the design is simple, the combustion process is very complex.
The South China Morning Post notes that boron is an essential element for hypersonic weapon fuels. The highly reactive element could quickly become a hotly contested resource as China, Russia and the United States vie for dominance in hypersonic weapons.
The Chinese researchers noted that controlling the burn rate of the fuel rods is the biggest challenge in their design. Although their design features adjustable inlets and exhaust nozzles to maintain combustion efficiency in different environments, the fuel rods present a problem.
They note that boron takes up 30% of the total fuel weight in an air-breathing missile due to the other chemicals needed to control and prolong the intense burn. Their proposed design has twice the boron content, which produces greater thrust than aluminum in the water.
However, the researchers noted that the increased boron content could cause problems with mass production, ignition, and combustion control. Additionally, thrust control is an inherent challenge of solid fuel engines.
In their design, boron powder behaves as both a solid and a liquid when injected into the combustion chamber, making physical modeling or combustion control difficult. Also, because their design is solid fuel, the combustion process cannot be stopped once lit.
Still, the research team pointed out that modifying the boron particles, improving the manufacturing process, and further studying the properties of the grain mass can solve the problems. They also noted that China has made several breakthroughs in solid rocket fuel, including applying multiple coatings to nanofuel particles to control their explosive properties.
While in theory this new anti-ship missile can be a formidable weapon, its unique flight characteristics and capabilities present technical challenges. Specifically, China’s new anti-ship missile could encounter problems in its guidance systems.
Sea skimming is a flight profile used by fighter jets and many other anti-ship missiles to minimize the chance of detection. This involves flying as close to the surface of the water as possible, using a combination of very low altitude and sea state to fly under radar and greatly increase the difficulty of being shot down.
As noted by the South China Morning Post, the new anti-ship missile goes into supersonic sea-skimming mode before going into supercavitating torpedo mode.
However, in an article for Naval Post, Ryan White mentions that supersonic sea-skimming missiles get extremely hot in flight, precluding the use of infrared seekers. He also notes that during supersonic flight, a hot layer of ionized gas forms around the missile, which blocks radar waves and data link communications.
These limitations necessitate the use of active radar seekers, which presents challenges.
Active radar seekers are more expensive than semi-active radar seekers because they have both radar transceivers and receivers in a single unit. Also, due to their battery usage and small size, they have limited range and power compared to larger models. Nor are they sufficient to hit long-range targets without the aid of more powerful ground, naval or airborne radar systems.
China’s new anti-ship missile could encounter similar problems in supercavitating torpedo mode. Supercavitation uses the effects of cavitation to create a pocket of air or vapor surrounding an object moving through water, reducing drag and allowing it to travel at very high speeds.
In a separate article for Naval Post, Dorian White notes several limitations of supercavitating torpedoes. First, supercavitation torpedoes have limited maneuverability, as sharp turns risk the torpedo’s control surfaces touching the water, which could tear off parts.
In addition, supercavitation is very energy inefficient, which may explain the short range of China’s new anti-ship missile in supercavitation mode. Additionally, supercavitating torpedoes have a much smaller warhead than conventional torpedoes because much of their energy is spent maintaining supercavitation in the water.
As a supercavitating torpedo is essentially an underwater rocket, the weapon’s fire is extremely strong, which could easily be detected by sonar, allowing the target to perform evasive maneuvers or locate the launching vessel or the submarine for a counterattack.
Supercavitating torpedoes are also blind, as their high speed prevents the wire guidance used by conventional torpedoes and, therefore, depends on their target not moving. However, their strong signature shot can negate their high-velocity surprise advantage.
As supersonic anti-ship missiles and supercavitating torpedoes have not yet been tested in combat, it is unclear how the new Chinese weapon combining the characteristics of both would perform in actual use.