Missile, torpedo or both? China is developing a supersonic boron-fueled weapon that can ‘fly high’, ‘dive deep’ to hit its target
Scientists in China are working to develop a boron-fueled anti-ship missile that can not only travel faster than any existing torpedo, but also travel greater distances, according to Chinese media.
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A team of rocket scientists from the College of Aerospace Science and Engineering of the Changsha National University of Defense Technology revealed a blueprint for a boron-based missile propulsion system in the September 8 issue. from the Journal of Solid Rocket Technology, published by the Chinese Astronautical Society.
Boron is a “metalloid”, with both metallic and non-metallic properties, and is commonly used in washing powders, antiseptics, etc. It is also known to react violently when exposed to water and air, giving off massive heat.
It burns with green flames and is said to release 40% more energy per kilogram than conventional aviation fuel.
New anti-ship missile
The new anti-ship missile designed by Changsha scientists is intended to fly through the air before plunging into the water and hitting its target.
According to the scientists’ claims, the new boron-based propulsion system will allow the five-meter-long missile to cruise at 2.5 Mach – 2.5 times the speed of sound – at an altitude of around 10,000 meters, up to a distance of 200 kilometers before diving and moving underwater up to 20 kilometers.
Once the missile is within 10 kilometers of its target, it goes into torpedo mode, traveling underwater at up to 100 meters per second using supercavitation – the formation of a giant air bubble around of it which significantly reduces drag, according to the researchers.
The researchers further claimed that the projectile could also alter its trajectory at will or dive to a depth of 100 kilometers to dodge underwater defense systems without losing momentum.
Senior scientist Li Pengfei and his team said no existing ship defense system could handle a rapid “cross-media” attack. “It can greatly improve the penetration capability of the missile,” they said.
China is not the first country to explore the use of boron as an aviation fuel. The US Air Force in the 1950s began work on boron-based aviation fuels based on intelligence reports of green flames coming out of the exhaust of an experimental Soviet rocket.
Conventional aviation fuels are based on hydrocarbons refined from fossil fuels, in which hydrogen, a highly explosive element, is bonded to carbon atoms.
While ideally hydrogen is the best fuel if used independently, it takes up a lot of space even when cooled in cryogenic liquid. It is difficult and dangerous to manage alone. Therefore, it combines carbon atoms, which makes the fuel tightly packed and easier to control.
However, hydrocarbon-based fuels did not produce enough energy per unit to meet the US military’s need for supersonic aircraft capable of flying halfway around the world.
Consequently, American engineers decided to use boron, which is found right next to carbon in the periodic table, which gave rise to a new family of fuels based on “hydro-boron” compounds, or “boranes”. ‘, developed under the code name ‘Project Zip’, ‘ hence their nickname ‘zip fuels’.
Initially, these fuels held great promise due to the energy produced. They were to be used on the XB-70 Valkyrie strategic bomber, the XF-108 Rapier long-range interceptor and the BOMARC missile. In addition, there were plans to convert existing jet engines so that they could also burn boranes.
However, these plans were abandoned in 1959 as boranes proved to be very dangerous due to their toxicity, requiring those working with them to use unique gas masks. In addition, boron particles are difficult to control, as they ignite spontaneously and can even explode.
At least eight people involved in the Zip project have died in borane-related accidents.
Also, when placed inside the jets, the borane did not burn completely and left a sticky residue layer on the turbine blades, gradually reducing engine performance.
Hypersonic racing revives interest in boron
In recent years, the ongoing hypersonic race has revived interest in boron. For example, last year China reportedly built air-breathing scramjet engines using solid fuel containing boron nanoparticles to accelerate missiles to Mach five or more.
Even the United States is working to develop boron-based fuels. Last year, the United States Navy invited proposals for a new research project aimed at determining “a form of boron or boron-based chemical pathway that leads to the implementation of boron in energetic compounds, particularly fuels (solid and liquid)”.
Reports suggest that the element’s new physical form, called “allotropes”, may overcome problems such as partial combustion and toxicity of boron-based fuels. Allotropes of the same element can have very different properties; for example, graphite and diamond are allotropes of carbon.
The idea is that a new “allotrope of boron”, possibly in combination with another chemical material, could provide a completely combustible and non-toxic fuel.
Researchers in the United States are also exploring potential structural applications of boron in aircraft to reach hypersonic speeds. Currently, specific aircraft structures use carbon nanotubes (CNTs) because they can withstand high temperatures when an aircraft is traveling at high speed.
In 2017, engineers from NASA and Binghamton University published a study, apparently funded by the US Navy, which found that a combination of boron and nitrogen could also be used to make nanotubes for aircraft structures.
CNTs can withstand temperatures up to 450 degrees Celsius. A NASA study showed that boron nitride nanotubes could withstand 900 degrees Celsius, making them suitable for use in supersonic or even hypersonic jet structures.
Moreover, boron nitride nanotubes are lighter and better than CNTs, with high tensile strength and chemical and thermal stability.
The use of boron remains difficult and risky
As previously reported, Pengfei and his rocket scientists in Changsha designed a boron-fueled ramjet that could operate both in the air and underwater. This is quite unusual, as most boron engines are designed to operate only in the air.
Researchers generally prefer aluminum or magnesium as fuel for supercavitating torpedoes due to their high reactivity with water.
Therefore, the ramjet designed by Pengfei and his colleagues includes unique components such as adjustable air intakes and exhaust nozzles to maintain boron combustion efficiency in different environments. However, the biggest change concerns the composition of the fuel, according to their article.
Boron typically makes up about 30% of the total fuel weight in an air-breathing missile due to the requirement of several other chemicals to control and sustain intense combustion.
However, Pengfei’s team doubled the percentage of boron in the fuel, which they believe could result in more thrust than aluminum in the water.
At the same time, the team also said that increasing the boron percentage could cause issues with mass production, ignition, and combustion control, but these “can be solved by modifying the boron particles, improving the manufacturing process and studying the properties of grain mass.
It is also difficult to adjust the thrust of a solid fuel engine. For example, boron powder behaves as both a solid and a fluid when injected into the combustion chamber, which makes it difficult to physically simulate or regulate the combustion process.
Moreover, China risks depending on borofuels to manufacture mass-produced weapons, according to a Beijing-based materials scientist who studies the element boron. Half of China’s boron ores come from overseas, and a large portion comes from the United States.