Scientists in China are working to develop a boron-powered anti-ship missile that can not only travel faster than any existing torpedo but also travel greater distances, as per reports in Chinese media.
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A team of rocket scientists from the college of aerospace science and engineering at the National University of Defense Technology in Changsha revealed a blueprint of a boron-based missile propulsion system in the September 8 issue of the peer-reviewed Journal of Solid Rocket Technology, published by the Chinese Society of Astronautics.
Boron is a ‘metalloid,’ with properties of both metals and non-metals, and it is usually used in washing powders, antiseptics, etc. It is also known to react violently when exposed to water and air, releasing massive heat.
It burns with green flames and is said to release 40% more energy per kilogram when compared to conventional aviation fuel.
New Anti-Ship Missile
The new anti-ship missile designed by the scientists from Changsha is intended to fly in the air before diving into the water and hitting its target.
As per the claims of the scientists, the new boron-based propulsion system will enable the five-meters 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 for up to 20 kilometers.
Once the missile is within 10 kilometers of its target, it will go into torpedo mode, traveling underwater at up to 100 meters per second using supercavitation – the formation of a giant air bubble around it which significantly reduces drag, according to the researchers.
The researchers further claimed that the projectile could also alter its course at will or crash-dive down to a depth of 100 kilometers to dodge underwater defense systems without losing momentum.
Lead scientist Li Pengfei and his team said that no existing ship defense system could handle a fast “cross-media” attack. “This can greatly improve the missile’s penetration capability,” they said.
China is not the first country to explore using boron as aviation fuel. US Air Force, in the 1950s, began working on boron-based aviation fuels based on intelligence reports of green flames emerging from 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 with carbon atoms.
While ideally, hydrogen is the best fuel if used independently, it takes a lot of space even when cooled into a cryogenic liquid. It is challenging and dangerous to handle on its own. Therefore, it combines carbon atoms, making the fuel closely packed and easier to control.
However, the hydrocarbon-based fuels did not produce sufficient energy per unit to meet the US military’s requirement of supersonic jets that can fly halfway across the world.
Therefore, American engineers decided to use boron that sits right next to carbon in the periodic table, which gave birth to a new family of fuels based on ‘hydro-boron’ compounds, or ‘boranes’ developed under the code name ‘Project Zip,’ hence they were nicknamed “zip fuels.”
Initially, these fuels were very promising because of the energy produced. They were planned to be used on the XB-70 Valkyrie strategic bomber, XF-108 Rapier long-range interceptor, and BOMARC missile. Also, there were plans to convert the existing jet engines so that they could burn boranes as well.
However, these plans were abandoned in 1959 because boranes proved very dangerous due to their toxicity, requiring those working with them to use unique gas masks. Also, the boron particles are difficult to control, as they ignite spontaneously and may even explode.
At least eight people involved in Project Zip died in borane-related accidents.
Furthermore, when put inside jets, the borane did not burn completely and left a layer of sticky residue on the turbine blades, gradually reducing engine performance.
Hypersonic Race Brings Back Interest In Boron
In recent years, the ongoing hypersonic race has revived the interest in boron. For example, last year, China reportedly built air-breathing scramjet engines using a solid fuel containing boron nano-particles to accelerate the missiles to five Mach or above.
Even the US is working to develop boron-based fuels. Last year, the US Navy solicited proposals for a new research project to determine “a form of boron or a boron-based chemical pathway that leads to the implementation of boron in energetic compounds, especially fuels (solid and liquid).”
Reports suggest the new physical form of the element, called the ‘allotropes,’ may overcome the 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 ‘boron allotrope,’ probably in combination with some other chemical material, could provide a completely combustible, non-toxic fuel.
Researchers in the US are also exploring the potential structural applications of boron in an aircraft to achieve hypersonic speeds. Currently, specific aircraft structures use carbon nanotubes (CNTs), as they can withstand high temperatures when an aircraft travels at high speeds.
In 2017, engineers from NASA and Binghamton University published a study, reportedly 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 of up to 450 degrees Celsius. A NASA study showed that boron nitride nanotubes could withstand 900 degrees Celsius, making them suitable for use in structures of supersonic or even hypersonic jets.
Also, the boron nitride nanotubes are lighter and better than CNTs, with high tensile strength and chemical and thermal stability.
Use Of Boron Still Challenging & Risky
As stated earlier, Pengfei and his rocket scientists from Changsha have designed a boron-powered ramjet engine that could work both in the air and underwater. This is quite unusual, as most boron-powered engines are designed to work only in the air.
Researchers generally prefer aluminum or magnesium as fuel for supercavitation torpedoes because of their high reactivity with water.
Therefore, the ramjet engine designed by Pengfei and his colleagues features some unique components like adjustable inlets and exhaust nozzles to maintain the boron’s burn efficiency in different environments. However, the biggest change is in the fuel composition, per their paper.
Boron usually amounts to around 30% of the total fuel weight in an air-breathing missile due to the requirement of several other chemicals for controlling and sustaining intense combustion.
However, Pengfei’s team doubled the percentage of boron in the fuel, which they estimated could result in a thrust exceeding that of aluminum in water.
At the same time, the team also said that the increased boron percentage could cause some problems in mass production, ignition, and combustion control, but these “can be solved by the modification of boron particles, improvement of the manufacturing process, and the study of grain mass properties.”
It is also difficult to adjust the thrust of a solid fuel engine. For example, the boron powder behaves as both solid and fluid when injected into the combustion chamber, making it challenging to simulate or regulate the burning process physically.
Moreover, China faces risks of relying on borofuels for mass-produced weapons, according to a Beijing-based material scientist who studies the boron element. Half of China’s boron ores are sourced from overseas, and a large portion is from the US.