Engineers face extreme hurdles as hypersonic weapon development accelerates

Just three weeks into its invasion of Ukraine, Russia was already facing stalemate on many fronts.

Searching for a quick win, it deployed a new hypersonic missile for the first time – the air-to-surface Kinzhal, or ‘dagger’. Russia claimed to have destroyed an ammunitions store in Delyatin, western Ukraine.

Western allies responded quickly to the use of an air-launched missile capable of Mach 5 and above. On 5 April, the Australia-UK-US (Aukus) partnership committed to new co-operation on hypersonic weapons and counter-hypersonics.

Hypersonic weapons themselves are nothing new – intercontinental ballistic missiles (ICBMs) fly at speeds of about Mach 20. A new generation promises high manoeuvrability at lower altitudes, however, potentially confounding attempts to track and defend against them. These new weapons could offer warring nations a strategic advantage, but engineers have some hurdles to overcome.

Material challenges
Iain Boyd, aerospace engineer and director of the Centre for National Security Initiatives at the University of Colorado, describes the three types of non-ICBM hypersonic weapons in an online article . These are: aero-ballistic, such as the Kinzhal, which is dropped from an aircraft before accelerating to hypersonic speed using a rocket; hypersonic boost-glide weapons, which launch to a high altitude on a rocket before gliding to their target, manoeuvring during the glide; and cruise missiles, which use a rocket to reach hypersonic speed before an air-breathing engine known as a scramjet takes over to sustain speed.

Each branch of the US military is investigating hypersonic weapons, with a focus on the boost-glide type. Materials are the main challenge, Boyd told Professional Engineering – they need to be cost effective, lightweight and able to withstand extreme temperatures.

“They go so fast that they get very, very hot,” he said. “The materials, the thermal challenges, are what limit the speed.”

A range of materials is being investigated, from metals and carbon composites to exotics made with ceramics such as hafnium diboride and zirconium diboride. Companies are also investigating active cooling, flowing fluid through capillary-like structures near the surface to cool missiles down.

Plasma blackout
The quest for manoeuvrability and the element of surprise compounds the challenges, said Boyd, as new hypersonic weapons might fly through the atmosphere for much longer than conventional ballistic missiles. “These new systems can go to many different destinations,” he said. “It puts a lot more burden on sensing – you have to know where you are, you have to be able to know you know where you’re going and how to get there through manoeuvring.

“The environment around the hypersonic vehicle can get in the way of sensing. There’s this thing called plasma blackout… you get charged particles formed around hypersonic vehicles, ions and electrons, and they can interfere with radio communications.”

The scramjets within cruise missiles are an additional challenge. While the US has successfully tested a Lockheed Martin missile known as the Hypersonic Air-breathing Weapon Concept, there are considerable challenges in consistently sustaining combustion and mixing fuel with air at very high speeds.

Ultimately, said Boyd, these new weapons will be very expensive, so they will be used “very, very carefully and strategically” – attacking high-value targets on the first day of an invasion to clear space for aircraft and troops, for example. “It’s not a silver bullet that ends the war, but it can make a very big difference.” (IMECHE)

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