Flying naked: Chinese scientists find laser weapons can strip the coating off hypersonic missiles with unexpected ease

Researchers have found that doubling the strength of a laser weapon actually causes less peeling of a hypersonic missile’s coating
Without the special coating on a hypersonic weapon, it can be prone to overheating, destabilising or falling apart mid-flight

Science

Stephen Chenin Beijing

Published: 6:00pm, 21 Mar 2024

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When using laser weapons to defend against hypersonic missiles, cranking up the power does not automatically guarantee better outcomes.

That is what a team of aerospace defence engineers and scientists from Beijing found after conducting wind tunnel tests to examine a scenario in which a missile travelling at Mach 6 is hit by a laser beam.

When the beam’s power density reached 1kW/sq cm, it caused significant peeling of the coating on the missile’s surface.

This special coating is what gives China’s hypersonic weapons their edge. Without it, they would be prone to overheating, destabilising or even falling apart mid-flight.

But here’s the kicker: when the scientists doubled the laser’s power density, the area of peeling actually decreased.

“Under the influence of hypersonic airflow, the coating sustains more damage when hit by a lower-powered laser,” wrote a team led by senior engineer Lin Jian with the Chinese Academy of Aerospace Aerodynamics in a peer-reviewed paper published in the Chinese academic journal Physics of Gases in January.

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The academy, located in the Chinese capital, is affiliated with the China Aerospace Science and Technology Corporation, the nation’s largest aerospace defence contractor. It was founded in 1956 by Qian Xuesen, the father of Chinese aerospace, and is one of the main institutions for research and development of hypersonic weapons in China.

The debate rages on about the viability of lasers as a countermeasure against hypersonic weapons. Proponents argue that lasers have a low cost of operation and can travel at near the speed of light in the atmosphere, making them one of the best means to counter the threat of hypersonic weapons.

But opponents claim current laser technology produces insufficient power and has limited range, making it difficult to cause effective damage to incoming missiles within a limited time frame.

Lin’s team said previous research had not accurately replicated the conditions of hypersonic weapons flying in the atmosphere, with “airflow always playing a cooling role”.

“In actual flight environments, aircraft are usually heated up,” they wrote.

Current research also fails to consider the feedback interference of burning on the airflow.

“The destruction of materials by laser irradiation is bound to change the structure of the airflow field, and the corresponding mechanism of airflow on the material will also change,” Lin and his colleagues said.

Opponents of the use of laser weapons against hypersonic missiles say the current technology is not strong enough to cause effective damage. Picture: Handout

In new wind tunnel experiments, they found that the vaporised material under laser action forms a very complex interfering flow structure in the Mach 6 airflow and evolves into a droplet-shaped shock wave on the surface of the aircraft.

Under the high-power beam of 2kW/sq cm, the coating can be burned through in one second, and then the burning damage extends to the underlying metal material.

At a lower power density of 1kw/sq cm, the laser is not enough to damage the base metal, but the energy diffusion is obvious, causing more peeling of the coating material, they said.

A popular belief is that the coating of hypersonic weapons can withstand temperatures of thousands of degrees Celsius, making them highly resistant to laser attacks.

Li’s team found that this is true in static conditions, as lower power density lasers cannot cause any damage to the coating.

However, during high-speed flight, the hot air promotes burning, “causing the upstream coating to quickly detach under the viscous action of the airflow”, they wrote.

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Previously, the main goal of laser weapon development was to burn through the hull of the target. Now, the discovery of coating destruction “promises to broaden the horizons of application for laser countermeasures”, Li’s team said.

This experiment also highlights the challenges in using lasers to shoot down China’s hypersonic weapons.

In a 2020 test conducted by the US military, a 150kW laser weapon took 15 seconds to shoot down a low-speed small drone. In that amount of time, a hypersonic missile could travel at least 30km.

According to calculations by some scientists, the current megawatt-class lasers being developed in the US can only generate light spots on a target – and that is with power densities of hundreds of watts per square centimetre. To cause damage to targets at long distances, the laser power may need to be increased to the gigawatt level.

Even if future laser weapons achieve this level of power, scientists and engineers developing hypersonic weapons can still mitigate or even avoid burns by improving coating materials or allowing the missile body to rotate in flight.