As armed forces and their suppliers work on costly lasers to knock down cheap drones, the drone makers can easily reach for inexpensive responses from the building industry.
Fire engineers have quite a few ways of handling heat and doing so for much longer than the time a laser would need to down a propeller-driven cruise missile, also known as a strike drone.
And because this is civil construction that we’re talking about, the materials are not at all expensive by aeronautical standards. They wouldn’t be heavy, either.
The most obvious ideas that fire engineers could share with drone makers are reflective coatings, other materials that diffuse heat, and paints that become insulators when hot. Good old plasterboard inside the leading edge of a drone wing could also stop a laser from breaking up the structure.
These simple technologies work at two stages to protect buildings against fire. They handle energy as soon as it impinges on a surface – for example, from an intense bushfire a few metres away – and they handle it once it’s in the structure to prevent catastrophic temperature rises. They can do just the same for drones.
Stage 1: handling heat at the surface
A laser defeats a drone – the Shahed-class strike drone being a prime example – by putting intense heat into a small area until something fails: a wing skin softens, a spar buckles or a propeller breaks. The laser needs to hold that energy on the same spot long enough to cause that failure, a period engineers call dwell time.
The first line of defence is to reflect as much of that energy as possible before it enters the skin. Emergency services wrap heritage huts in reflective foil during bushfire season for exactly this reason. Foil would betray a drone to radar, but the ceramic paints already sprayed onto Australian rooftops to cut air-conditioning loads serve the same reflective purpose and are transparent to radar. Commercially available formulations can reflect most near-infrared light at wavelengths typical of solid-state combat lasers, can be applied easily and are compatible with a standard matte-black finish. The drone does not need to look different, and it will return most of the beam’s energy before anything important gets too hot.
Some heat will still enter the surface. That won’t be catastrophic if it doesn’t reach the structure.
A supplementary idea, not from the construction industry, would be to mount a small camera that detects which surface is being heated and triggers a lateral oscillation, periodically presenting the opposite wing edge to the beam. Every time the beam starts to bite, the geometry changes. The drone is not evading; it’s just making the laser restart its work.
Stage 2: protecting the structure
If enough heat conducts through the fibreglass skin of a typical strike drone, the second stage begins just behind the outer surface.
Gypsum, the mineral that makes gives fire-resisting properties to plasterboard, starts as a slurry and sets into any shape its mould provides. Builders use this for cornices and decorative ceiling panels. In a drone’s leading edge, the cavity itself can be the mould: the slurry can be poured in during the manufacturing process and when setting would bond to the inner surface. When the laser played on the outer skin, the gypsum would absorb the heat by turning crystallised water it contains into steam, the same mechanism that fire-rates a wall.
Open-cell aluminium foam, the metallic sponge that has been used in industrial laser-safety beam dumps, enclosures that prevent laser energy escaping into a workspace. The material conducts heat laterally rather than letting it concentrate. A laser trying to punch through a foam-filled panel is not heating one spot. The beam is stretched across its porous internal surfaces, heating a wide surface area of a thermally conductive material that becomes a reflective mirror when molten. The laser has to work much harder to cause local failure.
Intumescent paints are routinely applied to structural steel for fire-rating. When heated, they expand dramatically, forming a thick, low-conductivity char. On a drone’s wing spar, the same coating would respond to laser heating by expanding into an insulating layer precisely where the beam is focused. The hotter the beam, the thicker the char. The mechanism is self-reinforcing.
None of these measures needs to work indefinitely. Assuming a shipboard laser can effectively engage at 10 km, a jet-powered strike drone at 600 km per hour covers the distance in about a minute – during which some of the laser energy is lost in heating the atmosphere and water vapour. The protection needs only to outlast that window.
An attacker need not deploy all these layers. Even one or two, applied to the right parts of the airframe, may be enough to outlast a one-minute engagement. The whole collection would be an over-engineered solution to a one-minute problem.
Much less than a minute may be available for dealing with strike drones flying low over land and obscured by hills and trees.
The asymmetry that matters
The economics of this asymmetry are stark. Australia is investing up to A$7 billion in directed-energy counter-drone capabilities over the next decade. The weapons being purchased cost millions of dollars each. A baseline hardening package using materials discussed here – including ceramic topcoat, gypsum leading edge, aluminium foam and intumescent coat on spar – adds a few kilograms and costs a few hundred dollars per drone at production scale. The weight would probably come out of the payload or fuel load and still leave a quite effective weapon.
Russia’s Alabuga facility produces hundreds of Shahed-class drones per week and has iterated design changes in cycles of four to 16 weeks. A hardening modification derived from first principles in construction physics is the kind of change that a production line absorbs in a single quarter.
Much of the case for directed-energy weapons rests on cost: a laser shot is cheap; a missile is not. That argument is sound. But it assumes the targets will remain as easy to kill as they are today. The building industry has already solved the problem of keeping structures intact under intense heat. The materials are on the shelf. The knowledge is in every fire engineer’s training. If that knowledge has not yet reached drone designers, it will.
This then leaves the question of whether a laser, engaging one target at a time, is worth paying for. The hardened drones don’t have to come at widely spaced intervals; they can arrive together in a wave.
Australia’s directed-energy procurement should be tested against drones that have learned a little building science, not just against the drones we have seen so far.
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