10 May 2016
Death beams and ray guns may be science fiction staples, but the idea of directed energy weapons (DEWs) was around long before Captain Kirk boldly went anywhere, or anyone named Skywalker ever thought to pick up a lightsaber. Now, as DEWs look close to becoming reality, the next question on everyone’s lips is: If for every measure there is a countermeasure, what counters direct energy? Could it be the forcefield? Dr Gareth Evans reports.
Over two thousand years ago, during the Siege of Syracuse, Archimedes is said to have channelled the heat of the sun into a ray that set the invading Roman fleet on fire - or at least that's the way Lucian told the tale, writing nearly four hundred years later. Despite a number of tests having been conducted in modern times, whether or not such a heat ray would actually have been possible back in 214BC remains unclear - but either way the story virtually guaranteed that DEWs have been high on the military's future wish-lists almost ever since.
Research in this sector received a major boost during the Star Wars programme of the 1980s, President Regan's Strategic Defence Initiative (SDI) leading to advances being made in a number of potential weapons systems. Although the abandonment of SDI ultimately meant that R&D was scaled back, DEWs remained of significant interest for future military use, and now, after decades of work and a series of 'false dawns', energy weapons finally look close to becoming established on the battlefields of the future.
DEWs on the battlefield
They have appeared there already, albeit briefly. The US deployed a non-lethal microwave 'heat ray' - the vehicle-mounted Active Denial System - to Afghanistan in 2010, but withdrew it before it saw combat. However, some observers think that the latest test successes of the US Army's 10kW high energy laser mobile demonstrator against drones and incoming mortar rounds could herald in a new era for ground warfare - and possibly before too long. A larger 60kW weapon is scheduled to be tested in 2017.
A range of DEW technologies have also been successfully demonstrated in the air and perhaps most notably, on the sea. In a nod to Archimedes' apocryphal feat, in 2011 the US Navy showcased a laser system which, though lacking the instant 'zap' of a movie blaster, was able to burn, albeit slowly, through a small boat's outboard motor and disable it. Three years later, in August 2014, the USS Ponce was deployed to the Persian Gulf armed with a 30kW demonstrator laser weapon system (LaWS) designed for self-defence against just the kind of low-level asymmetric threat that swarms of such boats might pose.
It represents a big jump forward, but it is still a long way from the phaser-banks of the Starship Enterprise.
Limitless firepower
A fully functional DEW has two principal advantages over conventional weapons relying on gunpowder or rocket-propelled projectiles; once the necessary energy generation systems are in place, the price-per-shot becomes orders of magnitude lower, and the magazine is limitless. It also fires the ultimate high-velocity round - quite literally at the speed of light. However, meeting the demand for all that energy, both in absolute terms and within a practically deployable package, is not something to discount lightly.
"At full capacity, the 30kW LaWS can fry sensors, detonate explosives and burn its way through outboard motors."
At full capacity, the 30kW LaWS can fry sensors, detonate explosives and burn its way through outboard motors, but to bring down bigger, faster threats such as anti-ship missiles, an energy weapon might need to be capable of delivering a beam of 500kW or more - and generating that calls for a lot of power.
Masers and lasers
The DEW field is largely dominated by two main technologies - microwaves and lasers - but both kinds of weapons share close links, both in terms of the underlying physics and their developmental history.
At their core, both are amplifiers of electromagnetic radiation - the 'ASER' in the acronyms laser and maser standing for "amplification by the stimulated emission of radiation." In practical terms, the energy added to the system causes the atoms or molecules to become temporarily 'excited' and as they subsequently drop down from their heightened energy state, they emit a photon of a specific wavelength in the light or microwave spectrum. With enough energy and enough photons, a cascade effect ensues and a stream of light or microwaves of a particular colour or frequency emerges, and hence the maser or laser beam is produced.
Technology limitations
Weapons research initially focussed on chemical lasers - potent devices driven by chemical reaction and capable of generating megawatt levels of power. However, despite a number of major successes under test conditions, the toxic nature of the chemicals involved and the need for a ready supply to keep the lasing reaction going - effectively negating the 'limitless magazine' advantage - has left them increasingly out of favour.
The emphasis today, at least in the US, is on electrically powered solid-state lasers, which avoid the problems of chemical laser technology, but have their own limitations, primarily in terms of lower power, reduced efficiency and significant cooling demands. Overcoming these constraints is, inevitably, the subject of ongoing work.
Shields up!
Research, however, seldom takes place in isolation, and interest in DEWs is by no means confined to the US alone. With all the evidence pointing to active, and in many cases successful, energy weapons programmes underway in Russia and China, amongst others, on a future battlefield, defence against DEWs will be every bit as potentially important as the weaponised lasers and masers themselves.
Enter that other long-running sci-fi favourite - the forcefield.
The force(field) awakens
"Boeing's recently granted US patent represents the first awakenings of genuine deflector shield technology."
"Method and system for shockwave attenuation via electromagnetic arc" may not exactly come over as a particularly snappy title, but Boeing's recently granted US patent represents the first awakenings of genuine deflector shield technology.
Although the system it describes is not specifically designed to be impervious to actual incoming laser bolts, it is intended to protect a potential target, such as a building or vehicle, from one of the most common energy threats on today's battlefield - explosive shockwaves.
It will work by superheating the air between the intended target and the blast, using an arc generator to create a plasma shield, using methods which might include high intensity laser pulses, conductive ion pellets, sacrificial conductors, projectiles trailing electrical wires or magnetic induction. Once in place, the denser-than-air plasma shield will deflect and reduce the incident blast energy, significantly minimising the damage done.
A long road ahead
It is, of course, a long road from a patent to a Humvee with its deflectors up, and there are a lot of practical considerations to be ironed out before the forcefield will work at all. The physics of a superheated plasma column of air, for instance, dictates that it is not something that can simply be put in place permanently, even if there was the ongoing power capacity to support it. For a viable system you first need to solve how you detect the threat, charge, aim and energise the shield arc, all within the milliseconds available before the shockwave hits.
Nevertheless, US patent 8981261 does represent a significant breakthrough in protection against the devastating damage wrought by present-day energy waves, and may ultimately lead to a time when the IED no longer poses such a huge threat. In the long run, it might also prove to be a milestone in defence against energy weapons of the future.
Early in the Cold War, Soviet Admiral Sergei Gorshkov commented that "the next war will be won by whichever side best exploits the electromagnetic spectrum."He was, at the time, alluding to the then burgeoning radar and communications technologies, but the irony is that in 1935, British research into radar had itself begun as a result of the Air Ministry's fear of rumoured German radio-wave 'death rays.' Looking to the battlefield 60 years on from the end of the Cold War, it could well be DEWs and forcefields which are the ascendant technologies; Gorshkov's words would seem as relevant as ever.
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