SOLDIERS kitted up in expectation of their first taste of combat often reflect on how much of their bodies a bulletproof jacket and helmet do not cover. About 81%, it turns out. More armour than this would be impractically heavy. Indeed, many soldiers already carry at least 50kg of kit and supplies, which is more than double what America’s Army Science Board advises as the limit if damage to a soldier’s skeleton and musculature is to be avoided.

The answer, many suggest, is a second, external skeleton, complete with artificial muscles, that would let its wearer carry far more weight without strain. Such exoskeletons, moreover, are no longer the stuff of science fiction. Interest in their uses, both on and off the battlefield, is growing.

One of the most advanced is the Kinetic Operations Suit (KOS) made by Revision Military, a firm in Vermont. For a soldier this triples his armour-protection while adding little burden to his movement. An artificial articulated spine transfers most of the weight of the suit’s helmet (which fully encases the wearer’s head) to armour on his shoulders. The weight of the armour protecting his torso is similarly transferred to his hips and legs through another section of artificial spine. All this reduces strain on his neck and lower back, the natural skeleton’s weakest links. His legs must still bear the extra weight, however. To assist with this, the KOS uses titanium-aluminium shafts which are strapped, along with armour, to his lower limbs. Electric motors, taking their cue from accelerometers and other sensors embedded in the suit, move these shafts in step with the way the soldier moves his legs.

According to Brian Dowling, a former special-forces soldier in the American army who works for Revision Military, the system is both nimble enough and robust enough to help its wearer run, fully laden, across uneven terrain. The armies of several countries, America’s included, are now evaluating such claims.

A second military exoskeleton, more ambitious even than KOS, is being developed by the special forces themselves. This project’s contractors include many of the most famous names of America’s defence establishment, such as General Dynamics, Lockheed Martin and Raytheon. Intriguingly, they also include Legacy Effects, the firm that designed the exoskeletons which feature in the “Iron Man” science-fiction films. The device these firms have come up with is called the Tactical Assault Light Operator Suit, a name crafted to yield the acronym TALOS, the ancient Greek name of a mythical animated bronze statue.

TALOS will weigh twice as much as the soldier inside it. The components contributing to this weight will, however, make it bullet- and shrapnel-proof. They will also offer its wearer a cooling system; a set of sensors that monitor his physiology; and superhuman strength. The result, according to General Joseph Votel, head of the Special Operations Command, will be “peerless tactical capability”.

If, of course, it works. That is not certain. To start with, the actuators that operate TALOS will need to become more agile. Replicating the movements of the shoulder joint, the human body’s most mobile, remains particularly difficult. The device will also need far more power than portable batteries can provide. General Atomics, another of the military-industrial complex’s usual suspects, has proposed designing a small internal-combustion engine to run the whole thing. But such engines are noisy, which could alert the enemy. Also, soldiers might, quite reasonably, be reluctant to wear a tank of petrol into battle.

Power down

A prototype of TALOS should be available by 2018, though a battle-ready version is at least a decade away. And even Revision Military’s more modest system will probably not be fit for combat for several years. In the meantime, though, the world’s armed forces are looking at the idea of unpowered exoskeletons.

Australia’s Department of Defence, to take one example, has designed a skeleton that diverts much of the weight of a backpack, or of armour designed to protect the torso, directly to its wearer’s boots. Two steel cables—encased in flexible tubes which are, in turn, held in place by loops in the wearer’s trousers—run directly from the backpack or armour to the soles of the boots. It is these cables that transmit the load. The tubes stop them buckling, letting them support their burden while retaining sufficient flexibility for the wearer to walk or run unhindered. The system is a prototype. But two other unpowered exoskeletons, one developed by Lockheed Martin and the other by BAE Systems, a British defence giant, are already in use—not for combat, but for industry.

A worker holding a rivet gun or other similarly heavy tool may have to set it down to shake out his arms and recover his strength so often that he is resting nearly half the time he is on a job. To help, Lockheed Martin has designed FORTIS, a 17.5kg unpowered exoskeleton now being tried out by the American navy and also by nearly a dozen manufacturing companies. FORTIS’s articulated aluminium frame supports a gimballed arm (see picture). One end of this arm, in front of the worker, is attached to the tool being used. The other end, behind him, carries an appropriate counterweight. Whether he is standing or kneeling to do the job in question, the combined weight of both tool and counterweight is transferred to the ground through the exoskeleton rather than through his bones. The tool itself thus seems weightless, and the worker does not so much wield as guide it. And, because that tool is attached to the exoskeleton, rather than being carried in the worker’s hands, this arrangement also prevents injuries caused by dropped tools.

Both FORTIS and BAE’s competing system, the Orthotic Load Assistance Device, boost productivity by about 50%, reckons Dana Ellis of the National Centre for Manufacturing Sciences. This industry body, based in Ann Arbor, Michigan, is helping both manufacturers and America’s Department of Defence adopt the technology. At American naval shipyards, FORTIS lets two workers do more with a grinder than the three-man team they have replaced, says Trish Aelker, exoskeletons boss at Lockheed Martin. At the end of their shift, she adds, workers are no longer so fatigued that they routinely “go home and crash on the couch”.

Carmakers are interested, too. Earlier this year Audi and Daimler, along with three other firms that prefer to remain anonymous, began testing a device called the Chairless Chair, made by Noonee, a Swiss firm. The Chairless Chair is a padded titanium exoskeleton that a worker straps to his buttocks, thighs and calves. Internal hydraulics allow its configuration to be locked at the push of a button, holding the wearer in a sitting position until he tries to stand up. Doing so automatically disengages the lock, permitting him to rise. The device weighs less than 4kg, so someone wearing it does not feel encumbered when standing or walking around. But, the button pushed, it lets him crouch comfortably inside the frame of a half-built car in order to add to its structure. According to Tanja Schembera-Kneifel, who runs Audi’s tests of the product, by reducing workers’ musculoskeletal problems, the Chairless Chair has also reduced absenteeism. Audi plans to deploy the device widely.

Other partial exoskeletons are in the works. One, the Personal Lift Assist Device, designed by Mohammad Abdoli-Eramaki of Ryerson University in Toronto, is also being tested by carmakers. Dr Abdoli-Eramaki’s invention involves a sheathed spring that runs down the spine. When the wearer bends to grasp and lift something, the spring stretches, reducing the effort required to stop gravity pulling his body to the floor. Then, when he stands up, the spring contracts, pulling on his torso enough to reduce by more than 15% the effort his muscles have to use to lift him.

Another partial skeleton, unveiled earlier this year by researchers at Carnegie Mellon University, in Pittsburgh, is called the Walking Assist Clutch. It is worn around the ankle and the calf, and uses a short elastic cord to reduce the work required of the muscles that pull on the Achilles’ tendon of one foot while the other is in the air. As the cord stretches, it stores energy which, a moment later, is released to tug the heel up, helping that foot push off the ground. According to its inventor, Steven Collins, the Walking Assist Clutch decreases the effort involved in walking around by 7%. For someone like an infantryman, that would be a valuable gain.

Step up

In the end, though, the future of exoskeletons probably does lie with powered versions. The European Union, for example, is putting €15m ($17m) into a transnational project to develop a system called Robo-Mate. This is an exoskeleton with upper- and lower-arm motors that reduces the perceived weight of an object by 90%. Trials begin in 2016. One of the guinea pigs is Fiat, another carmaker (whose chairman, John Elkann, sits on the board of The Economist’s parent company). The second is INDRA, a French firm whose business is the even-more-labour-intensive one of dismantling and recycling vehicles.

Nor is Robo-Mate alone. Power Loader from Activelink, a subsidiary of Panasonic, a Japanese company; Hal from Cyberdyne, another Japanese firm; and the Body Extender from Percro, a robotics laboratory at the Scuola Superiore Sant’Anna in Pisa, Italy, are all in development, too. They may do more than make existing workers safer and more productive. Carmen Constantinescu, Robo-Mate’s project manager at the Fraunhofer Institute campus in Stuttgart, Germany, observes that they will also redefine who can become a worker. By abolishing the strength advantage enjoyed by men, exoskeletons will open up to women jobs that many now find too strenuous. They will also help older men, who might otherwise have to give up work.

The group whose lives may be changed most by powered exoskeletons, though, are paraplegics. Both ReWalk Robotics, an Israeli firm, and Parker Hannifin, of Cleveland, Ohio, make devices that consist of an artificial pelvic girdle sporting two powered, jointed, limb-like appendages that strap to the wearer’s legs. Combined with a pair of walking sticks attached to his forearms, these let a user walk for hours at a time before the batteries run out. They can even permit him to climb a flight of stairs.

ReWalk’s device has been available in Europe since 2012, and in America since 2014. Parker Hannifin’s was approved for use in Europe in November, and American approval is expected soon. Exoskeletons, then, come in many guises. Some may help on the field of battle. But sometimes, conquering a staircase will be enough.