The soldier exoskeleton has moved from the realm of science fiction to reality, with contractors like Raytheon and Lockheed Martin partnering with smaller firms to bring products to market. But one big challenge remains: convenient and safe power for these machines.

Helping troops lug the weight of their equipment around is serious business, and the U.S. Army is actively pursuing solutions.

“You can’t hump a rucksack at 11,000 ft. for 15 months and not have that have an impact on your body,” Gen. Pete Chiarelli, the Army’s vice chief of staff, told reporters in January. The Army and Marines are witnessing a rise in musculoskeletal injuries. “There’s no doubt our non-deployable rates are increasing.”

Heavier body armor and equipment, compounded by the challenging terrain faced by troops in Afghanistan, mean those numbers are going to grow.

For nearly a decade, a project launched by the Defense Advanced Research Projects Agency has been looking at ways to help with the heavy lifting. The Exoskeletons for Human Performance Augmentation, a program whose stated goal in 2000 was “to develop devices and machines that will increase the speed, strength and endurance of soldiers in combat environments,” is finally a reality. At the behest of the Army, a team at Raytheon Sarcos, led by Stephen Jacobsen, built an exoskeleton called XOS. Video of the device in action shows software engineer Rex Jameson in the metal suit running, jumping, even speed boxing a punching bag. Jameson also does a lengthy series of reps on a weight machine, pulling down 200 lb. (see photo). “He stopped because he got bored,” Jacobsen says, “not because he was tired.”

“Qualitatively the suit has good mobility,” says Jeff Schiffman of the Army’s Natick Soldier Research, Development and Engineering Center, who has worked on the project for several years. He says the XOS provides a roughly 10:1 gain for a human. “The idea is that if you’re holding a 200-lb. box, it’ll feel like 20 lb.,” he says. Schiffman and his team evaluate the suit for its biomechanical and physiological aspects. How comfortable will operating the XOS be for a soldier?

Human factors issues have been relatively easy to navigate, Schiffman says. The Natick team’s goal, he adds, is to combine all the processes so a soldier can easily operate and get in and out of the suit without help.

And then there’s the matter of powering the suit. The first suit Raytheon Sarcos built in 2002 was not powered. The XOS now is tethered to a hydraulic pump that gets its energy from an external power supply that can run on propane, hydrogen or gasoline (and in later iterations, diesel), says Jacobsen.

“Before you do it right, you have to do it at all,” he adds. He breaks down the power issue into several levels. “First you have to show you can do the biomechanics, that it can move like you move,” he says. Then you have to determine how large your actuators need to be to accomplish those movements, as well as how much power those basic movements (including step, squat, walk, run, stumble) will consume.

Jacobsen’s team built numerous backpacks powered by electricity and fuel, but to get the power they needed, they had to develop their own valve system, which he says was “as hard as anything we did.” The servo valves control the hydraulic fluid feed to the actuators. Jacobsen was forced to engineer the valves to meet the size, reliability and efficiency demands he sought for the suit.