Within the next three years, the U.S. military will test the feasibility of sending a quadruped robot out into the field as a trusty pack mule to carry supplies for its troops, wherever they go. If the testing goes well for Boston Dynamics's Legged Squad Support System (LS3), company founder Marc Raibert will have come a long way from the one-legged hopping robots he pioneered in the 1980s.

Actually Raibert has already come a long way, to the point where the U.S. Defense Advanced Research Projects Agency's (DARPA) Tactical Technology Office and the U.S. Marine Corps awarded his company a 30-month, $32-million contract last week to deliver a prototype LS3. This would be the first step in fulfilling the military's call for an autonomous, legged robot that can carry up to 181 kilograms of supplies for at least 32 kilometers without refueling.

The military already uses unmanned aerial vehicles for reconnaissance or to attack enemy targets, and DARPA has sponsored several contests in recent years to determine the feasibility of developing autonomic ground transportation. Automation has been much more difficult to introduce to the infantry, however, because of the need to traverse rough terrain where robots operating on wheels or tracks cannot go.

The LS3 is the latest in a series of legged robots developed by Raibert, who got his start in 1980, when he founded a robotics workshop at Carnegie Mellon University in Pittsburgh called the Leg Laboratory. Raibert moved the Leg Lab to Massachusetts Institute of Technology in 1986 after becoming a professor of electrical engineering and computer science there. The lab, which he directed until 1995, did good work, he says, "but it always felt like we were kicking the can down the street, making scientific progress, but not worrying about a system that could operate out in the real world."

Boston Dynamics, which Raibert founded in 1992, scored a breakthrough in 2003 when DARPA began funding the development of BigDog, a 75-kilogram mechanical workhorse and the LS3's predecessor. BigDog did not use cameras or laser sensors to determine its location. Instead, it stepped first and then reacted to the terrain, quickly determining its position at any given time and comparing that with its desired position, immediately taking corrective action based on the difference between these two.

But BigDog was not an instant success. "In the first year or so it was creaky, I'll tell you," Raibert says. Getting the robot's legs, each of which featured four joints, to move in a synchronized fashion—not to mention adjust dynamically to slippery surfaces such as ice—proved challenging. Over time, however, the quadruped robot's endurance and stamina improved—as did its software for balance and control—to the point where it could maneuver out in the real world. "There reached a point about three years ago with BigDog where we started to see the light at the end of the tunnel," he says.

With BigDog, Boston Dynamics demonstrated to DARPA the feasibility of a legged robot, which was significant for its potential to traverse sand, rocks, mud and snow under conditions that would strand a robot that ran on wheels or tracks. The company tested its technology at Marine Corps Base Quantico in Virginia, where it showed that BigDog could carry about half its own body weight up difficult hiking trails and that it could carry 1.5 times its body weight on flat level terrain. Testing also showed that it could operate without a driver, using an onboard computer vision system to follow a leader who wore a special vest (not unlike an actual dog tagging along behind its master), and that it could travel autonomously using a global positioning system to locations specified on a map (correcting for balance on uneven terrain as it went). The BigDog could march 19 kilometers before needing to refuel.

The LS3—which could end up resembling the Imperial walkers from the Star Wars movies, albeit on a smaller scale—is essentially "BigDog on steroids," Raibert says. The LS3 will have a leg up on its predecessor via its ability to travel autonomously without the need for preset coordinates or soldiers to wear special clothing. The new quadruped will have "a higher level of maturity in terms of system and autonomous operation," Raibert says. "The challenge is to make this fit within a certain size." One of DARPA's specifications is that the LS3 weigh no more than 570 kilograms when fully loaded.

Although LS3's propulsion system is still being designed, BigDog's used a two-stroke, go-kart gasoline combustion engine to drive a hydraulic pump. Whereas BigDog had an 18-horsepower engine, Raibert says he wants the LS3's power plant to be at least 40 horsepower. The LS3 will also have to operate no louder than 70 decibels, significantly quieter than BigDog. (This video of BigDog released by Boston Dynamics in 2008 demonstrates just how loud BigDog can be when on the move, thanks at least in part to its engine.)

The first 30 months of the project constitute phase 1, at the end of which Boston Dynamics will have to deliver two prototype LS3s that can carry the required weight (181 kilograms) a required distance (at least 32 kilometers) across a relatively flat surface. The LS3s will also have to be able to run up to 16 kilometers per hour and feature at least a rudimentary version of the systems it will need to operate autonomously.

Boston Dynamics has enlisted the aid of engineers and scientists at defense contractor AAI Corp., aircraft-maker Bell Helicopter, Carnegie Mellon's National Robotics Engineering Center, NASA's Jet Propulsion Laboratory and motion-control systems provider Woodward HRT to develop the LS3's hydraulics, propulsion and guidance systems. Although JPL previously did some work with Boston Dynamics on the BigDog's vision guidance systems, this is the first time the company has collaborated outside its walls to develop its robots.