An artist's concept of how future soldiers will look when wearing exoskeletal machines.

Photo courtesy DARPA

Morphing Man and Machine

In the 2000s, the quest for a real-life Iron Man suit finally started to get somewhere.

The Defense Advanced Research Projects Agency (DARPA), the Pentagon's incubator for exotic, cutting-edge technology, came up with the funding for a $75 million program, Exoskeletons for Human Performance Augmentation, to speed things along. DARPA's wish list for a powered armored suit was pretty ambitious: It wanted a machine that would allow a soldier to lug hundreds of pounds of gear for days tirelessly, handle big heavy weapons that normally require two operators, and be able to carry other wounded soldiers off the field on its back. It also wanted the machine to be invulnerable to gunfire, and to be able to jump really, really high. Some researchers dismissed the idea as impossible, but others were willing to think big [source: Mone].

A company called Sarcos -- led by robot-maker Steve Jacobsen, whose previous projects included an 80-ton mechanized dinosaur -- came up with an innovative system in which sensors detect contractions of a human user's muscles and use them to operate a series of valves, which in turn regulate the flow of high-pressure hydraulic fluid to the joints. Those mechanical joints then move cylinders with cables attached to them to simulate the tendons that attach human muscle. The result was an experimental prototype called the XOS, which looked something like a human-insect hybrid out of a sci-fi movie. By 2005, the XOS emerged as the device that was closest to the military's vision, and the project moved to the development stage. Sarcos eventually was acquired by Raytheon, which continued the work [source: Mone].

Meanwhile, other outfits, such as Berkeley Bionics, worked on reducing the amount of energy that artificial limbs require, so that a powered exoskeleton could function long enough in the field to be practical. One mid-2000s design, the Human Load Carrier, reportedly was capable of operating for 20 hours without recharging [source: Mone].

Near the end of the decade, a Japanese company called Cyberdyne developed the Robot Suit HAL, an even more ingenious concept. Instead of relying on a human operator's muscle contractions to move the limbs, HAL incorporated sensors that picked up the electrical messages sent by the operator's brain. Theoretically, an exoskeleton based on the HAL-5 concept would enable a user to do whatever he or she wanted without moving a muscle, simply by thinking about it [source: Cyberdyne].

In the next section, we'll look at the current state of the art in powered exoskeletons, and where the technology may soon lead.