Robots go where people can't: collapsed underground mine shafts, on one-way trips into deep space and down into the bone-crushing bottom of the sea. With inhuman strength and smarts, robots routinely explore inhospitable territory in which high radiation, extreme temperatures or complete lack of atmospheric pressure would cause human beings to suffocate, freeze solid, explode into tiny chunks or all of the above at the same time. Even so, robots are far from invincible. Over the next several columns, we will explore the grave and mortal challenges faced by robots that boldly go where humankind cannot or will not. Robots are tougher than you are, but in the end you can feel better about yourself knowing that even the metal ones are vulnerable to Mother Nature.
First, a fun fact to know and tell: More people have traveled into outer space than have traveled to the deep ocean. (If there were ever a brawl between astronauts and aquanauts, the astronauts would thrash the water dwellers.) The deep sea crushes puny humans, but she reveals her secrets to intrepid robot explorers called autonomous underwater vehicles (AUVs). These metallic Jacques Cousteaus map the sea floor, study life in the deepest ocean trenches and, in the case of an almost 30-foot-long untethered AUV named Seahorse, do it alone based on the Navy's pre-programming and artificial intelligence. While robots may be immune to low temperatures and lack of oxygen, they must face a host of other calamities, especially these five.... —Daniel H. Wilson, Resident Roboticist
Submersible robots must be pressure-rated before being declared sea-ready. The cheapest approach: Place delicate electronics inside one-atmosphere glass spheres. Unfortunately, even a tiny scratch can compromise the sphere, causing an implosion and catastrophic failure, especially if the waterlogged sphere sinks the craft. Another solution is to use titanium or carbon fiber pressure housings; they look like metal spheres or tubes with sturdy caps on both ends.
The electronics encased within a pressure housing still need to communicate with the motors, sensors and, in the case of some Dorado-class AUVs at the Monterey Bay Aquarium Research Institute, elaborate underwater docking mechanisms. Running a cable out without letting water in is tricky: Connectors are usually surrounded by epoxy, and the pressure housing itself may be compensated (i.e. filled) with an oil that is somewhat positively pressurized. The positive pressure means that oil may leak out, but no water will come in.
Radio frequency communication does not work underwater, so AUVs must communicate with each other acoustically, like whales. Talking to humans is even more difficult—AUVs may have traveled to inhospitable waters miles away from the nearest ship. For AUVs such as the BlueFin Glider, the only option is to surface and establish a bi-directional satellite link, sending data and receiving new commands. Data is often transferred randomly so that in case of interruption the scientists will still have a random sampling of information. Back at home, scientists may choose to receive AUV status updates just like any teenager would—by cellphone text messages.
With minimal communication to the surface, AUVs rely on artificial intelligence to operate autonomously on a day-to-day basis—dealing on their own with strong currents, storms and noisy sensor readings. Submersed robots follow algorithms inspired by schools of fish to efficiently explore huge rectangular swathes of ocean. During the journey, only a limited number of measurements are possible, so many AUVs use adaptive sampling to take measurements only when something interesting happens.
But what if the worst—a water leak, a mechanical failure, a shark attack—happens? AUVs may be extremely isolated, but human rescue is possible—just as long as the robot doesn't sink. For this reason, many AUVs are designed to be positively buoyant; they simply float to the surface if motors fail. For these buoyant AUVs, traveling down to 4000 meters (about 2.5 miles) can take up to an entire day. Other AUVs contain burn-wires—electrical circuits that activate and burn out in emergencies, dropping a jettison weight that helps the robot surface quickly to radio for help.
Submersible robots like the Navy's 10,800-lb. unmanned Seahorse must be pressure-rated before being declared sea-ready. PHOTOGRAPH BY JOHN F. WILLIAMS/U.S. NAVY (CLICK TO ENLARGE
The Seahorse-class Autonomous Underwater Vehicle (AUV) from the applied research laboratory at Penn State University is lowered into the water prior to undergoing launch and recovery testing with Sea Fighter (FSF-1). PHOTOGRAPH BY JOHN F. WILLIAMS/U.S. NAVY (CLICK TO ENLARGE)
The crew aboard the mine hunter coastal ship USS Falcon recover the Bluefin--an unmanned anti-mine warfare vehicle designed to travel along a preset coarse once launched. PHOTOGRAPH COURTESY U.S. NAVY (CLICK TO ENLARGE)