Robot Subs in Space

A Giant Orange Eyeball

Some 575 million miles from Europa, on the back lot of a secure government testing facility in Austin, Texas, a round robot floats in the center of a test tank like an orange bobbing in a giant pot of holiday grog. On a platform beside the tank is a metal-sided trailer office, the kind you´d find on a construction site. A man´s voice comes from inside. "It´s time," he says. The robo-orange, which is about seven feet across, rotates neatly in place, expels air with a bubbling hiss like a breaching whale, and drops below the surface.

It´s late October, and I´ve come to Austin´s Applied Research Laboratories (ARL) to watch one of the final days of tank testing before DepthX is deployed at Zacatn. Inside the metal trailer are several members of the DepthX team. There´s John Kerr, the lab manager of Stone Aerospace, which specializes in autonomous vehicles, life-support equipment, and laser and sonar imaging devices. Kerr is joined by George Kantor and Dominic Jonak, roboticists from Carnegie Mellon University, and John Spear, a biologist from the University of Colorado. The gang´s demeanor is low-key, but there´s an undercurrent of tension. If DepthX goes awry, it could damage both itself and the multimillion-dollar test tank. If the test goes well, the team will be one step closer to a landmark achievement in autonomous robotics.

To understand the audacity of what Stone is attempting, consider the capabilities of Spirit and Opportunity, the semi-autonomous rovers currently exploring the surface of Mars. Though hugely successful at gathering data and imagery, the rovers are essentially highly sophisticated remote-control cars; they receive marching orders from human mission controllers whose decisions are informed by pictures of the terrain around the robots. The ultimate goal for DepthX, meanwhile, is to be fully autonomous. Alone in an unknown environment, it will have to figure out where it is, where to go and what to do.

Inside the trailer, Kantor scans a computer that´s monitoring the robot´s performance, while Kerr stands outside watching DepthX. The robot´s navigation systems are being tested, and it slowly traces the outline of a square at a depth of about 10 feet. The maneuver looks precise, but apparently it wasn´t perfect. "It overshot the corner of its box," Kantor says, squinting at lines of code.

DepthX, at its most basic level, is a giant eyeball. Ringed with 54 sonar sensors, it collects data from thousands of sonar hits every minute to build what Stone calls "a hugely dense picture" of the environment around it. The robot not only charts a three-dimensional map of the world but also knows its place within it, using an inertial guidance unit, accelerometer, depth gauge and other sensors to pinpoint position. Together, these capabilities are known as Simultaneous Localization and Mapping (SLAM).

"This is the first instance of full 3-D SLAM underwater," Kantor says. In fact, it may be the first instance of full 3-D SLAM in any environment. Existing autonomous vehicles-the driverless SUVs in the Darpa Grand Challenge, for instance-have a relatively narrow, forward-looking field of vision because that´s all they need. As a caving robot, though, DepthX might encounter obstacles in any direction, so it must be all-seeing as well.

The robot´s predecessor was a device Stone invented called the Wakulla Springs Mapper, which was mounted on the tip of a torpedo-shaped propulsion unit and piloted by a scuba diver. In the late 1990s he used the craft to chart several thousand feet of passages in Wakulla Springs, Florida, creating the world´s first digitally generated, three-dimensional cave map. DepthX is far more complex than the device that inspired it-not least because it must function independently at a depth of 1,000 feet or more at Zacatn-but the fundamental concept remains the same.

"In theory, theory and practice are the same, but in practice, they´re not," says John Rummel, the NASA astrobiologist who is overseeing Stone´s work. "Bill clearly has a lot of practical experience with cave environments that came to fruition in the design of DepthX."