This spring, an underwater robot named Deep Phreatic Thermal Explorer (DEPTHX) will start to explore the depths of the Zacaton Cenote in central Mexico, which is over 1,000 feet deep (more than 300 meters). According to Carnegie Mellon University (CMU), this robot will navigate through this sink hole by using a software called simultaneous localization and mapping, or SLAM. The goal is to discover what kinds of organisms are still living in the deepest flooded sink hole in the world. If the experiment is a success, this robot will be reconditioned and reprogrammed to explore the Solar system to discover other possible living organisms.
David Wettergreen of Carnegie Mellon’s Robotics Institute has developed DEPTHX navigational software. Here is a short comment.
Wettergreen said that the project’s ultimate goal is to study the sinkhole’s underwater environment by collecting water samples while also creating a three-dimensional map of the sinkhole. "We need a vehicle ... that can move through complex cave systems without getting lost or trapped," said Wettergreen.
But what is the DEPTHX autonomous underwater vehicle (AUV)?
The vehicle is seven feet in diameter, and it can spin and move in any direction. Also, its buoyancy is very high, and the center of mass is very low, making it ideal for underwater exploration. "It really wants to float upright in the water — it turns out to be extremely stable," Wettergreen said.
Below is a model of the DEPTHX vehicle structure and components. "Eleven pressure vessels house computing, batteries, sensors, and science instruments. Diameter is approximately 2 meters, weight 1.3 metric tons." (Credit: Stone Aerospace)
And below is the DEPTHX vehicle in the test tank (Credit: CMU Robotics Institute).
But how this AUV will 'see' at the bottom of the Zacaton Cenote? This is where the CMU's software comes into action.
In the DepthX project, Wettergreen helped develop software that enables the robot to map its environment. This particular kind of software is called simultaneous localization and mapping, or SLAM.
Project leader and Pittsburgh native Bill Stone of Stone Aerospace said that in the bottom of Zacaton Cenote, "things get very complicated, very fast." He said that SLAM is a clever way to determine the vehicle’s location because it allows the vehicle to build a map of its three-dimensional surroundings. The map also includes information on the water’s temperature and salinity levels.
It is interesting to note that previous explorations into Zacatone Cenote have not gone deeper than 30 meters back in 2005. But this spring, the team is confident its robot can reach the bottom of the sink hole and discover previously unknown forms of life.
So what will be next?
The robot could also be used to explore Jupiter’s ice-covered moon Europa. Stone said that a half-dozen planets have bodies of water that could contain life. "The software technology can be applied to a number of underwater exploration problems," Wettergreen said. Stone said that an environment must contain water, carbon, and electricity for life to exist, and there is reason to believe that Europa satisfies these criteria.
For more information about this project, you should read several pages available from the CMU's Field Robotics Center: about David Wettergreen, about the Underwater Cave Exploration in general and this particular page which contains many details and pictures.
And if you specifically want to know more about the SLAM software used to manage the underwater robot, a scientific paper should soon be published by the Journal of Field Robotics under the name "Real-Time SLAM with Octree Evidence Grids for Exploration in Underwater Tunnels." Here is a link to this full paper (PDF format, 17 pages, 1.78 MB) from which the above illustrations have been extracted.
The University of Texas at Austin also maintains a site about the DEPTHX Project.
Finally, don't miss a paper from the Houston Chronicle which was centered on Bill Stone of Stone Aerospace, "Underwater robot could explore ocean on Jupiter moon in future" (Michael Ray Taylor, The Houston Chronicle, November 7, 2006).
Sources: Michael M. Whiston, The Tartan, Carnegie Mellon University's student-run newspaper, January 22, 2007; and various other websites
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