Diving deep: robot explores waters in central Mexico for life

Michael M. Whiston Jan 22, 2007

Carnegie Mellon’s Robotics Institute recently developed software to be used in a deep-sea exploration project called DepthX.

Deep Phreatic Thermal Explorer (DepthX) is a mission to deploy an autonomous underwater vehicle (AUV) to the bottom of Zacaton Cenote, a sinkhole in central Mexico over 1000 feet deep.
Dr. David Wettergreen of Carnegie Mellon’s Robotics Institute developed the robot’s navigational software. Wettergreen’s past research has focused on robotics exloration, but this is his first underwater mission with Carnegie Mellon.

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.

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.

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.

Wettergreen said that previous explorations into Zacatone Cenote have not gone deeper than 30 meters. Nonetheless, these exploration missions have turned up some interesting results. In particular, the water contains low amounts of dissolved oxygen, and the water’s temperature is unusually warm — 90°F. Wettergreen said that DepthX may provide some data that explains these findings.

In May of 2005, the robotics team tested the vehicle’s sonar equipment in Mexico. According to the team’s field report, the sonar successfully reached from wall to wall, and researchers were able to confirm that the sinkhole neither widens nor narrows at a depth of 200 meters.

This spring, the team plans to reach the bottom of the sinkhole. Wettergreen said that there could be life much deeper in the sinkhole.

Wettergreen said, “Probably, we’ll find various kinds of slime and that’s what we’ll be sampling, but no one really knows, this is really exploration into the unknown.”

If successful, DepthX might provide researchers with the tools that they need for robotics exploration elsewhere. In Antarctica, for instance, researchers are hoping to deploy the vehicle under perched lakes (lakes that are sealed off by a layer of ice).

“It’s more than just going from A to B to C to D,” Wettergreen said. “You need a model for what measurements are more important than others.”

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.

When microbiologists search for microbial life, Stone said, they look for changes in the energy levels of an environment, which could indicate the presence of a warm spring. Similarly, the DepthX vehicle looks for microbial life by tracking energy gradients. “We’re simply giving these behavioral characteristics to the robot,” he said.

After reaching its destination, the vehicle extends a probe to collect water samples. The robot then analyzes these samples under a microscope.

The vehicle is specially designed to handle extreme temperatures, such as those found in Antarctica and on Europa. On the other hand, Stone said, researchers will need to slightly modify the vehicle before sending it to Europa.

Stone said, “This system has to be able to survive the journey there, which is a completely different environment than we’re looking in right now.” In particular, the vehicle must be built to handle space shuttle vibrations and thermal cycling, or energy change within a robot’s motor.

The team will be heading to Mexico in February for further tests before deploying the robot into Zecaton Cenote this spring.

Wettergreen said that this is Carnegie Mellon’s first project involving an underwater vehicle. He said that he would like to build similar systems in the future.

“I’m hopeful that this is something we can continue,” he said.