Carnegie Mellon University The DEPTHX explorer robot, with its sampling arm extended, prepares to take a sample from the underwater wall of the cenote known as La Pilita in Mexico.

By David Templeton, Pittsburgh Post-Gazette

Sinkholes in Mexico -- those watery geological enigmas that have lured people to their banks for centuries -- don't easily reveal their deep, dark secrets.

But scientists are now collecting a mother lode of information about sinkholes known as "cenotes" in Mexico's central Gulf region, with help from roboticists at Carnegie Mellon University.

	Robin Rombach, Post-Gazette David Wettergreen helped develop the DEPTHX robot with his expertise in other exploration robots, including Nomad, behind him, which was used in Antarctica to search for meteorites. Click photo for larger image.

Stone Aerospace Inc. of Austin, Texas, recruited David Wettergreen, associate research professor at CMU's Robotics Institute, to help develop the Deep Phreatic Thermal Explorer known as DEPTHX. The autonomous robot is now being deployed to explore sinkholes whose dangerous depths have long confounded scientists.

Controlled by CMU software, DEPTHX already has proven its value as a top-flight cenote explorer.

In a project funded by NASA, the robot that resembles a flattened orange last month explored La Pilita Cenote, which is 105 meters deep, and returned with maps, measurements, scientific analysis and other novel detail.

DEPTHX's first three-hour exploration of La Pilita on Feb. 5 ended with it surfacing on its own.

"It was like religious experience," said Bill Stone, owner of Stone Aerospace, who assembled the team of scientists from CMU and the universities of Arizona, Texas and Colorado to develop the robot.

Exploration of La Pilita is a warmup for a May 14-27 mission to plumb the 300-meter depths of El Zacaton Cenote, the world's deepest hydrothermal spring, and return with new details about its size, shape, possible origins and whether it harbors life.

While the deep-water journeys add to science, they also aid in developing DEPTHX's successors, which will be equipped to melt through Antarctic ice to explore hidden polar lakes and in time explore Jupiter's moon, Europa, where scientists hope it can melt through 10 kilometers of ice to search its oceans for signs of life.

DEPTHX has 36 on-board computers and 96 sensors including sonar, which operate on 100,000 lines of computer code. The robot also has onboard electrical power equivalent of 10 kilos of TNT stored in some of the largest lithium batteries ever assembled, Dr. Stone said.

As a result, DEPTHX can operate underwater for eight hours.

"Extraordinary," Dr. Stone said, describing DEPTHX as the leading edge of autonomous robotics. "To me, that's a pretty impressive thing for people to pull off."

But a setback did occur last week during a test dive. Due to a software glitch, DEPTHX got caught under an overhang 25 feet underwater and had to be rescued by humans. Dr. Stone said it prompted improvements. Since then successful missions have been run.

"In my opinion, the super tough nuts have been cracked with DEPTHX," Dr. Stone said. More sophisticated sensors and other advances will be necessary for future missions.

Dr. Stone said he recruited Dr. Wettergreen because of CMU's expertise in software systems to run robots. CMU developed "system executive software" to navigate and guide the robot to map the cenote and autonomously create an exploration strategy. That includes judging whether it has sufficient power or is moving too close to walls.

CMU researchers also helped to develop a mapping system that reduces scanned areas to a series of cubes where mathematics and probability are used to predict accurately what the robotic is seeing.

The robot originally was tested at the end of a tether. Then it took dives that progressively got longer. Ultimately they released DEPTHX into La Pilita and waited for it to resurface.

"It started its largest dive at 9 p.m. and when it came up, we were happy," Dr. Wettergreen said. "We were watching movies. We had nothing to do until 2 hours and 55 minutes. We knew it had only 3 hours."

La Pilita, he said, "looks like a weird duck pond in the middle of a field in Mexico." But below the surface, this is not the typical duck pond. La Pilita is 340 feet deep. It also extends under the ground surface, making it difficult for a robot to find its way back to the surface.

Mexican sinkholes are situated in volcanic regions whose warmth and acidity carved through limestone to create enormous voids that filled with water.

Dry land robots created by Dr. Wettergreen and others are ideal for exploring dangerous caves, volcanic craters and other geological constructs that provide difficult access for humans. They are also proving ideal for underwater exploration.

The next goal is to explore El Zacaton, "a bottomless pit" that's the world's largest sinkhole. It represents the inverse of scaling Mount Everest, Dr. Wettergreen said.

Simply stated, DEPTHX must explore the unknown water environment, then find its way out, he said.

"The exploration process will take a big look and fill in the details," he said.

A key mystery to be solved is why El Zacaton's water contains no oxygen. DEPTHX will take samples and study biology and chemical composition to provide data to support or refute hypotheses. It also could discover if water comes from underground passageways.

Dana Yoerger, an associate scientist with the Woods Hole Oceanographic Institution in Woods Hole, Mass., said he's been cheering on the project from a distance.

"They are trying to do something that's really hard to do. My hat is off to them based on that -- the idea of an autonomous vehicle maneuvering in a poorly known, very threatening environment," said Dr. Yoerger, whose expertise is robotics in oceanic research that includes exploring hydrothermal vents. "I'm very respectful of the difficulty of what they are undertaking.

"I'm a really big fan."

For more DEPTHX photos and field journal from Mexico, see www.frc.ri.cmu.edu/projects/depthx.