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Underground opportunity: The Quecreek accident restored interest in subterranean robotics at CMU

Monday, December 23, 2002

By Byron Spice, Post-Gazette Science Editor

Four months ago, it began as a simple notion: that robotic technology could be used to map abandoned mines, reducing the risk of a repeat of July's Quecreek Mine inundation.

Carnegie Mellon University students and researchers have since built a pair of mine-mapping robots and prowled through several mines, including an unprecedented venture into a long-abandoned, water-and-muck-filled coal mine in Burgettstown.

But now, William "Red" Whittaker, the Carnegie Mellon University robotics professor who launched the initiative, suspects that he and his colleagues may be on to something bigger, a whole new field he calls "subterranean robotics."

William "Red" Whittaker and the Groundhog. (Martha Rial, Post-Gazette)

"What we're discovering," Whittaker said, "is millions of miles of underground spaces"-- not just mines, but sewers, aqueducts and caves. And for every underground space, there seems to be somebody who wants it explored or monitored in ways particularly suited to robots.

He has fielded a variety of inquiries. Kentucky mining officials are interested in using robots to mine layers of high-value coal that are too deep to strip mine and, at less than 2 feet, too thin to economically deep mine. U.S. Energy Department officials would like robots to monitor the Yucca Mountain caverns in Nevada that will be used as a nuclear waste repository.

Some military officials reportedly are intrigued with the idea of a robot that could map sewers in enemy-occupied cities, perhaps identifying underground routes that commandoes could use for infiltration.

"There's been a surprising demand for 'fish,' " Whittaker said, referring to swimming robots.

The Carnegie Mellon team even has a paying job. Early next year, they will send a robot called Ferret to Kansas City, Kansas, where it will be used to study the collapse of a limestone mine ceiling that has forced the closure of a busy residential street overhead. Later, the same robot will be used to map Kansas salt caverns that are used to store natural gas, looking for irregularities that would allow gas to escape.

"We map where the sun don't shine," was the motto of Whittaker's Mobile Robot Development class, which used mine mapping as its project this fall. Working in concert with that class is a Carnegie Mellon business entrepreneurial class led by Tom Emerson.

That group already has sketched out a business plan for a company supplying subterranean mapping services. The company, Black Rabbit, is to be launched this spring, with annual revenues of $12.5 million projected by 2008, said Idan Mor, one of the students.

Taking another look

Though Whittaker has been a pioneer in using mobile robots in unusual environments -- robots for examining and cleaning up the Three Mile Island reactor building, robots to explore active volcanoes, robots to look for meteorites in Antarctica -- he hadn't explored underground applications since a brief period in the mid-1980s.

But when the Quecreek Mine accident was blamed on faulty, outdated maps for an adjoining, abandoned mine, Whittaker began to think about robots and mines anew. New advances in automated, three-dimensional mapping, autonomous navigation and power supplies convinced him that a robot might both survive in an abandoned mine and be able to draw reliable maps.

His fall robotics class, together with an automated mapping course led by Sebastian Thrun, responded by building two devices: Groundhog, a wheeled robot the size of a golf cart, and Ferret, a machine that could go down a borehole, pop its head into a mine and use lasers to build a map of what it sees. Groundhog also uses a laser rangefinder to build maps, though other devices such as sonars could be used for mapping.

 
  Online Graphic: A look at subterranean robotics

   
 

They began work on Groundhog by welding together the front ends of two Honda all-terrain vehicles, giving them a chassis with four-wheel drive and four-wheel steering. A golf cart motor and transmission were added, resulting in an 800-pound machine they planned to drive into the old Saxman mine, the abandoned mine mistakenly breached by the Quecreek miners. But the unshielded electric motor was an explosive hazard in a mine, so the researchers were sent back to the drawing board.

The golf cart drivetrain was swapped for a hydraulic system, powered by an electric motor encased in an explosion-proof box.

This version, about twice as heavy as the original, was tested several times in the U.S. Experimental Mine in South Park Township and, in late October, was twice sent into the former Florence Mine at Burgettstown. A satellite link to Charleston, W.Va., allowed mining officials gathered for a mine-mapping conference to follow Groundhog's progress inside the Burgettstown mine and see the 3-D maps it produced.

Ferret is much simpler. The long, cylindrical machine is designed to be lowered through a 10-inch diameter borehole, allowing it entry to otherwise inaccessible mines. Ferret has arms to anchor itself to the borehole walls and, at its bottom end, a laser rangefinder for building 3-D maps. The laser has a half-mile range.

"There's been overwhelming interest in this," said Aaron Morris, the graduate student who put much of Ferret together, "because it's immediately deployable."

Early next year, the Carnegie Mellon team will take Ferret to Kansas City, where the roof of a limestone mine gave way, allowing overlying rock and sediments to fall into the mine. This "dome out" created a large void underneath Holliday Drive, a busy residential road.

Though no surface subsidence has occurred yet, the road has been closed until the void can be filled with fly ash concrete, said Bill Shef-chik, a geologist with Burns & McDonnell, an engineering consulting firm in Kansas City.

The mine itself is accessible -- the limestone mines under Kansas City are dry and often used as warehouse space -- so contractors have been able to pile up earth and gravel around the area of the "dome out" in preparation for filling it with concrete. But engineers would like to get a look at the void above the mine and that's not so easy, Shefchik said.

Video cameras can be placed through a borehole to view the void, but lighting is a problem and the images are poor, he noted. With Ferret, the engineers should be able to build a precise map and obtain an exact measure of how much concrete is needed.

Later, Ferret will be used in the salt beds outside of Hutchinson, Kansas. Salt was mined there using a system in which water was pumped into the beds, dissolved the salt and was pumped out as brine. This created large caverns subsequently used to store natural gas. But when gas escaped from one of the caverns a year ago, natural gas geysers, explosions and fires wracked downtown Hutchinson.

Shefchik said old, abandoned wells provided a conduit for the escaping gas and efforts are now under way to better understand the salt caverns. "Visually, no one's ever seen them," he said. Sonar tools can provide an approximation of their size and shape, but Ferret may be able to provide detailed, 3-D maps of the caverns and identify sites where leaks might occur.

Other uses for subterranean robots abound, Shefchik said. A wheeled rover that could patrol through active limestone mines, abandoned mines and underground warehouses might provide an early warning of dome outs, for instance.

Mapping active mines

Even if robots aren't used for mining abandoned mines, Mor sees a market for automated mapping of active mines. The machines produce accurate 3-D maps, so running a robot through a mine every few weeks would allow mining companies to calculate exactly what volume of coal has been removed, as well as to automatically produce mining maps.

Whittaker said plans for a spring class call for building a robot, Magellan, that would combine aspects of both Groundhog and Ferret.

Like Groundhog, Magellan would be a four-wheeled rover that could navigate autonomously through a mine for up to 2 1/2 miles as it builds maps. Like Ferret, it would be small enough to lower into a mine through a borehole and would have balloon-like tires that would be inflated only after it was lowered into the mine.

But he also said that those plans may change. Most abandoned mines in Pennsylvania are filled with water and, even when water is pumped out, have floors covered with a thick layer of muck. The Carnegie Mellon team's firsthand experience with the muck at the Burgettstown mine, combined with the interest expressed by some potential users, suggests that the team may want to shift direction and build a swimming robot next, he added.


Byron Spice can be reached at bspice@post-gazette.com or 412-263-1578.

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