Bill Stone has managed to cram several lifetimes worth of exploration into one, and he’s not done yet.
By Daniel Oberhaus
Deep in southern Mexico’s Sierra Juarez mountain range is a small clearing of pine that backs up against the austere face of a limestone ridge. To the untrained eye, it doesn’t look like much — just more trees and rocks in a vast expanse of wilderness. But to Bill Stone, PhD ’80, this unremarkable patch of dirt is like a second home. For the last three decades, Stone and a team of elite cavers have used this clearing as a basecamp for expeditions into the nearby Cheve cave system, which they believe to be the deepest in the world — about 8,800 feet, nearly one-and-a-half times the depth of the Grand Canyon at its deepest points.
The entrance to Cheve is tucked into the limestone ridges and its gargantuan mouth hints at the vast network of caverns and tunnels that lies beyond. Just inside the chamber, a large stone slab rises from the cave’s floor. Judging by the bones found scattered around the rock when it was discovered in 1986, this slab was once used by ancient Cuicatec Native Americans as an altar for human sacrifice. It’s not exactly a welcome mat, but for Stone and others who feel the irresistible call of the deep, it’s not enough to turn them away, either.
In February, Stone left his Austin home for a three-month expedition to Cheve with the intention of setting a world depth record, among other more scientific goals. Over the course of the expedition, each member of the 35-person crew spent a total of several weeks beneath the surface using lasers to map the cave. From basecamp, it’s a three-day journey underground to reach uncharted territory, which means cavers are often in the cave for well over a week at a time. (Stone’s record for contiguous days underground is 19.5; In total, he says he’s spent 688 days — or nearly two years of his life — underground.)
The descent into Cheve is grueling, both psychologically and physically. Going deep means squeezing through tunnels coated in sharp rocks that are barely wide enough for human passage and rappelling into massive holes that drop straight down for hundreds of feet. The darkness in the cave is total, and temperatures hover around 50 degrees Fahrenheit. The uncomfortable conditions are compounded by the fact that Stone and his team are often wet from climbing through the waterfalls and rivers that cascade from the surface into the deepest parts of Cheve. At certain points, they don scuba gear to bypass what are known as sumps: below-the-surface tunnels filled with pools of water.
Through it all, the cavers on the lead team are more isolated than astronauts on the International Space Station — or, for that matter, the moon. Their only connection to the outside world is a single-wire telephone line that connects some of the subterranean camps with the surface. Anything short of a razor-sharp focus on the details of the mission can lead to a fatal misstep. Underground, a broken leg or an incorrectly configured rappel rack could easily spell a caver’s death. And on one occasion in Cheve, it has.
“We’re hitting degrees of remoteness that no one has ever encountered before,” Stone says. “But that’s kind of the attraction.”
Standing 6 feet, 4 inches tall with hardly an ounce of fat on his lanky frame, Stone cuts an imposing figure. Beneath a mop of short dark hair is the chiseled face of a seasoned explorer, his characteristic mustache is just beginning to turn gray. And while he wields his encyclopedic knowledge of caving and space exploration with the seriousness that these extreme pursuits deserve, he’s also quick to crack a joke, his sense of humor etched in the laugh lines that run like tributaries toward his bright blue eyes.
Stone’s life has been defined by pushing boundaries, and he has been a fascination for the press, which has chronicled his adventures in magazines like The New Yorker and National Geographic. He has alternately been painted as a type-A fanatic who will stop at nothing to achieve his goals, a technical wizard, and an unsung hero of exploration who deserves to be mentioned alongside the likes of Roald Amundsen and Edmund Hillary, the first to reach the south pole and the summit of Everest, respectively.
But Stone’s career speaks for itself. Over the course of the last three decades, he has set caving records and lost them, invented scuba technology that eluded even the U.S. Navy, explored dozens of kilometers of uncharted territory, recovered the bodies of friends from deep in the Earth, and started a company to create space technologies to explore the outer solar system. He’s seemingly managed to cram several lifetimes’ worth of exploration into one.
Born and raised in Pittsburgh, Pennsylvania, Stone demonstrated an unusual aptitude for science at a young age, building homemade rockets and learning chemistry in a lab he built in his parents’ basement. As the son of a would-be professional baseball player whose dreams were cut short by World War II, Stone also had a natural athleticism. He wasn’t interested in typical high school sports like football or basketball, but one day a presentation by a local spelunking club caught his attention. “I didn’t know what that word meant so I got my mom to take me over there and listen to it,” Stone says. Caving was a natural way to marry his scientific mind with his competitive spirit, so Stone joined the club, and cut his teeth climbing in nearby caves.
By the time Stone was an undergraduate at Rensselaer Polytechnic Institute in New York, he was putting his skills to the test in the biggest natural caves in America and northern Mexico. During his first expedition to Fantastic Pit in Georgia, the longest cave free-rappel in the continental U.S. (meaning cavers aren’t in contact with the wall as they descend on a rope), Stone learned of Oaxaca’s cave systems from Marion Smith, who would go on to set the record for the most caves ever explored. It was a conversation that changed the trajectory of Stone’s entire life. The caves in southern Mexico, Marion told him, were emerging as candidates for the deepest in the world.
When Stone graduated from RPI with a degree in civil engineering, he enrolled at UT Austin, as much for its reputation as a top engineering school as its proximity to Oaxacan caves. If you were an American caver, Austin was the place to be, the jump-off point for the subterranean worlds in southern Mexico. Stone joined UT’s civil engineering program in 1976 working under UT professor Jack Breen.
Breen said he didn’t know about Stone’s background in caving until 1978, well into Stone’s second year at UT, when he visited Breen in his office with an emergency. According to Breen, Stone had organized a rescue mission to Mexico to recover some trapped cavers that involved coordinating with the Texas Air National Guard. Stone already had all his gear packed when he told Breen he’d be gone for a few weeks, and when Breen assented to his absence, Stone hopped in his Chevy Suburban, drove it straight on to the deck of a C130 transport plane, and was ferried to Mexico by the Texas Air National Guard.
“You have to put this into context,” Breen says. “This was a graduate student in his mid-20s and he had coordinated all this. You just had to admire that and wonder how he was able to do it all. To say he was an unusual student would be the understatement of the year.”
Indeed, it hadn’t taken Stone long to find his place in the burgeoning Austin caving community. These highly skilled depth-junkies mostly congregated in a low-rent housing development on Kirkwood Road, which at one point was home to around 30 elite American cavers. Among them was Bill Steele, a well known figure among American cavers who ignited interest in Mexican caves with a series of expeditions in the 1970s. The “Kirkwood Cowboys,” as journalist James Tabor called them, would spend their days working odd jobs (or in Stone’s case, working on his PhD) during the offseason, when rain made Mexico’s caves impassable, biding their time until they could get back underground.
“Expeditions would roll through town, stage at Kirkwood, and then go down across the border,” Stone says. “A couple of months later they’d come back with crazy tales and then everyone would try to figure out the next move.”
In 1976, Steele invited Stone on his first Mexican caving expedition to Huautla, a cave in Oaxaca that appeared to have extreme depth potential. It had been discovered over a decade prior, but only explored to about 1,000 feet. On Stone’s first expedition to Huautla, they pushed the cave to a depth of 2,600 feet. An expedition the following year, of which Stone was not a part, was stopped in its tracks by the San Agustin sump, a massive lake about 2,800 feet below the surface. If humans were going to push Huautla any deeper, it would require a totally different approach to cave diving.
One of the biggest problems in extreme caving, Stone says, is also one of the most mundane: the supply chain from the surface to the depths. Since cavers often spend weeks at a time in underground camps, they need to carry hundreds of pounds of gear and food with them. In the late ’70s, scuba gear was remarkably primitive and bulky compared to the relatively
lightweight, computer-driven systems used today, and the heavy tanks made navigating the narrow and treacherous passages of a cave all the more difficult.
Evidence was mounting that Oaxaca was home to the deepest cave in the world, and Stone, armed with his PhD in structural engineering, wanted to find a way to explore it. So he buckled down on developing a rebreather, a type of scuba system that recycles a diver’s carbon dioxide and pumps fresh oxygen back into the system. Recycling carbon dioxide could lengthen dive times dramatically, and perhaps more importantly, would eliminate the need to carry dozens of bulky and heavy oxygen tanks into the cave. But in the late ’70s and early ’80s, rebreathers were prohibitively expensive and pretty much only available to military divers for use in open water. Making your own rebreather was a herculean task by every conceivable metric. Not only would Stone have to build the rebreather tech from the ground up, he would also have to make the device strong enough to withstand battering in a cave and light enough to be carried to extreme depths.
In 1984, after half a decade of work, Stone had a working prototype of his rebreather. Although he initially intended to use it in the exploration of Huautla, the discovery of Cheve in 1986 quickly changed his plans. During an early expedition of Cheve, a dye mixture was added to the river at the entrance. When the dye was seen reemerging from underground 2,700 meters below the entrance, it became a candidate for the world’s deepest cave. Claiming the world record, though, requires more than dye. It requires finding passages that could bring humans to the cave’s lowest point. Stone joined an expedition to Cheve in 1988, and has focused on pushing the boundaries of the cave system ever since.
To this day, they’ve yet to reach the bottom. Meanwhile, other cavers have continued to set depth records half a world away in Eastern Europe. In March, 2018, a caving expedition in Abkhazia, Georgia, set the world depth record in the Veryovkina cave when they reached 7,257 feet below sea-level. While Cheve is still thousands of feet shy of the Veryovkina cave — the deepest Stone’s team has pushed Cheve is 5,000 feet — he says he still believes they can claim the depth record in Mexico. The only way to know for sure is to keep coming back.
“Each expedition is a tactical move in a grand game of 3-D subterranean chess,” Stone says. “This is raw, no-holds-barred exploration.”
Even if Stone and his team can’t push Cheve deeper than the caves in Abkhazia, Stone may still set an exploration record elsewhere. As the CEO and founder of Stone Aerospace, he has spent the last 17 years designing autonomous underwater vehicles with the goal of eventually sending them to Europa, a frozen moon of Jupiter that is believed to harbor a planet-wide ocean under a thick layer of ice. NASA considers Europa’s ocean to be a leading candidate for finding extraterrestrial microbial life, but needs to send a robot that is capable of penetrating the miles-thick ice crust and then exploring the ocean and relaying data back to Earth. Stone Aerospace may have the answer.
Stone is, in many ways, the ideal engineer to undertake such an ambitious mission profile. After UT, he found himself working on autonomous robotic systems and spacecraft design. Breen had used his connections at the National Institute of Standards and Technologies to help Stone land his initial job at NIST: a research structural engineer. From there, Stone ended up leading the Construction Metrology and Automation Group, a position with the unusual stipulation that Stone be allowed to take off months at a time to continue his cave exploration.
While Stone’s work at NIST is outside the wheelhouse of what most would consider the domain of a civil engineer, Stone says treating his education merely as a specialization in one field is missing the point. It’s a perspective he learned from Breen after he defended his dissertation.
“Jack sat me down and said, ‘Do you know what you got here today?’ and I naively said, ‘My ticket out of town?’” Stone recalls with a laugh. “He said, ‘No, what you’ve got here is a toolkit to approach and resolve unknown problems. You’re not really confined to what you’ve done here.’ I took that to heart.”
In the four decades since Stone left the Forty Acres, Stone has been married and divorced (his three grown children are all accomplished alpinists), and, he estimates, has changed professional disciplines four times. His biggest professional leap was in 2004, when he left his position at NIST to focus on Stone Aerospace full time.
“That was kind of the branch point,” Stone says. “I could either work until retirement at the national lab, a nice secure place, or go try to do something super exciting and lead the effort myself. I took the latter and never looked back.”
Stone’s experience working on autonomous vehicles at NIST gave him the foundation to undertake the extreme engineering challenges of sending an autonomous submarine to the bottom of the ocean on another planet. The mission will involve three main robots: a lander, a cryobot for digging through miles of ice, and an autonomous underwater vehicle (AUV) for exploring the subsurface ocean. Once the lander reaches the surface of Europa after a six-year, 390 million-mile journey through the solar system, it will deploy the cryobot to spend the next several months penetrating the moon’s icy crust.
Stone and his colleagues are developing cryobots and AUVs for NASA at the Robot Ranch, the company’s lab just east of Austin-Bergstrom International Airport. The Texas climate is a far cry from the extreme conditions found on Europa, though, so they have made do by bringing their cryobots and AUVs to some of the coldest spots on Earth for field testing.
In 2015, Stone and a handful of engineers from Stone Aerospace made their second trip to Antarctica to give their third-generation alien-hunting submarine, ARTEMIS, its first field test. The AUV demonstrated that it was capable of autonomously exploring 3 miles radially away from its deployment hole in the ice access before returning and automatically docking itself at the deployment station.
But landing a AUV like ARTEMIS on Europa won’t do much good if the vehicle can’t penetrate the thick layer of ice that coats the planet’s surface. To this end, Stone’s company has developed a suite of cryobots that use lasers to penetrate thick sheets of ice. The first generation of cryobot was VALKYRIE, which was essentially a 10-foot-long soldering iron that used lasers to warm a heat exchanger to heat melt water from the front of the robot. This hot water was then used to actively jet a hole in the ice. Future versions of the cryobot will forego the water heat exchange altogether and use lasers to directly melt the ice.
Stone and his colleagues are now focusing on three new NASA projects that will miniaturize and refine some key cryobot components, namely the laser probe and hot water heat exchanger, so that they more closely resemble the types of systems that could land on Europa.
Down the road, Stone wants to see a “Europa Station” constructed in Antarctica. This would be a full-time field site where researchers could simulate most of the Europa mission, using a cryobot and AUV to search for life beneath an Antarctic ice shelf. Stone says this would be up to a decade-long effort that would hopefully refine the technologies to the point that they are ready to be sent to explore Europa.
The future looks bright for Stone and those in the space community hoping to one day search for extraterrestrial life in the oceans of another planet. But in life there are no guarantees and this is especially true for explorers like Stone. That he may never see the deepest place on Earth or the seabed of an alien world is just a fact of life, one of the many risks inherent to exploration. But like Hillary, Amundsen, or any of the other explorers who risked life and limb to advance the limits of the world and understand our place in it, exploration for Stone doesn’t seem like so much an option as a necessity. Stone hasn’t found the end of the world yet — and he doesn’t plan to stop until he has.