A Thousand Diving Robots

The new plan for exploring the ocean: let a thousand robots roam.

By Robert Kunzig
Apr 1, 1996 6:00 AMNov 12, 2019 6:52 AM


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A few years before he died in 1992, Henry Stommel sketched a vision of the future of oceanography. It makes poignant reading now. Stommel was the man who had figured out why there is a Gulf Stream. He had helped establish the basic theory for how ocean currents work. In the process he had received every prize and accolade he possibly could. But in his little essay in the magazine Oceanography, Stommel imagined giving up all that. He pictured himself in the twenty-first century, looking back from middle age on a second youth and a second career that was just getting started in 1996. It was a career that had been transformed by a single invention.

Stommel’s first career, like that of all oceanographers, had been plagued by one problem above all: a lack of good data. Compared with the means they have to study it, the ocean is too big, and it changes too fast. Meteorologists have it much better: they drown in data every day. Their thermometers and barometers are everywhere on land; satellites tell them when the next hurricane is coming; and twice a day without fail, at around noon and midnight Greenwich time, they let fly more than 800 helium balloons from stations around the planet. Rising through the atmosphere, those balloons radio back the temperatures, pressures, and wind speeds they encounter before they burst about 20 miles up.

Pity the oceanographer, though, who wants to know what the water is like somewhere deep inside the ocean--the better to understand how currents transport heat around the globe; the better, ultimately, to un- derstand how our climate is likely to change over the long haul. He must set sail with a ship and a crew of dozens. The simple act of sticking a thermometer in the middle of the Pacific costs him, or rather his government, hundreds of thousands of dollars. Steaming across the ocean in a straight line, he stops every so often to repeat the same routine measurement at stations no oceanographer is likely to visit again for decades. It is tedious, expensive work--and it isn’t done nearly often enough.

So Stommel imagined a machine that could do it. It would be the oceanographic equivalent of those helium balloons, only better. It would be a small, cheap, torpedolike drone that would glide around in the ocean on its own, with an ingenious new engine that would draw power not from batteries but from the ocean itself. Stommel envisioned a thousand of these robots porpoising through the sea at once, staying out for five years and collecting data with a few simple sensors. And several times a day each one of them would broach the surface to report via satellite to Mission Control.

That is where Stommel would sit: on an unspoiled island off Cape Cod, not far from the Woods Hole Oceanographic Institution, where he had spent most of his first career. The island was to be a kind of sanctuary. It would have few permanent residents and no automobiles--just a narrow- gauge railway, like the one Stommel had once built in his own yard to amuse his grandchildren and himself. Outside the headquarters building, sheep would graze on the grass bank that sloped down to the sea; inside, virtual- reality displays would immerse oceanographers in the latest data from the scattered robot fleet. In Stommel’s vision, twenty-first-century technology coexisted peacefully with the shade of Henry David Thoreau.

The right kind of technology, he thought, could set oceanographers free--free from the quiet desperation of lives spent looking for a ship; free to do the equivalent of designing Central Park, as Stommel once explained it, instead of just mowing the lawn. The robots would handle the lawn mowing: they would conduct on a continuous basis the routine surveys that ships could do only every few decades. Meanwhile, around 200 of them would be reserved to pursue the inspired whims of individual researchers--to track a pod of whales, say. In my heart, Stommel told an audience of oceanographers at around the time he published his essay, I believe that, for a scientist, it is his personal mental wrestling match with some aspect of the universe that is his central activity and reward. All alone, one confronts the unknown and divines some meaning from it. Just so would Stommel’s robots confront the ocean alone, without a tether, each of them part amanuensis and part alter ego to the man who had dispatched them. They were to be called Slocums, after Joshua Slocum, who in 1898 had become the first man to circumnavigate the globe single- handedly. Before the robots settled down to science, Stommel planned for them too to race around the world.

He did not live to see the first one dunk its nose in the ocean. But last fall it finally happened anyway--for the Slocum was not Stommel’s vision alone, or even primarily. The thing itself was invented in a cottage across the road from Stommel’s house in Falmouth, just north of Woods Hole, by an independent engineer named Doug Webb. The device Webb and his colleagues dropped into the Atlantic off Bermuda in October was just a prototype--it only bobs up and down in the water rather than gliding through it--but it was the first sea trial of Webb’s innovative engine, and it worked perfectly. Moreover, Webb is not the only engineer at work on an autonomous underwater vehicle, or AUV; nor is his project even the furthest along. At MIT, for instance, a researcher named Jim Bellingham has built an AUV called Odyssey, in its own way just as thrifty and ingenious as the Slocum, that is already at sea doing science. Four years after Stommel died, it is beginning to seem possible that mariner-robots really will go down to the sea in large numbers one day--and that they may transform our understanding of this water-covered planet.

Undersea robots were not always thought of as inexpensive tools for oceanographic research. When the first ones were conceived in the 1960s, the impulse behind most of them was military: the Navy wanted robots that could map underwater minefields laid out by the Soviet Union. To carry out so sophisticated a mission, it was thought an AUV would need a lot of computer power and a lot of batteries, and so it would need to be large. Draper Laboratories in Cambridge, Massachusetts, is still working on such a robotic mine scout; it is around 40 feet long and weighs seven tons, just about the size and weight of a Tyrannosaurus rex. To Jim Bellingham, a buoyant and boyish engineer who works down the street from Draper at the MIT Sea Grant laboratory, it is a dinosaur in other ways as well.

Around the time Stommel was writing his essay, in 1989, Bellingham was getting started at Sea Grant, his first job after graduate school. His Ph.D. was in physics, and his graduate work had involved superconductivity--but that turned out not to be what he wanted to do with his life. Around that time the high-temperature superconductors were discovered, he recalls, and that totally changed the complexion of the field. Conferences and workshops where there had been 50 people suddenly had 2,000 people, you know, from big semiconductor companies and big industrial outfits who were getting into the game.

On the one hand, it looked very lucrative, and on the other hand, it didn’t look like there was much prospect for somebody to really make a contribution in a field when suddenly it had become so enormous. What I wanted to do was find a field where there was an enormous amount of promise but there wasn’t an enormous amount of activity yet, because it was a little bit too far out. Where people said, ‘Yeah, it will work, but maybe sometime in the next century.’

AUVs met that requirement. So when Sea Grant offered him the job of building one, Bellingham grabbed it. His first toe into the water was Sea Squirt, a three-foot-long, 77-pound clunker that made up in ease of use what it lacked in elegance. Sea Squirt was a test bed: Bellingham and his students crammed it with sensors of all types. Above all, they used it to test a new approach to robot intelligence, called layered control, that was just then being pioneered at MIT by an engineer named Rodney Brooks.

The traditional approach to controlling a robot is to try to give it a crude version of human intelligence, along with a map of its environment; as the machine continuously updates the map with information from its sensors, it chooses from many possible actions the one most likely to lead to its goal. All that mapping and intelligent decision making, though, requires a lot of computer power, which makes for big, expensive robots. It also makes for a robot that, in a turbulent ocean, would be in danger of running onto the rocks while updating its map.

Layered control, in contrast, takes insects rather than humans as its models of intelligence. In place of a big central brain and a map of the world it puts a hierarchy of behaviors, each one independent of the others. One of Sea Squirt’s priorities, for instance, was obstacle avoidance--not smacking into a rock. Any time the signals from its sonars seemed to demand it, that survival behavior could take control of the robot from the more goal-oriented behaviors, such as searching for a target. Bellingham and his crew found that layered control worked well in Sea Squirt (although deciding which behavior was to be in charge when survival was not at stake proved tricky). The little drone could navigate the Charles River, a few blocks from the Sea Grant lab, without sinking any sailboats and without sinking itself. It could even produce a survey of the water temperature.

After a couple of years of this, though, Bellingham’s boss, Sea Grant director Chryssostomos Chryssostomidis, began prodding him to think deeper--a few miles deeper. The point, after all, was to explore the ocean, not the Charles. To dive to the ocean floor, a robot needed to be able to withstand the immense pressures produced by the several miles of water above it. As Bellingham started to ponder this problem, he knew he had to ponder on a budget. Sea Grant was not the Navy, and the Navy, funder of behemoth AUVs, was not impressed with Sea Squirt. The question facing Bellingham was this: Would it be possible to build a robotic submarine that would dive to the ocean floor, do something useful, and come back alive, all for, say, $50,000?

The money constraint forced Bellingham to think new thoughts. His first one concerned the robot’s hull. The conventional way to protect an AUV’s insides from hundreds of atmospheres of pressure would be to build the hull of titanium, which is strong, corrosion-resistant, and relatively light--but a titanium hull would have blown Bellingham’s budget directly. Nosing around some labs in Woods Hole, he came across an alternative: glass. A company called Benthos in Falmouth does a brisk business supplying oceanographers with 17-inch-diameter glass spheres for housing instruments on the ocean floor; when the spheres are sealed, they are strong enough to withstand a full ocean of pressure. And they cost only a few hundred dollars apiece.

Once Bellingham discovered the Benthos spheres, his deep-ocean robot quickly began to take shape. One glass sphere, he decided, could hold the personal computer containing the robot’s insectlike brain, along with a compass and pitch-and-roll sensors for navigation. Another sphere could hold batteries to power the electronics and the motor. Mount the two of them in a hard-plastic frame and you have the nucleus of an AUV. The motor and most of the sensors you might need--the sonars, the camera, the temperature and salinity sensors--could be arrayed around the glass spheres; they did not need to be inside. All those things come with their own pressure housings when you purchase them from marine equipment manufacturers--in fact, it is more expensive to buy them without. With Benthos spheres and off-the-shelf gear, Bellingham realized, he could do without a watertight titanium hull. He could just slap a plastic fairing around his gear to give it a nice aerodynamic shape--cost: $2,000--and let the water flood into it. The rudders at the tail were a nice finishing touch: they came from a sailboard manufacturer.

The result was odyssey, an eight-foot-long, 350-pound submarine that soon outgrew the Charles. Its first trip to sea came in 1993, when an oceanographer friend at MIT invited Bellingham and his crew along on a cruise to the Antarctic. Sitting in a rubber boat in the white-capped Drake Passage, running Odyssey from a laptop computer cradled on his lap, Bellingham got a chance to confront the primal fear of any AUV builder-- which is that someday maybe the little bugger won’t come back. On the first two dives, everything went fine. Then came the third. It turns out acoustic conditions were such that I lost tracking on the vehicle as it came up, Bellingham recalls. Well, you figure, ‘This is not so bad. We’ll spot the vehicle again when it comes up to the surface.’ We had a radio direction finder too, and we had a strobe--we had three different location devices. By this time, it’s our third run, so we’re feeling a little more confident.

Well, the problem is, the darn vehicle should have surfaced, and we’re not picking it up on the radio direction finder, and we’re not picking up the acoustic beacon, and it’s daylight out, so the strobe is no good anyhow. So I start to get worried. I start looking around for it. And pretty soon we have everybody up on the ship with binoculars out there looking for it. It wasn’t really that long, maybe an hour total, that we couldn’t find the vehicle--which to me was a very miserable hour. I thought we’d lost it.

But the captain finally spotted it. He was looking out for birds, actually, and he saw this one giant petrel that was circling the sky for a while, and then it would land on the surface for a bit. And then it would take off again and circle in the sky. He saw this a couple of times and looked under the bird--and sure enough, there was the vehicle. What happened was, as this big bird would land on our vehicle, it would drive it underwater. It’s slowly drifting back up to the point where it’s breaking the surface again--and the bird lands on it and drives it back down. So the radio beacon is now underwater and you can’t pick it up. How do you plan for that?

Of course, the other thing wrong was, in the Charles a white vehicle is easily visible. In the Drake Passage, with breaking waves all over the place, a white vehicle is invisible. Which is why all our new vehicles are yellow.

In Antarctica, Bellingham proved not only that he was willing to put his baby at risk but also that he could make it work in the ocean. After that his phone started ringing. People wanted to work with him. Even the Navy got interested--which is how, a little over a year after the Antarctic trip, Bellingham found himself at the other end of the world, 150 miles off the North Slope of Alaska at a Navy ice camp in the Beaufort Sea, carrying a rifle in case of polar bears. In the Arctic his faith in his own engineering was put to an even sterner test: Odyssey proved that it can be dropped through a hole cut through the six-foot-thick ice, cruise around for a while, and then find the hole again. The Navy now wants to use Odyssey to study how the polar ice tends to break up--a poorly understood process that is of interest for submarines navigating under the ice and that also affects how Earth will respond to global warming. Bellingham didn’t get to do too much of that research on his first trip to the Arctic, though: the ice camp itself broke up after two weeks.

Last summer Odyssey made its deepest dives yet, plunging nearly a mile into the Pacific off the coast of Washington, onto the crest of a volcanic mountain chain called a midocean ridge. Once the oceanographers he was working with have an Odyssey of their own, says Bellingham, they won’t have to wait their turn, every year or two, to take a research ship out to see the volcanoes; as soon as their seafloor listening devices tell them an eruption has begun, they will simply load the robot onto a fishing boat and be out at sea taking pictures within hours. Bellingham expects a lot of research institutions to have Odysseys of their own eventually. His lab has already built half a dozen of the robots and is in the process of licensing the design to a private company that supplies the oil industry with offshore equipment. Apparently Odyssey has a future in monitoring undersea pipelines for oil leaks.

Getting things off into the commercial world and used on the broader problems of society--I’d view that as a real feather in our cap, says Bellingham. Particularly since it will be the first AUV that has actually gone into commercial production. I mean, that’s a big deal. If you look at the history of flight, for a long time lots of people were building airplanes, but none was a commercial success. Then finally the DC-3 came along. If we end up with the DC-3 of AUVs, then we will have made a difference.

Odyssey is certainly as flexible as the DC-3, because its design is so thoroughly modular. Sensors can be added or subtracted to fit the mission; secured inside the yellow fairing, they don’t affect the vehicle’s performance in the water. Different behaviors can be added to the software without rewriting the whole program; Bellingham did it sitting in his tent one day at the ice camp. And a third glass sphere can be added and filled with batteries to extend the range of the vehicle to 100 miles or so.

On the other hand, that range is still relatively short. It means that Odyssey will generally be operated in a limited region, going off on forays that last a few hours or a few days at most before it returns to the mother ship or goes to an underwater docking station where it can recharge its batteries. Whereas what Doug Webb and Hank Stommel had in mind was a robot that would do without a ship entirely and stay out for five years, longer even than Joshua Slocum himself.

Stommel once wrote a profile of his friend Webb for Oceanus, a magazine put out by the Woods Hole Oceanographic Institution. Doug Webb appears to be a cautious and deliberate man, the piece began, but his career shows that he is actually unusually daring. Webb certainly does not fit the movie image of a daredevil. He is 66 now and stocky, with a thinning thatch of hair covering his broad head. He has a taste, in summer, for shirts with epaulets and Bermuda shorts that do not hide his skinny legs. He does not seem like a man who would leave his native Ontario at age 23 to go to Manchester University in England to work in a lab that included Alan Turing, the computer pioneer; nor like a man who would spend part of his time there racing Bugatti sports cars; nor yet like a man who would drop academia and go off to work on computers for Olivetti, the Italian office-equipment manufacturer. Least of all does he look or sound like a man who would ever speak Italian. His manner, though not aloof or unfriendly, is careful and even formal. Stommel once said of himself that he had chosen a career in the physical sciences--he had also considered the ministry--because he was convinced that he was emotionally better adapted to dealing with physical laws than with human affairs. One senses in Webb a similar uncertainty about how best to deal with recalcitrant human materials. I try to be careful not to be threatening, he says.

People are not always what they seem on cursory acquaintance to be, however, and Webb loved Italy. He and his wife, Shirley, whom he met when they were chemistry lab partners in high school, lived there for six years and might have stayed for good had not family ties pulled them back to North America--family ties, and Webb’s urgent desire for a career change. By that time, he says, by 1962, believe it or not, it was clear to me that the computer industry was going to become quite large and that I was going to be a specialist in that industry. Computers were initially a place for generalists, and I decided I was more cut out to be a generalist. I made up a list of industries that I didn’t think would go through that cycle, and oceanography, I thought, would offer opportunities.

The opportunity Webb found in 1962 was at Woods Hole, working as an engineer with physical oceanographers--the ones who study ocean currents. One of the basic methods such researchers use is to track currents with things that float. Not so long ago those floats were cards or bottles with messages in them, but today they tend to be more sophisticated devices. At Woods Hole, Webb became known as a master float builder. His most famously successful creation was the SOFAR float. SOFAR stands for Sound Fixing and Ranging, and it refers to a layer of the ocean, typically around 3,000 feet below the surface, that tends to trap sound and channel it over long distances. Following up on an idea tossed off by Stommel in 1949, Webb and an oceanographer named Tom Rossby built a device that could drift along on a subsurface current, all the while emitting huge booming sounds that would travel through the SOFAR channel and allow faraway oceanographers to track the float. In the 1970s and 1980s, researchers chucked hundreds of SOFAR floats into the ocean--although chucked is perhaps not the right word: a SOFAR float weighs half a ton and is around 25 feet long, most of it aluminum piping. In the profile Stommel wrote there is an old photo of Webb standing on the dock at Woods Hole next to an upright SOFAR float, looking proud and very small.

He’s a giant, says Bellingham. I had heard about him long before I met him. You know, there are people who have great ideas, and then there are people who really have made things work. His floats are almost at the point where they don’t seem like a big deal anymore. It’s like ‘Oh yeah, there’s a hundred of those out there.’ ‘Yeah, and they all work.’ He’s the guy who made them work and had the vision to create them.

The vision of Slocum came to Webb slowly. In 1974, while he was still in the throes of the SOFAR project, he first started thinking about an AUV that could cross the Atlantic under its own power rather than drifting at the mercy of the currents. But it was not until 1988, while working on a SOFAR spin-off called the Bobber--a float that could bob up and down in the water as it drifted along--that Webb saw where that power might come from. Every time the Bobber wanted to ascend, it inflated an external rubber bladder with oil pumped from an internal reservoir; this increased its volume without changing its mass and so made the float more buoyant. When it was time to descend, the Bobber simply transferred the oil back to the internal reservoir and sank. The work was done by a battery- powered oil pump. Webb realized there was a more natural way to make something expand and contract: you could just heat it and cool it. Maybe, it occurred to him, there was some way you could power a bobbing AUV by drawing heat out of the ocean and then putting it back. That was my first glimpse of thermal propulsion for an underwater vehicle, he says. The Bobber was a very intensive project, though, and I didn’t have time to stop. But when it was over, I went back and I picked up those loose threads.

Then he had his second idea. The dream, after all, was not just to build a better Bobber; it was to build a robot that would cross the Atlantic. Once you have it bobbing up and down, though, it is easy-- conceptually, anyway--to make it move horizontally as well: you just put wings on it and let it glide. As the robot fell through the ocean, water flowing over those wings would generate lift, which would carry it down and forward rather than straight down--let a paper glider fall from your hand and you will see it is true. At some nadir in the depth, the glider would then change its buoyancy and start climbing again. All the while its thermal engine would be refueling on the fly: at the warm, sunlit surface it would draw heat from the water; in the cold depths it would put the heat back. Flying for free, without need of batteries for power, the robot could cruise across the Atlantic. In principle it could go around the world.

The whole concept was simple and beautiful and--as Webb would put it--sweet. Webb sensed he was onto an idea that would be a nice way to close out his career. By this time, though, he had long since abandoned the structured security of the oceanographic institution to start his own float-building company, Webb Research, in the cottage behind his house. He was a businessman now, dependent on contracts obtained from oceanographers, who in turn had to get grants from the government. He employed half a dozen people, including his son. His ideas had to pay salaries. He might have 10 or 20 inventions knocking around his head at any one time, but for any one of them to go anywhere, an oceanographer had to get excited about it. Making the rounds in 1988 with his thermally powered ocean-crossing glider scheme, Webb didn’t have much luck, in spite of his track record. The idea was too radical to be greeted with anything but skepticism.

So at some point in the proceedings Webb took the obvious step: he walked across the street to Hank Stommel’s house. It was a well-trodden path in both directions. The two men had been going to sea together for decades, and they had been neighbors on land since 1966, when Webb bought his house from Stommel and Stommel moved across Palmer Avenue. Their personalities were not at all alike. Stommel was gregarious and open and always bubbling with ideas, which he gave away freely to less gifted colleagues; Webb was and is careful and shy and nervous about collaboration. And yet there was a deeper commonality between the two men. It had its roots, perhaps, in the fact that both were inventors. Webb invented machines, Stommel invented physical theories--but a theory is not so different from a machine. It is designed to solve some problem, and it has parts that have to fit and work together. It can be simple and elegant- -as Stommel’s explanation of the Gulf Stream was--or complex and unwieldy. It can be a radical departure from the past--as Stommel’s theory of powerful deep ocean currents was in the late 1950s, when most people thought they didn’t exist--or a modest elaboration of it. Webb and Stommel both liked the simple and the radical. They shared an aesthetic. They found the same things sweet.

And along with the aesthetic went an ethic. If what you strive for is simplicity, and if your aim is to put something truly new in this world, then it is best not to be an organization man, because large organizations are seldom sympathetic to overly inventive individuals. People feel threatened by inventors, says Webb. They change the world, and all the things that you’ve done might be made obsolete. Most people would like things to go on just about the way they are, and make incremental changes to keep ahead. If someone comes along and says, ‘I’d like to make some big change over here’--God! You know, all that investment is gone, and all of that database is worthless.

I think it’s a human thing, not just a scientific thing. In engineering, in commercial enterprises--Ford and General Motors and Chrysler are just kind of incrementally trying to find some advantage with respect to the others. They don’t want anything radical to appear. That upsets everybody in a big way.

Well, that never troubled Hank.

Stommel was interested in Webb’s thermally powered AUV right away. One of his many passions was steam machinery--in his backyard he kept a Canadian Pacific railroad whistle, with which he would periodically startle the neighbors--and what Webb was proposing was analogous to an underwater steam engine. In a steam engine, as water changes state from a liquid to a vapor--at precisely 212 degrees Fahrenheit--its volume expands by a factor of 1,800, and that expansion drives a piston that turns the engine. The heat to make the steam comes from burning coal.

Webb’s AUV wasn’t going to be coal fired, of course, and it wasn’t actually going to use steam. He had in mind a different working fluid, one that would change from solid to liquid as its temperature rose from around 40 degrees Fahrenheit to around 60 degrees--which is what would happen as the robot climbed from a mile deep in the ocean up to the surface. As the solid expanded to a liquid, it would be made to compress nitrogen in a neighboring tank. That compressed nitrogen would store energy, the way a coiled spring does. When next the robot was a mile deep and wanting to climb, a flip of a valve would allow the nitrogen to uncoil and push oil into an external bladder. The inflated bladder would buoy the robot back to the surface, just as it had done to the Bobber--only now the work would no longer be done by a battery-powered pump. The robot would still need a few batteries to power the crucial valve, as well as its steering mechanism and the radio it used to talk via satellite with its human masters. But it would get its propulsion for free.

Nothing like it had ever been built before, which must have recommended the idea to Stommel. He began to get seriously excited, Webb recalls, when Webb mentioned the possibility of round-the-world robot races. It was then that Stommel suggested naming the robots after Joshua Slocum, and it was then that he wrote his little essay in Oceanography. He was hoping to get his colleagues excited about the idea, too. Meanwhile, to get the project started, Stommel persuaded the Navy to give him a three- year development grant, with a subcontract to Webb.

The money allowed Webb to start work on some of the hurdles Slocum would need to leap on its way from the drawing board to the ocean. To begin with, Webb had to find the right working fluid. The solution he came up with, after long hours of leafing through the pages of the Handbook of Chemistry and Physics and experimenting in his shop, was a pure hydrocarbon, one that at low temperatures forms a waxy solid, much like paraffin. But at precisely 50 degrees Fahrenheit the wax melts, and when it does, its volume expands by 10 percent. That expansion, Webb calculated, would be enough to compress the nitrogen and ultimately to pump a slug of liquid glycol into the external bladder, against crushing deep-sea pressures.

The inflated bladder would provide a buoyancy force of around four ounces to the 90-pound Slocum. That is not much in the way of propulsion: it would push the little robot to only half a knot--a speed so slow it raised a whole new set of problems. Could a glider move that slowly and still remain stable? Could it navigate a course and turn when commanded to do so? And could it do all that without the wing flaps and other movable control surfaces an airplane relies on? Such control surfaces, Webb decided, would gobble too much battery power; they would wear out over a five-year mission; and because they would have to be connected to their motors through holes in the fuselage, they would be apt to cause leaks. Slocum would fly with fixed wings and tail.

In a way, it would be much more like a blimp than a heavier-than- air plane. An airplane is kept aloft by the force of air rushing over its wings, whereas a Slocum, like a blimp, is simply less dense than the fluid below it, so it floats. To ascend and descend it adjusts its buoyancy slightly--and it could steer, Webb decided, by making equally minute adjustments of its center of gravity. The sloshing of a few ounces of liquid glycol in and out of the external bladder would be enough to point the probe’s nose up for the ascent and down for the descent. To bank to one side, Slocum would rotate the stack of D-cell batteries it carried at its midsection; because of the way the batteries were arranged, that action would move the center of gravity slightly to one side of the robot’s central axis, causing its left or right wing to roll. For this system to work, however, the weight of each component of Slocum would have to be known to within a fraction of an ounce, and its position to within a fraction of an inch. It would all have to fit together just so.

Having the great idea, Webb knew, was just the beginning. It’s always possible that we will run into some problem that is essentially terminal, he said in the spring of 1991, when he was still in the thick of his personal mental wrestling match with Slocum. And in the first half- year of working on this, I was concerned about one day coming in and spotting that terminal flaw. Now I think it’s much less likely, although instead we may find something that’s a serious compromise--that makes it heavier, uglier than I first hoped. The great fear is that you start off with a very simple concept, and you run into a problem, and you add some complexity here, then you find another problem and add some complexity over there. And before you’re finished, it turns out not to be simple, but really very complex, expensive, and difficult to handle.

It was an intense period, those first two years of the project, with Webb trying to spend as much time as possible on Slocum without neglecting the other floats that were his company’s bread and butter. Sunday mornings would often find him over at Stommel’s house, talking Slocum while Stommel’s wife, Chickie, was playing the organ at church. During the week Stommel would sometimes stop by Webb’s cottage when he came home for lunch. Hank enjoyed walking across the street to our shop and seeing what was going on--because something was happening there, Webb recalls. If you’ve worked, as he did, almost entirely in your head, it’s sometimes nice to see some fast results.

In the end the results did not come as fast as either man wished. But by the fall of 1991 Slocum was ready for its first real test, in Lake Seneca in upstate New York--the most readily accessible body of water, aside from the open ocean itself, that was deep enough and cold enough to give Slocum a gallop. The engineer Webb had hired to work on Slocum, Paul Simonetti, had already tested the glider in a shallow, crystal-clear lake in Florida, watching it through a glass-bottom boat. Now he and Webb were going to let Slocum out of their sight for the first time. Before loading it into the van for the trip, Webb brought it across the street to Stommel’s house. He carried it into the kitchen to show Chickie Stommel what all the fuss had been about. It was, she remembers, a happy and very exciting day.

At Lake Seneca in November, Simonetti and his colleague Josh Hunt found two feet of snow on the ground and a 29-foot motorboat for rent cheap. The sky was overcast, the water was calm, there was no traffic on the lake, and Simonetti and Hunt were really quite confident when they dropped Slocum over the side for the first time and watched it sink slowly out of sight. In test tanks it had responded vigorously to their commands. But they also had a fail-safe mechanism. We had put a lot of work into this thing, and we didn’t want to lose it, says Simonetti. With these things, you never can tell what’s going to happen--something totally absurd may happen. So what we did was, we had a little buoy on the surface. On the tail end of the vehicle we had a spool of fishing line that would just pay itself out without any tension, and we attached the other end to the buoy. So in case it did fail, we could get it back just by pulling up the line.

It never came to that. Simonetti and Hunt tested the glider again and again, and Webb joined them after a few days for more tests. They programmed Slocum to go one way, then threw it in the water pointing in the wrong direction and watched as the autopilot software banked the glider and brought it around until it was pulling the surface buoy on the programmed course. Once the robot found that course, it stayed on it; it didn’t toss around at random. And it always came back to the surface.

For those tests Webb and his colleagues didn’t have the thermal engine in their glider; they had a battery-powered pump. The thermal engine had been tested separately in Lake Seneca, in a device that just bobbed straight up and down, and it had worked well. The engineers had wanted to test each technology separately before taking the risk of marrying them. Driving back to Woods Hole in mid-November, though, they knew they were ready to put the whole thing together. They believed now that they really were going to be able to build a glider that would cross an ocean. Another year or so of development work ought to do the trick. Two months later, in January 1992, Hank Stommel went into the hospital to undergo surgery for liver cancer and never came home. He was 71.

If in the midst of an often crass and strident society, we have learned to love this world, if we have managed to control our avarice and learned to give rather than take, and above all to give ourselves to fellow human beings, then we may discover how, with grace, to give ourselves to death. Stommel had written those words in a column for the local newspaper in 1985, after his first battle with cancer. After his death the column was reprinted in a special issue of Oceanus, along with the reminiscences of scores of people who had known him over the years. In tribute after tribute, people remarked on his generosity, his manic energy, his pyromania (he was a fireworks impresario), and his mechanophilia (to clear brush from his pond, he once bought a coal-fired steam shovel from a shipyard in Boston). Shirley Webb, Doug’s wife, recalled Stommel the painter, who showed the influence of Henri Rousseau and was surprisingly proficient in a rambunctious, childlike way. On one canvas from his disaster period, a grand old hotel near Stommel’s house is on fire and a fireman is being chased by a rhinoceros while other East African animals look on. Hank would often appear at our kitchen door at unlikely times, with a book, an idea, or a bag of fruit or vegetables. . . , Shirley Webb wrote. He would sit and visit, then disappear abruptly, thinking a new thought, probably.

Doug Webb did not contribute to the Oceanus volume. Hank’s death was traumatic both personally and professionally is all he will say. Webb’s business, though, has prospered since 1992. He has had great success with a bobbing float called ALACE, hundreds of which are now drifting around the world’s oceans. He has been able to move his company out of his cottage and into a new headquarters building. Everyone at Webb Research has an office now, and there is a well-appointed conference room. A plaque on the door identifies it as the Stommel Room.

But Slocum hit the doldrums after Stommel died. In the summer of 1992 the Navy did not renew its funding of the project. Slocum can operate only where it has deep, cold water to dive into, and after the Persian Gulf War and the collapse of the Soviet Union, the Navy’s interest shifted to shallow-water oceanography. Had Stommel been around, the Navy might have been inclined to renew his grant anyway; but Stommel was no longer around.

Webb didn’t give up, though. He put the development of the glider on hold, but he kept Simonetti working on the thermal engine, paying his salary out of internal funds. His hope was that there might be scientific interest in a profiling device that would simply go straight up and down in the ocean--and for five years, thanks to its thermal engine. He turned out to be right. The National Oceanic and Atmospheric Administration came forward with a small grant, and last October the first prototype profiler went into the ocean off Bermuda. As of early February it was still working, sinking down to 4,500 feet and rising back to the surface every two days, and radioing its temperature measurements back to Webb Research via satellite. Apparently Webb’s thermal engine works in the ocean too, not just in Lake Seneca.

Meanwhile the glider has finally emerged from enforced hibernation--at least the battery-powered version that was tested in Lake Seneca. Unlike a thermal Slocum, it can glide in shallow water as well as deep. The Navy, which is already committed to Jim Bellingham’s Odyssey, has decided that an electric Slocum glider might be a useful partner to it. Early this year the Office of Naval Research awarded Webb a subcontract to build electric gliders for a large experiment that is scheduled to begin later this year in the Labrador Sea. The Labrador Sea is one of just a few places in the world where deep-ocean currents are born from the sinking of cold, salty water--a sporadic process that has a large influence on Earth’s climate. The electric gliders will sweep through the area, measuring the temperature and salinity variations that cause water to sink in narrow chimneys. When they find something interesting, an Odyssey will be dispatched to investigate in more detail.

Webb likes the Labrador Sea experiment; he thinks it is daring. And he admires Odyssey and Bellingham’s off-the-shelf approach to robot design. In some narrow sense Bellingham is a younger version of Webb himself--younger, and perhaps a bit more practical. Webb is an engineer who loves to find novel and sexy solutions to problems, says an oceanographer who has worked with him, meaning sexy rather than easy or obvious. Webb would just say he is an inventor.

The Labrador Sea is a stepping-stone for him. A success there, he hopes, along with the success of his thermally powered profiler, will convince skeptical oceanographers that his two ideas should be married at last. Before he retires, he would like to see thermal Slocums porpoising through the ocean--chasing eddies, cruising the meridians, and patrolling their designated stations like faithful sentinels. He would like to start the job of freeing the individual oceanographer, and our knowledge of the ocean, from the constraint of needing a ship. Most of all, he would like to prove that he and his friend were right, and a robot really could be made to cross the ocean and maybe even circle the globe. We had a good team here, and it will be hard to get that back, he says. A lot of people say Slocum’s a great idea--and they’d love to use it when we’re finished with it. It took someone of Hank’s stature to keep it going. But we’ll sneak up on it yet.

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