Mission:
Stone Aerospace is developing the SUNFISH® autonomous underwater vehicle (AUV) to address many of the challenges of remote, autonomous exploration in complex environments. The AUV was designed to operate in a wide variety of 3D spaces, ranging from man-made (e.g. piers or harbors) to natural (e.g. reefs or caves).

SUNFISH is a person-portable, hovering vehicle with built-in precision navigation and control, multibeam sonar mapping, imaging, and CTD capabilities. We have developed capabilities for performing simultaneous localization and mapping (SLAM), exploration, path planning, and precision docking. In October 2017 we ran a series of tests and demonstrations in the unstructured labyrinthine cave environment of Peacock Springs. SUNFISH was able to autonomously explore this environment, creating a real-time map which it used to navigate through the cave. SUNFISH penetrated 120 m into the Peacock 1 cave site, reaching a second cave entrance called “Pothole Sink.” The robot was then able to autonomously find its way back to the starting point using the map it had just created.

The capabilities developed for SUNFISH have direct application to general inspection, monitoring, and survey tasks, as well as providing a basis for the types of autonomous vehicles that will explore where humans cannot go.

Site Description:
Northern Florida is home to one of the most popular cave diving areas in the world. The limestone in this region is rich with sinkholes, springs, and caves. Warm, crystal clear water — and the lure of the unknown — inspire cave divers to explore these features. Cave diving in the area began in the 1950s and by the 1960s and 1970s north Florida was at the forefront of the scene for this new sport. Many standard cave diving techniques and safety practices were first developed in Florida, and much of the equipment that allows divers to push the limits of human exploration was pioneered here as well. Peacock Springs, in the heart of Florida’s “Cave Country,” is a complex labyrinth of flooded cave passages. It’s one of the longest underwater caves systems in the United States and, to this day, many open-water divers receive their first cave diving training here. Given all of this history, what better place could we choose to test a robot with aspirations of becoming a cave diver?

Mission:
Lake Guinas, 37 kilometers west of Tsumeb, lies at the bottom of a 50-meter deep sinkhole in the flat scrub plain. A final 30-meter shear drop takes one to the 40-meter wide, 100-meter long lake. As of August 2019 no one knew how deep or how far the lake extended below ground. Rumors said it connected to Lake Otjikoto. SUNFISH ultimately circumnavigated the entire cenote on August 11, discovering the bottom to be an hour-glass shaped void nearly 300 meters long and 150 meters wide, reaching a water depth of 133 meters.

Site Description:
There are not many lakes in Namibia. Farms fortunate enough to be located adjacent one are easily identifiable in satellite images from the presence of anomalous bright green crop circles kept alive in the desert through center-pivot irrigation. One such site, located 37 kilometers west of Tsumeb was to be our shake down site for SUNFISH operations. Lake Guinas is perhaps a misnomer. One used to seeing lakes in the United States would assume you could walk up to the edge of the water and launch the vehicle. Not so at Guinas. It had much more in common with cenotes of the Zacaton cenote complex in Mexico. From the flat, red-dust scrub plain we descended into a broad sinkhole, revealing for the first time the jagged karst that became suddenly exposed as we entered the farm. Soon we came to a shear walled pit, some 30 meters deep, ending in a deep blue pool. The oval shaped cenote shaft measured 140 meters long by 50 meters wide. We had been informed by Chris Steencamp that Namibian divers Boetie Scheun and Eben Benade had reached a depth of 132 m here using traditional scuba in 1989. Little else was known about the site. The edges of the shaft apparently belled out beneath the surface as the divers had descended a free hanging shot line. And although the visibility is extraordinary, no one had ever seen the walls nor the floor except where the descent line landed.

Mission:
Prior to our mission, it was known that the cave beneath the 100-meter long, 40-meter wide lake at the bottom of Harasib shaft pretty much continued the trend of the air-filled portion above it, which is to say, it plummeted vertically straight down and out of sight. Diver Don Shirley had reported during briefings at the Harasib farmhouse that he had personally descended the shaft and had seen a horizontal tunnel roof at a depth of 120 m in Harasib and that the floor, far below that ceiling, had continued downward as a sloping breakdown pile of small boulders covered by a layer of fine silt. Several years after his dive there Cobus Briel and Almero Retief had reached a depth of 162 m in Harasib, using helium and rebreathers in July of 2016.

SUNFISH ultimately explored 450m of new cave, discovering what appeared to be the bottom at -265 m, along with an enormous room, 80m wide, over 100m tall and 200m in length before it tapered down to where the descending talus pile merged with the steeper-descending ceiling, deep below the main chamber. SUNFISH had bottomed Harasib Shaft and come home with a highly detailed 3D map of the entire cave.

Site Description:
Located on Farm Harasib, about 30 kilometers south southeast of Tsumeb, Harasib Shaft is three kilometers out on a red dust road from our basecamp in an old farmhouse. The road climbs abruptly to the north, up into the limestone hills. At a point about 50 meters above the arid red plain is the shaft. It's a classic pit in ragged, sharp, heavily weathered karst and measures about 40 meters in diameter. The drop to the water surface is 112 meters, and nearly freefall. Not exactly what one would call an "easy access" diving location. Aging, rusting, remnants of heavy, post WW1 water pumping equipment is all about. Today the farm gets it's precious water from submersible pumps down on the valley floor that had tapped the aquifer. In the old days, they saw the water and went for it in a straight forward manner of running pipes vertically down to the lake. The original settlers had commissioned a series of hand-forged iron link ladders and lowered them down one side of the gaping pit. By clinging to the walls on the west side they had been able to proceed down in segments, except for the final 50 meters, which hung absolutely free. The farm children down-climbed this vertigo-inducing series of ladders, without any safety lines, in the summer to go swimming. We rigged the shaft entirely freefall using modern vertical rope techniques. In addition Chris Steencamp had developed an ingenious cable tyrolean and a trolley with a 55-gallon bucket for transporting heavy equipment down to the dive site, using descenders for lowering and a gas-powered capstan winch for raising.

Mission:
At the beginning of this mission, the limit of human exploration in Dragon's Breath was 132 m, and it's entire depth unknown. With five vertical shafts and a significant section where the walls were less than 50 cm apart, it was a tedious exercise to transport equipment to the dive site. The last 20 meter pitch was freefall and landed directly in the lake; the water depth at that location was known to be over 60 meters. John Harman, Chris Steencamp and Bill Stone spent several days rigging the cave, inflating work platforms and boats and installing a base for SUNFISH that was rock bolted to a nearby wall from where the rope landed in the lake. SUNFISH's preliminary map outlined the cross section of a descending tunnel 175 meters wide and 60 meters tall. SUNFISH returned to this tunnel and explored it for a half kilometer until finding the cave's end, at a depth of 205 meters. No side tunnels led off of the main passage.

Site Description:
Like Harasib Cave, Dragon's Breath Cave is located on Farm Harasib, about 30 kilometers south southeast of Tsumeb. Light filters down into the entrance tunnel from overhead skylights. Unlike the surface, which has been wind and rain eroded to a broad field of sharp rillenkaren, the inside of Dragon's Breath cave seems smooth, no sharp edges. The name of the cave draws from the unusual subterranean wind it produces. The massive underground lake lies just 60 meters beneath the red dust plain. It is large enough – 200 meters long by more than 100 meters wide and rising up to 20 or more meters above the water – to have sufficient volume to respond to the external weather. If a strong breeze blows by and reduces the air pressure at the entrance the lake chamber forcefully expels hot, incredibly humid air. When the reverse occurs cool dry air is sucked back into the cave. It seems to cycle several times an hour. The result is that the upper part of the cave from the entrance to the first vertical rope descent is cool and dry, and below that point it's like being in a 34C sauna.

Site Description:
Hudson Grotto formed when the roof of a limestone cave collapsed. While the age of the grotto itself is unknown, the limestone it formed in was deposited between approximately 50 and 23 million years ago. Fossils of creatures living during that time period are preserved in the grotto's walls. While Hudson Grotto is now fully submerged below the water table, it was completely dry about 12,000 years ago when ice sheets stretched across North America and sea level was about 120 meters (400 ft) lower. As the ice sheets melted, rising seas filled Hudson Grotto with water as they pushed the water table closer to the surface. The sinkhole is connected to the ocean through the aquifer and contains two main layers of water, which rise and fall with the tides. The upper layer is about eight times saltier than most of Florida's freshwater lakes and rivers. The salinity of the water increases sharply between 30 and 38 meters, where a deeper, even saltier layer extends to the bottom. This deeper layer of water has about half the salinity of ocean water and is devoid of oxygen. Without oxygen, microbes living in this deeper layer of water convert sulfate, one of the components of salt water, to hydrogen sulfide for energy, much like animals convert oxygen to carbon dioxide. The hydrogen sulfide that divers notice in the deeper layer is produced entirely by these microbes. Mixing between the top and bottom water masses creates a halocline, a zone where the salinity between water layers changes sharply. Light is diffracted when passing through haloclines, which makes objects in them appear blurry. White clouds of microbes are also commonly observed to float on top of the halocline.

Hudson Grotto has been known by several names over the years and the presence of Native American artifacts in the sinkhole indicates that humans have known about the site for a very long time. In modern history it was once called Pat Sink. In the late 1960s it was renamed by the well-known cave diving pioneer Sheck Exley; he called it Edward Sink in honor of his deceased brother. The sinkhole has attracted divers for decades. The property passed through a few different owners over the years and was eventually purchased by cave diver and instructor, Paul Heinerth. He renamed it Hudson Grotto in 1993 and built a floating dock for divers. He established the Scuba West dive shop across the street making Hudson Grotto a one-stop-shop for dive gear, instruction, and cavern diving. In 2006 the dive shop and Hudson Grotto were bought by the current (2020) owner, Jeff Tobey. Today the grotto continues to be a popular cave diving site in the area.