DEPTHX
Autonomous underwater vehicle that mapped the deepest water-filled sinkhole.
The Deep Phreatic Thermal Explorer, or DEPTHX, is an autonomous underwater vehicle created by the Austin, Texas-based aerospace firm Stone Aerospace. Its purpose was to independently navigate and map underwater sinkholes in northern Mexico while also gathering water samples and core samples from the walls. DEPTHX achieved this using a self-directed form of navigation called A-Navigation. It was the first of three vehicles Stone Aerospace built with NASA funding, all aimed at developing technology for exploring the subsurface oceans of Jupiter’s moon Europa in the search for extraterrestrial life.
Stone Aerospace served as the lead investigator on the DEPTHX project. Partner organizations included Carnegie Mellon University, which developed the navigation and guidance software; the Southwest Research Institute, which built the scientific instruments; and research scientists from the University of Texas at Austin, the Colorado School of Mines, and NASA Ames Research Center.
The project’s origins trace back to 1999, when Bill Stone worked on an underwater survey at Wakulla Springs, Florida. For that effort, Stone created a digital wall mapper pushed by a diver propulsion vehicle and steered by divers, using an array of sonars and other advanced sensors to produce a 3-D map. The success of this Wakulla Springs 2 Project caught the attention of planetary scientist Dan Durda at the Southwest Research Institute, who wanted a similar device that could operate autonomously for exploring Europa’s oceans. Stone took on the challenge, and after several collaborative proposals to NASA, the agency funded DEPTHX in 2003 as a three-year, $5 million project.
Over the next few years, engineers at Stone Aerospace considered various designs. Early concepts favored a less ellipsoidal shape, but these were dropped due to worries that such a form would be hard to maneuver in tight, unknown spaces. During this period, the DEPTHX team conducted a field campaign at Cenote Zacatón using a drop sonde to gather preliminary data for the software team, which influenced the final design. The definitive design was settled on in 2006, and construction began.
The finished vehicle measured about 7 feet in diameter and weighed roughly 3,300 pounds.
- Builder
- Stone Aerospace
- Location
- Austin, Texas
- Diameter
- about 7 ft
- Weight
- about 3300 lb
- Funding
- $5 million project funded by NASA in 2003
- Navigation
- A-Navigation (autonomous form of navigation)
- Collaborators
- Carnegie Mellon University, Southwest Research Institute, University of Texas at Austin, Colorado School of Mines, NASA Ames Research Center
Lore & Background
In 1999, Bill Stone had been involved in an underwater surveying project in Wakulla Springs, Florida. For that project, Stone had devised a digital wall mapper propelled by a diver propulsion vehicle and steered by divers, designed to create a 3-D map using sonars and other sensors. The success of this project attracted the interest of planetary scientist Dan Durda from the Southwest Research Institute, who wished to create a similar autonomous technology to explore the oceans of Europa. Stone accepted the challenge, and several collaborative proposals were submitted to NASA. It was not until 2003 that NASA funded DEPTHX as a three-year, $5 million project.
The vehicle underwent several different design concepts over the next couple of years. Initial designs focused on a less ellipsoidal shape, but these were abandoned due to concerns that such a shape would be difficult to maneuver out of potentially tight spots. The DEPTHX team did a field campaign at Cenote Zacatón using a drop sonde to acquire initial data for the software team. The final design was decided upon in 2006, at which point construction began. The completed vehicle had redundant navigation systems including 54 sonars, an inertial measurement unit, doppler velocity logger, depth gauges and accelerometers. Propulsion systems were also redundant, having six thrusters and two equivalent battery stacks. It was outfitted with a variable buoyancy system and a science payload that included the ability to take water and solid core samples, as well as an onboard microscope to analyze water samples in real time.
Reader's Guide
During the DEPTHX 2007 deployment, the vehicle created 3-D maps of four cenotes in Sistema Zacatón in Tamaulipas, Mexico. This was the first autonomous system to explore and map a cavern. The mapping of Cenote Zacatón was particularly notable because its depth was previously unknown, as human divers had not been successful in attempts to reach the bottom. DEPTHX created the first map of the bottom of Zacatón, which has a depth of over 1000 ft. DEPTHX was the first robotic system of any kind to implement three-dimensional simultaneous localization and mapping (SLAM). It was also the first such system to make its own decisions on where and how to collect samples. From these samples, at least three new divisions of bacteria were discovered. The success of the DEPTHX mission led to the funding of the follow-on project, ENDURANCE, which reused the frame and a number of systems from DEPTHX but was considerably reconfigured for the needs of the Antarctic environment.
Did You Know?
- It was the first robotic system to implement three-dimensional simultaneous localization and mapping (SLAM).
- At least three new divisions of bacteria were discovered from samples collected by DEPTHX.
Frequently Asked Questions
What is DEPTHX?
DEPTHX, short for Deep Phreatic Thermal Explorer, is a roughly seven-foot-diameter autonomous underwater vehicle weighing about 3,300 pounds. It was engineered to independently explore and map underwater sinkholes in northern Mexico.
Who built DEPTHX and who funded it?
Stone Aerospace, an aerospace firm headquartered in Austin, Texas, developed the vehicle as part of a $5 million NASA grant awarded in 2003. It was the first of three subsurface-exploration drones the company produced under that contract.
What is DEPTHX's primary mission?
The vehicle was tasked with autonomously navigating and mapping underwater sinkholes while simultaneously collecting water samples and core samples from the surrounding walls. It notably succeeded in mapping the deepest water-filled sinkhole on record.
How does DEPTHX navigate without a human pilot?
It relies on a self-directed navigation system called A-Navigation, which lets the vehicle plan and execute its own path through complex underwater terrain. This autonomy was essential for reaching deep, remote sinkhole environments where real-time remote control is impractical.
Why is DEPTHX significant in the broader drone landscape?
Beyond its sinkhole-mapping achievements, DEPTHX served as a technology testbed for future missions to probe the subsurface oceans of Jupiter's moon Europa in the search for extraterrestrial life. As the first of three NASA-funded vehicles Stone Aerospace built toward that goal, it laid the groundwork for deep-space subsurface exploration.
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