A University of Hawai‘i research team has built one of the most advanced semi-
autonomous submarines on Earth for complex missions in the deep oceans
The majority of the surface of the Earth is covered with oceans. While surface exploration of these bodies of water is largely complete, beneath the waves the oceans remain by and large mysterious. This is due, in part, to the inability of humans to observe these environs in great detail for extended periods of time. While subsea surveys of shallow coastal zones have filled in some of the information gaps, far less is known about the deep oceans. In these offshore areas, the sea floor lies 6,000 meters beneath waves (reaching depths as great as 12,000 meters for the deep trenches).
Beyond scientific inquiry, the deep oceans also hold myriad treasures. These include sunken ships or crashed military planes with top-secret gear on board, archaeological finds from ancient civilizations, mineral and petroleum reserves, and geological treasures like subsea volcanoes. Specialized submarines to take humans to these depths are few in number and wildly expensive to operate. These vehicles require a surface tender vessel, at a cost of $30,000 to $50,000 per day. Additionally, humans have unavoidable needs—air, water, food—that are nearly impossible to support for extended missions in the deep
To address extended deep ocean missions, the Autonomous Systems Laboratory (ASL) at the University of Hawai‘i at Mānoa has spent the last 14 years building the Semi-Autonomous Underwater Vehicle for Intervention Missions (SAUVIM). In 2010, SAUVIM passed with flying colors its official field trial in Oahu’s Keehi Lagoon. In that trial SAUVIM navigated murky 50-foot deep (16m) waters to locate and manipulate a target object. Funded by grants from the U.S. Navy’s Office of Naval Research (ONR), SAUVIM is one of a handful of highly advanced submarine vehicles designed to perform complex tasks while under remote operation and without the benefit of a tether cable for power transmission or command and control input. “ONR wanted a vehicle that would autonomously navigate underwater and only required a single button to be pushed. The vehicle must be able to find a target and perform tasks—fix a broken valve, retrieve a distinct object, or tag locations of interest for further investigation,” explains Song
K. Choi, one of the principal investigators at the ASL, which is a part of the College of Engineering at UH Mānoa. “This requires not only autonomous navigation but also autonomous manipulation. That is what sets SAUVIM apart from other underwater research projects.”
The engineering challenges to building a vehicle like SAUVIM are enormous. Tethered subsea vehicles can receive power from the surface that enable direct digital links and command and control capabilities. But tethers exert too much drag to be viable for extended deep ocean work over large swatches of the sea floor. For this reason, SAUVIM had to be designed without trailing wires or cables. Unfortunately, untethered vehicles have limited power supplies to drive their electric motors or operate onboard electronics. Further, designing an unpressurized vehicle to operate at such depths meant excruciating engineering detail to eliminate liquids or gases that could potentially implode upon submersion or explode upon ascension.
Command and control of the vehicle was likewise a difficult task. Wireless signals cannot traverse the depths for remote control. While acoustic signals can be used for simplistic commands, the limited bandwidth and time delay required for acoustic command relay makes it impossible to direct an autonomous submarine from the surface with real precision or acceptable response times. In general, an untethered deep-sea vehicle performing complex tasks must rely on self-directed computer algorithms akin to the types of capabilities seen in the Mars rover vehicles or extremely sophisticated terrestrial robots.
But the most challenging part of the mission was to create the software algorithms and system intelligence to enable the type of autonomous navigation required by ONR. These types of autonomous navigation technologies have gained prominence in recent years with popular competitions between university engineering teams to build vehicles that can autonomously drive across the country and search engine company Google’s revelation that its self-driving vehicles had been navigating Bay Area roads for some time. Driving on land, however, where Global Position System (GPS) satellite signals are accessible, is far less complicated than building the intelligence to navigate a vehicle in the deep ocean. Not only are GPS signals unavailable in the deep ocean but also underwater vehicles’ movements are far less affected by gravity and friction. Thus, compensation for inertia is more difficult and fine-grained controls challenging to operate. The vehicle must navigate and perform intelligent actions but also self-calibrate to ensure that its capabilities remain robust throughout an extended mission.
To create these capabilities and this intelligence, Choi and his team developed a cluster of relatively low-powered computer processors with each linked to different sensors on the SAUVIM (e.g. different types of sonar, optical cameras). “The system architecture was very similar to how we would perform these sorts of functions biologically with our own nerve and sensory system,” explains Choi “Our sensors only process information they deem to be useful and we needed to recreate that in order to focus SAUVIM on the
appropriate intervention tasks.”
Over the 14-year history of SAUVIM, the project has brought in more than $14 million in grants and contracts, and employed dozens of engineers and graduate students in the ASL. “We built everything here in Hawai‘i except for the pressure vessels. We’ve had as many as 33 people working on it at a single point in time. We developed the hardware, programmed the software and fabricated the vehicle and many of its key parts,” says Choi.
At present, the future of the SAUVIM is unclear. The Navy undertook a final site visit last year and is considering how it might use these new types of sub-sea vehicles. While there are no guarantees that the Navy will support final commercialization of the SAUVIM, which exists now in advanced prototype stage, Choi is sanguine. “We’re still very early in the adoption cycle,” explains Choi. “The U.S. military had unmanned aerial vehicles (UAVs) for 10 years before they began to aggressively deploy them. I would expect the same to happen with smart autonomous submarines, as well.”
About the Researcher
Song K. Choi is an assistant dean and professor at the College of Engineering, UH Mānoa. His specialization is in robotics, autonomous vehicle design, novel sensor systems, alternative/renewable power sources, and graphic monitoring systems for unmanned vehicles.
This article originally appeared in the Summer 2011 print edition of Kaunānā. It has been corrected to reflect the 2010 field trial date for SAUVIM.