Robotics

Titan’s submersible disaster underscores the dangers of deep-sea exploration – an engineer explains why most marine science is done with unmanned submarines

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Researchers are increasingly using small autonomous underwater robots to collect data on the world’s oceans. NOAA’s Teacher Program at Sea, NOAA’s Ship PISCES, CC BY-SA

By Nina Mahmoudian (Associate Professor of Mechanical Engineering, Purdue University)

Rescuers view debris from the tourist submarine Titan on the seabed near the Titanic wreck on June 22, 2023, indicating that the ship suffered a catastrophic failure and the five people on board were killed.

Bringing people to the bottom of the deep sea is inherently dangerous. At the same time, climate change means collecting data from the world’s oceans is more important than ever. Purdue University mechanical engineer Nina Mahmoudian describes how researchers reduce the risks and costs associated with deep-sea exploration: Lower the submarine, but keep the people on the surface.

Why is most underwater research conducted by remotely operated, autonomous underwater vehicles?

When we talk about water studies, we are talking about a very large area. And covering large areas requires tools that can work for long periods of time, sometimes months. Having people onboard underwater vehicles, especially for long periods of time, is both expensive and dangerous.

One of the tools that researchers use is remotely operated vehicles, or ROVs. Basically there is a cable between the vehicle and the operator which allows the operator to command and move the vehicle, and the vehicle can convey data in real time. ROV technology has advanced rapidly to the point where it can reach the deep sea – up to a depth of 6,000 meters (19,685 feet). It is also better able to provide the mobility needed to survey the seafloor and collect data.

Autonomous underwater vehicle provides another opportunity for underwater exploration. They are usually not moored to ships. They are usually pre-programmed to carry out a specific mission. And when they’re underwater, they usually don’t communicate constantly. At certain intervals, they emerge, convey the entire amount of data they have collected, replace the battery or recharge and receive new instructions before sinking again and continuing their mission.

What can remotely operated, autonomous underwater vehicles do that manned submarines cannot, and vice versa?

Manned submarines will appeal to the public and those involved and help enhance human-driven capabilities to operate instruments and make decisions, similar to manned space exploration. However, it will be significantly more expensive compared to unmanned exploration due to the size of the platform required and the need for life support and safety systems. Manned submarines today costs tens of thousands of dollars a day operate.

The use of unmanned systems will provide better opportunities for exploration at lower cost and risk in operating over large areas and in inhospitable locations. Using autonomous, remotely operated underwater vehicles gives operators the opportunity to perform tasks that are hazardous to humans, such as observing under ice and detecting underwater mines.

Remotely operated vehicles can operate under Antarctic ice and other hazardous places.

How has deep-sea research technology developed?

Technology has advanced dramatically in recent years due to advances in sensors and computing. There has been great progress in miniaturization of acoustic and sonar sensors for use underwater. Computers are also becoming more mini, capable and power efficient. There has been a lot of work on waterproof battery and connector technology. Additive manufacturing and 3D printing also help build the ship’s hull and components that can withstand high stresses at depth at a much lower cost.

There has also been major progress towards increasing autonomy using more advanced algorithms, in addition to traditional methods of navigation, localization and detection. For example, machine learning algorithms can help vehicles detect and classify objectsis it still like a pipe or moving like a school of fish.

What kinds of discoveries have been made using remotely operated, autonomous underwater vehicles?

One example is the underwater glider. It is an autonomous underwater vehicle propelled by buoyancy. They can stay in water for months. They can collect data on pressure, temperature and salinity as they rise and fall in the water. All of this is very helpful for researchers to have an understanding of the changes that occur in the oceans.

One of these platforms travels across the North Atlantic Ocean from the Massachusetts coast to Ireland for nearly a year in 2016 and 2017. The amount of data captured in that time is unprecedented. In short, such a vehicle costs around $200,000. The operator is far away. Every eight hours the glider surfaces, connects to the GPS and says, “Hey, I’m here,” and the crew essentially lays out a plan for the next mission. If a manned ship were sent out to collect that much data over that time, it would cost millions.

In 2019, researchers used an autonomous underwater vehicle to collect invaluable data about seabed under the Thwaites glacier in Antarctica.

Energy companies are also using autonomous, remotely operated underwater vehicles inspection and supervision offshore renewable energy and oil and gas infrastructure on the seabed.

Where is technology headed?

Underwater systems are slow-moving platforms, and if researchers can deploy them in large numbers it will give them the advantage of covering large areas of the ocean. Much effort is being put into the coordination and fleet-oriented autonomy of these platforms, as well as advancing data collection using onboard sensors such as cameras, sonar, and dissolved oxygen sensors. Another aspect of advancing vehicle autonomy is real-time underwater decision making and data analysis.

What is the focus of your research on this submarine?

My team and I are focused on developing navigational and mission planning algorithms for continuous operations, meaning long-range missions with minimal human oversight. The aim is to respond to two major constraints in the deployment of autonomous systems. One of them is battery life. Everything else is an unknown situation.

The authors’ research includes a project to allow autonomous underwater vehicles to recharge their batteries without human intervention.

As for battery life, we work on recharging at sea, both underwater and surface water. We are developing tools for autonomous deployment, recovery, reloading and data transfer for longer missions at sea. For unknown situations, we work to recognize and avoid obstacles and adapt to different ocean currents – essentially enabling vehicles to navigate on their own in difficult conditions.

In order to adapt to the changing dynamics and component failures, we are working on a methodology to help vehicles detect changes and compensate in order to continue and complete missions.

This effort will enable long-term ocean studies including observing environmental conditions and mapping uncharted areas.

Conversation


Nina Mahmoudian receives funding from the National Science Foundation and the Office of Naval Research.

This article is republished from Conversation under Creative Commons license. Read original article.


The Conversation is an independent source of news and views, sourced from the academic and research communities and delivered directly to the public.

The Conversation is an independent source of news and views, sourced from the academic and research communities and delivered directly to the public.

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