"At the depth of the Titanic, nearly 4,000 meters down, a ship was subjected to 5,689 pounds (2,580 kilograms) of pressure per square inch," Lenkewitz said. That's 400 times the average pressure we experience at sea level.
In addition, autonomous submersibles face challenges when navigating deep underwater.
On the surface, autonomous submersibles can use sensors to look around and recognize things. It can also rely on precise satellite positioning systems such as GPS. Autonomous submersibles do not have these luxury features.
Because the light from deep in the ocean is insignificant, it can only see very close to itself. Sonar can help it see further, but it can only detect objects in very specific directions. On top of that, the lack of satellite connectivity underwater makes it difficult for the submersible to find its position. Researchers use complex calculations to track the spacecraft's position, but these aren't always accurate.
"There's always an error rate with these location estimation algorithms," Lenkewitz says. The longer you spend underwater, the worse the errors. After just a few hours, you could be hundreds of meters away from where you think you are, depending on the quality of the sensor."
Continuous exploration
Another challenge for long-term submersibles is energy. These submersibles need electricity to operate, but underwater, there is no obvious power source available. Paul Kula, a professor of ocean engineering at Texas A&M University, said that solving this problem will be one of the keys to exploring the deep sea more deeply.
"Our dream is to have a permanently operational vehicle that uses renewable energy to monitor the ocean and keep us informed of any changes," he added.
Some submersibles are already taking steps to realize this vision. Underwater gliders absorb water to make them glide downward, then release water again to lift themselves up and control themselves with their wings. In this way, they can float up and down on the ocean for months. But even then, they are ultimately limited by battery life.
To overcome this, there are several options. Although the sun does not penetrate deep into the surface, autonomous submersibles can periodically surface to store energy before sinking again. But Kula said the small size of the submersible would limit the amount of solar energy it could collect.
Another scenario the researchers are considering is floating charging stations across the ocean, where submersibles can dock and recharge. What's the problem? This requires a high start-up investment.
"The initial uptick was very slow," Kula notes. You need an Elon Musk-type figure to make this happen and standardize the Marine charging connector."
Another option is to use ocean currents or hydrothermal vents on the ocean floor, although these are not always available everywhere. Kula is also developing a system that uses the thermal difference between water at different depths to generate energy. In this way, the submersible can move up and down in the water and generate the power needed to sustain itself.
Getting any such machine to work in harsh ocean conditions is not easy. Still, Kula is optimistic.
"The timing seemed right," he said. Interest and funding continue to grow, and technology continues to advance. That being said, if we funded deep-sea exploration the way we fund space, we'd already be much further along."
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