Breaking the Ice

Nereid Under Ice remotely controlled inspection and survey vehicle. Image: Woods Hole Oceanographic Institution

So much of the Arctic’s sea life remains undiscovered, but it’s hard to tell just what kind of life is there when it’s shielded from view by a ceiling of ice, sometimes meters thick. And humans won’t exactly be doing a lot of diving below that ice sheet—hypothermia would be an understatement in that environment. Of course, underwater vehicles can be an answer but how do they communicate what they sees through the ice? And how would they retrieve what they find?

The Nereid Under-Ice vehicle takes on these kinds of ice-related challenges.

The Importance of Communication

Louis Whitcomb, mechanical engineering professor and chair of the mechanical engineering department at Johns Hopkins University, was co-principal investigator on the vehicle design-and-build project to help scientists better explore under ice. Currently in use at the Woods Hole Oceanographic Institute in Woods Hole, MA, he explains that the vehicle they created is connected to the ship via a very lightweight, glass fiber tether, a quarter of a millimeter in diameter. “You can send a vast amount of data and it’s important because you need to have remote control with human operators,” he says. “The vehicle is under the ice so we need to send video and data back to the human operator to navigate and send commands to the vehicle to move or ‘take a sample here.’”

Nereid Under Ice two-body system sea trials. Image: Woods Hole Oceanographic Institution

 

 

 

To communicate with the vehicle with any significant bandwidth (like sending video images and audio), there is an umbilical, which carries the data at a high rate.

Communication also contributes to one of the most significant parts of success: saving the robot from getting lost. “If the tether was severed, which does happen during a dive, we could maintain limited communication via acoustic modem. The vehicle has the ability to report its status back to us. We could have control and navigation where, when the tether is lost during the dive, we can send a series of commands to the vehicle to navigate back to the ship for recovery.”

Navigation and Speed

In terms of navigation, GPS doesn’t work underwater, he says, so you need to use other means of navigation. Where there’s ice, they figure out where the vehicle is by using a type of sonar to measure the vehicle’s velocity relative to the ice overhead. The ice is the reference body.

The Nereid can dive 2,000 meters and can go at a maximum speed of about 3 knots. In terms of the motor, Whitcomb says it has a number of thrusters: three vertical thrusters, four thrusters for pushing forward and backward, and a lateral thruster for turning sideways. “It’s designed so we should be able to get the vehicle back even if we have the failure of two thrusters,” he explains.

As much as Whitcomb has enjoyed being a part of the vehicle coming to life, the bigger payoff, he says, was seeing scientists on an expedition be helped in doing their work—at sea during the previous summer.

“This wasn’t created just to do that work,” he says. “We did it for them so that they’ll find out amazing things to help all of us.”

And Whitcomb says readers can expect improvements to be made. “For example, we need to get it to range further from the ship and add additional devices like a robot arm,” he says. “But we’re just getting started.”

Eric Butterman is an independent writer.

For Further Discussion

We need to get it to range further from the ship and add additional devices like a robot arm. But we’re just getting started.

Prof. Louis Whitcomb, Johns Hopkins University