They call it the ladder of death

. But soon it could be robots—not U.S. Navy sailors—making the descent.

U.S. Navy Visit, Board, Search, and Seizure (VBSS) teams carry out thousands of operations every year, inspecting vessels suspected of smuggling, piracy, or breaking embargoes. The eight-man team approaches in a small boat; if the vessel to be inspected refuses to lower a ladder, the Navy team must board with grappling hooks and rope ladders. The "ladder of death" leads down into the dark bowels of the ship, and the sinister name reflects the risk that the first man down could run into an ambush or a booby trap.

Hoa Nguyen, of the Navy's Space and Naval Warfare Systems Center Pacific in San Diego, says a new robot called Stingray could take some of the risk out of VBSS operations. The military and police can already toss small robots, or throwbots, through a door or over a wall to send back video from the other side. But after working with VBSS teams, Nguyen developed the specifications for a specialized boarding robot that could go on a hostile vessel ahead of the sailors.

After a competition that tested several robot designs, the result is the Stingray from MacroUSA. It's based on the Armadillo robot already used by the military. During boarding, the robot will be thrown on deck, even from 60 feet below. Some robots are too light or too heavy for such a throw, but Stingray's weight of 3 pounds puts it in the sweet spot, Nguyen says. Its robust carbon-fiber and aluminum chassis can withstand long drops. Throwing it accurately can be tricky; in tests, surrogate robots sometimes bounced off the side of the ship and into the water. So Stingray is waterproof and buoyant for easy recovery.

Stingray's special tracks allow it to paddle along the surface of the water. This amphibious capability is particularly useful for exploring the flooded compartments often found on dhows.

Stingray will not need to climb through doorways and hatches. Instead, the idea is that the VBSS team will pick up the bot and toss it forward, keeping it one compartment ahead of the clearing team. "It has enough mobility for a cluttered ship deck or room floor, but depends on the human to toss it over long distances to match the current pace of the clearing operation," Nguyen says.

Why not build a quadrotor that could fly about a ship? Nguyen says an operator in a boat that was pitching up and down would have a hard time controlling a remote helicopter, especially out of line of sight and in high winds. Flying indoors in very confined spaces can be difficult, and a ground robot is much better for covert infiltration. Self-driving robots are not ideal for this mission, either: They're more expensive, slower than humans, and heavier, Nguyen says.

Stingray's video camera has a 185-degree field of view, and it can quickly spin round to give a full view of a compartment. It also has an infrared light to see through the darkness of a ship's hold, plus a brilliant flashing strobe light to deploy against any enemies it encounters. "It functions similarly to flashbang grenades, without the audio portion, but is reuseable," Nguyen says. "It is meant to temporarily blind the hostile personnel in a confined, dark space." Dazzled pirates or smugglers will be much less able to shoot accurately or put up effective resistance, especially when they have been spotted and have lost the element of surprise.

The Stingray operates for about an hour on one battery charge. It is also supplied with a telescopic carbon-fiber pole so it can be turned into a "camera on a stick" for looking into inaccessible spaces, and it has an attachment point for a line so it can be lowered through a hatch.

A single control unit can operate two Stingrays. The one that's not being actively controlled acts as an intruder alarm, keeping watch and alerting the user if it sees any movement. Stingray also has the capacity to carry additional sensors. A Picatinny rail allows users to attach gas and radiation detectors or other gear required for a particular mission.

The first two systems, each comprising two Stingrays and a control unit, will be delivered later this year. They will go through extensive user validation testing to ensure that they work as planned. After that, it may not be long before VBSS teams get a chance to have a look on the deck of a ship to see what's waiting before they board.

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