New Applications, Markets Sought For Underwater Communication System

By Stew Magnuson
A new technology designed to communicate with submarines as they travel stealthily at great depths and speeds is now being looked at as a means to send messages to special operations divers and commands to unmanned underwater vehicles.

The Deep Siren tactical paging system, produced by Raytheon, seeks to answer a need that the Navy has had for years: how to link to its submarines as they travel underwater without exposing their positions to potential enemies.

Company representatives said Deep Siren is at an advanced technology readiness level — seven in a one-through-nine ranking, which means it has been successfully tested in operational environments. But the Navy has not made any decisions on whether to add the system to its submarine fleet. The Navy awarded Raytheon a $5.2 million contract in 2007 to develop the technology and run a series of tests.

Since then, the United Kingdom’s Royal Navy has also tried out the underwater communication system.

“We know the product works. It’s now a matter of demonstrating it to customers,” said Trevor Barron, Deep Siren system engineer. “We continue to evolve the product’s capabilities with our internal funding.”

Submarine commanders can be ordered to run silent and deep for months without any way to send or receive messages.

Communicating with a command center often means rising close to the surface where a periscope with an antenna can be raised above water. That makes the ship vulnerable and can expose its presence to the enemy.

The Space and Naval Warfare Systems Center ran the first tests on Deep Siren, which allows a submarine to “send a page” to surface ships or command and control centers or vice versa without having to surface or stop its engines.

It was developed as part of the Navy’s communications at speed and depth program. The 2008 trials used a buoy ejected from the submarine’s trash chute to establish a link to the outside world. It enabled a submarine to be connected to the network while actively participating in military operations.

After the buoy is ejected from the trash chute, it hovers at a predetermined depth as the submarine continues its journey, explained Barry Murphy, director of undersea networked communications at Raytheon.

When the submarine is far enough away, the buoy ascends to the surface, deploys floatation devices and sends a message to a command and control center through an Iridium satellite. Once a link between the buoy and the command center is established, it then lowers an antenna deep into the water.

A transducer takes messages, translates them into acoustic energy and sends a pulse out through the water in an area greater than 50 nautical square miles.

How many miles and how deep the transmitter operates are classified.

Sending these pulses through ocean waters that have different thermal layers, with different consistencies was one of the challenges. Adjustments on the fly are the most difficult part, Murphy said.

The transmitter sends out multiple signals to overcome this problem, he added.

After a predetermined number of days, the buoy either self-scuttles, and drops to the ocean floor, or the surface command center sends a message to the buoy ordering it to cease operations and allow itself to sink.

Before that, the submarine and command center can send hundreds of text messages if needed.

The system works both ways. If a submarine has orders not to surface, but a command center wants to contact it, the buoy can be dropped from an aircraft or tossed over the side of a ship.

Once the transmitter is deployed, it can send out the pulse so the submarine can establish a link.

One of its advantages is that it does rely on strong energy pulses to send messages, Barron said. A submarine using a lot of power to transmit a message could reveal its location. Yet the system has to be reliable when a message is being transmitted to the submarine. Officers at the command and control center need to have confidence that the text message arrived because the submarine may not be able to confirm its receipt.

“We’re not interested in having submarines put energy in the water and give their position away, so we have to have very high confidence that the message sent will be received,” Murphy said.

In the 2008 test, a Navy submarine deployed 12 buoys at the Atlantic Undersea Test and Evaluation Center’s deep water range in the Bahamas, according to Raytheon. The buoy established a link between the submarine and a command center in Norfolk, Va.

The Royal Navy during its Taurus 2009 exercise a year later in the Mediterranean dropped a buoy from the air to establish contact with a submarine in excess of 100 nautical miles. A Royal Navy statement released afterwards gushed about the results of the test.

Deep Siren would be “the first step towards a transformational capability that will change the way we operate submarines in the future,” it said.

However, funding challenges have prevented the Royal Navy from moving forward, Murphy said.

The latest Deep Siren trial took place in March during the Navy’s ICEX (Ice Exercise 2011), a semi-annual event that serves as a test for submarine forces, which conduct operations in the Arctic. A base camp set up on an ice sheet used Deep Siren as a beacon to bring a Virginia-class submarine the USS New Hampshire (SSN 778) and the Sea Wolf-class USS Connecticut (SSN 22) to its location, according to the Navy Live, the service’s official blog.

“Though it has several different components to it, we are using only one segment of it that will allow us to do one-way, acoustic communications with the submarines,” Jeff Gossett, the Arctic Submarine Laboratory’s ICEX 2011 exercise director wrote in the blog.

“In the ‘rendezvous’ mode, our Deep Siren beacon transmits our position into the water every 10 minutes,” he wrote.

Meanwhile, Raytheon is preparing for demonstrations that will take place later this year with the German and French navies, Murphy added.

“We keep getting asked to do trials. There is a lot of international interest and we’re supporting those trials,” said Barron.

As the U.S. and U.K. navies await the go-ahead to deploy the system, Raytheon is adapting the technology for underwater diver and submersible robot applications.

For special operators carrying out covert missions underwater, the system has a two-way capability. It would be able to send text messages from a frogman to a command and control center and visa versa.

“Digital voice is something we are looking at, but right now we’re focused on flexible type text messaging,” said Barron. Raytheon has come up with a different set of commands tailored to special operators who need to send or receive short messages.

Deep Siren can be adjusted for short or long-range communications. The advantages for using it over present systems for communicating with divers would be its range and the fact that it emits little energy, making it difficult to detect, he said.

That is also an advantage for sending commands to unmanned underwater vehicles (UUVs). One of the issues with those systems has been a lack of battery power on board.

“The ability to communicate [with UUVs] using very low amounts of power has a huge benefit,” Barron said. Other technologies can send commands to the drones at about one kilometer. Barron couldn’t reveal current Navy requirements to extend that range, but said Deep Siren is “long range” compared to them.

Another overlooked benefit for the low energy transmissions would be minimizing potential damage to marine mammals, he added.

The belief that Navy sonars damage or hinder dolphins, whales and other ocean life that use the biological equivalent — biosonar — to navigate has been the source of controversy for many years.

“Existing communication systems put out a tremendous amount of power,” Barron added.          

Topics: Robotics, Unmanned Underwater Vehicles

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