Silent Service Connects
Navy heads toward Seaweb, a distributed undersea bi-directional communications and sensor network. 
The USS Chicago, a Los Angeles-class attack submarine, glides along
at periscope depth in the western Pacific Ocean off the coast of Malaysia.
The U.S. Navy is developing technologies to enable submarines to communicate at speed and depth during antisubmarine warfare operations and for missions in the littorals.
An expendable one-way gateway buoy that provides a paging system for submarines is undergoing technology demonstrations in the
Indeed, dramatic changes are taking place in undersea force network communications that exploit the latest in commercial information technologies. The Navy resolutely is transforming the submarine from an intermittent node operating at periscope depth into a persistent cooperative network node functioning at speed and depth—without sacrificing inherent stealth.
Moreover, the Navy is moving to integrate distributed and netted sensors with unmanned underwater vehicles (UUVs), submarines, and surface and aerial platforms. The objective is to gain situational awareness of the undersea battlespace to locate and engage threats rapidly in littoral areas. This mobile ad hoc network is being developed around wireless nodes that can function cooperatively and spontaneously without a fixed infrastructure. Early elements of this system already are emerging.
The Navy’s submarine force steadfastly is moving toward a long-term Seaweb concept—a bi-directional communications capability between patrolling submarines, the theater commander and various undersea off-board sensors. In response to a request for information from industry for communications at speed and depth, the sea service received 58 white papers that addressed more than 80 technologies for evaluation. These responses have been grouped into eight categories, both near- and long-term. They have been winnowed further to some 22 alternatives that are more technically mature.
A funding request from the Navy calls for acceleration of key submarine communications programs by two years, fiscal year 2007 rather than 2009. Innovative technologies for speeding up submarine communications include the acoustic-to-radio-frequency gateway buoy, a tethered Iridium two-way expendable buoy, an Iridium-based BRT-6 follow-on one-way buoy and a tethered ultrahigh frequency (UHF) satellite communications expendable buoy.
The Raytheon Company is under a small $500,000 technology demonstration contract for the tactical paging buoy, called Deep Siren (SIGNAL, December 2000, page 53), as part of the Communications at Speed and Depth (CSD) program, Leo deCardenas explains. He is the company’s Navy programs senior business development manager, network-centric systems. “This untethered tactical paging buoy is designed to operate on the surface and interface with one of the 66 Iridium satellites in circular low earth orbit.” As the constellation orbits over the oceans, Iridium delivers essential voice and data communications to and from remote areas. These cross-linking satellites act as a fully meshed network.
“While the Navy pursues both one- and two-way submarine communications options, the paging buoy can be dispensed from a surface ship, an aircraft or from the submarine itself,” deCardenas says. Once the buoy takes position on the surface, it immediately establishes communications with an Iridium spacecraft within range via a radio frequency (RF) link. While in contact with the satellite, the buoy deploys a hydrophone down to a fixed depth and converts RF satellite signals into an acoustic frequency (AF) transmission, sending it through the water at a much lower audio range.
AF signals will travel significant distances from the buoy. The submarine does not have to come to a more shallow operating depth to receive the acoustic signals. The depth and distance at which the buoy’s signals can be received depend on the hydrophone and submarine being within the same ocean thermalcline boundary layer. Water temperature and salinity also are critical factors in the acoustic signal’s range, deCardenas reveals.
In earlier experiments in various ocean locations, the paging message was transmitted in excess of 100 miles to significant depths. In shallow, noisy littoral waters, the distance was reduced to about a third of the deep-water range. “The buoy transmission is not restricted by the speed of the submarine, as long as it is not outrunning audio frequency waves,” deCardenas notes.
In the past, submarines had to sacrifice some degree of stealth whenever the vessel needed to communicate. This situation makes the CSD the sine qua non for a network that integrates the undersea force with the rest of a battle group and the fleet, including aircraft for Tomahawk cruise missiles and special operations, deCardenas points out. Deep Siren’s buoy design also allows the submerged submarine to launch the device and send it to the surface. Once on the surface, the buoy receives Iridium signals, while the submerged boat listens for the communications response.
A surface ship, an aircraft or any submerged vessel also can launch the Deep Siren buoy to communicate with submarines. The buoy quickly establishes the satellite link and drops its hydrophone. A surface ship, as an example, dials up the satellite and sends a message to the spacecraft’s transponder, which, in turn, is received by the buoy. Once the buoy is in the water, any vessel also can employ the Iridium link to that buoy to transmit a paging message, deCardenas discloses. “The buoy’s battery power lasts approximately three days with intermittent communications but only about 30 minutes with constant transmissions. Once the battery is dead, the buoy scuttles itself.”
The Navy anticipates using this tactical paging buoy technology during the upcoming Trident Warrior 2006 exercise in the Pacific. DeCardenas reports that the U.S. Navy and
Capt. Robert Gurczynski, USN, relates that without submarine force network integration, today’s architecture provides periscope-depth operations that rely on legacy pathways, which are limited to 4.8-kilobit-per-second text-only data transfer. The captain is the director for command, control, communications, computers and intelligence (C4I), N-6, Commander, Naval Submarine Forces,
Today, intermittent Internet protocol (IP) data rates are up to 64 kilobits per second, with limited access and limited links in the extremely high frequency (EHF) range at medium data rates, the captain observes. Primary communications are via shared 32-kilobit-per-second access, with limited high-volume transfer via the Global Broadcast System (GBS) in a shore-to-ship-only transmission. There also is limited tactical network integration. At speed and depth, the submarine is now limited to very low data rates of 50 to 75 baud, with no IP connectivity and a receive-only capability, he adds.
Submarine force network integration between 2007 and circa 2012 is intended to eliminate legacy pathways and to provide fully netted worldwide IP connectivity. This approach will make multiple links available: super high frequency (SHF), EHF at medium data rates and UHF, Capt. Gurczynski explains. Technology upgrades in the developmental pipeline will provide IP connectivity at speed and depth with persistent real-time communications with the warfare commander and his coalition forces.
“Tomorrow’s architecture will make the submarine force a covert player in network-centric warfare with an open architecture—shipboard tactical systems fully integrated as part of the Submarine Warfare Federated Tactical System (SWFTS). This SWFTS architecture will be integrated into the force network through the external communications system,” the captain continues. “The fully netted submarine force connectivity will provide UHF satellite link data rates up to 32 kilobits per second for IP messaging, Web and e-mail access; a Tomahawk strike network; and tactical voice communications.”
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| Chief Electronics Tech. Jerry A. Bolte, USN, co-pilot, and Senior Chief Machinist’s Mate Scott McIntire, USN, pilot, operate the controls of the attack submarine PCU Virginia. Unlike the submarines before it, the Virginia eliminates the traditional helmsman, planesman, chief of the watch and diving officer of the watch stations by combining them into two watch stations. |
“The Navy intends to have some technologies for CSD fielded by 2008, the earliest that funding can be made available in the procurement process. There are only three technologies that we can move forward with that quickly, and the Raytheon tactical paging buoy falls into that category,” the captain claims. Meanwhile, the undersea force is shifting every system on board its submarines to an IP base, including combat systems, and all of its sensors.
Recent demonstrations in noisy water emulated acoustic conditions in the littorals. The tests were to determine that sufficient power in the gateway buoy could transmit the signal through the water and have it received despite a submarine’s baffles, including directly astern with the submarine traveling at a fast speed. “We were able to do this at almost flank speed, and the worst case condition was at approximately 40 nautical miles with the contact in the baffles,” according to Capt. Gurczynski.
In addition to the gateway buoy, the Navy will upgrade other submarine communications systems, replacing equipment that has been in the fleet for years, according to Capt. Dean A. Richter, USN. He is in the Space and Naval Warfare Systems Command (SPAWAR) program executive office for C4I and space, PMW-770. “These improvements include new modern radio sets and modems with high data rates that provide fairly long ranges. One- and two-way optically tethered communications buoys are being developed but not just for use with the Iridium satellites. Eventually, the buoys will interface with UHF military satellite communications.”
A retrievable tethered fiber optic buoy for communications and surveillance is another important long-term research opportunity of the CSD. The submarine deploys the buoy, which surfaces as the cable plays out. While at depth, the submarine can travel up to a distance of about two miles from the buoy, which provides an RF interface for satellite communications. Once the cable is fully deployed, communications terminate and the buoy is recovered from the surface automatically for reuse, Capt. Richter reveals. The tethered buoy could be carried on an SSGN, or guided missile, submarine, or potentially on the sail of the advanced Virginia-class boat.
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Various types of acoustic technologies are being considered for the CSD. The communications systems include hull-to-hull, submarine-to-submarine, submarine-to-surface ship and submarine-to-UUV as part of a mobile distributed undersea network, Capt. Richter maintains.
The stationkeeping energy-harvesting buoys and ocean gliders are other technologies for the CSD. “The gliders operate on a concept of changing their buoyancy by flooding water into the nose and diving to significant depths before pumping water out and traveling to the surface. Depending on the glider’s wingspan, a speed of advance of three to four knots can be achieved over vast ocean distances. While deep, the gliders can receive acoustic messages, store them and, when they surface, use an antenna to transmit RF messages to satellites,” the captain discloses. “With a school of the gliders, you can have an acoustic/RF gateway distributed network for a variety of unique applications. We have already tested the technology in the water during an exercise.”
A submariner, who has served on a number of boats, including tours as executive officer of the USS Alabama and commanding officer of the USS Jefferson City, Capt. Richter reports that the concept development and demonstration phases of the acquisition program are beginning. “We would like to field the first increment of a family of systems with a near-term capability in fiscal year 2007,” the captain says. “This would give us some type of operational evaluation later that year to begin fielding operational systems throughout the fleet in fiscal year 2008.” He adds that a competitive contract will be sought for all of the systems.
The gateway buoy will enable a strike group commander to tactically page a submarine, either in a one- or two-way fashion acoustically. The submarine can receive the message on its sonar system and can respond in kind acoustically, or via some other means—a buoyant cable antenna attached to the submarine and floating on the surface, an expendable buoy or a fixed antenna at periscope depth, Capt. Richter says.
Approximately 100 yards long, the cable is a floating copper wire antenna for high frequency communications embedded in highly buoyant foam. While laying on the surface, the wire can receive and transmit at bandwidths of 128 to 256 kilobits per second as the submarine operates in the littorals or performs antisubmarine warfare missions.
Two-way laser communication between submarines and various aircraft is another potential for the CSD capability, along with the possible development of a submarine-launched small UAV to support this concept. Laser communications, already tested and used on submarines in the fleet, are likely to expand to airborne and space-based systems. The CSD makes the submarine a far more valuable tool for the battle group commander. The Seaweb distributed undersea network will open up a wide variety of submarine capabilities and missions.
Web Resource
Space and Naval Warfare Systems Command/PEO C4I & Space Extremely Low Frequency Communications Systems (pdf): enterprise.spawar.navy.mil/getfile.cfm?contentId-781&type=R
