Tech Briefs

UUVs could provide critical data link between submarines and command center.

Nuclear powered submarines can stay submerged for days at a time and only have to come to periscope depth (PD) for communications and minor house-keeping items. Submarines are completely reliant on satellites for communications and orders from their commanders ashore. A command and control denied environment (C2DE) is an area in which communications are jammed or degraded. There is no technology currently available that allows submarines to conduct communications in a C2DE. The only method currently available is for the submarine to navigate to unaffected waters, conduct all of its communications, and then to travel back to the C2DE, wasting valuable time and possibly compromising the submarine’s mission.

Figure 1. Interface between submarine, UUV, and data nodes.

The Navy’s current communication workhorse is the Milstar satellite network. The system consists of five satellites, two Milstar I, and three Milstar II, which have peak data transfer rates of 2400 bits per second (bps) and 1.544 mega-bits per second (Mbps), respectively. This low data rate means that the submarine has to maintain PD for long periods of time, thus exposing itself to unnecessary risk of detection or collision.

New line-of-sight (LOS) communication technologies, like the bluegreen laser, are being developed to overcome the communications vulnerability. The laser works in much the same way as a fiber optic cable, with the medium for data transfer being the air instead of the cable. As long as there is a clear LOS between the transmitter and receiver, high data transfer rates are available. Recent tests revealed a 99% reliable data stream at 90 Mbps at 10 km distance.

The technology also works under water, but the range of transmission is greatly diminished. Data transfer rates of between 7 and 10 Mbps with a 99.99% success rate were observed, but only in the 10 to 20 meter range. This initially appears to pose a difficult challenge, but with the application of an underwater network of data transfer nodes and UUV carriers, short data transfer ranges may not be an insurmountable issue.

The Navy is investing heavily in the use of unmanned underwater vehicles (UUVs) to help in areas including mine warfare, oceanography, salvage, and rescue operations. Used in conjunction with the blue-green laser, the UUV would be able to meet all of the submarine’s communication needs without the submarine ever coming to PD. The laser-fitted UUVs relay information from anchored data nodes to a sensor in the submarine’s sail. Figure 1 illustrates how this would work.

The modeled UUVs will patrol a linear area recharging at the completion of each patrol at an undersea garage. The garage will receive continuous updates from a sensor placed outside of the C2DE, but tethered to the garage. The garage will update the UUVs while they recharge and relay its continuous data feed to data links spaced along the patrol route of the UUVs. The UUVs will then download updates while passing by the data links to refresh their current information (Figure 2). When a submarine comes in contact with one of these UUVs, it will slow down and allow the UUV to approach. The submarine will then receive the UUVs broadcast via LOS blue-green laser transmission from above.

Figure 2. UUV patrol route

This configuration is modeled in agent based modeling software called Map Aware Non-uniform Automata (MANA). The scenarios consist of a submarine entering a network of UUVs and data nodes and determining how long it takes for the UUV to find and transfer data to the submarine, and the latency of the transferred data. Factors varied in the modeling include: the number and speed of the UUVs, the number of data nodes, the range at which the UUV and submarine detects each other, and how long the data transfer takes to complete. Thirty-six separate models are required to capture all of the discrete combinations of number of UUVs and data nodes, as well as the UUV’s speed.

This work was done by Forest B. Mclaughlin of the Naval Post Graduate School. NRL-0064

This Brief includes a Technical Support Package (TSP).


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