The Flying Plug was a prototype underwater data connectivity device developed by SSC San Diego under the ONT Blue Sky Program and subsequently adopted by the ONR Surveillance Program. It was designed for deployment from submarines, aircraft and surface vessels.
In an information-based society, the ability to reliably retrieve, transfer and process large quantities of digital data in a timely fashion becomes a critical technology issue. Few operating environments place more limitations on the ability to transfer data than underwater, either in the deep ocean or in littoral regions. In the sea, the conductive medium places strict limits upon RF propagation, visibility greatly restricts the bounds of optical transmission and ambient noise, ray-bending and multipath dominate the acoustic environment. In practice, data transfer rates were limited to at most a few kilobits per second in spite of the technology employed, even under fairly favorable conditions, unless a hard connection via a cable was established. However, adverse logistics associated with underwater cables and their associated infrastructure could render a system concept totally impractical from a technical or economic standpoint, in spite of the ability of the cable to sustain reliable data transfer underwater at a high rate.
In order to circumvent some of these issues, nearly a decade ago the US Navy developed expendable fiber optic microcable (FOMC). FOMC was developed by SSC San Diego and transitioned into commercial production via the Navy's Manufacturing Technology program in 1990. FOMC is a tiny fiber optic cable, consisting of a single commercial optical fiber surrounded by a concentric strength-member of fiberglass-reinforced polymer, which can be manufactured inexpensively enough to be thrown away after each use. FOMC can be deployed underwater from a freestanding coil at high speeds and serves to establish a reliable transmission channel that is capable of supporting megabit-to-gigabit per second data transfer rates. Microcable was demonstrated to support high data rate communication requirements for several point-to-point military applications, including torpedoes and Unmanned Undersea Vehicles (UUVs), while exacting a minimal impact upon the logistical and operational capabilities of the system. However, FOMC still could not support the potentially vast number of advanced undersea system architectures which require make-break or network communications without the subsequent development of supporting underwater connectivity technology.
An underwater vehicle was a means for establishing the physical connection required for fiber optic data transfer. A small UUV carrying a coil of FOMC launched from a support platform was a good candidate for establishing a fiber optic link between a remote, cooperative data node and the support platform. Signal processing and guidance and control functions were readily remoted to computers aboard the support platform by means of the fiber optic channel during the acquisition phase of the mission. The same FOMC subsequently supported data transfer after the vehicle had docked with the node. Partitioning of hardware in this manner helped to keep the system inexpensive to manufacture and ultimately permited an expendable vehicle to be designed. The Flying Plug system was a developmental prototype of such an underwater communication system.
The Flying Plug system consists of a potentially expendable underwater vehicle and a reusable underwater docking station called the Socket. In order to reduce recurring costs, the vehicle itself consisted only of a minimal wet-end system, which provides propulsion, homing sensors, electrical energy and data couplers. The vehicle would be autonomously guided by signal processing and control computers located at its launch point by means of a deployed FOMC, and all signal processing and command/control associated with the Flying Plug is performed via its FOMC.
The Socket acts as a transponder during the initial homing phase, which is accomplished acoustically, and additionally provides a light source to support the terminal docking phase, which is implemented optically. Once docked, the vehicle's body is latched into place by moveable pins in the Socket in order to line up pairs of optical data couplers located in the Flying Plug and the Socket.
The FOMC used to guide the vehicle can then support data transfer. Optical data transmission via the FOMC permits rapid transfer of bidirectional data between the Flying Plug's launch point and the data source connected to the Socket. After data transfer is complete the Flying Plug undocks and either scuttles or returns to the surface for refurbishment, depending upon the specific mission.
The Flying Plug concept was also a key component of SSC San Diego's Distributed Serveillance Sensor Network (DSSN).
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