Primary or Backbone Cable
The OOI RSN relies on telecom industry sub-sea cable to provide power (10 kV DC, up to 8 A) and communications (10 Gb/s) via fiber-optics and copper between the Primary Nodes and the Shore Station. These cables are routinely deployed across ocean basins and margins for long lifetimes; they generally become obsolete before they fail (see Wet Plant Primary Infrastructure White Paper, 2007). The backbone cable was installed Summer 2011 using the commercial cable laying ship, the TE SubCom Dependable.
Approximately 900 km of primary cables were installed from the Shore Station in Pacific City Oregon to the Primary Nodes locations at seven different sites. These include PN1A at the base of the subduction zone west of Newport Oregon, PN1B at Southern Hydrate Ridge, PN1C at a 600 m site on the Newport margin, PN5A in the middle of the plate, PN3A at the base of Axial Seamount, and PN3B at the summit of the volcano. The primary nodes are being installed in summer 2012. A major function of the Primary Nodes is to pass power and bandwidth on to nodes further offshore, e.g. Primary Node 5 will send power and bandwidth on to Primary Node 3A. One line of the backbone/primary cable connects the OOI RSN to the Coastal Scale Nodes (CSN) Endurance Oregon Line. Extension cables to Low-Voltage and Medium-Voltage Nodes are part of the Secondary Infrastructure, providing power and bandwidth to myriad sensors and instrumented full water-column moorings.
Extension Cables provide power and communication links between the Primary Infrastructure, Secondary Infrastructure, and instruments. Extension Cables link Primary Nodes to LV Nodes to J-Boxes, and to instruments across the RSN. This cabling will be installed in various seafloor conditions from harsh areas (sharp rocks, inside the caldera of an active undersea volcano, across an active fault line) to benign areas, and will be powering different types of loads, therefore different types of cables are necessary. Primary Nodes are set at depths down to ~3000 m and extension cables link to elements along the bottom and from the bottom to near the surface. The additional details are described in the RSN Secondary Infrastructure White_Paper, 2007 and in an update here. All extension cables have been documented in terms of their power/communications requirements and in consideration of special environmental requirements. This includes various levels of armoring for deployments in volcanic areas such as the flanks and caldera of Axial Seamount. These are included in the block diagrams and budgeted appropriately.
Two fundamental characteristics of the RSN as part of the OOI are the ability to expand the coverage area and number of sensors, and the ability to operate for over 25 years. To support this, ROV wet-mate connectors are used in many of the extension cable assemblies to allow for additional cables to be added to the system and for existing components to be temporarily removed from the system for maintenance.