Like a power strip at the end of an oversized extension cord, the bright-orange MARS science node lies at the end of a 52-km (32-mile) cable connecting the unit to power and computers at MBARI. Electronics within the node can route electricity and data to up to eight science experiments, each of which may incorporate multiple sensors.

The MARS power and data cable follows a 52-km (32-mile) arc across Monterey Bay to the MARS observatory site. This curved route was chosen to avoid areas of rocky bottom and submarine landslides around Monterey Canyon. Along most of its route, the cable is buried about one meter (three feet) below the seafloor to minimize its effects on marine life and reduce the chance of its being snagged by anchors or fishing gear. In order to minimize the cable’s impacts, MBARI scientists spent over a year studying the effects of a cable that runs offshore from Half Moon Bay.

The MARS science node consists of two pieces: the massive orange “trawl-resistant frame” and the electronics package, which fits inside this frame.

The trawl-resistant frame consists of a truncated pyramid made of steel plates that is 3.7 by 4.6 meters (12 by 15 feet) wide at the base and 1.2 meters (4 feet) tall. This frame protects the node’s electronic components from boat anchors or commercial fishing gear. Its smooth corners and sloping sides are designed to prevent such gear from snagging. Doors on each side of the frame can be opened, allowing remotely operated vehicles to plug or unplug experiments.

The heart of the science node, the electronics package, consists of two titanium pressure housings suspended beneath a block of yellow buoyant foam. Inside one housing is electronic equipment for routing data and controlling power to the instruments. Inside the second housing is the equivalent of an electrical substation, to convert the high voltage in the cable to lower voltages used by science instruments.

The MARS cable carries 10,000 volts of electricity directly to the science node. This high voltage minimizes power loss as the electricity moves through the 52-km (32-mile) seafloor cable. Within the science node, transformers convert the 10,000 volts to an instrument-friendly 375 and 48 volts (DC).

Using the eight ports on the science node, each science experiment can send up to 100 megabits per second of data back to scientists’ computers on shore. Scientists, in turn are able to send commands back to reprogram or reset their instruments.

The trawl-resistant frame was installed on the seafloor during the cable-laying process. Later, the science node, with its yellow floatation pack, was lowered into the frame by ROV Ventana, a remote-controlled submarine. Each time a new experiment is added to the observatory, the ROV will use its robotic arm to plug an underwater “extension cord” from the experiment into one of eight “wet-mateable connectors” (waterproof power and data outlets) on the side of the science node. Once connected, each experiment will communicate directly with electronics in the science node or use a science instrument interface module to convert power and data from the science node so that they can be used by the experiment.