Submarines: U.S. Robotic Subs Search For MH370 Wreckage


April 17, 2014: The continuing search for the missing Malaysian airliner (flight MH370) eventually involved a lot of U.S. Navy resources. One of the key ships now being used to search for wreckage on the ocean floor is an American AUV (Autonomous Underwater Vehicle) called Bluefin. This particular robot has been around for a decade, but rarely made it into the news.

Back in 2004 the U.S. Navy and Coast Guard were still evaluating Bluefin, which looked like a torpedo. That was no coincidence as Bluefin used some components found in lightweight (320mm/12.75 inch) torpedoes. The original Bluefin was 2.9 meters (112 inches) long, 32 cm in diameter and weighed 137 kg (300 pounds). It could stay under water (at depths of up to 200 meters/650 feet) for 12 hours (moving at 5-6 kilometers an hour). It had an inertial navigation system, but could communicate with a surface ship via acoustic signals.

The Bluefin type AUVs were first developed for civilian use (for Ocean Science and Engineering work as well as oil exploration.) The militarized Bluefin looked a lot like the civilian version and is many times smaller than the previous generation of AUVs. There were already larger versions of Bluefin that could fit in the standard (53 cm/21 inch) torpedo tubes of submarines. But the original Bluefin evaluated by the navy was intended for use by surface ships for things like clearing mines and mapping the sea bottoms in coastal waters. The U.S. Navy’s new LCS (Littoral Combat Ship) was designed to carry, and use, several AUVs, UAVs and USVs (Autonomous Surface Vehicle).

The appearance of something like the Bluefin should be no surprise. The American Mark 48 torpedo, introduced in 1972, were constantly upgraded with additional electronics and improved maneuverability. While the Mark 48 weighs nearly two tons, most of that is the warhead and the powerful motor that drives it at up to 50 kilometers an hour. Replace that with newer, lightweight gear and you have something like Bluefin.

The navy eventually adopted the larger version of Bluefin, called Bluefin 21. This one was the size of a standard torpedo (53cm diameter) and is 4.9 meters (16.2 feet) long and weighs 750 kg (1,650 pounds). It is designed to operate at depths of up to 5,000 meters (16,500 feet). Its batteries allow it to operate for up to 25 hours, moving at a speed of 5.5 kilometers an hour. It carries sonar and solid-state memory storage of four GB for the operation of the AUV plus multiple TB (thousands of GB) storage for recording sonar data.  It carries several navigation systems and instruments to enable it to operate reliably.  Bluefin 21’s primary job is finding mines but can also be used to map the ocean floor at great depths. That capability is being used to find the MH370 wreckage.

Chemical monitors, cameras, and various other instruments can also be carried by Bluefin. For clearing mines, an AUV basically goes near the sea bottom and uses it's sonar and camera to map a lane clear of anything resembling a bottom mine (a mine that sits on the sea bottom but can detect a ship passing above it and detonate a large enough charge to sink a ship or sub.) Once a mine has been identified, another AUV goes down and drops an explosive charge on the mine, scoots away and the mine is destroyed. Several AUVs, controlled by their own software, can work on clearing a path free of mines for ships. Human operators only have to intervene to confirm that a mine has been found, and then send another AUV to destroy the mine. The U.S. Navy has a growing number of Bluefin 21s, which are seen as a major defense against the growing naval mine threat. Bluefin 21s can be quickly flown to any part of the world and put to work from just about any ship with a crane (to out Bluefin into the water and take it out again for battery recharging, data transfer and any needed maintenance). A Bluefin can map about 90 square kilometers of seabed a day and the search area could ultimately grow to include over 600,000 square kilometers but for the moment the search is concentrated on 600 square kilometers of ocean bottom. Each daily mission includes two hours getting to the ocean floor 4,500 meters below and two more hours to come back up. It then takes several hours to ready the Bluefin for another mission. This search operation will be the longest time so many Bluefins have spent at these extreme depths and searching 600 square kilometers could take up to 60 days.

Most manned subs cannot go deeper than 500 meters. Some special research subs can go down to nearly 11,000 meters (the deepest part of the oceans, off the east coast of the Philippines).  Bluefin is a lot cheaper to operate even though it can only go down to about 5,000 meters.



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