SMD's Rock Trencher 1 is currently the world's most powerful seabed tractor. Image copyright SMD.

Advanced Subsea Crawlers
Tech Level: 11
Manned Subsea Crawlers
Tech Level: 12
Mobile Underwater Habitat
Tech Level: 13
Mobile Drilling Station
Tech Level: 13

Subsea crawlers (also called seabed/subsea/underwater/ocean tractors or tanks) are remotely-operated vehicles designed to traverse the ocean floor. They use much of the same technology pioneered for AUVs (Autonomous Underwater Vehicles.) The main difference is that they usually use tracked transmission for propulsion on the seabed instead of propellers in the open water, and are not designed to float on their own. Crawlers may be built to be partially buoyant in order to offset some of their weight, and the smaller of them can be rigged with variable buoyancy systems to allow for greater mobility around obstacles and to surface for retrieval by tending ships.

Undersea crawlers have been employed in the real world for a number of years now, used for exploration, excavation, and the laying of underwater cables and piping. Most are designed to handle the wide variety of uneven surfaces encountered on the ocean floor. They are usually controlled through long cables, either connected to a surface ship or to a facility on land, if relatively near the shore. These cables not only handle communication, but can also supply power, and it the case of crawlers controlled by surface ships, serve as hauling cables for retrieval.

Subsea crawlers are not meant to be speedy vehicles. They designed with toughness and stamina in mind, as their applications usually require long-term stays underwater, sometimes beyond comfortable depths for divers or submersibles. Without the need for buoyancy, a crawler can typically pack a much heavier loads and battery packs than propeller-driven UAVs of comparable size. This endurance and ability to carry heavy machinery is what makes them very useful for industrial-sized tasks, like seabed excavation or laying undersea cable.

Tech Level: 11
South Korea's proposed Search and Rescue crawler.

As manned presence under the waves expands, undersea crawlers will likely find many new niches that may need their specific capabilities. Different types of subsea crawler present and future may include:

-- Cable Layer: Lays cable or flexible pipe over long expanses of the sea floor. May or may not be able to function as a cable maintenance crawler.

-- Cable Maintenance: Runs along already-laid cable or pipe to help spot or patch damaged sections.

-- Excavation Tractor: used to clear rocks and other debris for construction, such as for habitats or bridge pylons.

-- Exploration Probe: These are usually fairly small crawlers used exploration and scouting.

-- Search and Rescue Drone: Also usually small, these crawlers would be used to search suspected areas of shipwrecks for debris and ship remains.

-- Aquaculture Tractor: Used primarily for tending crops in seabed aquaculture.

-- Survey Crawler: Designed to do in depth, on-site mineralogical surveys of the ocean floor.

-- Mine Layer/Remover: A crawler designed to anchor cable for floating mines. A crawler would be advantageous over ships for increased stealth. Also can be used to remove said mines.

-- Mining Drone: Designed to actually drill or plant explosives for excavation.

-- Maintenance Drone: Designed for repairing and maintaining undersea structures. This may include underwater portions of mostly above-ground structures, like bridges.

-- Salvager: Used to help salvage and recover sunken vessels.

-- Construction Crawler: Used in the construction of subsea structures. Will have a number of analogs to land-going construction vehicles. I.e., bulldozer, backhoe, steamroller, etc.

-- Subsea Truck: Used to haul heavy loads that may be too big or unwieldy for available submersibles.

-- Weapons Platform: Would be slower than submersibles, but would also be stealthier (no propellers) and harder to pick up on sonar. They may carry conventional or supercavitating torpedoes to use against other sea-borne targets, or long-range strategic missiles for use against land targets.

Currently, all crawlers use tracked or wheeled transmissions. However, in the near future, crawlers using robotic legs could be feasible as well.

South Korea is currently researching small legged crawlers meant for search and rescue operations. Officials there believe that such units could have sped up search efforts of the Cheonan sinking incident in 2010, which took place in the West Sea with strong tidal currents and poor visibility.

The South Korean initiative envisions small six-legged crawlers armed with advanced sensors and variable buoyancy systems, allowing them to float and swim as needed with their legs acting as paddles or fins. Designs call for them to walk at speeds of up to 98 feet per minute and swim at up to 59 feet per minute. They could also operate at extreme depths, far below what divers or even conventional submarines could manage.

Legs on the ocean floor may be more advantageous than wheels or tracks in handling mud or silt covered surfaces. However, robotic legs are more complicated as well, and for operating at deep depths, this increases the chances for a malfunction.

Control of crawlers is usually by long communication cables. Power cables are still an option, but because crawlers can carry much heavier battery packs, they are not as much a necessity as on some other AUVs.

As computer systems advance, future crawlers may become semi- or fully autonomous. Semi-autonomous means they would be able to perform their assigned tasks with a minimum of human supervision (similarly to the Mars rovers Spirit and Opportunity), whereas fully autonomous means they may be able to actually make decisions on their own as to how best to proceed when encountering obstacles (like the small robots in the movie Silent Running.)

Cables may still be attached for both safety reasons and to allow a human to control the crawler via teleoperations if it runs across a truly formidable setback. Or the crawler may be fully on its own, and communicate with its human operates via Ultra Low Frequency radio or by occasionally sending up small, retractable antenna buoy on a long tether to the surface.

Tech Level: 12

Information on possible manned versions of this technology is very sparse; what follows is mostly speculation on the part of the author.

This is the straight-forward marriage of subsea crawler technology with existing submersible life support systems. Manned crawlers are preferable in situations where on-site human expertise is needed, such as in underwater construction and excavation, seabed aquaculture, rescue operations, and so on.

Manned subsea crawlers are often visualized as being underwater versions of land-based heavy duty vehicles, such as bulldozers, trucks, and so on. Buoyant craft such as submersibles will likely remain the primary means of transporting people, while crawlers will bear the burdens of the heavy work. However, because of their potential expense, manned crawlers may be made modular, with a central chassis with engine and life support module, designed to be fitted and modified with different tools and attachments as the job requires.

Open-pressure crawlers are possible, where the air pressure within the vehicle is equalized with the water pressure without. This would make exiting and entering the crawler while underwater much easier to manage. They would also be easier to engineer, build, and maintain than closed-pressure vehicles. However, most open-pressure vehicles could operate optimally only within about 30 meters of the surface; any lower and the operator may have to start dealing with various pressure-related complications. Even with compensating techniques such as specialized gas mixtures, the absolute deepest any such vehicle could safely operate would be around 200 meters or so, and even then the crew will likely start developing pressure sickness symptoms.

Closed pressure systems are another matter. Closed pressure systems maintain sea-level atmospheric pressure for the operator and crew no matter the actual depth. They are able to operate at much more extreme depths, but in general are more expensive and harder to engineer and maintain than open-pressure systems. Using contemporary technology, a closed-pressure manned crawler could possibly operate at depths down to approximately 1000 meters. In general however, the deeper it is designed to operate, the more difficult it will be to engineer and the more expensive it will be build. More advanced Tech Levels may allow for deeper operating depths and/or cheaper construction costs for the same performance.

Manned crawlers using robotic legs instead of treads or wheels are possible. In fact, legged vehicles may see their first real practical uses underwater instead of on land. Under the sea, the vessel can be made partially buoyant, taking a great deal of weight stress off the legs and allowing them to operate much more efficiently, at least as far as forward locomotion is concerned. Like in the proposed South Korean Search and Rescue crawlers mentioned in the last section, its also possible to equip the crawler with a variable buoyancy system, allowing it fully float and to use its legs as flippers or paddles for swimming.

Tech level: 13

Taking a cue from a proposal for creating a Moonbase, These would be similar to the manned, multi-person underwater outposts used today, such as the AQUARIUS habitat run by NOAA and the University of North Carolina, but outfitted with heavy-duty treads, wheels, or even legs to allow it to slowly move across the ocean floor.

The purposes of such a habitat may be twofold. First and foremost, it could operate as a mobile laboratory, exploring and observing the environment of the seabed. It may mostly operate along the shallows of the continental shelves, so that the crew can use an open pressure system and easily exit and enter the habitat on dives to collect and observe flora and fauna.

Secondly, mobile habitats could make it easier to create a larger underwater habitat. Two or more such habitats can be maneuvered into place and linked altogether through adaptive universal airlocks into a single base. They can also be reconfigured as needed if conditions change. Though mobile habitats may be more expensive than normal habitat modules, their use may make building a larger consolidated habitat easier and quicker, which may ultimately make up for the added building cost.

Tech Level: 13
An Ancient mobile geothermal drilling platform, from Stargate: Atlantis. Image copyright MGM.

The featured setting of the movie The Abyss, this was essentially an oil drilling platform designed to not only operate completely underwater, but also able to move itself to optimize its drilling location. A more advanced version of the idea was also seen in the ‘Submersion’ episode of Stargate: Atlantis.

The station in both sources was approximately as large as a modern seagoing drilling platform but with a sealed environment designed for long-term habitation under the ocean.

The Abyss version was an open-pressure system habitat, with large diving moon pool and a number of small excursion submersibles. Though the main habitat was open-pressure, the submersibles were closed-pressure, able to dive deeper than the station, but set at the pressure of the main habitat to allow easy access in and out.

Presumably the drilling station in the movie did not actually have to transport itself over hundred of miles to its drilling site, but was rather transported via ship like a normal drilling platform and lowered into place. Once on the seabed, it could adjust its own position for maximum efficiency. The station seemed to move itself on a series of massive treads, with anchoring stilts keeping it in place once it settles into a location. Moving speed was implied to be very slow, less than a mile or so an hour, but given its mass that was to be expected.

The mobile drilling station seen in Stargate: Atlantis, built by the uber-tech Ancients, was far more advanced. Its exact means of propulsion wasn’t disclosed, but it was implied that it could move itself at fairly good clip and could operate at depths of many thousands of meters. It was a closed pressure system that maintained the same atmospheric pressure as sea level.

Whereas The Abyss station was meant to drill for oil, the Stargate: Atlantis platform was meant to drill into various crustal hotspots and use them to generate geothermal energy.


Article added 30 November 2010