For over a decade AUVs (autonomous unmanned underwater vehicles) have been used commercially for underwater research. For a decade the military has been using AUVs to monitor underwater conditions to assist submarine operations or even detect the presence of a passing submarine. What the navy wanted was a surface version, or ASV (autonomous unmanned surface vehicle). Now they have one; the Saildrone Explorer. This is a seven meter (23 feet) long vessel propelled by a five meter (15 foot) high sail and powered by solar panels on the sail. Underneath the Explorer are two fins that stabilize the ASV and maintain or change direction. Average speed is nearly six kilometers an hour. Range and endurance are virtually unlimited as the Explorer was designed to withstand rough seas and high winds. Many missions last up to a year, at which point the Explorer is directed to a location where it can be picked up, checked out and, if needed, have repairs made, upgrades added or a new sensor package installed.
Currently there are three sensor packages. The Metocean package monitors and records water salinity, temperature, dissolved oxygen, chlorophyll, wind speed/direction and wave height/duration. The Carbon package monitors atmospheric and dissolved carbon dioxide. The Fisheries package monitors ocean currents, fish biomass and backscatter. The navy wants to add an intel package that would monitor the presence of surface ships using day/night cameras, radar and radio receivers to detect the automated transponders all large vessels are supposed to carry. The Explorer has onboard GPS and a computer containing software that can determine which data is most significant and use the encrypted satellite data link to send it back to the Saildrone control center in California, where operators monitor the location of many Explorer ASVs and can send them instructions on where to move to next. Usually, an Explorer is given a route to monitor or traverse. This was tested, along with the durability of Explorer, when one made a 196-day voyage around Antarctica. During that voyage the ASV endured freezing temperatures, detected and avoided icebergs, and bumped into a few, while surviving 16-meter (50 foot) waves and winds of up to 140 kilometer (80 miles) an hour. This voyage covered over 24,000 kilometers (nearly 14,000 nautical miles). This epic test began and ended in New Zealand. So far Explorer ASVs have spent over 15,000 days at sea and none have been lost.
Explorer carrying a military intel sensor package would be more expensive and vulnerable to detection and destruction by hostile ships and aircraft. Saildrone is continually lowering the cost of the Explorer, which is already much cheaper than using a manned ship for this kind of data collection. The navy might find this ASV too vulnerable for wartime use, but effective when there is not a war going on.
Meanwhile the navy has lots of less detectable ASVs and AUVs in service. The latest is the Wave Glider SV3 AUV which also contains an underwater component, connected to the surface AUV float by an eight-meter (25 foot) cable that transmits power and data from the float to the underwater component, and data collected by the underwater component to the AUV float that contains solar panels and communications equipment to transmit position back to a land base via a satellite phone. This enables a surface ship to get close enough to use to collect all accumulated data from the Wave Rider and send new instructions about where Wave Rider is to search. The surface component weighs 90 kg (198 pounds) while the underwater portion weighs 155 kg (340 pounds).
Wave Rider has been around since 2007 as a commercial product. There have been two upgrades, the latest in 2017, enabled Wave Rider to operate in rough seas and farther north and south than previous models. Wave Rider can be used individually or in small groups to monitor ocean conditions as well as weather. Individual Wave Riders stay at sea for up to six months, or more, before being hauled aboard a ship for repairs, maintenance or upgrades. Basic Wave Riders cost about $300,000. That can increase by a third or more with some of the more expensive sensors available. Wave Rider data can be used for military purposes, but that is secondary to the task of monitoring the state of oceans in general. In 2012-2013 the record for Wave Rider duration was one that remained at sea for a year and traveled 14,000 kilometers from central California to northeastern Australia. Normally single or groups of Wave Riders monitor one portion of the ocean.
For over a decade the waters of the western Pacific have been increasingly populated by UUVs (Unmanned Undersea Vehicle) set loose to collect technical data on the water all the way from the surface to the sea bottom. The UUVs have been getting cheaper, more capable and proliferating.
These AUVs are silent, very small, and able to operate on their own for up to a year. The first models were two meters (six feet) long, weighed 59 kg (130 pounds) and operated completely on their own, collecting valuable information about underwater “weather”. What this AUV does is automatically move slowly (30-70 kilometers a day) underwater, collecting data on salinity and temperature and transmitting back via a satellite link every hour or so as the AUV briefly reaches the surface. This data improves the effectiveness of sonars used by friendly forces, making it easier to detect and track enemy submarines. That’s because the speed of sound traveling through water varies according to the temperature and salinity of the water. Having more precise data on salinity and temperature in a large body of water makes your underwater sensors (sonar, which detects sound to determine what is out there) more accurate. This data can also assist submarines in better avoiding detection. The first of these navy AUVs could dive as far down as 200 meters (620 feet) and later models were able to go down to 1,000 meters or more.
The Wave Rider is simply an advanced design based on the earlier underwater only AUVs. Wave Rider and the earlier UUVs use a unique form of propulsion. They have wings, and a small pump that fills and empties a chamber. This changes its buoyancy, causing it to glide down, then back up. This maneuver moves the UUV forward. Equipped with GPS and a navigation and communications computer, the UUV is programmed (or instructed via the sat link) to monitor a particular area. The small pump uses less electricity than a propeller moving the UUV at the same speed. As a result of this all UUVs UAVs can remain at sea for up to a year on one battery charge. Before the battery runs out the owner has to direct the UAV and a ship to a rendezvous where the AUV will remain on the surface and the ship will haul it aboard, replace the battery and perform any other needed maintenance.
Wave Rider uses the surface component to carry solar panels to recharge the battery and power more sensors. Small UUV maintenance detachments (of two or three sailors) can be flown to a ship that is close enough to make the rendezvous. In some cases, you can direct the UUV to move close to land, which makes it even easier to find a boat to go out and get the AUV. These UUVs can be launched from ships or shore. In 2009 an UUV of this type crossed the Atlantic on its own, as part of a civilian research project. A few years later a Wave Rider traveled even farther and crossed the Pacific.
The U.S. Navy currently has over 2000 of these UUVs and about twenty Wave Riders in service or on order and plans to keep increasing this robotic UUV fleet as long as they keep demonstrating they can do the job. This is part of a plan to have UUVs replace many of the ocean survey ships currently used for this kind of work. The survey ships take temperature and salinity readings from instruments deployed from the ship as well as a global network of several thousand research buoys. Unlike the survey ships the UUVs could be deployed in areas where hostile subs are believed to be operating, and be kept at it as long as needed. If successful in regular use, larger versions are planned, equipped with more sensors and longer duration.
