Author: Ioseba Tena, Global Business Manager – Defence and Robotics
In the early days of unmanned underwater vehicle (UUV) development, people were touting their future potential as a submarine replacement. Many were skeptical, many still are. Replacing the human is no easy task. Our ability to reason, adapt and deal with changes is not easily replicated.
Back then, the challenges were thought of as being insurmountable. Instead, we focused on developing smaller platforms operated by human crews from vessels of opportunity.
These smaller UUVs have demonstrated excellent value for money. They are used to produce great quality seafloor data products at an affordable rate. They are also constantly getting better. As a result expectations have become more demanding. Today, a common set of emerging requirements are to extend UUV’s range, endurance and autonomy. The US Navy’s Orca programme is leading these developments. Others are following closely. For example, the UK has requested proposals to help inform future capability and understanding. The aim is to send an autonomous underwater vehicle (AUV) on its way and have it run for months or years, gathering vast amounts of data. This means more batteries (a lot more batteries) and, as a result, much larger AUV systems. Oh yes! And new sets of challenges too.
Launch and recovery, challenge solved
If you have operated a UUV you will be familiar with different launch and recovery concepts. Placing a UUV on the water’s surface from a ship is a simple task that gets progressively more complicated as the sea state worsens. Recovering a UUV from the sea and on to the vessel is hard, even in calm waters. As UUV systems become larger, the process becomes more challenging. However, an extra-large UUV (XLUUV) equipped with enough batteries to last for months does not need to be launched from a vessel, nor will it need to be recovered onto one. On shore operations will be possible; just deploy the AUV in a confined and safe harbour environment.
USVs can be deployed in support of AUV launch and recovery operations – transiting from the launch point to the open sea and providing the AUV with navigational data, as well as being a visible reference for other ships.
You can then track and communicate with it using acoustics, like our Ranger 2 Ultra-Short BaseLine system. These can be mounted on a small vessel of opportunity or the dockside. You can use Ranger 2 to guide the UUV to a safe UUV transit channel. The UUV will then travel to its mission location autonomously. When the mission is complete, the UUV will transit back to shore and, when in reach of our acoustic systems, we will communicate with it and track it so that it can safely make its way back into harbour. Longer endurance means the UUVs don’t need to be carried to the operations area – they can take themselves there.
Endurance like never seen before
When I say longer endurance, I mean it. Typical shallow water AUV operations last a handful of hours. Deepwater AUV systems can operate for up to 48 hours. The National Oceanography Centre’s (NOC) Autosub Long Range (ALR) has been designed to operate for up to six months. New, XLUUV concepts want to operate longer and to transit thousands of nautical miles. For their mission to be successful, they will need to know their position, with a high degree of accuracy.
That is a problem. If you’re familiar with our blogs, you will know by now that, underwater, there is no GPS coverage. That means that AUVs need to work out their position using other means. Traditionally, they have used inertial navigation systems (INS) aided by other sensors.Our instruments, when combined, can limit the error drift to 0.04% of distance traveled. That’s 4m after 10km of travel or 400m after 1000km. Great at short distances. Amazing value over longer distances. Using these instruments, it will be simple for the UUV to get to within the vicinity of their pre-programmed area of operations, surface for a GPS fix and run a survey.
The US is investing substantial sums on extra-large UUV systems. The UK is exploring options. It’s early days for these platforms, but submarine replacement certainly looks and feels a lot more feasible today than 20 years ago. This is more so for operations like intelligence gathering, where an AUV transits to an area of interest, gathers data and returns home. Sending a manned crew is ineffective and a lot riskier. The tools to enable the navigational and operational needs of these long-endurance vehicles are now ready to make those visions possible. It’s an exciting time to be working on robotics!