Unmanned Systems Technology 007 | UMEX 2016 report | Navya ARMA | Launch & recovery systems | AIE 225CS | AUVs | Electric motors | Lethal autonomous weapons

45 Launch and recovery systems | Focus storage and refuelling/recharging pods. If drawn into the fuselage, where they would be accessible to the crew, they could have a sensor changed or be re- armed as well as refuelled. For the initial approach, a secure, encrypted data link enables the aircraft and the UAV to exchange speed and position data so that a rendezvous point can be calculated and updated, and flight path and speed adjustments made by the UAV autopilot. Precision guidance for final approach would involve an infrared light source in the centre of the drogue and an IR camera on the UAV’s probe, and the UAV autopilot could use a predictive probability-based approach adapted from a collision avoidance technique. With contact made, a latching mechanism secures the probe and a winch hauls in the UAV. Launch would be a simplified version of recovery, in reverse. From and to ships Ships have been launching and recovering boats over the side for centuries, and the types of crane and davit in service these days can trace their origins back many decades. Most are designed for fast rescue boats to comply with Safety Of Life At Sea regulations, while those aboard warships are also intended for more regular small boat operations, from helicopter guard to Visit, Board, Search and Seizure and special forces support. Slewing, C-frame davits and deckhead- mounted telescopic types with boats stored in bays are typical solutions. Recently these systems have been supplemented, and in some cases replaced, by stern ramps and, on larger vessels, floodable docks. Operations with maritime unmanned vehicles including USVs and UUVs have largely adopted these methods. Modern cranes and davits feature anti- pendulum devices designed to eliminate the swing, and heave compensation systems to take out wave motion are increasingly common. Modern davits with heave compensation can be used with the ship underway and in sea states up to 6. Many new ship designs now have stern ramps, which allow rapid launches and recoveries, with gravity launches typically completed in 10 s or less and with minimal personnel requirements. Recovery takes around 10-20 s. Ramps can be of either internal or extending design. The internal type is simpler, but requires stern doors that open far enough below the waterline to ensure that a manned boat or unmanned vehicle being recovered contacts the ramp above the sill at a shallow angle to avoid damage. That means the ramp sill depth must be greater than the draft of the vehicle being recovered. For example, the US Navy’s Freedom class of littoral combat ships feature a mission bay 3 ft above the waterline that contains a waterborne mission zone (WMZ) with an overhead crane to handle vehicles inside, including placing them on the ramp so that they can be deployed through the stern doors. With the doors open and the ramp deployed, the WMZ fills about halfway with water, illustrating one disadvantage of this approach – internal ramps remove significant displacement from the ship. An extending ramp allows for this even with doors that open above the waterline. Even so, the achievable sill depth is a limitation on stern ramps. The usability of stern ramps also decreases as sea state and ship size go up. In higher sea states, the boat or UUV’s response to the waves will be increasingly different from that of the mothership, rising and falling relative to the ramp to a point at which recovery becomes impossible. Even within these limits, recovering a manned boat requires the coxswain to pick the right moment to power up the ramp. Of course, a human operator could do the same thing using a remote control unit, but an autonomous vehicle would need motion prediction software and accurate relative position measurement to recover safely. Gone fishin’ One intriguing alternative to conventional methods proposes launching and recovering manned boats, USVs, UUVs and even UAVs over the stern with the ship underway using lines tensioned by a drag- producing depressor drogue deployed into a stable underwater region of the ship’s wake. The tensioned lines effectively form a launch ramp at a convenient angle, along which the vehicle is winched on a cradle. The developer claims that this system, known as Soft Rail, makes launches in conditions up to sea state 4 achievable, and that it is also fast, with manned boat launches in 40 s demonstrated. A Unmanned Systems Technology | April/May 2016 With wires tensioned and held stably at the correct angle by an underwater drogue/depressor akin to a fishing trawl, this launch and recovery system can be adapted to USVs, UUVs and even UAVs (Courtesy of Creative Technology Applications)