Unmanned Systems Technology 017 | AAC HAMR UAV | Autopilots | Airborne surveillance | Primoco 500 two-stroke | Faro ScanBot UGV | Transponders | Intergeo, CUAV Expo and CUAV Show reports

98 December/January 2018 | Unmanned Systems Technology PS | Searching for submarines A t the time of writing, the Argentine Navy’s submarine ARA San Juan and her crew of 44 had been missing for more than two weeks after reporting an electrical problem and then disappearing in the Gulf of St George in the South Atlantic (writes Peter Donaldson). The loss of communication, on November 15, led to a search involving a total of 27 ships, 30 aircraft and around 4000 people from 15 countries, but all to no avail by the end of November. It’s a stark reminder of the vastness of the oceans and the limitations of current search-and-rescue technology. Experts believe the cause of the submarine’s loss was a battery fire following a seawater leak and a short- circuit in the electrical system; this is supported by a transcript of the last message from the vessel. Unless it is located and recovered, however, the real cause may never be known. One could be forgiven for thinking that modern underwater systems, including manned and unmanned vehicles with advanced sensors of various kinds, should be able to find a submarine in such circumstances, but that is clearly not the case. Submarines are designed not to be found. They are the archetypal stealth platforms, and more technological effort has been put into detecting and locating them than any other category of vessel. Through two world wars, the Cold War and beyond, they have given governments around the world enormous motivation to find them. Governments and industry have invested huge sums in passive sonar to listen for sounds from a submarine – everything from propeller, gearbox and engine sounds and crews hammering desperately on the hull, to acoustic beacons and even the submarine’s own active sonar, one blast from which would result in its instant detection. Tactical active sonar, in its many forms and using both medium and low frequencies is routinely deployed from surface vessels, other submarines, fixed-wing aircraft, helicopters, UAVs and UUVs. Active systems put acoustic energy into the water in the hope of generating echoes that will detect and locate a submarine. Then there are side-scan sonars, synthetic aperture sonars and multi-beam echo sounders, which can all produce breathtakingly detailed images of the seabed and objects on it, particularly wrecks. However, none of them can offer the rapid coverage of large volumes of water that urgent searches such as that for the San Juan require, as any study of the maps of the search area and the tracks of the vessels and aircraft involved makes painfully clear. Arguably, large numbers of UUVs working in cooperative swarms and modifying their behaviour in response to what their sensors tell them represent the most promising approach to this kind of search. Sadly though for the San Juan ’s crew and their families, friends and comrades, that is not yet an operational reality. Ironically, when this kind of technology matures to the point where an uncooperative submarine could be found in time to save the crew, it would most likely spell the end of the submarine’s usefulness as a military platform. Now, here’s a thing “ ” More effort has been put into detecting and locating submarines than for any other category of vessel