Testing Sea Hunter

Excerpt from "A look to the future: USN research stretches from advanced systems to microbial power"
Publication: Jane's International Defence Review
Date Posted: 29-Sep-2017
SSC Pacific is leading the testing of the Defense Advanced Research Projects Agency (DARPA) and ONR’s Sea Hunter USV, formerly known as the anti-submarine warfare (ASW) continuous trail unmanned vessel (ACTUV).
Sea Hunter is a 132 ft (40.23 m)-long trimaran, just under 50 ft (15.24 m) across the beam. It was built by Leidos to have a wide beam to give the vessel stability and speed, up to 27 kt in every Sea State it has so far operated in. Sea Hunter has a 20,000 lb (9,071.84 kg) payload.

The 40.23 m-long Sea Hunter USV pier side in San Diego. The vessel is continuing COLREGS testing as DARPA prepares in the coming months to turn it over to the US Navy. (IHS Markit/Geoff Fein)
The intent is for Sea Hunter to be able to conduct a continuous 79-day mission. During a mission, Sea Hunter may not have all of its systems operating at 100%, but it will be able to make it back to port.
“If you look at what we have done with UAVs, they are now routinely operated as part  of conducting warfighting operations. But we haven't really made the stretch for the surface navy,” Russell said. “So [Sea Hunter] is the first step towards really making the surface navy unmanned.”
Initially a DARPA- funded programme, the agency will soon hand Sea Hunter over to ONR to focus more on naval uses for the vessel. SSC Pacific is conducting the test and evaluation on much of the autonomy that is being developed.
Because Sea Hunter is a lower-cost maritime platform, there is a presumption by many that if it is capable of operating on its own, the navy might be inclined to buy more of the vessels.
“If we can increase warfighting capability without building very expensive platforms, that is a total change in the economics of how we are going to do business and how we do warfighting,” Russell said. “Our targets now are much lower-cost targets and they are hard to defeat if you have many of them. [It puts] a little bit more of a challenge on our potential adversaries in terms of how they will fight us when there are multiple lower-cost targets.”
However, before the navy considers procuring more of the USVs the service has a lot of work to do with understanding how Sea Hunter will fit into the fleet.
“Frankly, the navy has to understand the CONOPS [concept of operations] – how we would use these vehicles, understanding if a technology is viable enough, and what systems you might put on there to increase the capability of these unmanned platforms. [Those are] areas of research that we are focusing on,” Russell said.
Currently, Sea Hunter testing is focused on COLREGS, the international regulations for preventing collisions at sea. It is a capability Sea Hunter, or any fully autonomous surface vehicle, must have.
COLREGS is analogous to what unmanned vehicle engineers and developers are working through
– how good does it have to be before testers decide it can move from being an experiment to being a fielded product, Scott Littlefield, DARPA programme manager for Sea Hunter, told Jane’s .
“The question the navy will eventually have to [answer] is how much testing is enough and how high a bar do you want to set in terms of your confidence that it's safe and reliable? That is a difficult decision,” he said.
Much of the early COLREGS testing involved the subject matter expert looking at the tracks and making a subjective judgement that not only did Sea Hunter behave in accordance with the rule, but whether it looked good in a more subjective way, Littlefield said.
“Now we are trying to apply a little more rigor in terms of scoring each COLREGS run in terms of: not only did it obey the rule, but did it do that with a minimum number of course and speed changes and with the minimum amount of excess travel out of the way of its path to the next waypoint?” he said. “By coming up with a numerical score like that it will be easier for us to track progress over time in terms of: are we really getting better?”
There is also a lot of analysis not only looking at the progress Sea Hunter makes, but trying to understand the COLREGS responses, both good and bad, and what went wrong and why it went wrong. Engineers then take that data and make software changes to fix the problems. They also have to go back and retest Sea Hunter to make sure that software changes have not introduced other problems, Littlefield added.
Over the last few months (and going well into next year) SSC Pacific set up COLREGS test scenarios where other craft worked with Sea Hunter. The USV performs manoeuvres with a safety officer and crew [onboard] to protect the craft and other vessels around it,” Jerry DeJaco, SSC Pacific test director for ACTUV, told Jane’s .
The safety officer is stationed in a temporary operations control station (TOCS): a small deckhouse that is bolted to Sea Hunter and can be removed once there is no longer a need for a human on board.

Looking from the bow towards the deckhouse/TOCS on Sea Hunter in San Diego. A safety officer is stationed in the TOCS during all COLREGS testing. (IHS Markit/Geoff Fein)
Because Sea Hunter was not designed to sustain personnel, there is no galley, berthing, or bathrooms on board, making it a tough job to be at sea for 8–9 hours during testing, DeJaco said.
Setting up a COLREGS scenario requires a few basic things, Littlefield noted, for example, other craft crossing from the right, crossing from the left, and seeing if Sea Hunter will exhibit the correct behavior and follow the rules. On a good day of testing, researchers can get about six of those done.
“You can imagine all the different scenarios you can launch and run through, and then if you want to really get statistics, what percentage of the time does it do what you expected it to do. It is very slow and difficult to get that,” he said. “In a good week of testing we can typically get 20 data points.”
Sea Hunter’s deckhouse is fitted with communications equipment and antennas. Towards the aft is a dual railing, which DeJaco referred to as roof racks. ONR is looking at possible payloads for the USV, including those that could be tethered to the railings. In fact, the first payload to be evaluated on board Sea Hunter was DARPA's Towed Airborne Lift of Naval Systems (TALONS), a prototype of a low-cost, elevated sensor mast.

Sea Hunter’s mounting railings, which enable the USV to carry payloads on its deck. (IHS Markit/Geoff Fein)
There is also ample space on Sea Hunter to carry additional fuel and batteries for extended endurance.
The safety features fitted on board Sea Hunter will be removed, in part because there will not be anyone on board and because the navy wants to make it difficult for people to board the vessel when it is at sea, DeJaco added.
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