On 22 June 2016, contractor Leidos completed initial performance trials of the technology demonstration vessel it is developing for the Defense Advanced Research Projects Agency’s (DARPA’s) Anti-Submarine Warfare Continuous Trail Unmanned Vessel (ACTUV) programme. The at-sea tests took place off the coast of San Diego, California.
The company said the 132ft trimaran, named Sea Hunter in a ceremony in April, met or surpassed all performance objectives for speed, manoeuvrability, stability, seakeeping, acceleration/deceleration, and fuel consumption, as well as establishing confidence in the reliability of mechanical systems in an open-ocean environment.
Sea Hunter is designed to operate for extended periods at sea with no operator on board and only sparse supervisory control throughout deployment. While initial vessel tests require a pilot on board the ship, later tests are planned to have no personnel on board. The unmanned vessel has two diesel engines, one port, and one starboard, with two shafts, two reduction gears, and so two completely separate propulsion trains. With both engines, it is capable of around 26knots.
The completion of Sea Hunter’s performance trials is the first milestone in the two-year test programme co-sponsored by DARPA and the Office of Naval Research (ONR). The next round of tests is expected to include testing of sensors, the vessel’s autonomy suite, compliance with maritime collision regulations, and proof-of-concept demonstrations for a variety of US Navy missions.
As reported in the May 2016 issue of Warship Technology, pages 17-18, the ACTUV is designed to traverse thousands of kilometres over the open seas for months at a time, without a crew. Potential missions include submarine tracking and countermine activities.
The latest phase of the project dates to September 2014, when DARPA signed a Memorandum of Agreement with the ONR to jointly fund an extended test phase of the ACTUV prototype. DARPA is collaborating with the ONR to fully test the capabilities of the vessel and several innovative payloads during open-water testing.
Speaking at the time that the vessel was named, Scott Littlefield, DARPA’s programme manager, described the ACTUV as a “truck that can carry more payload over greater distances, stay out longer, and be more capable than anything else – and do it highly autonomously because it’s a big vessel and it’s got that flexibility.” Rear Admiral Robert Girrier, Director, Unmanned Warfare Systems (OPNAV N99) said he believed that the unmanned surface vessel “heralds the look and shape of things to come.” The Honourable Robert Work, Deputy Secretary of Defense, said programmes such as the ACTUV would enable the US Navy “to be a navy unlike any navy in history” and would help create “a human-machine collaborative battle fleet that will confound our enemies.”
Littlefield said the US Navy had been experimenting with smaller unmanned sea vehicles of many different kinds for at least a couple of decades, including unmanned undersea vehicles and unmanned surface vehicles. “But typically with the idea that they’re relatively small vehicles that are launched and recovered from another ship,” he explained. “What we are doing in this programme is building something that’s substantially larger; that’s actually designed to go directly from the pier out to an objective area and come back. It has enough range and endurance that it can get anywhere in the world from US territory. It doesn’t rely on a host ship to launch and recover it. So, that’s one of the important aspects of the programme.
High level of autonomy
“One of the things that this essentially requires and that we’ve been focused on in the DARPA programme is providing ACTUV with a high degree of autonomy. We didn’t want to simply build a remote control boat; we actually wanted something that could behave appropriately and do complicated missions under what we call sparse supervisory control. That means that there’s still a human being in control but the human being is not joy-sticking the vessel around.
“There were a number of things we had to do to achieve that,” he said. “One of the key things we wanted to show in this programme is the ability of an unmanned surface vehicle to reliably obey the rules of the road at sea, collision regulations or ‘COLREGS.’ Those are the International Maritime Organization rules for avoiding collisions at sea. A lot of the testing that we’ve done up until now has been on a smaller vessel, which we call the surrogate boat, which is just a 40ft workboat, but basically has the same software, similar computing plan, and the same sensors that will be on our full-scale ACTUV prototype. We’ve been taking that out to sea to show that it can in fact obey the rules of the road at sea and not run into other vessels and do that without a human being piloting it around.”
Littlefield said construction and testing of the ACTUV was “intended to give the US Navy a chance to see it, understand the technology, and eventually, make some decisions about whether or not to go beyond a science and technology prototyping programme and actually build ACTUV as an acquisition programme.”
He explained that although the test makes use of the concept of sparse supervisory control, there is still a human being at the end of the satellite link who is monitoring and controlling what ACTUV does. “But we try to put that in terms of mission planning, rather than actually piloting the vessel. For example, the human being would make a decision for ACTUV to go to a particular place in the ocean and loiter and wait for further instructions, and then ACTUV would plan the way points to get to that place in the ocean and would take appropriate manoeuvres to avoid collisions with other ships on the way there. Then, once it’s at that loiter point waiting for further instructions, then a human being would have to intervene to give it a specific mission, which might be go to another point in the ocean and commence a search looking for a submarine. Once it detects a submarine, then it would get into trail on that submarine. So, it could do those kinds of defined missions without continued human involvement, but anytime it changes mission, those would be in response to human commands.”
Asked about payloads for the ACTUV, Littlefield said: “We didn’t want to build a one-trick pony. We really want to build a truck that’s versatile to carry lots of different kinds of payloads. Under the DARPA programme, the primary payload that it comes delivered with is an anti-submarine warfare system, so basically, a sonar system that helps it find submarines. However, as part of our cooperative programme with the Office of Naval Research, we’re also looking at some mine countermeasures payloads, and in particular, a mine sweeping payload. Some of that is really to show the versatility of the vessel to do a lot of different kinds of missions. I think that’s going to evolve over time; we’ll think of new ways to use it. Because it’s big, it’s got the space and weight carrying capacity and electric power that’s needed to host a lot of different things.”
Another thing that DARPA and the ONR want to explore with the US Navy is having the ACTUV work with other vessels cooperatively, both with other unmanned vessels but also with manned vessels. Littlefield also highlighted other important points that distinguish the ACTUV from a manned vessel. “Obviously, people are necessary and vital for a lot of things we do. But at the same time, when you put people on a ship and send them into harm’s way you have to do a lot to protect them. So, one of the benefits that a vessel like ACTUV brings is it reduces the requirement for survivability features that are primarily there to protect the crew. Potentially, it allows you to build a smaller and less costly vessel, and also potentially put it in situations where you would not be willing to put a manned vessel. ACTUV isn’t exactly expendable but in a conflict it would OK to lose some of them if as part of the overall campaign that reduced the threat to your manned ships.
Keeping costs down
“The other thing that’s important about unmanned is really trying to reduce costs. We want to build something that is very affordable and that then allows the US Navy to procure them in large numbers, which helps us to solve some capacity problems. We have tremendous capability in our manned warships and I don’t know that we’re going to go beyond that capability, but it’s limited because we have a finite number of ships and the navy isn’t expected to get a lot bigger. We just can’t be everywhere at once with a manned vessel, and this gives us the ability to be a lot more places and do a lot more things simultaneously.
“At the beginning, we said that we would like to get to a series production cost of about US$20 million a copy, which isn’t cheap but certainly is much less expensive than a manned warship. Through the process of actually building the first prototype, we’ve been trying to keep track of what the actual construction costs were and it looks like we’re going to deliver the first one for a construction cost of US$22-23 million. In terms of the daily cost to operate the ACTUV, we’ve done a cost model and we think that when you get into an operational mode with a platform like this it’s in the region of US$15,000-20,000 a day.”