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This paper considers the subject of straight-line target tracking for unmanned surface vehicles (USVs). Target-tracking represents motion control scenarios where no information about the target behavior is known in advance, i.e., the path that the target traverses is not defined apriori. Specifically, this work presents the design of a motion control system which enables an underactuated USV to track a target that moves in a straight line at high speed. The motion control system employs a guidance principle originally developed for interceptor missiles, as well as a novel velocity controller inspired by maneuverability and agility concepts found in fighter aircraft literature. The performance of the suggested design is illustrated through full-scale USV experiments in the Trondheimsfjord.

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This paper presents a three-layered hybrid collision avoidance (COLAV) system for autonomous surface vehicles, compliant with rules 8 and 13-17 of the International Regulations for Preventing Collisions at Sea (COLREGs). The COLAV system consists of a high-level planner producing an energy-optimized trajectory, a model predictive control based mid-level COLAV algorithm considering moving obstacles and the COLREGs, and the branching-course model predictive control algorithm for short-term COLAV handling emergency situations in accordance with the COLREGs. Previously developed algorithms by the authors are used for the high-level planner and short-term COLAV, while we in this paper further develop the mid-level algorithm to make it comply with COLREGs rules 13-17. This includes developing a state machine for classifying obstacle vessels using a combination of the geometrical situation, the distance and time to the closest point of approach (CPA) and a new CPA-like measure. The performance of the hybrid COLAV system is tested through numerical simulations for three scenarios representing a range of different challenges, including multi-obstacle situations with multiple simultaneously active COLREGs rules, and also obstacles ignoring the COLREGs. The COLAV system avoids collision in all the scenarios, and follows the energy-optimized trajectory when the obstacles do not interfere with it. Keywords: Hybrid collision avoidance, Autonomous surface vehicle (ASV), COLREGs, COLREGs compliant, Model predictive control (MPC), Energy-optimized control arXiv:1907.00198v2 [eess.SY] 14 Jul 20192018, Falco navigated autonomously between two ports in Finland 2 . Reports state that in excess of 75 % of maritime accidents are due to human errors (Chauvin, 2011;Levander, 2017), indicating that there is also a potential for increased safety in addition to the economical and environmental benefits.An obvious prerequisite for autonomous ship operations is the development of robust and wellfunctioning collision avoidance (COLAV) systems. In addition to generating collision-free maneuvers, a COLAV system must adhere to the "rules of the road" of the oceans, i.e. the International Regulations for Preventing Collisions at Sea (COLREGs) (Cockcroft and Lameijer, 2004). These rules are written for human ship operators and include qualitative requirements on how to perform safe and readily observable maneuvers. Part B of the COLREGs concern steering and sailing, and includes the following rules that are the most relevant to a motion control system: Rule 8Requires maneuvers to be readily observable and to be done in ample time. Rules 13-15 Describe the maneuvers to perform in cases of overtaking, head-on and crossing situations. Participants in crossing situations are defined by the terms give-way and stand-on vessels. Rule 16Requires that a give-way vessel must take early and substantial action to keep clear of the stand-on vessel. Rule 17Consists of two main parts. The first part requires a stand-on vessel to maintain its course and speed, whi...