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Page 201 Zhu et al. Intell Robot 2022;2(3):200­222 I http://dx.doi.org/10.20517/ir.2022.13

Meanwhile, unmanned underwater vehicles (UUVs) are being developed, which can be divided into remote-
operated vehicles (ROVs) and autonomous underwater vehicles (AUVs). The motion planning and tracking
control of UUVs are assumed to be significant technologies for accomplishing efficient underwater navigation
with a guaranteed response time and without direct contact with marine dangers. Research on the underwater
motion planning and tracking control of UUVs originated decades ago and has been under the spotlight in
recent years. The history of UUVs can be traced back to the mid-20th century when an unmanned vehicle
[4]
was invented by the US Navy to recover a hydrogen bomb lost off the coast of Spain . In 2009, the success
of finding cracked pieces of Air France 447 realized by a UUV verified the vehicle’s promising application
in underwater navigation. In 2014, the search for flight MH370 also brought out the growing attention on
demanding underwater navigation, which highly depends on UUV motion planning and tracking control
[5]
technologies . Nowadays, detecting deep into the ocean area for digging more available resources such as
undersea oil development also requires the continuous progress of the UUV motion planning and tracking
[6]
control .

According to the statistics collected by Web of Science, the number of organizations that devote efforts to un-
derwater vehicle research has impressively increased in the past years. This trend corresponds to the growing
demand for underwater navigation worldwide, where studies of underwater motion planning and tracking
control are regarded as hot topics among UUV research projects. Underwater motion planning and tracking
control form the most crucial part of underwater navigation. UUV motion planning is established on conven-
tional or intelligent technologies of vehicle posture planning, task assignment, and path planning, while UUV
tracking control is mainly about vehicle trajectory tracking. The paper focuses on UUV task assignment, path
planning, and trajectory tracking controls. Task assignment is designed for the multi-UUV system, where
multiple vehicles are arranged simultaneously to achieve the most efficient collective navigating plan without
mutual interference; the path planning of UUVs aims at giving the optimal instruction to the vehicle for arriv-
ing at the target, which can largely save the time and reduce the energy consumption; and trajectory tracking
study of UUVs guarantees the robustness and manner of the vehicle operation in practical cases. However,
studies related to underwater motion planning and tracking control have not been thoroughly investigated
due to the complexity of the ocean environment and the vehicle system [7,8] . In addition, to overcome the diffi-
culty of accomplishing complex underwater operations, the multi-UUV system, which refers to the system of
multiple UUVs and multiple targets, has pulled great attention owing to its high parallelism, robustness, and
efficiency [9–11] .

Motivated by the goal of realizing efficient and robust UUV navigation in ocean environments, studies related
totheUUVmotionplanningandtrackingcontrolsshould besystematicallysurveyed anddiscussed to address
their potential in applications. Meanwhile, progress in this field can be promoted by analyzing the deficiency
and possible developments of the relevant technologies. Therefore, the contribution of the paper is to collect
and analyze technologies that have been and can be applied to the motion planning and tracking control of
UUVs. The benefits and drawbacks of these technologies are discussed, and challenges and prospects are
derived based on the gap in the literature. These analyses and conclusions are supposed to provide a brief
overview of studies that can be developed on certain issues for researchers at the entry level in the field of
UUV motion planning and tracking control.

In this paper, a brief review of the technologies regarding the UUV motion planning and tracking control
is proposed. The review investigates the current development of the motion planning and tracking control
achievedbyUUVsandthenderivesthechallengesaswellaspossibleprospectsofthestudy. Theintroductionis
givenin Section1. InSections2and3, thecurrentresearchstatusisdescribed. MethodologiesofUUV motion
planning are organized into divisions of task assignment and path planning. In the tracking control section,
the trajectory tracking methods of the UUV are surveyed. In Section 4, challenges and possible prospects are
concluded and discussed.