China has a vast area of territorial waters and jurisdiction over an area of 3 million square kilometers of sea. With a coastline of over 18,000 kilometers, the coastal areas are densely populated and a major economic activity zone. As a result, the maritime regulatory tasks are arduous. Currently, China’s ports and coastal areas have established maritime regulatory systems that include Automatic Identification Systems (AIS), Vessel Traffic Management Systems (VTS), Very High Frequency (VHF) communications, and Closed Circuit Television (CCTV) monitoring systems.
Regarding airborne maritime regulatory methods, some maritime departments have introduced small fixed-wing unmanned aerial vehicles (UAVs), unmanned helicopters, and quadcopters for daily river, port, and channel patrols, ship exhaust monitoring, and marine environmental monitoring. Currently, the airborne regulatory platforms are concentrated in micro and small UAVs, which mainly operate near the coast as a supplement to other regulatory methods. There is still a significant lack of airborne maritime regulatory methods for deep-sea areas.
Currently, China’s maritime regulatory efforts in deep-sea areas such as the South China Sea mainly rely on patrol and law enforcement vessels. However, there are limitations in terms of slow speed, poor visibility, restrictions due to sea conditions, and high maintenance and operating costs, which limit the effectiveness of regulatory efforts. The “Fourteenth Five-Year Plan for the Development of the Maritime System” points out the need to “improve deep-sea safety regulation and navigation guarantee capabilities, focus on building a comprehensive ‘water-based traffic management’ system with all elements, establish a new model of cross-regional, multi-level, and full-coverage water-based traffic management, promote comprehensive control of ship dynamics in China’s jurisdictional waters, efficient on-site law enforcement, and effective response to emergencies.” Solar-powered UAVs, as a new concept electric aircraft, have the characteristics of long flight time, wide coverage, and high-altitude operation capabilities, and possess the characteristics of “quasi-satellites,” making them very suitable for remote maritime patrol and monitoring, as well as emergency response requirements. The application of solar-powered UAVs in maritime regulation is beneficial for constructing an integrated “land-sea-air-space” water-based transportation safety system, achieving “being able to reach, see, transmit, and manage,” and comprehensively ensuring China’s maritime rights and strategic interests.
Features of Solar-powered Drones
Compared with traditional aircraft, solar-powered drones have three remarkable features.
Firstly, they can fly high, but their payload capacity is relatively weak. Solar-powered drones usually adopt a high aspect ratio aerodynamic layout with a high lift-to-drag ratio, and can fly up to a maximum height of 30 km. At the same time, the drone’s wing loading is low, the weight of the whole aircraft is small, and the load capacity is weak. A solar-powered drone with a wingspan of 60m has a load capacity of 30-50 kg.
Secondly, they can fly for a long time, but there are many limitations to power extraction. Solar-powered drones do not consume fuel and can achieve ultra-long endurance flights for several months or even longer. However, solar cell conversion efficiency and energy storage battery-to-weight ratio have limitations, and the power supply capability is relatively weak. Its power supply capability is directly related to the intensity of sunlight and is suitable for use in low to mid-latitudes.
Thirdly, they have simple maintenance and low life-cycle costs with great potential. From the perspective of maintenance and support, the on-board system of solar-powered drones is simple, and the daily maintenance complexity is low. The long-endurance flight interval requires less maintenance and support. From the perspective of takeoff and landing support, solar-powered drones usually require a low speed of around 10 m/s for takeoff, and have low requirements for runway length and traditional refueling and other support equipment are not required. From the perspective of utilization benefits, due to their ultra-long endurance characteristics, compared with conventional aircraft, they do not require frequent replacement and rotation to complete long-term tasks, and the scale of aircraft deployed is greatly reduced.
Advantages of Solar-powered Drones
Solar-powered unmanned aerial vehicles (UAVs) have the notable ability to stay airborne for extended periods of time, hovering over designated areas as a stationary aerial platform, while also possessing the maneuverability to adjust their deployment location. Compared to small micro fixed-wing and rotary-wing UAVs, as well as large and medium fixed-wing UAVs, solar-powered UAVs are particularly suitable for maritime regulatory tasks with long mission durations (lasting over a week), located far from land and islands, and covering vast areas in low to mid-latitude sea areas.
Evaluating a solar-powered UAV with a wingspan of 60 meters, it is suitable for carrying lightweight, low-power task loads weighing no more than 50 kg, with power requirements ranging from several hundred watts to 1 kW. Its primary operating altitude is in the relatively stable stratosphere, where it can provide a platform for carrying on-board AIS communication terminals to perform wide-area dynamic ship monitoring tasks in deep-sea areas. It can also carry communication relay loads to provide emergency communication and network linking services, carry small-scale maritime search and tracking radar to provide maritime target search, tracking and monitoring services, or develop photovoltaic payloads suitable for high-altitude flight (above 20 km) to provide maritime surveillance and target verification services. Solar-powered UAVs have a large coverage area, with an average flight speed of around 100 km/h, capable of meeting the needs of tracking and monitoring low-speed civilian ships for the entire journey, with a day-and-night maneuvering range exceeding 2,000 km. They require low takeoff speeds and minimal runway length, allowing them to take off from inland airports. Compared to medium and large-sized cruise enforcement ships and manned aircraft, solar-powered UAVs have a low overall life-cycle cost and great potential.
“Land-Sea-Air-Space Integration” Maritime Regulatory System
In response to the shortcomings of the existing maritime regulatory system in deep-sea and large-scale maritime supervision, and leveraging the high-altitude persistence advantage of solar-powered drones, the solar-powered drone is incorporated into the existing maritime regulatory system. As shown in Figure 2, a “land-sea-air-space integration” maritime regulatory system is established, including onshore maritime regulatory systems, offshore patrol and law enforcement vessels, manned aircraft, near-space solar-powered drones, and space satellites. This forms a three-dimensional regulatory architecture with high and low matching and far and near connections, extending the normalized maritime regulatory capabilities from coastal waters (20 nautical miles) to waterways and island reef areas far from the mainland.
When performing maritime supervision and law enforcement tasks in deep-sea and far-ranging areas, the main enforcement force consists of solar-powered drones, cruising law enforcement ships, and manned aircraft. Solar-powered drones can make up for the shortcomings of law enforcement ships in terms of speed, coverage range, response speed, and the range and duration of manned aircraft. The solar-powered drone includes a line-of-sight link and a satellite link, with a control distance of more than 300 km in the line-of-sight link and can be reached within the satellite beam coverage range in the satellite link. The drone ground station combines control, communication, and data processing functions and is mobile, making it deployable on the mainland coastline or islands and reefs. The ground station can transmit drone mission payload information to the maritime command center through ground networks, satellite communications, and other means. The command center gathers reconnaissance information from drones, manned aircraft, and law enforcement ships to form a comprehensive analysis of the situation on the sea surface and directs the next action of each platform.
Solar-powered unmanned aerial vehicles for maritime regulation
(1) Dynamic regulation of ships in open sea
Taking the South China Sea as an example, it is an area of vast sea territory with busy maritime traffic, complex maritime situations, and constant conflicts over fisheries between coastal countries for many years. Illegal fishing, fishermen detentions, and other incidents have become severe challenges to maritime safety in the South China Sea. In particular, the normalization and even organized illegal intrusion activities of Vietnamese fishing boats into China’s nearshore waters and waters adjacent to islands and reefs in the South China Sea pose great challenges to the traffic regulation, fishing ban management, and law enforcement of frontline maritime and coast guard departments. According to the South China Sea Strategic Situation Awareness Plan, hundreds of Vietnamese fishing boats invade China’s internal waters, territorial waters, and exclusive economic zones in Guangxi, Hainan, and Guangdong for illegal fishing and espionage every month. The activities of Vietnamese fishing boats in the Xisha and Nansha waters are even more rampant. In December 2021 alone, 78,478 trajectory points of 6,760 Vietnamese fishing boats were recorded by AIS in the entire South China Sea. Considering that many Vietnamese fishing boats intentionally turn off their AIS terminals, modify AIS information, etc., the actual situation could be even worse. In such cases, it is challenging to track the movement of ships using existing regulatory methods. Solar-powered unmanned aerial vehicles can be used to monitor the activities of distant sea vessels.
When conducting maritime surveillance, solar-powered unmanned aerial vehicles can perform three types of mission modes: broad-area search, area stationary hovering, and target tracking. The broad-area search mode allows solar-powered unmanned aerial vehicles to conduct continuous reconnaissance and surveillance of a large sea area due to their advantage of continuous aerial presence. They can use AIS and SAR radar to obtain situational information about maritime targets and transmit the data to the shore-based command center for data processing and situational information fusion. The command center can obtain dynamic navigation information of maritime targets in the distant sea and identify illegal ships by comparative analysis (some ships may evade regulation by modifying AIS information, such as changing the ship type from fishing boats to merchant ships, modifying size, sharing a single maritime mobile satellite service identity (MMSI) number with multiple fishing boats, turning off AIS, etc.), providing information support for the next action plan of frontline law enforcement departments. The area stationary hovering mode uses solar-powered unmanned aerial vehicles for continuous high-altitude surveillance and communication relay activities in key sea areas to make up for the deficiency of the current methods in regulating the dynamic regulation of ships in open sea and the lack of the effectiveness of the Long-Range Identification and Tracking System (LRIT).
In addition, under the target tracking mode, solar-powered unmanned aerial vehicles can continuously track and monitor foreign ships invading China’s sea areas, ships engaging in illegal discharge, smuggling, and illegal immigration, etc., based on task instructions from the command center. They can use electro-optical reconnaissance payloads for evidence collection, voice communication payloads for shouting warnings or demanding the ship to stop for inspection, etc., to assist law enforcement vessels in maritime rights protection and law enforcement, significantly improving the efficiency of law enforcement vessels.
The task profile of a single solar-powered unmanned aerial vehicle is shown in Figure 4, with daily maintenance and support work carried out at the shore-based base before takeoff, loading and debugging of payloads according to mission requirements before takeoff, and planning for long-duration flight missions, etc.
(2) Emergency Maritime Rescue
In China’s key sea areas for maritime transportation, such as the Bohai Bay, the Yangtze River estuary, the Taiwan Strait, the Pearl River Delta, and the Qiongzhou Strait, a relatively complete salvage network has been established, which is centered on various levels of maritime search and rescue centers for command and coordination. It includes several rescue bureaus, salvage bureaus, rescue helicopter teams, rescue bases, and aviation rescue bases, with the ability to arrive within 1.5 hours in coastal key areas (within 50 nautical miles).
When a sudden event occurs, such as a collision between ships, large-scale pollution, or ship fires, the primary task of emergency rescue is to quickly obtain the situation at the scene of the event, so that the command center can carry out effective emergency command and dispatch according to the actual situation. For near-shore emergencies, rescue forces such as ships and rescue helicopters can quickly rush to the scene, and with the help of near-shore supervision and communication systems, they can quickly obtain the emergency situation and direct on-site forces to carry out rescue work. However, for emergencies in the open sea, there is a lack of the ability to quickly obtain and efficiently transmit on-site information.
Solar-powered unmanned aerial vehicles (UAVs) equipped with high-definition photoelectric reconnaissance equipment (or SAR radar), AIS, and VHF equipment, utilize their own long-time airborne capabilities and fly in a normal patrol mode during peacetime. In the event of an emergency or upon receiving relevant instructions, they fly to the emergency site to perform information security operations according to planned instructions.
Emergency report stage: After the occurrence of a maritime emergency, the distressed ship and personnel send out distress alarms through special communication equipment or regular communication methods. The onshore duty organization receives the alarm, preliminarily confirms the information and responds to the emergency.
Solar-powered UAV emergency response: Based on the situational assessment, the onshore command structure calls upon solar-powered UAVs patrolling over the task sea area for emergency support tasks. The UAV operation team modifies the UAV flight plan according to the task instructions and maneuvers to the emergency area upon arrival, hovering over the scene. Utilizing the AIS, reconnaissance equipment (optical or radar), voice communication payload and other equipment, it searches, identifies, confirms and locks the emergency target within a certain time frame, and continuously observes the target after locking it, transmitting the reconnaissance information such as images and videos to the command center in real-time.
Solar-powered UAV rescue support process: Prior to the arrival of professional rescue forces, based on the UAV reconnaissance results, the command center can immediately communicate with nearby ships to participate in the rescue in the emergency area and dispatch rescue aircraft and professional search and rescue ships to rescue. The solar-powered UAV continues to transmit image and AIS information collected by the UAV to the command center. After other emergency forces arrive at the emergency site, the UAV constructs a “machine (this system)-ship” or “machine (this system)-machine” information transmission link through the configured airborne and shipborne communication equipment, transmitting the collected image information to other emergency forces and transmitting the image information obtained by other emergency forces back to the command center. The “shore-machine (this system)-ship” or “shore-machine (this system)-machine” voice communication system is established through the onboard VHF system, enabling communication between the command center and emergency forces on-site.
End of emergency support stage: The solar-powered UAV ends its emergency support task and continues to perform task area surveillance and patrol tasks or returns to the base according to subsequent task arrangements.
On the Implementation of Solar-powered Drones
(1) Increase in Payload Capacity
The main limiting factor for the application of solar-powered unmanned aerial vehicles (UAVs) in maritime regulation is their payload capacity. Currently, the effective payload weight of mainstream 60N wing-span solar-powered UAVs is around 50 kg, which cannot simultaneously carry AIS payload, small-sized SAR radar, voice radio, electro-optical reconnaissance payload, and other equipment on one aircraft. Therefore, it is suggested that UAV R&D departments continue to explore weight reduction and power supply potential of UAV platforms. At the same time, specialized lightweight and low-power maritime regulation payloads suitable for the nearby space environment need to be developed rapidly. Through means such as equipment weight reduction design, power distribution, and integrated environmental control, the payload capacity can be improved to meet the ability to carry AIS + small-sized SAR radar (or electro-optical reconnaissance payload) + voice radio on a single aircraft.
(2) Analysis of UAV Operation and Management Modes
According to the use of manned and unmanned aircraft by various directly affiliated maritime bureaus of the maritime system, the current operation and management modes of maritime aircraft include system construction and purchasing services. System construction includes three modes: fully autonomous operation and maintenance, fully managed, and managed with personnel on board.
Solar-powered UAVs are highly compatible with maritime business and can perform multiple maritime patrol and emergency response operations simultaneously for a long time. It is recommended that the maritime department adopt a self-built system. Considering the large model and complex system, to ensure efficient and stable operation, it is recommended to use the managed with personnel on board mode after the system is built.
(3) Requirements for Takeoff and Landing Sites
The takeoff speed of solar-powered UAVs is low, and the requirement for runway takeoff and landing length is low, typically a few hundred meters is sufficient to meet the takeoff and landing requirements. However, solar-powered UAVs have a large wingspan and require an airport level of 4E or above. Considering the strong cross-regional maneuverability of UAVs, inland airports with less busy transportation can also be chosen as takeoff and landing bases. The lateral wind resistance and headwind resistance of UAV takeoff and landing are relatively poor, and the maritime department can also build a dedicated circular runway airport to expand the takeoff and landing window of UAVs. In addition to the runway, to ensure the normal operation of the UAV system, it is also necessary to rely on the airport to provide UAV hangars, supporting rooms, outdoor deployment sites, and related supporting facilities to meet the needs of UAV system equipment storage, maintenance and debugging, daily office, duty, and training, etc.
Translated from the article of Xiamen UAV Association by Mugin UAV.