# Design of an Autonomous Cooperative Drone Swarm for Inspections of Safety Critical Infrastructure
## 3 Concept of Operation  
An inspection mission is defined as a data structure that describes the objective and the associated data concerning the mission type, the starting and ending locations, a geofence of the inspection, camera settings, etc. A mission is divided into a set of tasks e.g., recording images at defined locations relative to the inspection target. Tasks are allocated to drones of the swarm in the operation. The swarm of autonomous drones carries out the inspection mission by executing the tasks of the mission until all tasks have been completed. First, drones navigate to the starting location of the mission guided by a global path plan. A task allocation protocol decides the allocation of individual mission tasks to drones. The drone swarm continuously executes new tasks when a previously assigned task has been completed. An inspection mission is constrained by the available energy (battery charge) of the drones. Each drone will need to go through several charging cycles during an inspection mission. Drones report telemetry data such as location, velocity, currently assigned task, and charging level to a Ground Control Station (GCS), which continuously monitors the progress of an inspection mission. They connect to the mission control in the cloud to upload data (e.g., images and classified faults) from the inspection. When all tasks of the mission are completed, the drone swarm is retrieved from the inspection area.  
Figure 2a shows an activity diagram describing the inspection initiation process. When drones are turned on, they connect to GCS. Communication in a wireless mesh formation ensures the foundation for cooperative functions. A mission is assigned to the drone swarm by retrieval of the mission specification from the cloud services. A validation step ensures that initial settings are in place and that the drone swarm is ready to begin the inspection mission.  
Figure 2b shows an activity diagram for a task inspection for a single drone of the swarm. The process presumes that the mission has been initialized. A task allocation protocol provides a set of prioritized inspection tasks. Individual drones perform tasks following their allocations and priority. Subsequently, a cooperative path planning process is completed that ensures that drones can fly together as a swarm along the same route without colliding [30]. A specification of the formation constraints is used as an input in the cooperative path planning. Part of the cooperative path planning embeds a waypoint-guided path planning that describes the inspection path a drone should undertake to position itself in the right viewpoints for taking inspection images. The telemetry reporting activity ensures that the progress and telemetry reports are sent to the GCS. The progress monitoring supervises the progress of the prioritized list of inspection tasks. When a task has been completed, it breaks out of the loop and proceeds to the end node through the join node. The energy monitoring provides the charge status of the drone and is continuously monitored. If the charge falls below a defined threshold, the drone breaks out of the loop  
and proceeds with a charging protocol. Finally, the inspection flying activity is responsible for the drone visiting the waypoints defined in the cooperative path plan and acquiring inspection images according to the specification provided in the task specification. The acquired images are transferred to a storage system from where they can be fetched and sent to the cloud services asynchronously.