# Reactive Planning-Driven Approach to Online UAVs Mission Rerouting and Rescheduling
## 2 Related Work  
A great number of publications are devoted to the study of various aspects of the construction [22; 23; 24] and operation [1; 4; 5; 12; 14] of UAVs and the possibilities for their use in various areas of civil missions (real-time monitoring, surveillance, reconnaissance, search and rescue) [25; 26; 27] and military areas (weapons delivery, guided missile support, directing artillery, spotting enemy positions). These publications also look at the methods for planning their missions [28]. The trend of research dedicated to online planning missions carried out by UAV teams has become increasingly noticeable. Research conducted in this area is devoted to the application of UAVs in emergency situations where they are used for transport of much-needed water, food, and medical supplies over hazardous (flooded) terrain. This is required due to climate change [29], necessitating the introduction of online UAV mission planning systems [20]. Other studies conducted in this area are devoted to various fields of application, e.g., reconnaissance and mapping [17], package delivery [3], delivery communication capabilities [22], healthcare [24; 25], and so on. Increasing interest in these kinds of issues follows on from a need to search for scenario-driven planning methods that are aimed at the preparation of plans for UAV missions and aimed at an interactive tool building that facilitates the analysis and comparison of different scenarios and an iterative identification of sound and efficient mitigation strategies. In the considered research domain, two directions can be distinguished. The first focuses on planning methods, taking into account weather uncertainty (e.g., investigating the manner in which energy consumption in UAV deliveries is affected by windy environmental conditions), and searching for route planning methods resistant to ad hoc changes in procurement conditions (e.g., studying the impact of changes in order terms and volumes to complete the planned delivery mission) [6; 7; 11]. In turn, the second research direction deals with methods of design and utilising networks of autonomous UAVs with complementary sensing and actuation equipment to collectively perform complicated tasks, i.e., the flying ad-hoc network (FANET) [30]. FANET spontaneously forms when UAVs connect and communicate with each other to facilitate long range missions and can be seen as a temporary type of local area network. Indicated research gaps have become an inspiration for conducting this study, focusing on hybrid planning, i.e., a combination of proactive and reactive planning of the UAVs' fleet delivery missions resistant to sudden changes in weather conditions and unforeseen changes in the arrangements for governing delivery schedules. To clarify the motivation standing behind the selection of the hybrid routing mode, we should note that the routes determined in proactive planning guarantee the achievement of the planned mission goal within the environment's parameters, including change in predetermined intervals. In turn, routes determined in proactive planning guarantee the achievement of the mission goal only in the event of a previously foreseen (pre-planned) occurrence of an assumed type of disturbance. This is because a number of reactive rules guaranteeing the existence of reactive end-to-end paths employed in the routing process scenario is limited to just few arbitrarily chosen environmental changes. In this context, this study proposes a novel model for proactive and reactive planning (different scenarios) that allow for a higher degree of realism, thus a higher likelihood of a mission being executed according to plan even when weather forecasts, order terms, and volumes to complete the planned delivery are changing. The novelty of this study results in the addition of a function of UAVs mission resistance to changes in weather conditions.