# Reactive Planning-Driven Approach to Online UAVs Mission Rerouting and Rescheduling
## 6 Computational Experiments  
Consider the network from Figure 1, in which the UAVs fleet \(\mathcal{U}=\left\{U_{1},U_{2},U_{3},U_{4}\right\}\) service delivery points \(N_{3}\)-\(N_{40}\). The structure of subsequent sub-missions \({}^{1}S,{}^{2}S,\ldots,{}^{6}S\) of the adopted mission plan \(S\) is presented in Figure 2.  
Let us assume (see Section 2) that at time \(t^{*}=3000\) [s] during execution of sub-mission \({}^{2}S\) the wind speed increases to \(vw~{}=~{}11\) m/s while its intensity and direction \(\theta=110^{\circ}-130^{\circ}\) remain unchanged. With such a change in weather conditions, it becomes necessary to re-plan the mission, including the introduction of the sub-missions \({}^{2}\overline{S},{}^{3}\overline{S},{}^{4}\overline{S},{}^{5}\overline{S},{}^{6}\overline{S}\) to correct its course. For this purpose, an algorithm described in our previous paper [30] has been used. Its implementation in the constraint programming environment IBM ILOG (Intel Core i7-M4800 MQ 2.7 GHz, 32 GB RAM) has shown that the solution time for problems of a size considered does not exceed 35 s.  
Figures 8a and 9a show the plan (i.e., the route and schedule) of mission \({}^{*}S\) adapted to the disturbance IS(3000). Rule 2 was used in assigning mission \({}^{*}S\), i.e., If there are UAVs that cannot continue to fly due to disturbance \(IS(t^{*})\), they should be returned to the base and it should be ensured that airborne UAVs can take over their tasks. Consequently, a decision to turn \(U_{3}\) back to base was made (see the sub-mission \({}^{2}\overline{S}\)--Figure 3) because there was a risk of premature battery depletion. Figure 8: Two kinds of response on the occurrence of a disruption: (**a**) the reaction after a finished mission in the given time window (sub-mission \(\overline{{}^{3}S}\)), (**b**) the “ad hoc” reaction (sub-mission \(\overline{{}^{2}S}\)). Figure 9: Two kinds of response on the occurrence of a disruption: (**a**) the reaction after a finished mission in the given time window and (**b**) the “ad hoc” reaction. Therefore, the goods to the node \(N_{7}\) will not delivered. At the same time, \(U_{4}\) continued its mission unchanged. This decision forced the necessity of rescheduling subsequent submissions \(\overline{3S},\overline{4S},\overline{5S},\overline{6S}\), enabling the designation of a new alternative plan \({}^{*}S\) taking into account the specificity of the disturbance IS(3000) that occurs. Of course, the scope of each revised plan depends on the timing of the decision to reschedule the plan. In Figure 8, the possible routes of the sub-mission depending on the timing of the re-scheduling decision are shown. Figure 8 presents the two kinds of reaction to the disruption. The first type of reaction results in mission re-scheduling (after the end of the sub-mission \(\overline{3S}\) affected by disruption), as shown in Figure 8a. In Figure 8b, the decision to re-plan the mission has been taken \"ad hoc\". This means the flight mission plan for each UAV belonging to the fleet \(K=\{U_{1},\ U_{2},\ U_{3},U_{4}\}\) has to be changed (see Figure 9b). In other words, the main ideas behind the two methods following alternative approaches to the sudden weather changes are illustrated in Figures 8 and 9. The cases presented in Figures 8a and 9a can be used in the situation when the vehicles started from base number 1, but these should be less exploited, e.g., due to the quality of the engines used, whereas in Figures 8b and 9b, the entire available fleet results in a shorter duration of the entire mission. In order to assess the scalability of proposed approach in terms of the possibility of its use in an online mode (i.e., to solve the problem in \(<\)600 s) in decision support systems, a series of quantitative experiments have been carried out. Table 1 contains the results of experiments that have been conducted for the three functions of forecasted weather \(\mathcal{F}\ (\theta)=11,\ 12,\ 13\ \mathrm{m/s}\).