Research Of Constraint Handling And Planning Method In Space Station Monthly Mission

Mission planning technology of space station operation is one of the key technologies to ensure the long-term stable operation of the space station and the effective implementation of space missions.In this paper,based on the actual requirements of China’s space station project,the monthly mission planning of the space station was studied from four aspects: domain modeling,constraint handling,scheme planning method,and re-planning method.The main achievements are summarized below:The domain model construction method of monthly mission planning was proposed.First,based on the basic planning process of space station monthly missions,from the perspectives of tasks,resources,and other elements,the characteristics of monthly mission planning were analyzed.Second,the elements were divided into planning entity elements and problem description elements,and the planning model framework of monthly missions was built.Third,the object-oriented method was adopted to formally describe the elements,and a unified description model for the elements was proposed,thus realizing the transformation from the conceptual model to the logical data planning model.Finally,by using the JSON data exchange format,the model of the elements was transformed into a machine-readable physical data model.The consistency checking method of time and logical constraints based on a constraint hierarchical network,and the constraint propagation method were proposed.First,the types and characteristics of the time and logical constraints among the monthly missions were analyzed to construct the time and logical constraint description model based on the “nominal time point + pre-and post-offset” format.Second,according to the characteristics of task sequential link,the division principles of task planning hierarchy were proposed,and the time and logical constraint hierarchical network was designed which can describe the inter-task time and logical constraints in graphics.Third,the consistency checking method of the time and logical constraint hierarchical network was proposed,and the time constraint propagation method based on task hierarchical processing was designed.The simulation results show that the time constraint propagation mode,which is layer-by-layer recurrence from the tasks with certain processing time to the time-uncertain tasks,can avoid the iterative repair process of constraints,reduce the solution space of planning variables,and increase the planning efficiency.The resource constraint processing method and the peak-shifting method for resource consumption based on a resource demand network were proposed.First,from the perspectives of utilization,numerical information,and recovery,the general resource description model was built,and the resource constraints were formally described.Second,the resource processing was described in the stages of starting point,ending point,and transition point;the resource demand network based on network topology was established;and the variable step size resource reasoning method promoted by the network nodes was designed.Third,the resource envelopment calculation method based on maximum flow was designed to predict the time points with resource conflicts,which were solved by the peak-shifting algorithm designed.The simulation results show that the variable step size resource reasoning method can effectively infer the resource consumption states on the timeline.Compared with the fixed step resource calculation method,this method can greatly reduce the resource calculation steps and improve the calculation efficiency.The peak-shifting processing method for resource consumption can realize more appropriate task planning and higher scheme robustness.The heuristic planning method with a customizable strategy and the intelligent optimization method based on individual repair were proposed.First,according to the time and logical constraint hierarchical network as well as the resource demand network,the planning framework of monthly missions was designed;the respective solutions to the time,logic,and resource constraints were designed;and the importance of the solutions was defined.Second,the customizable framework of the heuristic strategy was proposed;the expansion model of heuristic level and the customizable model of ordering rule were confirmed to describe different heuristic ordering strategies;and the order insertion algorithm of deleted tasks was proposed to fix the omission of feasible solutions in the planning process.Third,the differential evolution algorithm was adopted,and the single-objective global optimization method based on individual repairing was designed to obtain the global optimal solution of the task scheme.The planning results show that in the planning process by using a customized heuristic strategy,the quality of the planning results completely depends on the generation mode of the selected initial scheme and the customized heuristic strategy,and the order insertion algorithm of deleted tasks can improve the integrity of the scheme.In addition,in the process of using evolutionary algorithm to solve the problem,individual correction can enhance the planning efficiency,and the convergence speed when combined with an appropriate heuristic ordering strategy.The heuristic re-planning method the intelligent re-planning method for partial adjustment of the scheme were proposed.First,the influence of task modifications on the time and logical constraint hierarchical network and the extent thereof were analyzed,and the reconstruction algorithm for the time and logical constraint hierarchical network with the minimum disturbance in the local domain was designed.Second,the modification request satisfaction strategy and the scheme maintenance strategy were designed to meet the modification request satisfaction preferences and the scheme maintenance preferences.In addition,the paper designed the mission implementation time selection strategy and the heuristic re-planning process with minimum disturbance of the scheme.Third,the coding scheme and scheme inheritance index for limiting the randomness of optimization variables were designed,and the global optimal solution of re-planning was obtained based on the modification request satisfaction strategy.The planning results show that the heuristic re-planning algorithm can reduce the cost of adjustment,and re-plan the scheme in a short time.On the premise of meeting the requirements of scheme adjustment,the scheme with the minimum adjustment of mission implementation time can be obtained by the intelligent re-planning method.Based on China’s space station project,this paper focused on the constraint processing and planning methods of space station monthly missions.With the effective combination with the engineering elements,the results of the paper are closer to the actual project missions than the existing studies,and thus the paper can provide more accurate,flexible,and efficient planning technical support for space station operation.