In the multi-satellite and multi-ground station downlink task scheduling problem, the waiting time from the proposal of the task to the execution will affect its validity. If the satellite has multiple communicable ground stations when the downlink task is proposed, the selection problem needs to be solved first. After the selection, since the available time conflict between tasks of different satellites for the same ground station, the specific start time should be determined. To reduce the waiting time, a simulated annealing algorithm with a tabu list and start time decision (SATLD) is proposed. This method uses a two-stage scheduling strategy. In the first stage, the improved simulated annealing algorithm based on a tabu list is used to select the downlink ground station. The second stage combines downlink scheduling algorithm based on task arrival time (DSA-AT) method and downlink scheduling algorithm based on task requirement time (DSA-RT) method to determine the specific start time of each task of a single ground station. Simulation analysis prove the method has better selection efficiency of downlink task and shorter total task waiting time, and has practical value.

Aiming at the task planning and scheduling problem of space object detection LEO constellation (SODLC) for detecting space objects in deep space background, a method of SODLC task satellite selection based on observation window projection analysis is proposed. This method projects the spatial relative relationships of the SODLC observation blind zone, observation range, and the initial spatial position of the objects onto the surface of the earth for detectable analysis of satellites and targets and binds the dynamic observation conditions to the satellite trajectory after projection calculation of the visible relationship between target changes. On this basis, combined with the features of SODLC with high orbital symmetry, the task satellite selection is divided into two steps: orbit plane selection and task satellite selection. The orbit planes are selected based on the longitude range of the ascending node with the geographic location of the targets, and the task satellites are selected according to the relative motion relationship between the satellites and the targets together with the constraints of observable conditions. The selection method simplifies the calculation process of scheduling and selecting task satellites. Simulation analysis prove the method has better task satellite selection efficiency. The method has high practical value for task planning and scheduling for event-driven SODLC.