中轨道Walker导航星座在轨备份方案优化设计

针对中轨道Walker导航星座在轨备份方案的优化问题，首先提出了在轨备份星轨位优化设计方法，考虑星座运行期间在轨备份星与工作卫星存在共同提供服务的情况，选取PDOP值和可见卫星数作为轨位优化指标，建立了轨位优化模型，并基于NSGA-Ⅱ算法对不同轨位下在轨备份星对导航星座服务性能的提升效果进行仿真分析；然后，基于在轨备份星轨位的优化结果，建立在轨备份星替换的轨道机动模型，并综合考虑速度增量和替换时间，确定了以替换时间最少为优化目标的在轨备份星替换方案。结果表明，提出的在轨备份方案能有效满足备份星的设计需求，增强导航星座的服务性能，实现故障卫星的快速替换，可为导航星座备份星的建设提供借鉴。

Optimization of in-orbit backup scheme for medium orbit Walker navigation constellation

Aiming at the optimization problem of in-orbit backup scheme of medium orbit Walker navigation constellation, the optimization design method of in-orbit backup satellite orbital position was proposed firstly. Considering that backup satellites and working satellites provide services jointly during the constellation operation, orbital position optimization model was established with selecting PDOP value and number of visible satellites as optimization indexes, and based on the NSGA-II algorithm, the simulation analysis was carried out on the improvement of the service performance of the navigation constellation by backup satellites under different orbital positions. Then, based on the optimization results of backup satellites orbital position, the orbit maneuver model of replacement of in-orbit backup satellite was established, and the backup satellites replacement scheme with the minimum replacement time as the optimization objective was determined by considering the velocity increment and replacement time. The results show that in-orbit backup scheme proposed in this paper can effectively meet the design requirements of backup satellites, enhance the service performance of the navigation constellation, realize the rapid replacement of the failed satellite, and provide reference for the construction of the backup satellite of the navigation constellation.