Tsinghua University Tsinghua University Tsinghua University Tsinghua University Deploying a low-Earth orbit (LEO) satellite network typically requires substantial financial investment and long development cycles. To shorten deployment timelines and alleviate economic burdens, collaborative constellation deployment has gained attention. In such a model, multiple satellite network operators (SNOs) contribute their respective constellations to jointly deliver LEO connectivity services. Despite these potential benefits, the high mobility of LEO satellites introduces operational complexity. As satellites move rapidly across coverage regions, terrestrial users are frequently reassigned to different access satellites, which may be connected to distinct SNO core networks. These cross-operator handovers, referred to as inter-SNO handovers, can negatively affect service continuity and overall network robustness. To address these challenges, this document outlines a mobility management framework aimed at supporting cooperative LEO constellation operation. The framework separates the satellite access layer from individual SNO core infrastructures, thereby permitting flexible mapping between shared access satellites and multiple operator cores. Through this decoupled architecture, user sessions can remain associated with their original SNO core networks whenever operational conditions permit. The framework incorporates a dynamic SNO association strategy that seeks to limit the frequency of inter-SNO handovers. Furthermore, in scenarios where such handovers cannot be avoided, a proactive optimization procedure is employed to shorten interruption duration and enhance the efficiency of the handover process.