Link assignment of time-reference transfer from the space station to the BeiDou satellite constellation

Abstract

With the successful in-orbit operation of the cold atomic optical clock in the Mengtian laboratory cabin, a highly precise space time-reference will be formed. The BeiDou navigation satellite constellation has the ability of global coverage. By establishing time-transfer links with BeiDou satellites, the space station can realize precise transfer of its time-reference to wide area users. Aiming at the problem of highly precise and robust time-transfer link assignment from the space station to the BeiDou constellation, a link assignment model was established with taking the maximum hop and the connectivity as the evaluation indexes respectively of the accuracy and robustness of the time-transfer network. A topology optimization algorithm based on the genetic algorithm (GA) was further designed. Taking the time-reference transfer from the space station to the BeiDou Walker constellation as an example, the link assignment simulation was implemented in a minimum common orbit period. The precise time-reference transfer was realized using about 30% of inter-satellite link (ISL) timeslots. The maximum hop of the time-transfer links reached the theoretical optimal value, and the network connectivity was not less than 3. It was demonstrated that with the complex constraints of the ISL system, the payload quantity and visibility, the proposed assignment method could realize highly precise and robust time-reference transfer from the space station to the BeiDou constellation in any operation period.