Problem A of CTOC-9: Results found at Research Center of Flight Dynamics and Control of NUDT

The problem A of the 9 t h China Trajectory Optimization Competition (CTOC-9) requires monitoring 18 geostationary orbit (GEO) satellite beams using a satellite cluster which has three members. This paper summarizes the solution strategies and gives the best results found at Research Center of Flight Dynamics and Control of NUDT. The visibility conditions of the satellite beams are analyzed firstly. A circular configuration is selected for the satellite cluster due to its uniform monitoring performance, and several repeat-groundtrack orbits are chosen as the cluster's working orbits for their revisit feature. Since the satellite beams points to quite different directions in the space, a combination of two or three repeat-groundtrack orbits is adopted to reduce the mission duration. The optimal combination is found out by using exhaustive method. When the satellites transfer between different working orbits, the Particle Swarm Optimization (PSO) and Sequence Quadratic Programming (SQP) algorithms are used to minimize the fuel consumption. An orbit propagation algorithm that can quickly predict the beam visibility to the cluster is introduced to improve the computational efficiency. Two results were found according to two different orbit combinations. Specifically, when the combination of two repeat-groundtrack orbits is adopted, it requires 24.931 days and 244.531 kg fuel to complete the mission. When the combination of three repeat-groundtrack orbits is adopted, it requires 21.408 days and 450.640 kg fuel. The latter is the best result found by our team for the competition.