Low-thrust fuel-optimal trajectory optimization of multi-mode propulsion in Tianqin constellation

“Tianqin” is a space-borne gravitational wave detection project proposed by Sun Yat-sen University recently. The project requires three drag-free spacecraft to observe a specific gravitational wave source, J0806.3 ＋ 1527, for a minimum of 5 years in the “3 months on ＋ 3 months off” scheme. The spacecraft will need to make orbital maneuvers in three out of every 6 months to meet the orbital stability requirements of the observations. To reduce the fuel consumption and extend the orbital lifespan, this study combines the homotopic approach, a fixed-step integration with both switching and mode detection, to solve the dual-mode propulsion optimization problem of the fuel-optimal index. Preliminary numerical simulation results verify that dual-mode propulsion with the combination of the cold gas thruster and radio-frequency ion thruster can significantly reduce the fuel consumption compared to the use of only a single cold gas thruster. The research also qualitatively summarizes the necessary conditions for each thruster to make a considerable contribution to the orbital maneuver in dual-mode propulsion under the fuel-optimal index. All these research results provide prospective reference data for Tianqin's future design of detailed thruster parameters for multi-mode propulsion.