In recent years,defunct satellites mitigation in the geostationary orbit(GEO) has become a hot issue in the space field.How to transfer defunct geostationary satellites to the graveyard orbit safely,economically and efficiently presents new challenges to spacecraft dynamics and control.This paper conducts an in-depth investigation on tether-tugging de-orbit issues of defunct geostationary satellites.Firstly,a four-phase tether-tugging de-orbit scheme including acceleration,equilibrium,rotation and return is proposed.This scheme takes into consideration how to avoid the risks of tether ripping,tug-target collision,and tether twist,and how to achieve the mission objective of fuel saving.Secondly,the dynamics model of the tether combination system is established based on Lagrange equation,and the four phases of tether-tugging de-orbit scheme are simulated respectively.Simulation results indicate that the scheme is theoretically feasible and satisfies the design objectives of safety,economy and efficiency,providing a technical approach for engineering application. In recent years, defunct satellites mitigation in the geostationary orbit (GEO) has become a hot issue in the space field. How to transfer defunct geostationary satellites to the graveyard orbit safely, economically and efficiently presents new challenges to spacecraft dynamics and control.This paper conducts an in-depth investigation on tether-tugging de-orbit issues of defunct geostationary satellites. Firstly, a four-phase tether-tugging de-orbit scheme including acceleration, equilibrium, rotation and return is proposed. This scheme takes into consideration how to avoid the risks of tether ripping, tug-target collision, and tether twist, and how to achieve the mission objective of fuel saving. Secondarily, the dynamics model of the tether combination system is established based on Lagrange equation, and the four phases of tether -tugging de-orbit schemes are simulated respectively. Simulation result indicates that the scheme is theoretically feasible and meets the design objectives of safety, econom y and efficiency, providing a technical approach for engineering application.