Variable-mass gravity tractor for asteroid deflection: Full mission process optimization and deflection efficiency analysis

The Gravity Tractor (GT) is a spacecraft that deflects an asteroid using its gravitational force to gradually alter the asteroid’s trajectory without making physical contact. This paper proposes a comprehensive mission optimization framework to maximize orbital deflection distance in variable-mass GT missions, incorporating key constraints: launch performance, warning time, and operational strategies. Simulation results suggest that the deflection distance of GT does not increase linearly with warning time due to launch window constraints, and the three-pulse transfer scenario does not provide significantly greater deflection distance compared to the two-pulse transfer scenario. Moreover, in the static hovering scenario, the deflection distance first increases and then decreases with the effective tractor distance, whereas in the displaced orbit scenario, it decreases monotonically. Finally, considering the launch performance of CZ-5, a 10-year warning time enables the defense against 50-meter asteroids, while a 20-year warning time enables the defense against 100-meter asteroids. This research provides valuable insights into the evaluation of GT deflection efficiency and the engineering design of GT-based missions.