Abstract: This study aims to balance orbit-keeping accuracy，propellant consumption and computational efficiency for spacecraft station-keeping near Earth-Moon libration points. Traditional nonlinear model predictive control (NMPC) imposes a heavy onboard computational burden because it solves complex nonlinear optimization at every control step. A high-fidelity model is developed based on the circular restricted three-body problem combined with low-thrust orbital dynamics. The research introduces an event-triggered mechanism (ETM) and proposes two event-triggered NMPC (ET-NMPC) algorithms. Instead of fixed-period execution，the controller initiates online receding-horizon optimization only when the real-time position tracking error exceeds a preset threshold. Between triggers，when tracking performance remains satisfactory，two low-computation strategies are applied alternately：control-input freezing and control-input nullification. This design avoids numerous unnecessary online optimizations. Long-term numerical simulations show that the ET-NMPC strategies maintain control precision while greatly lowering computational load. With suitable thresholds，both methods reduce average computation time by over 50% and decrease the average triggering frequency by more than 77% compared with standard NMPC. The approach successfully balances control performance with limited onboard computational resources. The proposed control framework offers a novel ondemand optimization solution for deep-space orbital control under strict resource constraints. It significantly expands the practical applicability of nonlinear model predictive control in complex aerospace dynamical systems.

Key words: Earth-Moon system, circular restricted three-body problem, Halo orbit station-keeping, event-triggered mechanism, nonlinear model predictive control