Libration point orbit rendezvous using PWPF modulated terminal sliding mode control

The near-range rendezvous problem of two libration point orbit spacecraft in the Earth–Moon system is studied using the terminal sliding mode control which enables a time-fixed process with the flight time prescribed a priori. The underlying dynamics are the full nonlinear equations of motion for a complete Solar System model. For practical purposes, two means of pulse-width pulse-frequency (PWPF) modulation are employed to realize the theoretical continuous control with a series of thrust pulses. Extensive simulations with major errors taken into account show that the sliding mode controller can successfully guide the chaser to a given staging node with the final position and velocity errors, on average, lower than 20 m and 1 mm/s, respectively. Compared with the glideslope guidance previously studied, the proposed approach outperforms the former by saving approximately 50–60% of total delta-v.