OPTIMISATION OF LOW-THRUST ORBIT TRANSFERS USING THE Q-LAW FOR THE INITIAL GUESS

摘要

The Q-law is a Lyapunov feedback control law for effecting low-thrust orbit transfers between arbitrary pairs of orbits around a central body, provided the eccentricity remains below unity. The Q-law can automatically introduce judiciously positioned coast arcs to reduce pro-pellant consumption (at the expense of longer flight-time). Because the Q-law has been shown to produce results representative of optimal orbit transfers in the literature, in this work we use the Q-law to generate initial guesses for optimising a complex orbit transfer around the Earth. The Q-law produces transfer trajectories with different flight-times and propellant masses (depending on the amount of coasting). Each of the Q-law transfer trajectories is then optimised using the Static Dynamic Control algorithm. Initial guesses based on the Q-law, but with Q-law parameters optimised by a genetic algorithm, are also optimised. The optimal solutions obtained are compared with the Q-law initial guess. The speed of optimisation, and nature of the optimal solutions found, are compared with optimal solutions obtained using the previously available, simplistic initial guesses. The Q-law initial guesses and especially the genetic-algorithm-Q-law initial guesses provide many-fold reductions in optimisation run time over the simple initial guess, and they furthermore have performance representative of the optimal solutions found, unlike the simple initial guess.