Necessary conditions for singular arcs for general restricted multi-body problem

We analyze the optimality of intermediate thrust arcs (singular arcs) of a rocket trajectory subject to multiple gravitational bodies in the restricted multi-body problem. We derive a series of necessary conditions for optimality including the generalized Legendre-Clebsch condition, and an explicit formula for the singular optimal control law. Our derivations become identical to Lawden´s classical result if the equations of motion are reduced for a central gravity field. As a means to illustrate the practical nature of our results, we apply them to a Moon-Earth transfer problem and show that the extremal solution is bang-singular-bang.