This study presents the application of the canonic transformations theory in determining the optimal transfer problems' extremals. So we obtain a close form solution for the transfer arc problem by evaluating an undefined integral representing the complete solution in the case of elliptic motion in orbital transfer. The use of a sufficient canonicity condition allows to define an advantageous canonical transformation that involves the determination of the generating function as a solution of the Hamilton -Jacobi equation for the elliptic and parabolic cases.