1. Optimal Intermediate-Thrust Arcs in a Gravitational Field;Lawden;Astronautica Acta,1962
2. Minimal Rocket Trajectories
3. Hoelker R. F. and Silber R. The Bi-Elliptical Transfer Between Circular Coplanar Orbits. Army Ballistic Missile Agency, Redstone Arsenal, Alabama, Report No. DA-TM-2-59, 1959.