1. Interplanetary Rocket Trajectories;Lawden;Advances in Space Sci.,1959
2. 'Die Errcichbarkeit der Himmclskorper,';Hohmann,1925
3. Optimal transfer via tangential ellipses;Lawden;J. Brit. Interplanet. Soc.,1952
4. Inter-orbital transfer of a rocket;Lawden;J. Brit. Interplanet. Soc.,1952
5. The determination of minimal orbits;Lawden;J. Brit. Interplanet. Soc.,1952