1. Periodic orbits for interplanetary flight.
2. 2Menning, M. D. "Freefall Periodic Orbits Connecting Earth and Venus," M.S. Thesis,Dept. of Aeronautics and Astronautics, Massachusetts Inst. of Technology, Cambridge, MA,July 1968.
3. 3Rall, C. S. "Freefall Periodic Orbits Connecting Earth and Mars," Ph.D. Dissertation,Dept. of Aeronautics and Astronautics, Massachusetts Inst. of Technology, Cambridge, MA,Oct. 1969.