Presentation #204.03 in the session Dynamical Theory and Tools Posters.
Although Bob Farquhar considered halo orbits in 1959, before 1971 he focused on Lissajous orbits, and ways to change them with deltaV’s to keep a halo geometry. He showed this was better than earlier concepts for communicating with the lunar far side. These early “halos” needed about 100 m/sec/year of deltaV to maintain their geometry for an Earth-Moon 2nd libration-point (EM-L2) orbit. In 1971, Farquhar and Kamel expanded earlier work to 3 dimensions and 3rd-order, proving that natural 3-D quasi-periodic halo orbits existed. Details were given in Celestial Mechanics 50 years ago. These halo orbits need only a few m/sec/year of deltaV to cancel the unstable part of the motion. Farquhar promoted a comsat in an EM-L2 halo for critical Apollo far-side maneuvers. Although a lunar comsat at EM-L2 was not realized until 2018 by the Chinese Queqiao mission, Farquhar and Richardson applied the theory developed for EM-L2, to a Sun-Earth L1 halo orbit that led to the first halo orbit mission [2,3]. In 1990, Farquhar suggested that Sun-Earth L2 orbits would provide ideal locations for space observatories ; this idea was soon used by several missions. The rich history of the birth of halo orbits, and of libration-point missions, is described by Farquhar in his memoirs . Besides a summary of this history, with some new information, a table, with references, of the many libration-point missions that followed ISEE-3 will be presented.
 R. W. Farquhar and A. A. Kamel, “Quasi-Periodic Orbits About the Translunar Libration Point,” Cel. Mech., Vol. 7, No. 4, pp. 458-473, June 1973.
 R. W. Farquhar, “The Flight of ISEE-3/ICE: Origins, Mission History, and a Legacy”, J. Astronaut. Sci., Vol. 49, pp. 23-73, 2001.
 Dunham, D.W., Folta, D.C., Richardson, D.L., and Roberts, C.E., “The Third International Sun-Earth Explorer, the First Halo Orbiter”, Paper IAC-21-E4.2.11, 72nd I.A.C, Dubai, U.A. E., Oct. 2021.
 R. W. Farquhar and D. W. Dunham, “Use of Libration-Point Orbits for Space Observatories”, Observatories in Earth Orbit and Beyond, Y. Kondo, ed., pp. 391-395, Kluwer Acad. Pub., 1990.
 R. W. Farquhar, Fifty Years on the Space Frontier: Halo Orbits, Comets, Asteroids, and More, Outskirts Press, Denver, Colo., 2011.