Because the moon always has the same orientation to earth, if we want to have communications with manned or robotic explorers on the far side some type of relay would be needed for communication. Would a communication satellites used in lunar orbit be possible or would the tidal effects of earth disrupt the orbit to make it impossible/impractical?


It's not really about tidal effects of the Earth but about irregularities of lunar gravity (Mascons) necessitating large fuel expenditures for maintaining an orbit around the Moon.

GRAIL gravity anomaly map

Taken from: http://boingboing.net/2013/06/23/lunar-gravity-maps.html

The solution (first proposed in 1966 by R. Farquhar) is to place a comms relay into a halo orbit around the Earth-Moon L2 Lagrange point.

In 1973 Farquhar and Kamel found a "natural" halo orbit providing almost constant coverage (in-plane oscillation should be greater than 32379 kilometers):

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  • Farquhar, R. W. The Control and Use of Libration-Point Satellites. Ph.D. Dissertation, Dept. of Aeronautics and Astronautics, Stanford University, Stanford, CA, 1968.
  • J.Masdemont. Libration Point Orbits and Applications. 2003. P.47.

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