In the past, unmanned missions to Mars have accepted the inevitable communications blackout that occurs when Mars is in solar conjunctions. This interruption, which lasts several weeks, would seem to be unacceptable during a manned Mars mission. This paper proposes a relay satellite as a means of maintaining vital communications links during conjunction, and explores candidate orbits for such a spacecraft.

The basic approach to system design is to minimize size, weight, and power of spaceborne elements of the communications system, since it is more economical to compensate with large, heavy, and power-consuming elements on Earth. Ideally, it is the Earth-to-Mars link, which should drive the overall system design, with the Earth-to-relay and Mars-to-relay links impacting system design as little as possible. This ideal is approached by minimizing the length of the link between the relay spacecraft and Mars. An orbit whose period is one Martian year, but whose eccentricity and inclination both differ from that of Mars, assures communications between Earth and mars during conjunction while minimizing the length of the link between the communications satellite and the Mars mission.