  In this paper, architectures for interplanetary communications that feature
the use of a data relay are investigated. In the considered "two-leg"
architecture, a spacecraft orbiting the Earth, or in orbit at a Lagrange point,
receives data from a deep space probe (leg-1) and relays them towards ground
(leg-2). Different wireless technologies for the interplanetary link, namely,
radio frequencies above the Ka band and optical frequencies, are considered.
Moreover, the cases of transparent and regenerative relaying as well as
different different orbital configurations are addressed, offering a thorough
analysis of such systems from different viewpoints. Results show that, under
certain constraints in terms of pointing accuracy and onboard antenna size, the
adoption of a two-leg architecture can achieve the data rates supported by
direct space-to-Earth link configurations with remarkably smaller ground
station antennas.
