Stellar Gravitational Lens Engineering for Interstellar Communication and Artifact SETI

Several recent works have proposed "stellar relay" transmission system over interstellar distances, in which a transmitting spacecraft at the focus of a star’s gravitational lens achieves dramatic boosts in the gain of the outgoing beam. We examine some of the engineering requirements of a stellar relay system, evaluate the long-term sustainability of a gravitational relay, and describe the perturbations and drifts that must be actively countered to maintain a relay-star-target alignment. Our analysis is applicable to many of the myriad uses of a stellar gravitational lens, several of which have artifact SETI applications. We discuss at length the prospects for an artifact SETI search to observe stellar relays placed around the Sun by an extraterrestrial intelligence, and we suggest certain nearby stars that are relatively unperturbed by planetary systems as favorable nodes for such a stellar relay communications system.