A Self-Reproducing Interstellar Probe

Robert A. Freitas Jr.

The first serious proposal to use material space probes for interstellar exploration is properly credited to Bracewell [1,6]. According to his calculations, if the Galaxy is heavily populated with extraterrestrial civilizations (~10 light-years average separation then it makes sense to communicate using radio waves. if the Galaxy is only very thinly populated (~1000 light-years separation) communication is virtually impossible because of time lag and acquisition difficulties. However, if the Milky Way is populated at some intermediate level (~100 light%ears separation) then the best way to explore and contact other races is by automated messenger probe.

In the classical "Bracewell probe" contact scenario [2, 7], the automated device enters our Solar System, detects radio emissions of an unnatural character emanating from Earth, and subsequently positions itself in some convenient parking orbit around our planet. Upon receiving some arbitrary human transmission, the intelligent probe beams an identical copy of the message back to the transmitter site in hopes of gaining our attention. Once accomplished, language lessons soon follow; hopefully, meaningful discourse and cultural exchange between humanity and the automated alien ambassador ultimately take place.

Project Daedalus, a preliminary design study of a flyby probe mission to Barnard's star recently completed by members of the British Interplanetary Society [8], has demonstrated the feasibility of this approach to interstellar exploration and communication using foreseeable human technology sometime in the next century. The automated probe strategy has received further support from Freitas [
3], who shows that transmission of information across interstellar distances using energy-markers (photons) or matter-markers (probes) may be energetically and alternatives for highly developed technological civilizations Only such advanced societies realistically can afford either radio beacons or starprobes, and secondary distinguishability criteria suggest the possible superiority of intel ligent automata for contact and communication missions between extraterrestrial civilizations. The search for alien space artifacts in our own Solar System has already begun [9].

A major alternative to both the Daedalus flyby and "Bracewell probe" orbiter is the concept of the self -reproducing starprobe. Replicating spacefaring machines recently have received a cursory examination by Calder [4] and Boyce [5], I but the basic feasibility of this approach has never been seriously considered despite its tremendous potential. In theory, each self -reproducing device dispatched by the launching society would become an independent agent, slowly scouting the Galaxy for evidence of life, intelligence and civilization. While such machines might be costlier to design and construct, given sufficient time a relatively few replicating starprobes could search the entire Milky Way.

The present paper addresses the plausibility of self-reproducing starprobes and the basic parameters of feasibility. A subsequent paper [10] compares reproductive and nonreproductive probe search strategies for missions of interstellar and galactic exploration.

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Original source:
Journal of the British Interplanetary Society, Vol. 33, pp. 251-264 1980.