What a pleasure to discover that Robert Freitas’ Kinematic Self-Replicating Machines is now available online. The 2004 book (from Landes Bioscience of Georgetown TX) is the most comprehensive study of nanotechnology yet written, a compendium of information on self-replicating systems both proposed and experimentally studied. Moreover, it contains a survey of the historical development of nanotechnology, 200 illustrations and over 3000 references to the technical literature.

That nanotechnology (and self-replicating systems in particular) could change our ideas of interstellar flight now seems obvious, but not so long ago ago the concept of one machine building another was studied only at the macro-level. Thus Freitas’ previous work on a self-reproducing spacecraft he called REPRO. The scientist wrote the concept up in a 1980 issue of the Journal of the British Interplanetary Society, conceiving of a mammoth Daedalus-style spacecraft built in orbit around Jupiter and, like Daedalus, using helium-3 from the giant planet’s atmosphere in its fusion engine.

REPRO was a vast and ambitious project, equipped with numerous smaller probes for planetary exploration, but its key purpose was to reproduce. Each REPRO probe would create an automated factory that would build a new probe every 500 years. Probe by probe, star by star, the galaxy would be explored.

Just 25 years later, Freitas still ponders galactic exploration, but he now concentrates on the world of the very small, studying nanotechnological methods that could allow space probes the size of sewing needles. Containing the computing power of thousands of human brains, such probes could be sent out by the millions. If just one of them reached a planet, moon or asteroid around a nearby star, it could begin to reproduce, and in much shorter time frames than allowed for the earlier REPRO probe.

When I interviewed him for Centauri Dreams in 2003, Freitas put it this way:

“The fastest known bacteria I’m aware of is e. coli that can replicate in fifteen minutes at ideal temperature with an excess of nutrients. It is approximately one to two microns in size, which is roughly the same size as the sophisticated assemblers that will one day manipulate matter at this level. If such assemblers landed on an asteroid that was a great distance away from the suns of the Alpha Centauri system, where perhaps there would not be the best energy density, and where materials would have to be scavenged, this would not be an ideal ‘petri dish’ kind of environment. So you might have to add two or three orders of magnitude of time. But you’re still looking at replication times on the order of weeks.”

So nanotechnology’s implications for interstellar flight may be profound, particularly as they enable the vision of a survey of the entire galaxy within a million-year time frame. Some (Frank Tipler among them) have argued that the lack of evidence for extraterrestrial probes within our own Solar System demonstrates that no technical civilizations exist in our part of the universe, but if probes are built with nanotechnology, they may have little trouble avoiding detection in the systems they survey.

We need, then, to give nanotechnology a good look as we plan an interstellar future. Freitas’ Kinematic Self-Replicating Machines is an essential reference for anyone hoping to see how breakthrough methods may make robotic probes possible not just to the nearby stars but throughout the Milky Way.

Freitas’ REPRO paper is “A Self-Reproducing Interstellar Probe,” Journal of the British Interplanetary Society 33 (1980): 251–64. Also available in revised form on the Web. See also F. Valdes and Robert A. Freitas Jr., “Comparison of Reproducing and Nonreproducing Starprobe Strategies for Galactic Exploration,” Journal of the British Astronomical Society 33 (1980): 402–406.