Browsing through the correspondence that makes up Freeman Dyson’s wonderful Maker of Patterns: An Autobiography Through Letters (Liveright, 2018), I came across this missive, describing to his parents in 1958 why space exploration occupied his time at General Atomic, where he was working on Orion, the nuclear pulse concept that would explode atomic devices behind huge pusher plates to produce thrust. Dyson had no doubts about the value of humanity moving ever outward as it matured:

I am something of a fanatic on this subject. You might as well ask Columbus why he wasted his time discovering America when he could have been improving the methods of Spanish sheep farming. I think the parallel is a close one… We shall know what we go to Mars for only after we get there. The study of whatever forms of life exist on Mars is likely to lead to better understanding of life in general. This may well be of more benefit to humanity than irrigating ten Saharas. But that is only one of many reasons for going. The main purpose is a general enlargement of human horizons.

But there’s the thing, the driver for the entire Centauri Dreams effort these past twenty years. Just how do we go? And I mean that not only in terms of propulsion, the nuts and bolts of engines as well as the theory that drives them, but how we move outward carrying the cultural and scientific values of our species, Dyson thought deeply about these matters, as did Shklovskii and Sagan in their Intelligent Life in the Universe (Holden Day, 1966), who mused that an advanced civilization might view interstellar travel as a driver for creativity and philosophical growth. Perhaps culture remakes itself with each new exploration.

Greg Matloff’s investigations of these matters in numerous papers and key books like Deep Space Probes (Springer, 2005) have laid out the propulsion options from Project Orion to beamed lightsails, but his new paper, written with the artist C Bangs, draws on Dyson’s Astrochicken concept, first published in 1985, one of the few times I’ve seen it discussed in the literature (although I gave it a look in my 2005 Centauri Dreams book). Astrochicken was to be a one-kilogram probe to Uranus, a genetically engineered device powered by artificial intelligence.

As Dyson describes it in Infinite in All Directions (Harper & Row, 1988), “The plant component has to provide a basic life-support system using closed-cycle biochemistry with sunlight as the energy source. The animal component has to provide sensors and nerves and muscles with which it can observe and orient itself and navigate to its destination. The electronic component has to receive instructions from Earth and transmit back the results of its observations.”

Integrating all of this is artificial intelligence, creating a probe “…as agile as a hummingbird with a brain weighing no more than a gram.” Some years after Dyson introduced Astrochicken, Matloff discussed such a living probe, flitting from world to world, in Deep Space Probes, seeing elegance in the idea of wedding biology to technology. There he imagines a spacecraft like this fully fleshed out in the interstellar context, with a harvesting capability in the destination star system. He describes it thus:

…a living Astrochicken with miniaturized propulsion subsystems, autonomous computerized navigation via pulsar signals, and a laser communications link with Earth. The craft would be a bioengineered organism. After an interstellar crossing, such a living Astrochicken would establish orbit around a habitable planet. The ship (or being) could grow an incubator nursery using resources of the target solar system, and breed the first generation of human colonists using human eggs and sperm in cryogenic storage.

We have in this symbiosis of plant, animal and electronic components the possibility of leaving the Solar System and conceivably creating a von Neumann probe that combines engineering with the genetic manipulation of plant and animal DNA. Our probes need not be robotic, or at least entirely robotic, even if humans are not aboard.

Out of this seed comes Space Butterfly, aptly named for its large, thin wings that can unfurl for a close stellar pass for acceleration and trajectory adjustments. In the new paper in JBIS, Matloff notes that this is a spacecraft with an affinity for starlight, using its wings as solar panels to power up its suite of scientific and communications equipment. Driven by its AI brain, it would be capable of mining resources found in exoplanetary systems, moving between stellar systems in passages of millennial length. Here I’m reminded of the oft-cited fact that only a small fraction of the Sun’s projected lifetime would serve for such space butterflies to explore and fill the galaxy, even moving at velocities that exceed Voyager by only a small amount. Quoting the paper:

Using hyper thin all-metallic sails and close perihelion passes, Space Butterfly could traverse the separation between neighboring stars in a few millennia. If it elects to come to rest temporarily within a planetary system, it can decelerate by electromagnetically reflecting encountered interstellar photons and pointing the fully unfurled sail towards the destination star…

If ET elects to construct Space Butterflies with very long lives, many spare AI ‘brains’ could be carried. This should produce no major problem since these units could have masses well under one gram. Spare parts could also be carried to replace non-biological portions of Space Butterfly.

Image: Flitting from star to star, the Space Butterfly concept is perhaps more like a Space Moth, with its affinity to starlight. Credit: C Bangs.

Plugging in the known characteristics of the interstellar object ‘Oumuamua, Matloff speculates on its characteristics if it were a Space Butterfly, exploring the kinematics – trajectory, velocity, acceleration – of this kind of probe. He uses a framework of mathematical tools that have evolved for the analysis of sail technologies, ranging from the lightness number of the sail (the ratio of radiation pressure force on the sail and solar gravitational force on the spacecraft), as well as radiation pressure from the Sun at perihelion, given what we know about sail materials and thickness.

If ‘Oumuamua were a sail, it would be a slow one, moving at an interstellar cruise velocity in the range of 26 kilometers per second, and thus requiring a solid 50,000 years for a crossing between the Sun and the Alpha Centauri stars, for example. A Space Butterfly should be able to do a good deal better than that, but we are still talking about crossings involving thousands of years. Civilizations interested in filling the galaxy with such probes clearly would have long lifetimes and attention spans.

Such timeframes challenge all our assumptions about a civilization’s survival and indeed the lifespan of the beings who operate within its strictures. Given that we know of no extraterrestrial civilizations, we can only speculate, and in my view the prospect of an advanced culture operating over millennial timeframes in waves of slow exploration is as likely as one patterned on the human model. A sentient probe carrying perhaps a post-biological consciousness not at the mercy of time’s dictates might find ranging the interstellar depths a matter of endless fascination. For such a being, the journey of discovery and contemplation may be of more value than any single arrival.

The paper is Matloff & Bangs, “Space Butterfly: Combining Artificial Intelligence and Genetic Engineering to Explore Multiple Stellar Systems,” Journal of the British Interplanetary Society Vol. 77 (2024), 16-19.