[ExI] Von Neumann Probes

[Jason Resch]

On Sun, Jan 25, 2026, 11:28 AM spike jones via extropy-chat <
extropy-chat at lists.extropy.org> wrote:

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> *From:* John Clark <johnkclark at gmail.com>
> *Sent:* Sunday, 25 January, 2026 5:23 AM
> *To:* ExI chat list <extropy-chat at lists.extropy.org>
> *Cc:* spike at rainier66.com; Ben Zaiboc <benzaiboc at proton.me>
> *Subject:* Re: [ExI] Von Neumann Probes
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> On Sat, Jan 24, 2026 at 6:11 PM spike jones via extropy-chat <
> extropy-chat at lists.extropy.org> wrote:
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> *The other thing I'm trying to understand is how a bacterium-sized
> probetravelling at 1%c would last more than a few decades in interstellar
> space.Just one single collision with a grain of dust would destroy it.*
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> *According to Osmanov, although the logic (machinery) of A Von Neumann
> probe would theoretically only need a picogram of mass (10^-12 grams), to
> be practical the probe would require about 10^-3 grams, the size and mass
> of a grain of coarse sand. The extra mass would be used to make a Graphene
> shield needed to protect the probe from collisions with dust particles.*
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> *John K Clark*
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> *At .01c any collision with a dust particle or any particle consisting of
> even a few thousand atoms would make the material in the shield
> irrelevant.  Reasoning: do a calculation or even a reasonable estimate on
> the energy of collision, compare with the chemical bonding energy of
> whatever material you want or can plausibly imagine.*
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> *Here’s a paper on high speed collision, which is behind a paywall, but
> the introduction gives you an idea of what I am talking about:  *
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> *https://asmedigitalcollection.asme.org/fluidsengineering/article-abstract/95/2/276/412692/Hydrodynamic-Phenomena-During-High-Speed-Collision?redirectedFrom=fulltext
> <https://asmedigitalcollection.asme.org/fluidsengineering/article-abstract/95/2/276/412692/Hydrodynamic-Phenomena-During-High-Speed-Collision?redirectedFrom=fulltext>*
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> *More relevant than drag is erosion during interstellar travel, never mind
> what shield material is used (Arthur C Clarke proposed water ice.)
> Consider a comment Keith made a few days ago about how leaking steam
> behaves in a powerplant.  Estimate the velocity of steam escaping from a
> small leak, then consider his description of the escaping steam sawing off
> broomsticks.  The local machine shop had a tool for carving metal blocks
> using a hypervelocity water jet.  How many C is that?  Any reasonable
> estimate will do: a kilometer per second?  Two?  Ten?  Regardless of your
> reasonable estimate, it is still down in the range of a few micro-C.  *
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> *In light of that thought experiment, think of how absurd was my own
> calculation yesterday on the deceleration of the cubic millimeter one
> milligram probe from drag (sheesh, do I feel silly now.)  The drag from
> interstellar hydrogen is irrelevant if the probe burns up or erodes away
> long before its centuries-long journey at 10 milli-C.  *
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> *The energy in a collision increases as the square of the velocity.  Even
> intentionally overestimating the velocity of the water jet cutter gives us
> at least a three order of magnitude velocity ratio, which means a six order
> of magnitude ratio in energy of collision, taking us into energy levels far
> greater than the piddly covalent bond energy in diamond or whatever other
> material you prefer.  Ja I know the water jet is orders of magnitude more
> particles, however it does its precision erosion is orders of magnitude
> less time than the interstellar probe will be in flight.*
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> *Do offer a mathematically based refutation to my conclusion that any
> millimeter scale von Neumann probe at anywhere near .01C is completely
> impossible, regardless of any plausible future materials breakthroughs.  I
> might buy the notion of a micro-C however, and if so, it is much easier to
> imagine accelerating that milligram mass to that velocity and decelerating
> upon arrival.  It shouldn’t matter much if it takes millions of years to
> span the distance between the closest stars, ja?  What’s the big hurry?*
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> *John, Keith, Ben, others, what say ye?*
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Aren't there proposals in which an ionizing laser is shot forward of the
craft and then magnetic fields are used to steer those charged particles
out of the craft's path? I don't know how practical this is, but it might
avoid the erosion problem.

Jason



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> *spike  *
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