[ExI] Von Neumann Probes

[spike at rainier66.com]

> On Behalf Of Ben Zaiboc via extropy-chat



The other thing I'm trying to understand is how a bacterium-sized probe
travelling 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. I'd think,
for this reason, that von Neumann probes would need to be at least
millimetre or perhaps centimetre scale objects, capable of maintaining an
active power source to be able to self-repair. ...---
Ben

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Ben it wouldn't need to be a speck of dust, which is quite unlikely to
encounter in interstellar space.  But I agree with your concept for a
different reason: the probe going at .01c would erode from encountering
hydrogen.  It is easy enough to estimate if we want to go with Wiki's
estimate of a trillion molecules per cubic meter, then recognize at .01c,
you pass thru about 3 million cubic meters per second.

If the frontal area of the probe is one square millimeter, it is hitting
about 3 trillion molecules per second, and some ions, which is significant:
accelerating the ion from the collision creates radiation.  But before we
bother pondering radiation, estimate the drag from the 3 trillion molecules
per second hitting the probe at .01c.

spike