Re: Colonizing a Neutron Star

"Russell Wallace" <russell.no.spam@xxxxxxxxx> wrote in message
news:Ugj7i.19989$j7.373891@xxxxxxxxxxxxxxxxx
Logan Kearsley wrote:
Quite some time ago (

http://groups.google.com/group/rec.arts.sf.science/browse_frm/thread/ca7037c
587195f83/b8e53951254d164d ) I proposed the idea of Tide World- a
megascale
space habitat that makes use of tidal forces to generate gravity at
either
end- and noted that a neutron star would be an ideal place to build one,
since you can get large tides over fairly short distances, but then I
never
really went anywhere with that.

Interesting idea! I'd be curious about how the numbers work out, how big
can you make it assuming, say, carbon nanotubes for structural material?

Hmm, it's got to be long-axis oriented, and 1g at the habitable ends, so
the maximum length of self-supporting CNTs is, what, a few thousand
kilometers? so I suppose that would be the maximum size scale you'd be
looking at; maybe an order of magnitude smaller by the time you've
handled the asymmetry?

It doesn't *need* to be 1g. That's just convenient for us Earthlings. A good
place to start making estimates, though.
I'd cut it down by about half from the absolute maximum, whatever that is,
to give a margin of safety.

I'm wondering now, though, how exactly one might go about building a
space
habitat around a neutron star. I like using a tide world both just
because
you can, and because that provides an excuse to have some really long
tethers involved which could be used for generating large amounts of
electricity as the neutron star's magnetic field sweeps by. I expect you
could get some electricity out of the radiation environment- young, hot
ones
will be glowing a bit in visible light if nothing else works out- but
mining
the star's rotational kinetic energy via its magnetic field would
provide
enormously more power.

*nods* This has been proposed in other environments, including Earth and
gas giants. Alas, it doesn't work; if primary rotates slower than
satellite, energy for tether electricity comes from orbit of satellite,
which ends up crashing into primary. If primary rotates faster, energy
comes from rotation of primary which is fine except angular momentum
transfers to satellite, which drifts further and further away.

It's no good if the satellite crashes, but getting pushed away isn't nearly
so much of a problem; there are ways of moving it back in, and in the
meantime it just results in slightly lessened gravity and power production.

But lots of energy from radiation environment, even not so young neutron
stars quoted at several times 10^5 K, which makes them area for area
maybe a hundred million times brighter than a conventional star. Need to

That's countered by the fact that they have far less surface area and
reduced emissivity, though.
According to http://www.extrasolar.net/planettour.asp?PlanetID=26,
PSR-1257+12, with an effective temperature of 600,000K, would only look
about a bright as the full moon from its innermost planet at .19AU. Of
course, it's also emitting an enormous amount of non-visible radiation.

make sure close enough to get 1g tides doesn't also mean close enough
for neutron star's heat output to vaporize the habitat! Might end up
needing to pick an extremely old neutron star, don't know if universe is
old enough for any to have cooled enough.

Or just employ some highly effective cooling systems. One way to get power
out of the NS's high-energy radiation might be just to run a heat engine off
of the star-ward shielding, connected to some very large radiators oriented
perpendicularly to the NS.

Another thought comes to mind. If you've got an old, quiet neutron star,
and
maybe a convenient gas giant hanging around, would it be possible to
feed
hydrogen onto the surface at just the right rate to keep up a continuous
fusion burn, as opposed to setting off cyclic nova events as the
hydrogen
envelope builds up?

I don't know, but material hitting the surface of a neutron star will
deliver much more kinetic than nuclear energy, so if not, use nuclear
"ash", anything that's too heavy to go boom.

Stuff that's heavy enough to not go boom is probably stuff that you'd like
to keep around as building material. One could make sure that one's neutron
star never cools down too much over a few million years, and use it as a
radiant energy source like a normal star, just by dropping junk on it, but
one would also prefer that that junk not explode and kill you. And you don't
want it to fall too hard, to avoid annoying gamma-ray bursts.

Hm. Am reminded of a previous thread- if you've got sufficient shielding,
maybe you do want it to fall as hard as possible, and hopefully blow off
some heavy nuclei from the NS's crust.

-l.
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