From: dietz@cs.rochester.edu (Paul Dietz)
Newsgroups: sci.nanotech
Subject: Re: Teraforming Venus/ Throwing Snowballs
Date: 14 Aug 92 04:17:26 GMT


In article <Jul.22.21.05.41.1992.17421@planchet.rutgers.edu>, 71450.1773@compuserve.com (Steven B. Harris) writes:
...
|> Pluto).  "Retro-rocket" energies for stopping things in orbit at
|> 63 A.U. are still high enough that our project energy for a
|> 4*10^23 g snowball is (at least) 3*10^27 Joules.   This energy,
|> although less than 1/7 what is necessary to remove the Venusian
|> atmosphere directly, is still 750 billion megatons, which sounds
|> like more than could be easily done, even with fusion devices
|> (one can imagine moving a giant iceball/asteroid with bombs,
|> Heinlein style, but what kind of thing would a billion megaton
|> bomb be??).   
...
|>    So, in short, it looks like we're stuck on the issue of
|> teraforming Venus, unless we're willing to wait much longer than
|> several hundred years, or unless we find some way to spend energy
|> on Venus at a far higher rate than the rate Venus itself receives
|> energy from the Sun.  Perhaps putting up REALLY large numbers of
|> mirrors to broil Venus is the answer, as suggested by Drexler and
|> others (I believe).  The pesky planet's horrible climate combined
|> with its near proximity does seem an affront to good taste, and I
|> do agree that we ought to do something about it, if only for the
|> sake of aesthetics.


This doesn't really belong in this group, but...

The way to bootstrap more energy into the projectiles
is to exploit flybys of Jupiter to put them onto high
energy orbits intersecting Venus.  Jupiter can provide
a very large delta-V.  Some objects, like the Trojan Asteroids,
should be maneuverable onto Jupiter-approaching orbits
without too great a delta-V.

However, your first comment there hints at the better
solution:  blast the atmosphere into space by direct
use of nuclear energy.  If completely fused to helium,
you'd need a mass of deuterium equivalent to a sphere
of liquid deuterium some 8 kilometers in diameter (or several
times this, due to inefficiencies).  It just so happens that the
hydrogen in Venus's atmosphere is greatly enriched in deuterium
(about 1% deuterium) compared to average cosmic abundances, so
a good deal of the fuel could be produced locally (hydrogen
is scarce of Venus, so there may not be enough for the whole job).

The physics of the ejection would be straightforward.  Multiple
(a million?) explosions heat the atmosphere to tens of thousands
of degrees on a time scale short compared to the expansion
time.  This increases the pressure of the atmosphere, which then
begins to expand and accelerate outward in all directions.  The
time for the atmosphere to escape is on the order of (radius of Venus)/
(escape speed), or about 10 minutes.  Negligible energy is lost to
thermal radiation during this time.

Can fusion bombs be made large enough?  The public literature
suggests yes.  Also, large fusion bombs should actually be
easier to build than very small ones.  This is because for
a given level of compression and temperature, a mass of fusion
fuel will stay assembled for time proportional to (mass)^(1/3).
Larger bombs therefore have more time for their fuel to react,
and can either use less compression or more exotic fuels.  The
latter possibility might include reactions like p-6Li, p-11B, 2 x 3 He,
or perhaps others (p+15N?).

	Paul F. Dietz
	dietz@cs.rochester.edu