mining the 'pollies

Eugene Leitl (
Mon, 5 May 1997 22:40:45 +0200 (MET DST)

Me, a faithful lunatic, has always been mesmerized by the
Moon as the major future space industry location. However,
near-Earth asteroids might prove to be much more
interesting first target for prospection and mining.

The major minus of the Moon is the distance, its location
at the bottom of a (shallow, though) gravity well, and
kinetical unaccesibility of certain resources due to
differentiation in the course of ur-material accretion.
Vastly simplified, this means dense minerals accumulating
at the core (which is pretty inaccessible due to pressure,
and uncomfortably hot in the bargain), light in the outer
shell, and generic depletion of light elements, which
have escaped into space, being literally baked out
(especially true for our beloved, forever smallpox-marked

Ceres, the first planetoid, was discovered in 1801 in Palermo
(by one Piazzi). We now know more than 2 k objects in orbits
between Mars and Jupiter. More than 30 objects have orbits
with the perihelion within Mars orbit. About 20 objects
have their perihelions within the Earth orbit, this are
the Apollo asteroids. Asteroids are commonly classified
in Hirayama families by their orbit data; about 40 such
families are known. Additionally, there are the Trojans,
which move in 60 deg distance onto Jupiter orbit, as seen
from the Sun (as predicted by Lagrange).

These are but the largest primeval debris pieces, smaller ones
being inaccessible to astronomic observations. The smaller the
body, the larger the probability of a close encounter. For mining,
planetoids of few 10-100 m size are more than sufficient. Few
g/cm^3 density assuming, that's a lot of material outside the
Earth gravity well.

For prospection, appropriate targets must first be found. As now
widespread Peltier-cooled CCDs and "lightweight giant" amateur
telescopy has now reached very respectable dimensions, many
asteroids are discovered by hobbyists (notice NEAP's $500
bribe). Furthermore, recently emerged awareness for rare, but
desastrous hits by relatively small (few km) asteroids, might
soon grant us a new watchful chain of eyes.

Once discovered, not much information can be futhur gained
by remote sensing. Sure, we can measure the albedo (and
its fluctuations, which give us the rotation frequency,
and lots of information about geometry and surface
reflectance distribution), maybe utilize the Hubble, or
radar, but still, investigation by a probe will still be
mandatory. The intercepting probe must first match its
speed, then go into orbit (inasmuch a few 100 m body might
be said to have enough mass for a measureable orbit, whereas
the larger asteroids escape velocity cannot even be reached
by vigorous jumping) . The volume can be very precisely
measured by evaluation of a surface snapshot sequence,
while in orbit. Average density is available from orbit
data (we sure know the mass of the probe).

There are three types of chondrites known: carbonaceous
chondrites (further subdivided in types I, II, III), plain
chondrites, and enstatite chondrites.

chondrite type
component I II III plain enstatite
H_2O 20.54 13.23 1.00 0.27 0.62
C 3.77 2.44 0.46 <0.01 0.29
Na_2O 0.76 0.54 0.55 0.90 1.00
MgO 15.56 19.00 23.86 23.93 21.01
Al_2O_3 1.77 2.31 2.65 2.72 1.87
SiO_2 23.08 27.31 33.75 38.29 38.62
P_2O_5 0.27 0.27 0.32 0.20 0.20
S 6.16 3.13 2.22 - -
K_2O 0.07 0.05 0.05 0.10 0.11
CaO 1.51 2.03 2.32 1.90 0.97
TiO_2 0.08 0.10 0.12 0.11 0.06
Cr_2O_3 0.28 0.39 0.51 0.37 0.35
MnO 0.19 0.17 0.20 0.26 0.14
FeO 24.12 27.07 29.29 11.95 1.69
Fe_metal 0.11 <0.01 2.34 11.65 19.82
Co_metal <0.01 <0.01 0.06 0.08 0.12
Ni_metal 0.02 0.16 1.08 1.34 1.66
NiO 1.17 1.56 0.33 - -
FeS troilite - - - 5.89 10.70

density 2.2 2.7 3.4 3.6 3.65

(all in all, a darn funny, nay _unearly_ composition, no?
I already see a number of geologists developing a funny
stare, and a number of saliva stains upon their ties).

Heliothermics with flimsy (few um Al foil on a hyperbolic
truss mirror) may easily reach about 6 kK in space, albeit
requiring tracking, especially for rotating bodies (negation
of rotation is mandatory (orelse where to with all the pesky
oxygen?) on the middle run).

Electrolysing (PV electricity) a molten silicate poodle,
whether with metal or carbon (pyrographite from carbonaceous
chondrite) will result in silicon/metal/silicate multiphase
alloy, oxygen/carbon dioxide irreversibly escaping into space.
Electrolysed water may yield hydrogen for reduction, metal
and molten silicate glass material for truss rods construction
(imagine neoariadne agents, deftly spinning glass fibre in
space). Sputtered aluminum and iron are great material for
mirrors, ebeam cannons are useful for deploying these.
Inductive metallurgy is easy to do, under microgravitation
conditions, and lots of hard vacuum.

Producing semiconductor-grade silicon will be sure a chore
under this circumstances. Sad thing beam writers bein a
natural for space semiconductor production.

As usual, I now have run out of steam at the most interesting
spot. Sorry. 'gene