Date: 23 Apr 87 20:24:12 GMT
From: fluke!ssc-vax!eder@beaver.cs.washington.edu  (Dani Eder)
Subject: Re: Gold

Why bother recovering precious metals from asteroidal sources, when the
BIG market requires no separation at all.  The free metal in a
iron-nickel or stony-iron asteroid typically consists of 90% Iron, 9%
Nickel and 1% Cobalt.  This is already a very high grade steel.  The
world market for steel is ENORMOUS ($200 billion/year or so).  Your
problems are how to get the asteroid or part thereof back to earth
vicinity, then down to the ground.

Problem #1 can be solved by using the asteroid to bring itself back.
You do this by making sheet metal mirrors and solar-sailing back to
earth.  Now, I know that steel is a crummy reflector (about 50%
reflectivity), and it is dense (7800 kg/cubic meter), but the stuff is
there already.  At 2.5 AU, in the asteroid belt, a typical available
impulse will be 36 Newton-seconds/square meter/yr (light pressure is
(1+r)E/c , where r is reflectivity, the 1 comes from the momentum of
incident light, which is all used, E is the wattage of sunlight, and c
is the speed of light).  If your sheet is 25 microns thick (0.001 inch),
then 36 Newton-seconds/ square meter yields a 187m/s delta vee per year.
Thinner sheet will get you home faster.

The steel sheet is rolled between sintered and glazed ceramic rollers
made from local rock.  A stony-iron asteroid works best here as a
source.  Both the rollers and the steel are heat formed in solar
concetrators made of, you guessed it, steel sheet.  The whole process
bootstraps from a very small seed.

Problem #2 can be solved by wadding up the sheet after arrival in earth
orbit into a ball, then de-orbiting.  If the density is low enough, the
ball will not melt on re-entry and will float on water.  You then hook a
tugboat to the metal and haul away.

IF, and this is a very big if, you can do this for less than alternate
market prices for steel, you have a big enough market to justify the
high capital costs of space resource recovery.

Dani Eder/Advanced Space Transportation/Boeing/ssc-vax!eder