SPACE.com -- Riches in the Rubble

Torino Scale: Disaster Yardstick in Search of a Role


	Riches in the Rubble By Michael Paine Special to space.com posted: 06:07 pm ET 05 November 1999

Thirtyyears ago, when the Apollo astronauts brought rocks back from the Moon,nobody rushed to stake a mining claim. Only traces of useful materialswere found. The surface of the Moon turned out to be barren and unattractivefor commercial development.

Asteroids, however, are anothermatter. Nearly all the raw materials needed to build a self-sufficientspace colony are available on the most common type of asteroid. NASA plansto land a small robotic spacecraft on an asteroid within a few years, justone example of the belief that asteroids are both accessible and worthexploring.

Recipe for a Solar System

Most asteroids are made fromthe raw ingredients of the solar system, researchers believe. Those ingredientscame from supernova -- exploding overweight stars. The solidified debrisfrom these explosions contains mainly dust, rocks, water ice and iron (actuallyan alloy of iron, nickel and cobalt -- a natural stainless steel).

Nearly5 billion years ago, under the tug of gravity, debris from supernovas gatheredinto a spinning disk. Most of this material fell into the center of thedisk and formed our Sun. Further out the material formed many planets.As these planets circled the Sun they collided with each other and grewlarger, until just nine planets were left. The debris from these collisions,together with other leftover rubble, was either swallowed up in furthercollisions or was mostly herded into planet-free zones like the asteroidbelt between Mars and Jupiter.

Blast-furnace Planets

The inner planets (Mercury,Venus, Earth and Mars) likely started off as hot balls of molten metaland rock. Like a blast furnace used for making iron, most of the metalsank to the center of each planet and a thin, rocky crust formed on thesurface. The crust material of these planets generally has much less metalthan the raw ingredients of the solar system. Most crust is the equivalentof the slag, or discard, from a blast furnace, and there are just a fewplaces near the Earth's surface where metal ores are concentrated enoughto make mining worthwhile.

The good stuff is deep withinEarth's interior.

What's in a Meteorite?

Ironmeteorite	Stonymeteorite	Earth'scrust
Iron91% Nickel 8.5% Cobalt 0.6% Source: Encyclopaedia Britannica	Oxygen36% Iron 26% Silicon 18% Magnesium 14% Aluminum 1.5% Nickel 1.4% Calcium 1.3%	Oxygen49% Silicon 26% Aluminum 7.5% Iron 4.7% Calcium 3.4% Sodium 2.6% Potassium 2.4% Magnesium 1.9%

Riches in the Rubble

Solar system rubble still collideswith the Earth -- the smaller rocks reach the ground as meteorites. Somemeteorites are nearly pure stainless steel, born in ancient supernovas.

Most of the asteroids aremade of the same stuff as meteorites. They too are rich in useful metalsand chemicals such as water and carbon, and hence their commercial potential.

An example of the possibleriches amongst this rubble of the solar system is the asteroid Amun. Theorbit of this mile-wide object comes close to the Earth's orbit and, overmillions of years, it could be a threat to the Earth. Before then, however,it is likely that mankind will have visited the asteroid and mined it awayto nothing, because research indicates Amun is made from that primordialstainless steel. Planetary Scientist John Lewis, from the University ofArizona, estimates that the iron, nickel and cobalt in this single asteroidis worth about $20,000 billion at market prices.

Amun is unusually rich inmetals and is typical of perhaps only 5 percent of asteroids. Most asteroidscontain more rock than metal, but at least half of the material in theseso-called stony asteroids could also be put to human use.

Let the Asteroids Come toUs

Some half a million asteroids100 yards across or larger orbit the Sun along paths that cross or comeclose to the orbit of the Earth. In principle, it is easier to reach about100,000 of these "Near Earth Asteroids" and return a payload to the Earththan it is to return the same payload from the Moon.

Therecent Deep Space 1 flyby of asteroid Braille showed that we have the spacetechnology to reach Near Earth Asteroids. By using material mined in space,mission planners could avoid the very high cost of launching materialsfrom Earth.

The biggest technical difficultyin mining solid metal asteroids such as Amun might be the task of choppingchunks of metal from the main block. On Earth we have never had the luxuryof mining a giant lump of pure stainless steel, so we don't even know howto do it.

Still, there is plenty ofiron in common asteroids that could be mined using conventional techniques.These asteroids also contain water, which is not only important for survivingand manufacturing in space but also has potential as a rocket propellant.

A New Steam-powered "Rocket"

In 1829 George Stephensen wonthe first ever railway competition with a steam engine called the "Rocket."Although steam engines have now gone out of style on the surface of theEarth, there is great potential for steam-powered rockets in space.

In the vacuum of space acraft produces thrust by shooting matter at high speed out an exhaust portal.Conventional rockets burn exotic chemicals and the combustion productsare forced out of a rocket nozzle to produce thrust.

An alternative to a chemicalrocket is to heat a volatile material (a material which readily forms agas) and expel the resulting superheated gas from the rocket chamber. Thenatural choice for this expendable material is water. Possible sourcesof heat are nuclear or solar power.

The main obstacle to steampowered rockets is the cost of launching tons of water into space fromthe Earth's surface. At a current cost of thousands of dollars per poundlaunched, we might as well send exotic chemicals into space -- the costof the material becomes irrelevant.

But what if we could obtainwater in space? The Moon's polar regions are suspected of holding frozenwater, but the lunar poles are difficult to reach and launching payloadsfrom the Moon is technologically and economically difficult. The obvioussource of water is Near Earth Asteroids, because asteroids typically contain10 to 20 percent water in the form of permafrost or saturated minerals.Dormant comets also orbit the Sun near the Earth, and these "dirty snowballs"likely contain more than 50 percent water.

There is another advantageto using water in space rockets. A thick layer of water ice around a mannedspacecraft makes an excellent shield from radiation and small meteoroids.Water storage tanks could surround the habitable modules of spacecraft,like igloos in space.

The Next Giant Leap for Mankind

Our Earth-based technology formining and processing raw materials needs to be adapted for use in space-- for mining the asteroids. If the dreams of science fiction writers areto become a reality and humans are to colonize space, then the next stepis to tap into the vast resources of the rubble of the solar system.