It’s always interesting to me when people start bringing economics into such other worldly endeavors as space exploration. However financial gain will ultimately be the driving force to get us there.
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Twenty trillion USD is the estimated market value of a relatively small metallic asteroid that was first calculated by John S. Lewis in his book Mining The Sky: Untold Riches from the Asteroids, Comets, and Planets. Lewis argued that "using presently available or readily foreseeable technologies, we can relieve Earth of its energy problem, make astronomical amounts of raw materials available, and raise the living standard of people worldwide."
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For every billionaire, there are untold thousands of people in poverty. How will this raise the living standards for the poorest? It won't because the rich control the government, so no taxes for the rich, who won't give up their money without a fight. So let's please dispense with somehow describing the profit raping of space as a boon to all mankind.