>I just wonder if humanity’s adventurous nature is leading us away from a proper focus on the sustainability of our civilization, our specie, and our fragile planetary environment?
But we still need spaceflight at least for planetary defense against asteroids, mining asteroids(so we don't have to mine Earth), etc.
With chemical rockets, not much.
With "a propellant-less propulsion propulsion system such as solar sails or electric sails," bringing water (propellant) to low-earth orbit starts making sense [1], as does mining platinum, but only if "the quantity of platinum from space would substitute an equal quantity of terrestrial platinum," i.e. moving heavy industry off the Earth's surface [1].
Given asteroid-mining profitability is dominated by "the throughput rate, which depends on the mining process," it's possibly to see a path to certain rare-earth minerals becoming profitable to mine in space if environmental controls on Earth are tightened while constant-thrust propulsion technologies advance.
The energy involved in chemical rocketry is actually not that much. Getting a kilogram to LEO is roughly as expensive (in energy) as flying it to the other side of the world in an airliner. Getting stuff back from an earth-crossing asteroid can also be very cheap energetically, with very small delta-V (if one is willing to wait long enough).
Also, the materials we're talking about from asteroid mining, like platinum group elements, probably are shipped by air, just for security.
This whole argument is reminding me of the facile and bogus argument that launch to earth orbit from planet's surface is expensive because of the energy needed.
So far we have... "maybe platinum." Maybe!
Aside from the conspicuous absence of math, "maybe platinum" isn't remotely important enough a factor in earthbound mining to justify asteroid mining on the basis of preserving earth, obviously.
I don't need to argue things are practically mineable in space to rebut the point. I just need to argue if they aren't practically mineable, energy consumption isn't a reason.
I have already given you the counterargument.
> we have maybe platinum
Those making the energy argument need to rebut every possibility. The "it takes to much energy to ship back" is ludicrously wrong for platinum. The argument destroyed, why would we need to say more?
It takes as little as 0.1 km/s delta V to get onto an Earth-intersecting orbit from known NEOs. The energy of a mass moving at 100 m/s is 5x10^3 J/kg, or 1.4e-3 kWh. If a kWh costs $1 in space, this would be a fraction of a cent per kilogram. This delta-V is so small that the energy cost of sending back base metals would be affordable. Hell, the energy cost of shipping gravel from space would be affordable! Other costs, probably not, but that's not the claim we're addressing.
So far that's the best answer, so thanks for providing it.
You may also find in your scrolling that I did not say "it takes too much energy to ship back." I said "What resources are on asteroids that justify the energy expenditure to get from space and back?"
Obviously getting down is not the expensive part. We've all heard of gravity. Getting the equipment up that is needed to get stuff down is. This is also due to gravity.
I'm afraid you misread my first comment and responded as if I thought it was energy expensive to drop stuff onto earth.