I don't see how asteroid mining can be viable economically. You still need an enormous quantity of petrol to send things in space and judging by the rarefaction of said petrol its price is bound to increase a lot.
Cryogenic engines burn hydrogen from electrolysis and their fuel can be produced from renewable resources. All their atmospheric fuel is returned to the ocean by the water cycle, so little fuel is lost to the vacuum. Engine tuning limits greenhouse emissions. Magnetic projectiles can reach escape velocity with the right design.
Instead of one giant rocket, imagine swarms of small, reusable, low-emission projectiles whose payloads assemble into larger apparatuses in space.
