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Elon Musk seems to have a plan to deploy destructive capabilities to orbit within the next two years that are comparable to the nuclear arsenal of the late forties of the last century.
Little Boy that destroyed Hiroshima had a destructive power of 15 kilotons of TNT equivalents. A napkin calculation on Reddit put BFR to 16.22 kilotons of TNT equivalents.
Refueling in orbit means deploying that much explosive power to rockets in orbit.
There's almost no talk about about the cybersecurity of what he wants to build and it seems doubtful that the process he's currently using takes care of producing structure that keep out determined cyber attackers.
Getting to Mars is nice but it feels like the fact that we haven't had the ethical discussion about proliferation when it comes to Musk is a potential catastrophic error.
If a starship full of fuel is in orbit, and gets nudged downward, hitting the earths atmosphere, it gets very hot. If it doesn't have a giant heatshield, it will vaporize the fuel, leading to an explosion in the upper atmosphere. If you used the fuel to slow down, you could reach earth with mostly empty tanks, but still cause some damage if you hit a city.
It seems to me like fuel wise, a starship has enough full to start from earth, go to orbit and then come down with one tank. Most of the fuel is expended on launch. While you will need to expend some fuel to slow down, I don't see why the starship shouldn't be able to touch earth with a lot of fuel inside.