I'm not an expert on astrophysics, or millitary technology. Luckily, I have a friend who is an expert on both and has super-hard science fiction world building as his hobby. So I'm just going to quote him on why this isn't as big a deal as people think.
A related issue is the use of spacecraft as weapons against ground targets. This is unlikely, to say the least. As mentioned above, a sectional density of 10 tons/m2 is required to make it through the atmosphere with a reasonable amount of velocity remaining. While common ships might reach this threshold, they are almost certain to fail structurally long before impact. When they break up, the pieces are unlikely to retain sufficient sectional density to do damage. The result is a high-altitude airburst, which, given expected vessel sizes, is unlikely to do significant damage. It has even been suggested that vessels be intentionally designed to break up on atmospheric entry to reduce the risk to people on the ground.
This is from a recent paper meant as an introduction the theoretical space warfare community -of course that is a thing- consensus with an emphasis on what are called plausible mid-future scenarios.
This is from a recent paper meant as an introduction the theoretical space warfare community -of course that is a thing- consensus with an emphasis on what are called plausible mid-future scenarios.
Of course it's a thing. It's actually much more interesting than regular space opera stuff like Honor Harrington. If you have a spare day, read through Project Rho. (I drew on them a bunch for my own space warfare essay.)
A reality of physics, and one that doesn't get much play in science fiction, is that as soon as humanity gains space travel, anyone in the asteroid mining or space travel business will have city-busting capabilities at their fingertips.
It's there in classic sci-fi, but not so much recently.
This discussion was started in the comments to:
http://lesswrong.com/lw/gln/a_brief_history_of_ethically_concerned_scientists/
In the "Ethically Concerned Scientists" post, Izeinwinter commented:
A great start to a discussion here.
You've considered people going loons and some general security, but it would then become a hacker war along the lines of who could break the security and gain control of the space ships.
It doesn't address the problem of the leaders using the ships as threat weapons, since they have legitimate control, but can still make terrorist decisions.
And I'm terrified of your idea of turning spaceflight, which I see as the ultimate freedom, along the lines of Niven's Belters, into a state-controlled affair like the Soviet navy with political officers.
Now, one thing I think is a useful safety control that doesn't lead to worse problems is the destruct option. All major rockets have them right now, since if it goes out of control it's a huge hazard for a great distance. And although I don't like the idea of all personal spaceships being under a safety officers thumb, it might be better than the alternative of terrorist groups gaining control of asteroid mines and holding the world hostage.
You're right about great story potential though, in any of these scenarios.