Thanks to the film Gravity the Kessler syndrome is getting plenty of discussion at the moment. That's the idea that objects colliding in orbit could trigger a cascade, with the mass of debris produced potentially rendering spaceflight very hazardous, keeping us on the ground, grounded.
It's easy to imagine it used as a weapon, but for sci-fi and fantasy it could make for a strange new world - one not so far from the world we're in now.
Just think what would happen if in a few years private spaceflight did allow asteroids to be delivered to the Earth-Moon system and broken up for valuable metals - a mega-gold rush. Safe stations and comfortable space-based living could be made feasible. It could be a little like Elysium, the high frontier being the retreat for a small and very high class.
But Elysium suggests some of the potential problems, and it seems reasonable history could repeat, the powerful closing out the weak. And with these powerful people having robotic servants and orbital factories, the majority of the human race could become little more than a threat, a source only of instability. It would be a simple matter to collide a few asteroids and block the planet up for quite some time, especially if the capital of the space-living class is no longer available to help the development of orbital clearing tools.
They could drop a few asteroids to start a mass extinction of course, but might decide that would be crass, or prefer not to waste any, or have plans for the rest of the species.
Depending on how large a toehold they had, and how much of a headstart, by the time those on Earth opened a window back into space their repressors might be long-gone, possibly to other stars, possibly off along some hyperevolutionary track. Of course, the grounded might never make it back up, or be kept captive on the surface for a purpose...
It's an unusual background for a campaign, or a game world, a spin on the Morlock-Eloi relationship, or the power of the adeptus mechanicus, a study of the value of being first up - or having no one be first up. There'd also be a new layer of abandoned infrastructure.
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