10-07-2015, 04:41 PM
Orbital rings! I hadn't encountered that before. I'll have to think about those. My immediate reaction is that anything tethered to the ring at a speed different from the ring will find some variant of friction pulling it along with the ring, which can be overcome by using power for stationkeeping. Also questions about the strength needed to hold it together, but that's probably well understood and just requires homework on my part.
Meanwhile I found a different solution for throwing rocks. If you have moon-sized lumps of heavy stuff like iron or lead in orbit around the core, close passes to those moons can cause large changes in velocity. If you have an equal mass of rocks speeding up and slowing down, they'll cancel out and the heavy moon can maintain a normal orbit. If one pass isn't enough, have several such moons at appropriate distances. That way the first toss only has to reach the gravitational influence of the first moon, it doesn't have to get all the way to the outer shell on its own.
I was also worried about an outer shell (of whatever shape) billowing like an overly large soap bubble in the wind. Because any point of a shell is essentially a flat thin sheet, and can't push or pull against perpendicular forces. You could instead compensate in a sufficiently large ring around the billow, where there's been enough curvature that you can push along the shell rather than perpendicular to the shell. Any number of such compensations can be summed, so each point can push or pull appropriately to correct any billowing across the whole structure. You could punch the shell anywhere successfully, but the shell could always fix it relatively quickly.
Meanwhile I found a different solution for throwing rocks. If you have moon-sized lumps of heavy stuff like iron or lead in orbit around the core, close passes to those moons can cause large changes in velocity. If you have an equal mass of rocks speeding up and slowing down, they'll cancel out and the heavy moon can maintain a normal orbit. If one pass isn't enough, have several such moons at appropriate distances. That way the first toss only has to reach the gravitational influence of the first moon, it doesn't have to get all the way to the outer shell on its own.
I was also worried about an outer shell (of whatever shape) billowing like an overly large soap bubble in the wind. Because any point of a shell is essentially a flat thin sheet, and can't push or pull against perpendicular forces. You could instead compensate in a sufficiently large ring around the billow, where there's been enough curvature that you can push along the shell rather than perpendicular to the shell. Any number of such compensations can be summed, so each point can push or pull appropriately to correct any billowing across the whole structure. You could punch the shell anywhere successfully, but the shell could always fix it relatively quickly.