Ringworld Author:Larry Niven "I myself have dreamed up an intermediate step between Dyson Spheres and planets. Build a ring 93 million miles in radius - one Earth orbit - which would make it 600 millions miles long. If we have the mass of Juptier to work with, and if we make it a million miles wide, we get a thickness of about a thousand meters. The Ringworld would thus be ... more »much sturdier than a Dyson sphere. There are other advantages. We can spin it for gravity. A rotation on its axis of 770 miles/second would give the Ringworld one gravity outward. We wouldn't even have to roof it over. Put walls a thousand miles high at each rim, aimed at the sun, and very little air will leak over the edges. The thing is roomy enough: three million times the area of Earth. It will be some time before anyone complains of crowding."