Friday, January 14, 2011


From a thousand miles above the Earth - from, say, a space station in a two-hour orbit - the Earth is a great sphere. The kingdoms of the world revolve below. Details disappear around the horizon's curve; other, hidden features rotate into view. At night, glowing cities outline the continents.

But from a thousand miles above the Ringworld, the world is flat, and the kingdoms thereof are all there at once. The rim wall was of the same stuff as the Ringworld floor. Louis had walked on it, in places where eroded landscape let it show through. It had been greyish, translucent, and terribly slippery. Here the surface had been roughened for traction. But the pressure suit and backpack made Chmeee and Louis top-heavy. They moved with care. That first step would be a beauty.

At the bottom of a thousand miles of glassy cliff were broken layers of cloud, and seas: bodies of water from ten thousand to a couple of million square miles in area, spread more or less uniformly across the land, and linked by networks of rivers. As Louis raised his eyes, the seas grew smaller with distance ... smaller and a little hazy ... too small to see, until sea and fertile land and desert and cloud all blended into a blue knife-edge against black space.

To left and right it was the same, until the eye found a blue band swooping up from the infinity beyond the horizon. The Arch rose and narrowed and curved over and above itself, baby blue checked with midnight blue, to where a narrow ribbon of Arch lost itself behind a shrunken sun.

This part of the Ringworld had just passed its maximum distance from the sun… but a Sol-type star could still burn your eyes out. Louis blinked and shook his head, his eyes and mind dazzled. Those distances could grab your mind and hold it, leave you looking into infinity for hours or days. You could lose your soul to those distances. What was one man when set against an artefact so huge?

- Larry Niven, 1980

The Ringworld is a hoop-shape megastructure that is constructed around a star and its dimensions are so vast that it makes the physical sizes of entire planets seem insignificant in comparison. From afar, the Ringworld will appear as a circular ribbon-like structure which completely encircles a star. The Ringworld spins in order to generate artificial gravity from centrifugal forces to establish a habitable environment across its entire inner surface. In this article, I will be describing a hypothetical Ringworld which exists around a Sun-like star.

Spanning a diameter of 300 million kilometres, a circumference of 942.48 million kilometres and a width of 2 million kilometres, the Ringworld features a habitable Earth-like environment which spans an immense area of 1880 trillion square kilometres over its entire inner surface. This unimaginably huge area is almost 3.7 million times the total surface area of the Earth! This is like having 3.7 million Earths all mapped flat and joined edge to edge. With an average thickness of 40 kilometres and with an average density that is similar to the Earth’s crust, the Ringworld is estimated to have a total mass of about 33000 times the mass of the Earth or about 10 percent the mass of our Sun.

Rim walls that are over a thousand kilometres high are found along the edges at the inner surface of the Ringworld. These walls keep the atmosphere within the inner surface of the Ringworld by preventing the atmosphere from slipping off the edge into space. The Ringworld is so huge that journeying from one rim wall to the other will mean covering a distance that is equal to circling the Earth 50 times. Additionally, circumnavigating the entire Ringworld will mean covering a vastly greater distance that is equal to circling the Earth 23500 times. Travelling at a speed of one kilometre per second, it will take almost 30 years to completely circumnavigate the Ringworld!

The enormous size of the Ringworld allows equal scale maps of entire worlds to be reconstructed on its surface. If all the continents of the Earth were reconstructed to scale in one of the Ringworld’s many great oceans, the entire archipelago of continents will span only one percent the width of the Ringworld. To generate an Earth-like gravity on the inner surface of the Ringworld, the entire megastructure will have to spin at a rate of once every 777000 seconds. At this spin rate, the rim of the structure will be travelling at a speed of 1210 kilometres per second.

Interior to the Ringworld and located at a closer distance to the central sun, an enormous ring of equally spaced rectangular shades block the sun at regular intervals to provide a day-night cycle along the habitable inner surface of the Ringworld. During the day on the inner surface of the Ringworld, the sun always appears directly overhead and night arrives following an eclipse of the sun by one of the rectangular shades.

Between the Ringworld and its sun, a series of climate control shades are positioned into another ring which has the same spin rate as the Ringworld itself such that each climate control shade remains fixed over the same region of the Ringworld’s inner surface. These climate control shades block out various fractions of the Ringworld’s sun and create cold spots on the Ringworld’s inner surface which allow temperature gradients to be generated. These temperature gradients drive large scale atmospheric and oceanic circulations. Sufficient cooling by large enough climate control shades also lead to the creation of ice caps.