Ringworld Minimal

[Vile]

Now, then, this is a blast from the past. I ran a short adventure using one of these minimal ringworlds, unfortunately the group had to split up for various reasons so it barely got started. One of the interesting (but also constraining) things is how controlled access is between parts of the ring, if you leave out ships or other shortcuts. The game showed signs of crystallising as a sort of "how do we sneak past the next section in order to get to the one beyond?".

 

[Werner]

Not wanting to hijack anyone's ringworld or Dyson sphere threads, I've decided to post this as a seperate topic. IMTU, I'm currently tinkering with a ringworld at the opposite end of the scale. More of a 'ring station', really.

The occupied core is no more than 3km wide, with wider secondary rims for solar energy collection. A cross-section of the core ('left' to 'right') consists of: a mag-lev transport system in vacuum; an accomodation and leisure belt; a central roadway/plaza; an industrial belt (including hydroponics and life-support); and a canal. The layout was inspired by Paul di Filippo's story A Year in the Linear City.

The central section and the roadway are roofed with a transparent material. There is no inner shadow-sqare ring, as the environment is sealed and pressurised and sections can be darkened to provide a day/night cycle.

All the usual station devices are employed, such as docking rings, compartmentalisation, etc.

Now for the questions:

1: What's the smallest type of star that such a station could be built around? Would a white dwarf star system have enough material on hand to construct it?

2: If 'up' is towards the star, would it be necessary to use artificial gravity, or could spin-induced gravity be used?

3: Alternatively, for a star 'down' ring, what would be the smallest radius necessary to induce 1G?

4: Any thoughts on tech level?

Van Maanen's Star would make the best white dwarf for a ringworld in my opinion, it is a dim white dwarf, a type F, and its habitable zone is inside its 1g radius, that means your counterweight can have less mass than your spinning inhabited ring, after all the star is supposed to be your source of light and heat, so it makes sense to have it over your head rather than below your feet. Van Maanen's star is about 14 light years away, so it is something humans may be able to visit in the next couple centuries. Now what is the minimal tech we need to build it?

First we need to get there, so we need to have a starship that can reach 10% of the speed of light, the trip will take 140 years in a generation ship, we will need a fusion reactor and limited AI robots of some sort, there is evidence of material in orbit around Van Maanen's star as there have been metals detected in its atmosphere. Van Maanen's star is an old white dwarf, so any metals in its atmosphere would have slowly sunk to the core, so it must have fallen into the white dwarf recently, so it would be out of that material left orbiting the star that we would build our 3 km wide ringworld. Over all I'd say the minimum tech level to build this thing is tech level 8.

 

[Werner]

Bromgrev said, Well, your in luck, Class M V and M IV stars are the most common sorts of stars around. A fine example of such a star is Proxima Centauri with 0.00006 times the illumination of the Sun. To get to a distance where the illumination of this star equals that of our sun, you need to reduce the radius from Proxima's center to 1,139,322 km. Proxima is roughly the size of Jupiter or about 150,000 km in diameter. Tidal forces would be fairly strong at this distance, but since a ringworld is not a planet, this is not so important. I'd say a good width for this ringworld would be 20,037 km from rim wall to rim wall, as this represents the distance between Earth's north and south pole if one follows the curves of the Earth. This ringworld's circumference would be 7,158,571 km, or about 179 times Earth's circumference at the equator. The ringworld would need an inner ring not only to provide day and night, but also to shield the ringworld from those stellar flares that often double or triple these red dwarves luminosity for a time. Instead of shadow squares, the inner ring would consist of a grid with a bunch on tiny squares in it that can rotate on hinges 360 degrees, they can shut out all the light from Proxima at a moment's notice, it might also be preferable to have the entire ringworld experience night all at once, that way the ringworld's nights are glared out by reflected light from parts of the ringworld that aren't in shadow.

The rule is basically, the dimmer the star the easier it is to build a ringworld. For one thing you don't need to use as strong material as you would for a G-Class star. Another thing is that you don't need to provide a full 1-g of simulated gravity to retain the atmosphere if you build the walls high enough. A half a g is fine and it reduces the load on the ringworld floor material.

white dwarfs have stronger gravity fields than red dwarfs as the former are dead stars in which fusion in their cores have ceased. White dwarfs give off less radiation per unit mass as they are radiating away stored heat. Van Maanen has a spectrum that is closer to our Sun than a red dwarf like Proxima and so might be more suitable for us. And I think we might want to consider making it wider than just 3 km a 20,000 km wide ringworld would represent the distance between the poles as measured along Earth's curvature, so that would be a good size in my opinion.