04-22-2018, 03:20 AM
(This post was last modified: 04-22-2018, 03:29 AM by stevebowers.)
This is an intriguing concept. There would be a certain amount of stretching in a hoopworld of this kind, assuming we wanted to have it rotating; but I'm not sure that the value of the Earth's radius would be very relevant when considering the amount of stretching. After all, the stretching would always be along the length of the hoop, and the radius would remain the same. This stretching would represent 5.7 centimetres per kilometre - more stretching than I would expect a solid crust to absorb, actually, so the idea of having a series of flexible joints at intervals makes sense. Maybe section the planet's surface up into kilometre-sized rings or plates.
Note that most planets can be modeled as a fluid, so the hoopworld may as well be mostly made of fluid- how about making it a huge toroidal balloon full of water? Kilometre-wide landscape hoops or plates could float on top of this water, each connected by centimetre-scale flexible junctions. If the hoop is only filled with water, it could be much less dense, and would be bigger (but this makes the stretching problem worse). The centre of the hoop would be a ring of solid, high pressure ice, which would melt significantly because of the deformation (but the ice core would not melt completely, I think, instead becoming a kind of semiplastic solid).
Note also that the constant stretching and compression of the spinning hoop would gradually slow the hoop's spin, so you'd need to constantly pump energy into the hoop to maintain a constant diurnal rotation. This would warm the hoop - it would be a warm place, heated from below by friction, so you wouldn't want to put it too close to the local star- once again this would make the hoop even bigger than a simple model would predict. The ground would be warm - but the local star would appear dimmer than one might expect, because it would need to be further away to avoid overheating the surface.
Where would you get the material for this hoop from? If I were making such a hoop,, I'd either build it from an accretion disc around a T-Tauri star, which would include a lot more dust and water than a mature solar system; or I'd extract oxygen, hydrogen and other materials straight from the star, using star-mining tech as suggested by Paul Birch.
So this megastructure is doable, but it would require a constant input of energy, and could be much bigger than you suggest; the structure has some problems in common with Cableville, which also needs a flexible infrastructure and a constant input of energy to maintain rotation. If I were to put one in OA I'd put it around a red dwarf, or even a cool, old white dwarf, making it much more managable in scale.
Note that most planets can be modeled as a fluid, so the hoopworld may as well be mostly made of fluid- how about making it a huge toroidal balloon full of water? Kilometre-wide landscape hoops or plates could float on top of this water, each connected by centimetre-scale flexible junctions. If the hoop is only filled with water, it could be much less dense, and would be bigger (but this makes the stretching problem worse). The centre of the hoop would be a ring of solid, high pressure ice, which would melt significantly because of the deformation (but the ice core would not melt completely, I think, instead becoming a kind of semiplastic solid).
Note also that the constant stretching and compression of the spinning hoop would gradually slow the hoop's spin, so you'd need to constantly pump energy into the hoop to maintain a constant diurnal rotation. This would warm the hoop - it would be a warm place, heated from below by friction, so you wouldn't want to put it too close to the local star- once again this would make the hoop even bigger than a simple model would predict. The ground would be warm - but the local star would appear dimmer than one might expect, because it would need to be further away to avoid overheating the surface.
Where would you get the material for this hoop from? If I were making such a hoop,, I'd either build it from an accretion disc around a T-Tauri star, which would include a lot more dust and water than a mature solar system; or I'd extract oxygen, hydrogen and other materials straight from the star, using star-mining tech as suggested by Paul Birch.
So this megastructure is doable, but it would require a constant input of energy, and could be much bigger than you suggest; the structure has some problems in common with Cableville, which also needs a flexible infrastructure and a constant input of energy to maintain rotation. If I were to put one in OA I'd put it around a red dwarf, or even a cool, old white dwarf, making it much more managable in scale.