Re: Brainstorming a Ringworld adventure
Posted: Sat Jul 21, 2018 2:21 pm
A well known physicist, Issac Arthur Disagrees with you, he believes that ringworlds are quite possible, he also believe space fountains, space elevators, orbital ringsSigtrygg wrote: ↑Sat Jul 21, 2018 6:06 amRingworlds are not possible with known physics an material science limitations. Everything you mention as a solution to building a ringworld requires handwavium at best, unobtanium at worst.
You can not build a ringworld by just using more matter - 1000 times you say - as the mass of matter would be ripped apart by the centripetal force of the spinning ringworld.
My version of a ringworld, and also Isaac Arthur's is a version of an orbital ring. An orbital ring is a means of getting into space without rockets. One version is an arch, with a bunch of pellets circulating inside where centrifugal force holds the arch up, the upper end of the arch extends into space, and you can use the arch itself as a giant runway to accelerate up to orbital velocity. Another orbital ring can exist entirely in space, a part of it is a belt which spins faster than orbital velocity, like the ringworld I describeThe , and another part is stationary relative to the planet's surface below. If you overlap a number of orbital rings, it can support a shellworld around a planet, like for instance Venus or Jupiter. At the right distance from Jupiter, for example, the gravity would be the same as on Earth. One can build a shellworld around Jupiter, and hold up an Earthlike atmosphere and provide artificial illumination.
The ringworld I describe is a kind of orbital ring, the outside ring is where you can stand under the influence of the star's gravity.
The gravity of alpha centaur at 1.24 AU is 0.000785 G, that means using gravity alone to hold together the ringworld you need a ratio of 1:1273 where the 1 is the mass of the ringworld and 1273 is the mass of the stationary ring. If we balled up the masses of both stars into the Sun's radius its surface gravity would be 56 G, as the total mass of both stars is twice that of our Sun. the mass of Alpha Centauri B is 0.907 times that of our Sun, and our Sun's mass is 1.9885 x 10^30 kg, so the mass of Alpha Centauri is 1.791 x 10^30 kg, this would give the ringworld a mass of 0.001406 x 10^30 kg and would give the stationary ring a mass of 1.790 x 10^30 kg. My ringworld is 1,344,000 miles wide or 2,162,958 kilometers with a radius of 186,000,000 km, which gives a circumference of 1,168,672,467 km. To find the area in square kilometers multiply 2,162,958 by 1,168,672,467 and we get 2.5278 x 10^15 square kilometers which gives us 556,220,000,000 kg per square kilometer, as there are 1,000,000 square meters per square kilometer, this gives us 556,220 kg per square meter, the density of diamond is 3.5 grams per cubic centimeter or 3,500 kg per cubic meter, so we can make a ringworld out of diamond, the strongest known material, which is 159 meters thick. An Earth like atmosphere weighs 10,000 kg per square meter, so if we want an Earthlike atmosphere on our ringworld we divide 10,000 kg by 3,500 kg and we can shave off 3 meters from the ringworld's surface to compensate. So this gives us an atmosphere that is 100 kilometers thick and a diamond structure that is 156 meters thick. Ordinary rock is around 2,200 kg per cubic meter so if we want to add a 10 meter layer of rock, we need to remove an additional 6 meters of diamond structure, leaving us a 150 meter thick ringworld structure. Now if we shave off 50 meters from the ringworld's thickness town to 100 meters, this gives us a mass budget for oceans that have an average depth of 175 meters with water density at around 1000 kg per cubic meter, If we assume that 70% of the ringworld's surface is ocean this gives us an average ocean depth of 250 meters, and since the roxck layer will stay at 10 meters thick whether under the ocean or on dry land, that will remain the same. The 1000 mile high walls amount to a rounding era, since they are only found at the edges of the 1,344,000 mile wide ringworld.
So to sum it up, my ringworld has a diamond understructure 100 meters thick with a 10 meter layer of rock on top of that, and on 70% of its surface it has 250 meter thick oceans and on top of that 100 kilometers of atmosphere which weighs 10 tons per square meter. There are voids in the 100 meter thick ringworld structure to produce topography, the highest mountains are 8 kilometers tall, 8.25 kilometers if measuring from the bottoms of oceans, those mountains are in a few places compared to areas of flat land the under-structure of the ringworld, which is on average 50 meters thick warps and bends to produce topogravy while the remaining 50 meters is flat on the bottom with voids in between. Diamond is a fairly strong material, so you can get 8 kilometer hollow structures if you need them.
Now we can get into the thickness of the stationary ring remember the stationary ring has 1273 times the mass of the ringworld itself Liquid hydrogen is 70 kilograms per cubic meter, Since the ringworld is 556,220 kilograms per square meter, the stationary ring is 708,068,060 kg per square meter, divide this by 70 kilograms per square meter, we get a thickness of 10,115,258 meters or 10,115 kilometers thick, and we have about 17 Jupiter masses of stuff to form the tank walls and other machinery to keep the hydrogen and helium liquified at cyrogenic temperatures. the same machinery in fact that cools the ringworld to keep it habitable and comfortable under than constant noon time tropical Sun.