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### Re: Brainstorming a Ringworld adventure

Posted: Sat Jul 21, 2018 2:21 pm
Sigtrygg wrote:
Sat Jul 21, 2018 6:06 am
Ringworlds 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.
A well known physicist, Issac Arthur Disagrees with you, he believes that ringworlds are quite possible, he also believe space fountains, space elevators, orbital rings
https://youtu.be/yk-Ivm9MhYs
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.

### Re: Brainstorming a Ringworld adventure

Posted: Sat Jul 21, 2018 2:52 pm
Sorry Tom , but the maths doesn't work in your or Isaac's favour.

There is no known material that can withstand the stresses on a rotating ringworld of Niven's design - Isaac even says so in his video https://www.youtube.com/watch?v=yk-Ivm9MhYs&t=27s at 9:34.
All of his solutions require handwavium and unobtanium.

In Traveller there is an option though - you build a stationary ring and fit grav plates

Building a stationary ring around a star so that the inner surface is at the 1g point is doable, you can use the same trick around a gas giant. I've seen those episodes too

### Re: Brainstorming a Ringworld adventure

Posted: Sat Jul 21, 2018 5:11 pm
Sigtrygg wrote:
Sat Jul 21, 2018 2:52 pm
Sorry Tom , but the maths doesn't work in your or Isaac's favour.

There is no known material that can withstand the stresses on a rotating ringworld of Niven's design - Isaac even says so in his video https://www.youtube.com/watch?v=yk-Ivm9MhYs&t=27s at 9:34.
All of his solutions require handwavium and unobtanium.

In Traveller there is an option though - you build a stationary ring and fit grav plates

Building a stationary ring around a star so that the inner surface is at the 1g point is doable, you can use the same trick around a gas giant. I've seen those episodes too
Are you a physicist? Isaac Arthur is, I am not, so your argument really is with him, I am just using his examples and doing the numbers.

I tend to want to keep the handwavium and unobtainium to a minimum, because I like to use things that most likely can exist rather than rely heavily on science fantasy. I am thinking about our actual future here rather than just a setting for a role playing game. I am not out to prove you wrong either, nor am I trying to win a debate, I am just trying to push my ideas and give concrete examples. I don't think Larry Niven gave too much thought to the physics of his construct, he was too busy writing a story, he gave simple solutions to holding his ringworld together, he did not think to make his ringworld into a giant orbital ring! Your ringworld here is just as legitimate, if you want to use scrith, then go right ahead, I can't prove that it doesn't exist, nor can I prove that you can't have aritifical gravity or FTL drives either. As I say, I am not a physicist, I am merely a hard science fiction fan, I like my science fiction hard, because I like disapplined thinking. the thing about the OTU, is that it can most likely happen within a computer simulation, as could a D&D world for that matter. So long as the rules for the simulation are reasonably self-consistent, and computer can simulate them, if enough of the real world physics can be simulated, then we can also simulate human minds living within them, to them, the Universes we create would seem awfully real, and if we use real world physics to simulate them, we can also build them in the real world with the same thoughts and memories that existed in the sim world they came from, thus is the kernel of my idea.

### Re: Brainstorming a Ringworld adventure

Posted: Tue Jul 24, 2018 10:16 am
I understand it's a question of stress, and the need to create artificial gravity.

Optionally, a ring of islands:

### Re: Brainstorming a Ringworld adventure

Posted: Fri Jul 27, 2018 5:58 pm
Condottiere wrote:
Tue Jul 24, 2018 10:16 am
I understand it's a question of stress, and the need to create artificial gravity.

Optionally, a ring of islands:

I don't know what that is, is it something built by the United Arab Emirates by any chance?

### Re: Brainstorming a Ringworld adventure

Posted: Fri Jul 27, 2018 6:08 pm
Tom Kalbfus wrote:
Fri Jul 27, 2018 5:58 pm
I don't know what that is, is it something built by the United Arab Emirates by any chance?
Yup, one Dubai built:

https://en.wikipedia.org/wiki/The_World_(archipelago)