GURPS Ringworld 1,000,000 AD

[Tom Kalbfus]

I started this thread in THS, but perhaps it is entirely separate. Basically it is a ringworld that doesn't use rubber physics or Superscience, it is 1,000,000 miles wide, 93,000,000 miles in diameter and centered around our own Sun and in our own Solar System in the future, and it is in the deep future. There are three rings or bands around the Sun.

The innermost one is called the Occlusion Band, it is a film of smart material that is selectively transparent or opaque depending on the electronic signals it receives, it blocks more sunling toward its edges and less toward its middle when its transparent. The Occlusion ring has a 24 hour cycle, for 12 hours it is transparent and the following 12 hours it is opaque and blocks sunlight entirely towards the middle ring or habitation ring. The Occlusion ring is about where the orbit of Mercury once was.

The middle ring is the habitation ring, it occupipes the orbit of Earth is 93 million miles from the Sun and it rotates fast enough to produce 1 G of centrifugal force, and it is 1 million miles wide. at the edges of this band are walls that are 300 miles high and 100 miles wide, these walls are covered with rock and dirt so they slope up through the atmosphere over the top of the wall and onto an airless lunar landscape that suddenly drops off into a cliff on the other side.

The outer ring is the Atlas ring, it does not rotate and it bears the weight of the world on its shoulders so to speak. The entire setting is one million years in the future and the outer ring is home to cyberspace simulations of many different past Earths, much like the infinite Worlds campaign but all the alternates are artifical, although most of the inhabitants of them don't know that. Every once in a while the ringworld disgorges some of its cyberinhabitants and then actualizes them into reality on the ringworld floor via nanotechnology. Nanotechnology isn't all pervasive but it does have its uses. There is no single civilization on the ringworld surface although there once was over 900,000 years ago, the ringworld has since been a self-maintaining artifact in spite of whatever is happening on its surface. Every once in a while humans from the stars pay it a visit. There is no FTL technology, so those starships travel slower than light.

[Bruno]

Originally Posted by Tom Kalbfus

I started this thread in THS, but perhaps it is entirely separate. Basically it is a ringworld that doesn't use rubber physics or Superscience, it is 1,000,000 miles wide, 93,000,000 miles in diameter and centered around our own Sun and in our own Solar System in the future, and it is in the deep future.

You're going to need either rubber physics or superscience to explain what the ring is made of that's strong enough to withstand the tension its under. Niven invented scrith, which is an impossible material, to do the job in Ringworld.

[Tom Kalbfus]

Originally Posted by Bruno

You're going to need either rubber physics or superscience to explain what the ring is made of that's strong enough to withstand the tension its under. Niven invented scrith, which is an impossible material, to do the job in Ringworld.

Here is a diagram showing the concept of this Ringworld


Sun *



----------- Inner ring (Occlusion Ring) -->










_____________ Middle Ring (Habitation Ring) -------------------> Velocity
_____________ Outer Ring Surface (Atlas Ring)
###########
########### Outer Ring Interior (Atlas Ring) - No velocity
###########
----------------Outer Ring Surface


The inner ring determines whether the Middle Ring (Habitation ring) receives light.

The middle ring is where people live and rotates for gravity, but it doesn't support its own weight against centrifugal force.

The outer ring supports the weight of the middle ring. Unlike the middle ring, it does not rotate around the Sun, it instead stays fixed and non rotating and it is the most massive part of the ringworld system. As you know with any support bearing members the greater the thickness, the more tensile streght it has. Its also true that the greater its mass the more its weight, but its weight is the Sun's gravitational pull on it, and the Sun pulls it inward.

The middle ring's weight is outwards since it rotates.

The outward weight of the middle habitation ring of the ringworld is less than the tensile strength of the outer ring plus the Sun's inward gravitational pull on it. There is no requirement that the rotating middle ring must support its own weight with its own tensile strength.

Now the outward bottom of the middle ring and the inward top of the outer ring are magnetized and they both point their magnetic North Polarity toward each other, and as you know from high school physics, like magnetic poles repel each other. The two surfaces of the two rings do not contact each other, but their repulsive magnetic fields transfers the outward weight of the middle ring to the more massive outer ring that has adequate tensile strenght to prevent that middle ring from flying apart. All this material for building these rings comes from the Sun, and the Sun has plenty of it with mass dwarfing that of Jupiter and with plenty of all the elements needed to build this structure.

All the material in building this ringworld is ordinary matter, nothing scrithlike about it. If you get enough material together you can add to its collective tensile strength until it becomes adequate, and that outer ring has no outward weight since it does not spin. All you need to do is get enough mass in the outer ring to do the job. Its a giant Maglev track 1,000,000 miles wide that encircles the sun. The maglev "train" is the middle ring. The inner ring simply orbits the sun separately allows light to pass through it sometimes so the ringworld can experience day, and it completely blocks the light at other times so the ringworld can have night.

Remember why I call the outer ring the Atlas Ring, remeber they mythological Titan called Atlas who beared the weight of the world on his shoulders? That is the job of the Atlas Ring.

[Mysterious Dark Lord v3.2]

Ringworlds do depend on rubber physics (or at least unobtanium, which is what scrith is). A more realistic distant future megastructure would be the Grand Array (seen occasionally in the stories of Jonni Future published by ABC Comics - mediocre stories but the setting is full of potential).

The Grand Array is a Type-I Dyson Sphere - i.e. the planets dismantled to make several trillions of space habitats of all kinds orbiting the sun at a variety of distances. From the outside, the sun would be completely dark as all of the stations absord the solar energy. In this way, all of the sun's energy is accesible by local civilizations and the habitable area of the solar system increases by a factor of billions.

Such a megastructure does not depend on rubber physics at all, merely godlike engineering skills to dismantle the planets. Millions of civilizations of all kinds can co-exist without even knowing of each other's existence.

[Gef]

Its also true that the greater its mass the more its weight, but its weight is the Sun's gravitational pull on it, and the Sun pulls it inward.

Nope. The sun exerts no net gravitational pull on a ringworld at all!

Suppose the sun is off-center inside the ring.

Some part of the ring is closeset to the sun, experiencing a greater gravitational force. Some part is farthest away, experiencin a weaker force, and all other points in the ring are somewhere in between.

If you draw a line through the sun so it intercepts the shortest possible arc on the ring (can you visualize that?), you'll see a short section close to the sun and a large section that's mostly farther away.

The problem is that the extra mass in the larger portion exactly compensates for the distance.

What this all means is that the ring is under no net gravitational force from the sun at all, and so it tends to drift, until the inhabitants in one arc get cooked!

Suppose you put a big lump in one spot. Now the lump moves the center of gravity away from the middle, and the center of gravity orbits, but the whole structure will revolve around its center of gravity.

You could set it up with a rotational period of 1 year, i.e., one day equals one year, but rotations precess, and eventually you'd get that cooking effect again.

You'd need massive attitude jets to make this whole thing work.

Now, I understand your middle ring rotates inside the outer ring, and the outer ring supports it. That's good, because even though there's no net gravitational force from the sun, there's centrifugal force. The support ring either physical touches the middle ring, or else it interacts with some kind of force like mag lev. Either way, there's friction (or there's some system to mitigate friction which itself requires maintenance).

Short version, this thing requires a huge maintenance commitment. You design it to be self-maintaining. If the self-maintenance system ever fails, everybody on a big, big world dies.

What engineer would approve such a design? Do you propose that in 1M AD, engineers have discovered a way to reduce the mean-time-between-failures (MTBF) of complex system to infinity?

Actually, it's not as challenging as all that: You just hve to get the MTBF up to the remaining durtion of the univere.

GEF

[Tom Kalbfus]

Originally Posted by Gef

Its also true that the greater its mass the more its weight, but its weight is the Sun's gravitational pull on it, and the Sun pulls it inward.

Nope. The sun exerts no net gravitational pull on a ringworld at all!

Suppose the sun is off-center inside the ring.

The plasma Sails don't let the ringworld go off center from the sun. The plasma sails vary their cross sections to intercept varying amounts of solar wind to compensate for disturbances created by planetary gravitationa fields and asteroid impacts.

Originally Posted by Gef

Some part of the ring is closeset to the sun, experiencing a greater gravitational force. Some part is farthest away, experiencin a weaker force, and all other points in the ring are somewhere in between.

If you draw a line through the sun so it intercepts the shortest possible arc on the ring (can you visualize that?), you'll see a short section close to the sun and a large section that's mostly farther away.

The problem is that the extra mass in the larger portion exactly compensates for the distance.

What this all means is that the ring is under no net gravitational force from the sun at all, and so it tends to drift, until the inhabitants in one arc get cooked!

Suppose you put a big lump in one spot. Now the lump moves the center of gravity away from the middle, and the center of gravity orbits, but the whole structure will revolve around its center of gravity.

You could set it up with a rotational period of 1 year, i.e., one day equals one year, but rotations precess, and eventually you'd get that cooking effect again.

You'd need massive attitude jets to make this whole thing work.

Or plasma sails.

Originally Posted by Gef

Now, I understand your middle ring rotates inside the outer ring, and the outer ring supports it. That's good, because even though there's no net gravitational force from the sun, there's centrifugal force. The support ring either physical touches the middle ring, or else it interacts with some kind of force like mag lev. Either way, there's friction (or there's some system to mitigate friction which itself requires maintenance).

Short version, this thing requires a huge maintenance commitment. You design it to be self-maintaining. If the self-maintenance system ever fails, everybody on a big, big world dies.

What engineer would approve such a design? Do you propose that in 1M AD, engineers have discovered a way to reduce the mean-time-between-failures (MTBF) of complex system to infinity?

Actually, it's not as challenging as all that: You just hve to get the MTBF up to the remaining durtion of the univere.

GEF

The ringworld is an intelligent entity, and is basically a living thing made out of nanotechnology, it is a self-maintaining artifact from a type 2 civilization.

The ringworld even has active geology, below the crust are tungsten pipes that deliver magma to volcanos and nanotechnology makes plates slippery so that they slide against each other, building mountain chains. Yes little cylinders are easier to maintain, but a ringworld is alot of fun. I can even have different climatic zones and seasons. I'm thinking of introducing a 1:1 map of Earth somewhere. Only the continents are 1:1, the oceans are grossly distorted. I think a polar projection centered on the North Pole is best. Heat pumps below the surface make places cold that need to be cold.

[Fnord-Fnairlane]

The "non rotating mag-lev ring" idea does not work, there are several problems with it. You cannot build a ring-world out of normal materials, they do not have the required strength.

An example: no matter how much Jello (TM) you use, or how thick you make it, you can't build a scyscraper out of it, it isn't strong enough.

Your proposed mag-lev track will gravitationally collapse under it's own mass into a series of planet-like objects, almost certainly in unstable orbits. Magnets don't help.

The second problem is that there is nowhere NEAR enough matter in the solar system to build it unless you're mining the Sun for matter, which is a difficult engineering problem.

[Tom Kalbfus]

Originally Posted by Fnord-Fnairlane

The "non rotating mag-lev ring" idea does not work, there are several problems with it. You cannot build a ring-world out of normal materials, they do not have the required strength.

An example: no matter how much Jello (TM) you use, or how thick you make it, you can't build a scyscraper out of it, it isn't strong enough.

Your proposed mag-lev track will gravitationally collapse under it's own mass into a series of planet-like objects, almost certainly in unstable orbits. Magnets don't help.

The second problem is that there is nowhere NEAR enough matter in the solar system to build it unless you're mining the Sun for matter, which is a difficult engineering problem.

Well yes, I am assuming the mining of the Sun for Matter, the planets are left alone, except for the ones that get in the way of ringworld construction. I don't know what the required mass would be for the non-rotating ring, it has only to hold itself together and hold the middle ring together. If the mass of the ring is evenly distributed the ring should be stable as all that mass is spread out over 584 million miles of circumference. The outward weight of the middle ring is only pressing out at 1 G, so it would be equal to its mass. So what you need is an inward force generated by the outer ring that equals the mass of the middle ring, now how does that force translate into tensile strength, is their a formula to do this? Once we get the required tensile strength and we know the strength of materials, then we can find the required diameter ot the outer ring that is needed to hold the middle ring together.

[Mgellis]

No need for ringworlds, as I mentioned in a related thread. Large space habitats would allow for a wide range of socieities and environments. While habitats made of steel or titanium would probably be less than 10 km. in diameter, habitats built using advanced carbon materials might be much larger.

The amount of raw material in the solar system is staggering. A single cometary body with a diameter of 100 km. masses something like 500 trillion tons. Even assuming only 10% of this material could be used for building space habitats, it would enough to build thousands of billion-ton structures (e.g., a 2 km. x 10 km. cylinder habitat). And there are probably tens of thousands of such large cometary bodies in the Kuiper Belt.

Something to think about, huh?

Recommended reading...

Finney, B. R. and Jones, E. M., ed. Interstellar Migration and the Human Experience.

Savage, M. T. The Millennial Project.

McKendree, T. L. Implications of Molecular Nanotechnology Technical Performance Parameters on Previously Defined Space System Architectures. http://www.zyvex.com/nanotech/nano4/mckendreePaper.html

Kuiper Belt Page. http://www.ifa.hawaii.edu/faculty/jewitt/kb.html

[lwcamp]

Originally Posted by Tom Kalbfus

Now the outward bottom of the middle ring and the inward top of the outer ring are magnetized and they both point their magnetic North Polarity toward each other, and as you know from high school physics, like magnetic poles repel each other.

However, high school physics does not cover Earnshaw's theorem, which says there is always a way for something supported by a static combination of magnets and/or electric charges to flip around, move around, or otherwise become unstable such that it is no longer is supported by the magnets/charges. Thus, putting north magnetic poles facing north magnetic poles will not stably levitate the ringworld sections.

There are ways around Earnshaw's theorem. Superconducting levitation, alternating fields, or even a clever arrangement of rotating magnetic poles along a track over which something magnetically slides - but you cannot do it by naiively pointing the north poles (or south poles) at each other.

Luke