GURPS Ringworld 1,000,000 AD

[Tom Kalbfus]

Originally Posted by CraigR

It would, by definition, have to be enough mass to balance against the middle ring's mass + outward spin, using the star's distance-diminished gravity well to supply the weight. This mass, tens of thousands of miles thick, would far exceed the mass of the sun. The weight pressing down would have one of two effects:
(1) It would either collapse in on itself, as in a neutron star (unlikely as the pressure would be released perpendicular to the plane of the ring), OR
(2) a nuclear fusion reaction would result, cooking the inner ring and tearing itself apart as the whole mess becomes a group of new stars, possibly falling in to the center star.

Piling on baryonic matter will not work. Jupiter's size only works because it is just 1/6 the density of Earth. It's a big gas bubble, held spherical by gravity.

Then its back to nanotubes, thicker bands are stronger than thinner ones. Intermolecular forces are stronger than solar gravity at 1 AU, so less mass is required.

[Fnord-Fnairlane]

Originally Posted by Tom Kalbfus

Your not listening. If you pile enough baryonic matter in the outer nonrotating ring, you will achieve sufficient inward force to counter the outer centrifugal force of the middle ring and thus hold it in place. I don't know how much matter this will require. The outside limit will be to have it such that the outer ring weight under Solar Gravity equals the mass of the middle ring, this assumes that the outer ring has no tensile strength at all, it could be a pile of loose rubble on a tray for instance! I do think the outer ring will have some tensile strength, especially if it is made out of carbon nanotubes.

No, YOU are not listening - there isn't enough mass in the solar system to construct the ring as described by you, even if you mine the sun - you'd have to pull actual percentage points of the Sun's mass out of the sun. Then you need the energy to get the mas from the sun to earth orbit, then to speed it up to your 1g spin rate.

Originally Posted by Tom Kalbfus

Then its back to nanotubes, thicker bands are stronger than thinner ones. Intermolecular forces are stronger than solar gravity at 1 AU, so less mass is required.

Oh jeez, you just don't get it - pull out a spreadsheet and do the maths!

Baryonic matter is not strong enough to build non-spherical structures larger than planets: they collapse under their OWN gravity into spheres. Your ringworld is a million miles wide - A square chunk of dirt five yards deep across the ring is 3.33E+22 kg, which is enough to gravitationally collapse into a planetoid. The Sun's gravity is irrelevant, it collapses under it's own mass.

[sir_pudding]

Originally Posted by Tom Kalbfus

I just got the GURPS Ice Age Download. I think I'll make it the default setting for the Ringworld. Basically everything that's true in the Ice Age book applies to the surface of the Ringworld. That is the rule.

What happened is that the ringworld "banestormed"/Downloaded/replicated some Ice Age creatures, Cro-Magnons, Neanderthals, and Archaic Homo Sapiens onto the Ringworld's surface along with all sorts of attendant animals belonging to the Pleistocene epoc, most of the ringworld floor is covered with that.

Dave Wolverton's novels Serpent Catch and Path of the Hero are set on a world with an artificial Ice age ecology. They are quite good, and very gamable, I converted them to 3e long ago, but unfortunatly I no longer have those notes.

[Fnord-Fnairlane]

I worked out the mass ratio of the roatating to stationary ring, just for jollies. I'm not a physicist, so this is hopefully close, but I may have mosplaced a zero somewhere - but the numbers look right. Where's LWCamp when you need him....

The rotating ring is doing about 1,200 km per second to generate 1g, or about 43 times orbital velocity. Thus you need 43 times as much "Rubble in a tray" to balance the forces.

Assuming the moving ring is only 100 m thick of rock and dirt, and we have an Earth normal atmosphere on top, we're already at 1% of the Sun's mass.

Or about 2,900 Earth masses. Hell, we have 2.5 earth masses worth of air.

I should work out how much mass we have to feed into our total conversion powerplant to spin the ring up to 1,200 km / second....

[Fnord-Fnairlane]

Energy calculations done:

We need 2.86 * 10^38 Joules, which is about 9.0* 10^16 kg of mass fed into our total conversion power plants to spin the ring up.

Of course, since we're minig the Sun, all we need to do is tap 100% of it's energy output for about a century, and convert that at 100% effeciency into kinetic energy.

Note that this assume that the ring is only about 100 yards thick, not real dense (2.0), and that we can ignore the Laws of Thermodynamics regarding the conversion of energy. Feel free to add some multipliers if, you know, you want to use actual physics.

Have I made the point yet - or do you still think a RingWorld can be built of baryons?

[Fnord-Fnairlane]

Important point on the above energy calcs: it ignores the actual construction - I'm assuming the mass magically appears in the right spot - I didn't bother to work out how much energy it would take to get the mass out of the sun's gravity well.

We also, of course, ignoring whatever the "mag lev track" is supposedly made of, and how IT holds together under the forces applied to it.

Then, of course, there's the small matter of engineering when you have to construct it piecemeal, which is even more impossible than the final ring itself.

Sorry, but you have to invoke unobtanium to build it.

[naloth]

Originally Posted by Fnord-Fnairlane

Important point on the above energy calcs: it ignores the actual construction - I'm assuming the mass magically appears in the right spot - I didn't bother to work out how much energy it would take to get the mass out of the sun's gravity well.

Anyone capable of building this probably is constructing the star in the center as well...

[Fnord-Fnairlane]

Originally Posted by naloth

Anyone capable of building this probably is constructing the star in the center as well...

Not according to original poster. This is built where Earth was, by humans, without recourse to any rubber physics or imaginary materials. In fact, he seems to mostly be proposing materials manufacturable today (eg: nanotubes).

Originally Posted by Douglas Adams

This is, of course, impossible.

[Tom Kalbfus]

Originally Posted by Fnord-Fnairlane

I worked out the mass ratio of the roatating to stationary ring, just for jollies. I'm not a physicist, so this is hopefully close, but I may have mosplaced a zero somewhere - but the numbers look right. Where's LWCamp when you need him....

The rotating ring is doing about 1,200 km per second to generate 1g, or about 43 times orbital velocity. Thus you need 43 times as much "Rubble in a tray" to balance the forces.

Assuming the moving ring is only 100 m thick of rock and dirt, and we have an Earth normal atmosphere on top, we're already at 1% of the Sun's mass.

Or about 2,900 Earth masses. Hell, we have 2.5 earth masses worth of air.

I should work out how much mass we have to feed into our total conversion powerplant to spin the ring up to 1,200 km / second....

Its called 1,000,000 AD for a reason. In that amount of time, the Sun will make a number of close passes to other stars, the stars move after all. At some point in the next 1 million years another star will pass close enough to Sol for the inhabitants of the Sol System to mine it. Also the middle ring is about the Mass of Jupiter, but pile from 1 to 10 miles of rock and dirt on top of that, and I think you end up with the mass of something close to a red dwarf, one of those would likely be passing by the Solar System in the next 1,000,000 years. So the middle ring with rock and dirt has the mass of a brown dwarf, but its not bunched up in a ball, but in the shape of a ring, so its not a star. The outer ring may then be the mass of a red dwarf, being spread 1,000,000 miles wide and 584,300,000 miles around the sun, the gravity of they thing is probably still negligible. The mass of the Sun in the center still dominates, the mass of the system in whole is probably on the order of a binary system with one G2V class star and an M-something V star. A type 2 civilization might very well be capable of taking apart a red dwarf and making the outer ring out of it. Perhaps colliding two white dwarfs together would free up enough material for this. Some white dwarfs are made of carbon, and that would be perfect. The best place to find the material might instead by a nebulous cloud, like the Orion nebula for example, that's sure to contain enough carbon for this task.

[Tom Kalbfus]

Originally Posted by Fnord-Fnairlane

Important point on the above energy calcs: it ignores the actual construction - I'm assuming the mass magically appears in the right spot - I didn't bother to work out how much energy it would take to get the mass out of the sun's gravity well.

We also, of course, ignoring whatever the "mag lev track" is supposedly made of, and how IT holds together under the forces applied to it.

Then, of course, there's the small matter of engineering when you have to construct it piecemeal, which is even more impossible than the final ring itself.

Sorry, but you have to invoke unobtanium to build it.

But there are many centuries in 1,000,000 years, seems to me if you wait long enough one can accomplish almost anything.