Dyson Sphere (shell) - Dysonica Anyone?

[Capt JT Kohonez]

I've been toying the idea of using a dyson sphere (shell) as the background for a campaign.

 

Has anyone here done this before??

Any tips?

 

Kind of inspired by that ST:TNG episode.

[Seenar]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

I used on in a fantasy concept that never made it to a game. Basically, the whole universe was the size of a shell around a central light source. Night was caused by large orbs circling the sun in various directions. Of cousre in fantasy, the weird physics worked.

 

In SF, I would suggest you first settle on how fast people can travel. Are the suck on the Sphere? If they are having to use 20th Century levels of transportation, it will take them a long time to get around.

 

If you have not read Nivin's Ringworld, I would do so. His Bigger Than Worlds essey (in Neutron Star or Playgrounds of the Mind, I forget which) is good too.

[ThothAmon]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

Dyson Sphere implies very high levels of technology and intelligence on the part of the creators. Are you planning for the creators to still be around? Are they the PCs? Or are the PCs going to be 'fallen' descendants of the creators? Or something else entirely?

 

I'd echo the comments on reading 'Ringworld' for a look at how a large world can be explored by lower-tech protagonists.

[Lord Liaden]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

We've had some fruitful discussions on this topic, and some useful links have also been posted. Check out these threads:

 

http://www.herogames.com/forums/showthread.php?t=45189

 

http://www.herogames.com/forums/showthread.php?t=36890

 

http://www.herogames.com/forums/showthread.php?t=37430

[MPT]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

I used on in a fantasy concept that never made it to a game. Basically' date=' the whole universe was the size of a shell around a central light source. Night was caused by large orbs circling the sun in various directions. Of cousre in fantasy, the weird physics worked.[/quote']

 

I wanted to run a game like this as well. In my version the sphere was created as a present for the 'good' god's wife.The 'evil' brother killed the wife and was banished to outside the sphere (thus making the 'underground' a source for evil). The 'good' god then went inside the sun to sleep away his sorrow.

 

Unfortunately the players saw the word 'Dyson Sphere' and hated the idea as they did not like the idea of (potentially) no night, and also being able to see the other side of the world by looking up.

[Dale A. Ward]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

Unfortunately the players saw the word 'Dyson Sphere' and hated the idea as they did not like the idea of (potentially) no night' date=' and also being able to see the other side of the world by looking up.[/quote']

 

 

DAMN!! You have characters that can see out to 2 AUs?!?

[SirViss]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

DAMN!! You have characters that can see out to 2 AUs?!?

 

And through the glare of a STAR?!?

[Curufea]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

IMHO - you'd think the world was flat. At that minimal curvature you could not notice it before the atmosphere blocked your line of site.

[megaplayboy]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

I've toyed with the idea of an inverted Dyson sphere, with the people, atmosphere, etc. on the outside, and three stars orbiting the sphere at intervals to enable periods of day and night. If you made the thickness of the sphere about 1/3 the radius of the Earth, and the density comparable, it could have a comparable gravitational field at the surface.

 

Of course, depending on how large it's scaled, you could have a population larger than most galaxies...

[Dr. Anomaly]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

I've toyed with the idea of an inverted Dyson sphere, with the people, atmosphere, etc. on the outside, and three stars orbiting the sphere at intervals to enable periods of day and night. If you made the thickness of the sphere about 1/3 the radius of the Earth, and the density comparable, it could have a comparable gravitational field at the surface.

 

Of course, depending on how large it's scaled, you could have a population larger than most galaxies...

Farthest Star and Wall Around a Star by Frederick Pohl and Jack Williamson...

[Curufea]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

There is no reason you couldn't have both.

 

Actually, it would make sense to have nocturnal races on the outside, and diurnal on the inside. All power generation happens on the inside - and the heat is radiated on the outside.

[megaplayboy]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

let's see, surface area of a sphere = 4 pi * radius^2, right?

 

so, (1.5x 10^8 km)^2 *12.5(roughly)=2.8 x 10^16 sq km, or 28 quadrillion square km. divide by 10 billion people, that's 2.8 million sq km per person, or about a million square miles each.

 

That's a lot of lawn to mow.

[Alverant]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

Good math Megaplayboy, but that's with a perfectly smooth inside. A dyson sphere would have mountains, lakes, rivers, deserts, oceahs, and so on. So how much of that 28 quad is actually liveable?

[Curufea]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

I think the going rate of fertile land is around 68%

[Matt Frisbee]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

Hmmm...

 

This reminds me of a fantasy campaign I ran on a ringworld. I chose that setup to 1) make the climate relatively stable, 2) eliminate the problems involed in making maps on a sphere and 3) "never" run out of space for unknown lands.

 

The closest thing I ever came to a Dyson Sphere was an attempt at running a Pelucindar (sp?) post-apoc campaign. Still, the characters in one of my Star Trek campaigns ran across a generation ship built inside an enormous asteroid which spun to provide gravity.

 

In all of the above cases, I stuck to earthly proportions for land to water. In a Dyson sphere, I'd reserve the polar regions for oceans, with some seriously unique aquatic lifeforms which have developed in low gravity water. The entrance / exit to the sphere would probably be known as "The Well" or something like that, since that would be its appearance to those who lived within the sphere.

 

I always wondered what would be brighter -- the stellar primary or the background sphere since the latter would be so much larger than the former, regardless of the albedo. In any case, there would be serious issues with life forms having to be adjusted to constant light instead of a standard day/night cycle. However, since there are lifeforms on our planet which never see the light of day, I imagine there would be strange ones adapted for constant daylight as well.

 

Matt "Just-babbling-along" Frisbee

[Curufea]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

The far surface, while larger, would also have a much sparser difusion of photons radiating away from it - so would be considerably dimmer than the star.

 

As to polar regions - what polar regions? There is no reason for a Sphere to rotate. It must already be using some form of artificial gravity to keep it stable, reduce tidal forces and torque - and keep the internal inhabitants on the surface.

[austenandrews]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

Has anyone run the numbers on a Dyson shell built close enough to the star to have 1G on the outer surface?

[megaplayboy]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

Good math Megaplayboy' date=' but that's with a perfectly smooth inside. A dyson sphere would have mountains, lakes, rivers, deserts, oceahs, and so on. So how much of that 28 quad is actually liveable?[/quote']

 

well, our planet is 2/3 covered with water, and about half our land is habitable, so that'd be about 1/6th. If the water to land ratio were, say, 1/3, then maybe 1/3 of the surface would be habitable. Of course, if you adapted the sentient life forms for each environment...

[John Desmarais]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

Has anyone run the numbers on a Dyson shell built close enough to the star to have 1G on the outer surface?

 

Too close.

 

Actually, it's all very dependent on the mass (& radius) of the star, but we can use our sun as an example.

 

The force of gravity depends on a few things: your mass, the mass of the body you are standing on, and the distance from the center of the star. The farther you are from the center of the star, the weaker the pull between the star and your body. The force gets weaker quite rapidly. If you double your distance from the star, the force is one-fourth. If you triple your separation, the force drops by one-ninth. Ten times the distance, one-hundredth the force. See the pattern? The force drops off with the square of the distance.

 

In order for our sun to exert approximately 1G, you would need to be 3,614,000 KM from the center, or 2,919,000 KM from the surface. To put this into some type of perspective, Mercury is 69,800,000 KM from the sun, so 2.9 Million KM is really, really, really, close.

 

Now, what wasn't worked into this is the gravitational pull of the Dyson Sphere itself, which will be substantial as it's mass is going to quite high (although due to the rather low radius to mass ratio it will be much lower than you'd expect for such as mass as gravitational pull is based in part on your distance from the center of mass).

 

So, how much mass is your sphere going to have?

[austenandrews]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

Too close.

 

Actually, it's all very dependent on the mass (& radius) of the star, but we can use our sun as an example.

 

The force of gravity depends on a few things: your mass, the mass of the body you are standing on, and the distance from the center of the star. The farther you are from the center of the star, the weaker the pull between the star and your body. The force gets weaker quite rapidly. If you double your distance from the star, the force is one-fourth. If you triple your separation, the force drops by one-ninth. Ten times the distance, one-hundredth the force. See the pattern? The force drops off with the square of the distance.

 

In order for our sun to exert approximately 1G, you would need to be 3,614,000 KM from the center, or 2,919,000 KM from the surface. To put this into some type of perspective, Mercury is 69,800,000 KM from the sun, so 2.9 Million KM is really, really, really, close.

 

Now, what wasn't worked into this is the gravitational pull of the Dyson Sphere itself, which will be substantial as it's mass is going to quite high (although due to the rather low radius to mass ratio it will be much lower than you'd expect for such as mass as gravitational pull is based in part on your distance from the center of mass).

 

So, how much mass is your sphere going to have?

Surely the mass of the sphere would be negligible? If we somehow managed to render the total mass of all solar bodies into the shell, it would still be a drop in the bucket.

 

What would be the interior surface temperature of a shell 6 million km in diameter? What would the shell have to be made of to withstand that temperature? Or might it be possible to construct a ginormous magnetic containment field?

 

(I don't expect anyone to have these answers, btw. Just musing.)

[Cancer]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

The scaling relation boils down to:

 

(T / Tsun) = 1 / sqrt( R / Rsun )

 

Note that Rsun ~= 1/215 AU ~= 700,000 km. Tsun = 5800K.

 

So plug in 6e6 km, you get a hair less than 2000K. Too damn hot. Most materials aren't solid at that temperature.

[megaplayboy]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

gravity is a quality which diminishes as a quality of radius from center of mass squared, while normally planetary mass is a quality based upon the density x volume(a cubic function).

 

However, with a "hollow" spheroid, if the thickness of the shell is constant no matter the radius from the center, the gravitational pull at the surface will be constant as well. If the shell has density~earth density, and thickness = 1/3 the earth's radius, then the baseline gravity at the surface will be roughly 1 g, no matter how big the sphere is.

 

So, you could have a hollow sphere of 10,000 km, 10 million km, 10 billion km, or even 10 trillion km(1 LY), all with the same surface gravity.

[Curufea]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

A third thick as Earth is quite a lot of material

[megaplayboy]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

A third thick as Earth is quite a lot of material

 

well, yes, but if you raised the density, you could reduce the thickness(of course, you'd still have the same mass of material)...

[Matt Frisbee]

Re: Dyson Sphere (shell) - Dysonica Anyone?

 

The far surface, while larger, would also have a much sparser difusion of photons radiating away from it - so would be considerably dimmer than the star.

 

As to polar regions - what polar regions? There is no reason for a Sphere to rotate. It must already be using some form of artificial gravity to keep it stable, reduce tidal forces and torque - and keep the internal inhabitants on the surface.

 

Yeah, that's fine if you're doing artificial gravity. Personally, rotation is a cheap way to produce it. Instead of a sphere, how about a partial sphere with the pole areas shaved off? That would allow for spacecraft access from two directions. Gravity would get weird near the edges, but rugged mountains would keep all but the most adventurous inhabitants out of areas of reduced gravity.

 

Matt "Too-practical" Frisbee