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2002-Feb-18, 12:31 PM
Just sat down and watched an episode of Star Trek The Next Generation. The episode was "Relics". In it, the crew comes upon what is termed a Dyson's Sphere. This sphere is constructed completely around a star at the distance the Earth is from the sun. Inhabitants can then live on the inside skin of the sphere. Interesting.

I checked the web, There was actually a Freeman Dyson. But, given the task, and assuming that we could accomplish such an engineering feat, would something like this work? Or is it a baaad case of Bad Astronomy? I'm jsut thinking about the ramifications of the solar wind against the inside of the sphere. It could turn into the universes's largest microwave oven!!

Roy Batty
2002-Feb-18, 12:53 PM
Bad astronomy in Star Trek, never! /phpBB/images/smiles/icon_eek.gif /phpBB/images/smiles/icon_wink.gif
I guess a sphere would be a bit impractical since all that energy would be enclosed. I think a thin disc ala Larry Nivens 'Ringworld' & also the orbitals in Ian M Banks Culture novels, would be more practical from that point. Of course it would still need stabilising thrusters of some sort to keep it in orbit around the sun (net gravity in centre being zero).
I enjoyed that episode (Scottie instructing the holodeck to recreate the bridge of the original Enterprise.. 'NCC1701 & no bloody A B C or D' or something like that /phpBB/images/smiles/icon_smile.gif

GrapesOfWrath
2002-Feb-18, 12:58 PM
On 2002-02-18 07:31, trusty wrote:
I checked the web, There was actually a Freeman Dyson.
There's a few web references to Dyson Spheres too. Here's a Dyson Sphere FAQ (http://www.student.nada.kth.se/~nv91-asa/dysonFAQ.html) that seems pretty reasonable, although I didn't read all of it. It says:

The original proposal simply assumed there would be enough solar collectors around the star to absorb the starlight, not that they would form a continuous shell. Rather, the shell would consist of independently orbiting structures, around a million kilometres thick and containing more than 1e5 objects. But various science fiction authors seem to have misinterpreted the concept to mean a solid shell enclosing the star, usually having an inhabitable surface on the inside, and this idea was so compelling that it has been the main use of the term in science fiction. The earliest appearance of this version seems to be Robert Silverberg's novel Across a Billion Years.

Mnemonia
2002-Feb-18, 01:13 PM
Wouldn't be able to live on the inside surface (not without those imaginary "gravity boots" anyway). Gravity is balanced anywhere inside of a sphere; add a sun in the middle and the gravity toward the center and opposite side is now greater than what's under your feet, so you float right off toward the sun. What a cruel way to die after investing such enormous resources to build the thing.

<font size=-1>[ This Message was edited by: Mnemonia on 2002-02-18 08:14 ]</font>

GrapesOfWrath
2002-Feb-18, 01:20 PM
On 2002-02-18 08:13, Mnemonia wrote:
the gravity toward the center and opposite side is now greater than what's under your feet, so you float right off toward the sun.
Unless you, and what you are standing on, is in orbit. Then you'd just orbit together. You could fly.

Silas
2002-Feb-18, 02:44 PM
You spin the puppy... (Okay, it's made of Krell Steel, or Scritch, or Garble-lepton Buzzword matter...) At the equator, you have "gravity," which fades in strength the farther north or south you go...

I was disappointed in Star Trek for introducing something so vastly promising -- let's explore it and find all the new civilizations! -- and then just destroying it. Feh. Cowards.

(Credit to Deep Space 9 for introducing the first actual *CHANGE* in the Star Trek cosmos!)

Silas

Valiant Dancer
2002-Feb-18, 04:55 PM
On 2002-02-18 07:58, GrapesOfWrath wrote:


On 2002-02-18 07:31, trusty wrote:
I checked the web, There was actually a Freeman Dyson.
There's a few web references to Dyson Spheres too. Here's a Dyson Sphere FAQ (http://www.student.nada.kth.se/~nv91-asa/dysonFAQ.html) that seems pretty reasonable, although I didn't read all of it. It says:

The original proposal simply assumed there would be enough solar collectors around the star to absorb the starlight, not that they would form a continuous shell. Rather, the shell would consist of independently orbiting structures, around a million kilometres thick and containing more than 1e5 objects. But various science fiction authors seem to have misinterpreted the concept to mean a solid shell enclosing the star, usually having an inhabitable surface on the inside, and this idea was so compelling that it has been the main use of the term in science fiction. The earliest appearance of this version seems to be Robert Silverberg's novel Across a Billion Years.


Here's a site which explains the Dyson sphere from a Star Trek perspective.

http://www.ditl.org/ships/heddyson.htm

It even makes reference to Freeman Dyson.

Yeah, I'm a trekkie. Why do you ask? /phpBB/images/smiles/icon_lol.gif

Kaptain K
2002-Feb-18, 05:35 PM
I guess a sphere would be a bit impractical since all that energy would be enclosed.
Not really.
1) the energy per unit area is the same as that for a planet at the same distance. In other words, there may be a lot of energy, but there is a lot of area as well.

2) The whole point of a Dyson Sphere is that when a civilization reaches the point where it needs the entire energy output of a star, then the best way to harness the star's energy is to build a sphere around it.

Roy Batty
2002-Feb-18, 07:55 PM
1) true, well at least it would be the same as at a point 90 degrees to the incident rays on a planet ie one season all the time.. oh hang on theyd have sun blocking panels or something /phpBB/images/smiles/icon_smile.gif

2) Yes, & i guess such a technologically advanced builder would have a means of getting rid of any excess energy anyway.

I'll shut up & get me coat /phpBB/images/smiles/icon_smile.gif

Chuck
2002-Feb-19, 05:00 AM
Maybe the people should live on the outside of the sphere. Then the sun's gravity would hold them to the surface. Since the sun has about 330,000 time the mass of the earth, the sphere would have a surface area 330,000 times that of the earth if you want the same gravitational pull.

GrapesOfWrath
2002-Feb-19, 12:11 PM
On 2002-02-19 00:00, Chuck wrote:
Maybe the people should live on the outside of the sphere. Then the sun's gravity would hold them to the surface. Since the sun has about 330,000 time the mass of the earth, the sphere would have a surface area 330,000 times that of the earth if you want the same gravitational pull.

That would make it, what, five times the radius of the Sun now? You're going to have some hotfoots.

Chuck
2002-Feb-19, 01:24 PM
They could use air conditioners. They'd have plenty of solar power to run things.

Roy Batty
2002-Feb-19, 01:41 PM
On 2002-02-19 08:24, Chuck wrote:
They could use air conditioners. They'd have plenty of solar power to run things.


Lol!
btw i'm now crosseyed from looking at your website /phpBB/images/smiles/icon_smile.gif

SeanF
2002-Feb-19, 01:46 PM
They'd also need lights. If they're living on the outside of a solid sphere enclosing the sun, they're certainly not getting any direct sunlight!

BTW -- what would be the effect of the sun's gravity on such a sphere? Being that close, the gravity'd be pretty strong, wouldn't it?

We've discussed hollow spheres and gravity before, but that was within the context of the sphere's influence on an object inside it . . . what about the internal object's influence on the sphere itself?

GrapesOfWrath
2002-Feb-19, 03:51 PM
On 2002-02-19 08:46, SeanF wrote:
BTW -- what would be the effect of the sun's gravity on such a sphere? Being that close, the gravity'd be pretty strong, wouldn't it?

One g

Strong enough.

Kaptain K
2002-Feb-19, 04:48 PM
BTW -- what would be the effect of the sun's gravity on such a sphere? Being that close, the gravity'd be pretty strong, wouldn't it?
The relationship is symetrical. The sphere has no effect on the star and the star has no effecton the sphere. If an asteroid hits the sphere and gives it a nudge, eventually they will collide. If the star has an asymetric CME and starts drifting, eventually they will collide.
In other words, without active stabilization, eventually they will collide.

_________________
When all is said and done - sit down and shut up!

<font size=-1>[ This Message was edited by: Kaptain K on 2002-02-19 11:49 ]</font>

GrapesOfWrath
2002-Feb-19, 06:16 PM
On 2002-02-19 11:48, Kaptain K wrote:
The sphere has no effect on the star and the star has no effecton the sphere.
Yeah, in the same way that the earth has no effect on an apple hanging on a tree.

Since the gravity would be one g, the sunward force would be the same as on that apple. Or the roof of the superdome. Hey, that's what it would be--a gigantic dome held up by itself. The spans would be pretty flat, too.

The Bad Astronomer
2002-Feb-19, 06:44 PM
Yikes!

The Sun's gravity is not one g at the Earth's distance! The acceleration due to gravity is equal to G x m / r^2, where g = Newton's constant, m = mass and r = distance. For the Earth, that comes to the familiar 9.8 meters/second^2 at the surface.

Putting in the Sun's mass and distance, I get 0.006 m/s^2, or 0.0006 gravities at the surface of the Dyson sphere.


<font size=-1>[ This Message was edited by: The Bad Astronomer on 2002-02-19 13:46 ]</font>

GrapesOfWrath
2002-Feb-19, 07:31 PM
Sorry, BA, didn't mean to wake you up!

We were discussing Chuck's hypothetical Dyson sphere with only 300,000 times the surface area of the Earth. It's radius is only five solar radii, I think.

The Bad Astronomer
2002-Feb-19, 08:13 PM
Ah, I missed that reference. To get one gravity, I get a sphere with radius = 4.5 million kilometers, roughly 6.5 times the Sun's radius. That's a surface area of 6.4 x 10^13 square kilometers, compared to 1.3 x 10^8 for the Earth, a factor of roughly 500,000 times the Earth's surface area.

SeanF
2002-Feb-19, 08:43 PM
Okay, either my numbers are wrong or my math is. Sol's got a mass of 332946 Earth masses . . . square root of that is about 577.015, so at 577.015 times the distance, we'd have the same gravity, right?

Earth diameter = 12756Km, Sun diameter = 1,392,000Km, ratio = 1/109.1251, 577.015/109.1251 = approx. 5.29 solar radii.

I'm closer to Grapes' numbers than to the BA's, and that don't seem right! /phpBB/images/smiles/icon_wink.gif

The Bad Astronomer
2002-Feb-19, 09:00 PM
Um. I just redid the calculation a different way and now get a distance of 3.7 million kilometers, or 5.3 solar radii. I have no idea what I did before, but it was wrong.

Chuck
2002-Feb-19, 10:09 PM
Lighting would not be a problem. Drill a hole anywhere.

How hot would it be? If it's 5.3 solar radii from the sun it's surface area would be about 28 times that of the sun. Since it traps all of the sun's output it would eventually radiate at 1/28 the sun's surface temperature in Kelvins, right?

Chuck
2002-Feb-19, 10:13 PM
The calculation was easy. Since the gravitational pull decreases with the square of the distance and the area of the sphere increases with the square of the distance the two cancel out and the surface area is directly proportional to the mass of the star.

kucharek
2002-Feb-20, 07:52 AM
On 2002-02-19 17:09, Chuck wrote:
How hot would it be? If it's 5.3 solar radii from the sun it's surface area would be about 28 times that of the sun. Since it traps all of the sun's output it would eventually radiate at 1/28 the sun's surface temperature in Kelvins, right?

You mix temperature and energy and we talk about radiation.
You'll have 1/28th of the energy flow per area unit. But there is not a linear relation between
temperature and energy radiated. It is actually proportional to the fourth power of the temperature, that means, if you double the temperatur (in Kelvin) of a body, it radiates 16 times more energy. So, to get rid of 1/28 of the energy per area unit of the sun, tghe body must have a temperatur of 1/2.3 (~2/5th)
of the suns temperature.
I hope I'm not badly wrong with this.
Harald

GrapesOfWrath
2002-Feb-20, 10:22 AM
On 2002-02-20 02:52, kucharek wrote:
You mix temperature and energy and we talk about radiation.
Worse, there is a zone above the Sun's "surface" that is many times hotter.

Wiley
2002-Feb-20, 03:11 PM
On 2002-02-20 05:22, GrapesOfWrath wrote:
[quote]
Worse, there is a zone above the Sun's "surface" that is many times hotter.


The corona is so rarified, do you think it would make a difference? Sure, its 1,000,000K but it's also almost vacuum. Is there that much energy?

GrapesOfWrath
2002-Feb-20, 03:30 PM
On 2002-02-20 10:11, Wiley wrote:
The corona is so rarified, do you think it would make a difference? Sure, its 1,000,000K but it's also almost vacuum. Is there that much energy?
No, I'm sure it doesn't, I just meant to point out that you have to be careful in extrapolating temperatures by radius. Well, more than careful.

Darasen
2002-Feb-22, 04:56 AM
Something just occured to me. In the contaxt of the ST:TNG episode "Relics" version of the sphere. This thread has been assuming that there were people in it. If I remember the episode the crew found no signs if life. So, is it reasonable to say maybe the sphere was not such a great success after all ? /phpBB/images/smiles/icon_smile.gif

Darasen

Valiant Dancer
2002-Feb-22, 12:40 PM
On 2002-02-21 23:56, Darasen wrote:
Something just occured to me. In the contaxt of the ST:TNG episode "Relics" version of the sphere. This thread has been assuming that there were people in it. If I remember the episode the crew found no signs if life. So, is it reasonable to say maybe the sphere was not such a great success after all ? /phpBB/images/smiles/icon_smile.gif

Darasen


It was quite a success, until the star became unstable. Then it had to be abandoned. (although they never explained why)

DJ
2002-Feb-22, 08:53 PM
Love the concept, can't ever imagine it occurring. I did some web research on them as well, and basically, one could never really be built.

There simply is not enough material in our entire solar system to construct a full sphere around our sun. (Or probably any other sun.)

If a civilization could import the material, sure it could be built, but if you could go to another solar system to get the material, heck, why not just take up residence there.

There are some calculations which suggest that there could NEVER be enough matter in a single solar system to construct the sphere. If there was, then it would have evolved already into a binary system, or some other contrivance.

I suppose there are tons of theoretical solutions (nebula vacuuming comes to mind) but none really seem practical, no matter what the technological capability.

DJ

Darasen
2002-Feb-22, 09:42 PM
You could always use <h3>REALY</h3> Big replicators /phpBB/images/smiles/icon_smile.gif

Darasen

<font size=-1>[ This Message was edited by: Darasen on 2002-02-22 16:42 ]</font>

DJ
2002-Feb-22, 11:30 PM
Ayup, that would do it. Really really big. However, would it then be my understanding that replicator technology makes something from nothing?

If in fact they make something from something, then one would need an equal mass of some thing, whatever replicators eat I guess... so bzzzzzzzzt. /phpBB/images/smiles/icon_wink.gif

David Hall
2002-Feb-23, 02:39 PM
I remember reading somewhere about building a Dyson Sphere with some kind of energy-matter converter. Just set up a field of some sort around the star and use it's own radiating energy to create a shell of super-strong matter around it. Just a simple 2-step process. /phpBB/images/smiles/icon_lol.gif

As for "Relics", I remember one thing that bugged me about it. When the Enterprise was inside the sphere, the inner surface was covered with various highly visible terrain and water features. But of course, at that scale such features would have to be absolutely gigantic to be visible at all--I mean world-sized and bigger. There should have been no more than a vague blue-green haze all around them.

But then again, that wouldn't make for very good TV would it?

Chuck
2002-Feb-23, 09:41 PM
According to my calculations, if you convert the volume of the earth to a Dyson Sphere of 93 million miles radius it would be about .38cm thick. There's a lot more matter in the solar system than that. How thick would it have to be?

The most horrible thing about Relics is, when Scotty finds out his rescuers are from The Enterprise he says he wouldn't be surprised if Jim Kirk himself brought the ship out of mothballs to come looking for him. But in Star Trek: Generations, which takes place decades earlier, Scotty is aboard The Enterprise-B when Kirk is apparently killed by a hull breach. He should think that Kirk is dead.

Donnie B.
2002-Feb-24, 01:24 AM
Hmmm...

At m = e/c^2, you'd have to trap a whole lot of energy to make each gram of matter. Even at 100% efficiency, you couldn't accumulate mass faster than the star was burning it.

In its nuclear fusion processes, our sun loses about 5 million tons of mass per second. If it's one AU in radius, our Dyson sphere has a surface area of about 1.1x10^17 square miles. Assuming we can turn all that radiation back into mass, we'll get about one millionth of an ounce per square mile of our sphere's surface per second, or about three pounds of matter per square mile per year. And of course, this is a very optimistic scenario; any real conversion process would be considerably less than 100% efficient, even if it could trap the entire flux of the star.

We're gonna have to wait a long time before we call for the moving van...

(Sorry about the funky units, I didn't feel like converting everything to SI.)

...

Could that episode of ST-TNG have been made, or at least written, before the Generations script? Maybe it was the latter that was "wrong". Of course, there are numerous other ST non-sequiturs and contradictions. For example, we should have already had the "genetic wars" that led to Khan fleeing Earth.

...

By the way, Larry Niven has written some very entertaining speculations about ringworlds, Dyson spheres, and similar schemes. My favorite is the "spaghettiworld" concept: a relatively small tube (in cross section) stretching around the star, with windows to let in the light, rotating around its long axis for gravity. It's easy to build up from relatively small sections to much longer ones, and they can be extended all the way back to form a closed loop... or simply extended indefintely, looping around and around the star until you have a tangle of inhabited spaghetti.

Kaptain K
2002-Feb-24, 11:42 AM
I am fairly familiar with the works of Larry Niven , but I cannot recall reading about "spaghetti world". Could you point me to a book or story where he discusses it?

Donnie B.
2002-Feb-24, 01:27 PM
Niven's discussion on ringworlds and the like can be found in his collection A Hole In Space, in the essay titled "Bigger Than Worlds".

James
2002-Feb-25, 02:52 AM
On 2002-02-23 20:24, Donnie B. wrote:

Could that episode of ST-TNG have been made, or at least written, before the Generations script?

Relics (http://www.tvtome.com/StarTrekTheNextGeneration/season6.html#ep130) aired as the fourth episode of the sixth season. Generations (http://www.tvtome.com/tvtome/servlet/GuidePageServlet/showid-137/epid-34293/) was released six months after the series finale. IIRC, the filming started right after the end of filming on All Good Things... IMO, they just didn't do their research. Also, IIRC, it was said that he had degraded some while in the transporter buffer for 75 years.

David Hall
2002-Feb-25, 04:44 AM
On 2002-02-23 20:24, Donnie B. wrote:
Hmmm...

At m = e/c^2, you'd have to trap a whole lot of energy to make each gram of matter. Even at 100% efficiency, you couldn't accumulate mass faster than the star was burning it.

In its nuclear fusion processes, our sun loses about 5 million tons of mass per second. If it's one AU in radius, our Dyson sphere has a surface area of about 1.1x10^17 square miles. Assuming we can turn all that radiation back into mass, we'll get about one millionth of an ounce per square mile of our sphere's surface per second, or about three pounds of matter per square mile per year. And of course, this is a very optimistic scenario; any real conversion process would be considerably less than 100% efficient, even if it could trap the entire flux of the star.

We're gonna have to wait a long time before we call for the moving van...


Well, leave it to the brains to deflate my hopes. I was thinking of getting started right away and having it done in a couple of years. I guess I'll just call up Magrathea and order a custom-made planet instead. /phpBB/images/smiles/icon_biggrin.gif

Actually though, is it really such a big deal that the energy conversion would be so slow? I mean, do you think more conventional means would be that much faster? And this one would surely save a lot of trouble, just sit back and watch your bubble world grow, more or less.

Ok then brainiacs, at 2 pounds per square mile/year, about how long do you think I'd have to wait. I guess we should assume the converted matter is something along the lines of diamond but even stronger, maybe a kind of buckytube material? How thick would it have to be, 100 meters or so?

David Hall
2002-Feb-25, 05:02 AM
Continuing my last train of thought, you know, it doesn't have to be a simple solid sphere. I think it would be possible to create a better design to maximize the strength of the sphere and make it easier to build.

The way I envision it, start with a lattice of superstrong cables/girders. Stretch them out around the star in a geodesic pattern. This could then be used as a foundation to support a thinner surface covering. It also has an advantage in that once you have the structure down, you can work on laying down the surface at your leisure, a section at a time.

Also, since you'd probably be rotating it for gravity, the important part of the sphere is around the equator. So make that band very strong and specifically designed for habitation. As you reach further north and south, the sphere can be thinner and less complex. I suppose what I'm imagining is a kind of super-ringworld with a solid center ring and a simple shell of material or even just a lattice to fill out the rest of the sphere.

Kaptain K
2002-Feb-25, 07:42 AM
I guess I'll just call up Magrathea and order a custom-made planet instead.
Designed and supervised by Slartibartfast? /phpBB/images/smiles/icon_biggrin.gif

_________________
When all is said and done - sit down and shut up!

<font size=-1>[ This Message was edited by: Kaptain K on 2002-02-25 02:44 ]</font>

GrapesOfWrath
2002-Feb-25, 11:52 AM
Pomp and Circumstance (http://sentient.home.mindspring.com/dan/pomp.mid), a new bright and shining light (http://antwrp.gsfc.nasa.gov/apod/ap020221.html), blah blah blah blah, congratulations, etc., Doctor Kaptain K!

<font size=-1>[Just wanted to add a little fireworks (http://sentient.home.mindspring.com/dan/firework.gif).]</font>

<font size=-1>[ This Message was edited by: GrapesOfWrath on 2002-02-25 07:15 ]</font>

David Hall
2002-Feb-25, 02:47 PM
On 2002-02-25 02:42, Kaptain K wrote:

Designed and supervised by Slartibartfast? /phpBB/images/smiles/icon_biggrin.gif



Hmm. I hope not. I'd get fjords in all sorts of inconvenient locations. /phpBB/images/smiles/icon_razz.gif

And congrats from me too.

SpacedOut
2002-Mar-03, 11:13 AM
Just a note - Today 3/2/02 is James Doohan's 82nd birthday - HAPPY BIRTHDAY!!!!