What would a dyson sphere look like . . .

[Timo]

Of course, that's the problem with a solid Dyson shell to begin with -- not only do you have heat accumulating, but you have the stellar wind building up inside.

Rather than a problem, this could be seen as the prime reason for building a solid shell to begin with. If you are not technologically limited to what Dyson was able to imagine, but are at least on level with the 24th century Federation, building a solid shell is a good leap towards the absolute ideal: total collection of everything the star has to offer.

Heat buildup is good for you if you can make the gradient between the inside and the outside work to your benefit. So is the buildup of anything, really. Hell, you might even run conventional steam turbines on the heat differential! Not that you'd want to, with the amazing post-Federation technologies at your disposal.

The other problem is that the gravity inside a uniform spherical shell is zero at any point.

Which probably just simplifies things. Artificial gravity, which is notoriously short-ranged when used aboard starships, would be ideal for sticking the inhabitants to wherever they are best placed. The rather feeble pull of the star would not be a factor against such technology.

And while on the first approximation, placing the inhabitants on the inside defeats the solar collection functionality, it could be a choice dictated by safety concerns (inside is better than outside as far as threats go) and aesthetics (having a single sun might be nicer than using a number of suns circling on the outside, not to mention it's certainly less wasteful) once superior technology has already been applied in making full use of the central star's emissions.

After all, we saw no mechanisms for gathering those emissions. There were mountains, seas and cityscapes, but no megastructures. We could well assume that the technology for collecting the radiation is relatively refined and consists of things placed between the surface and the star; vast physical shadow disks, perhaps, but more probably something more advanced such as a "forcefield" that siphons off the radiation. Once that is in place, it becomes a triviality to choose between inside and outside for the habitation zone.

Realistically, why would you need something that dense?

That would probably be Ringworld thinking, not really applicable on a Sphereworld. The Ringworld rotated for gravity, needing the fantastic tensile strength of this "scrith" stuff, while the Sphere apparently doesn't. And scrith is Niventalk, while neutronium as a structural material is standard Trek fare...

Why would they need to invent anything? They live in a technological construct. Their ancestors probably invented watches millennia before they moved to the Dyson sphere.

Which probably implies that at least some appreciable percentage of the inhabitants have gone feral in the intervening millennia, perhaps regressing all the way back to stone age. The designers might have catered for such a possibility, taking pains in making their Sphere "caveman proof" much like the Stargates are. Depends a bit on what the purpose of the structure is or was.

One wonders if there is any life there. If the structure is caveman-proofed, it's probably proofed against high-tech intruders, too (that is, low-tech from the Dysonite POV). All scanning for advanced life might be automagically intercepted and tampered with, then. Perhaps the Sphere is a refuge for a dying civilization - or perhaps a nursery and boot camp for multiplying that civilization quadrillonfold and then unleashing it at the universe?

There might be some truth to the star's unability having forced abandoning of the structure, of course. The shots of the surface show no hints of green; everything might be sterilized down to artificial bedrock for all we know. OTOH, we never get anything conclusive about Data's scan for lifeforms, only the theory that the Sphere was "abandoned". By identifiable humanoids? By all life?

You've still got 179.5 degrees worth of sky to look at, all of which would be taken up with the surface of the sphere.

The episode itself gives a fairly realistic view of what the surface would look like when viewed from the inner vacuum, when the E-D streaks towards the door in her bid to escape. We see the curvature, and we see a mosaic of tiny, tiny surface features that must amount to oceans dozens or hundreds of Earths wide. Add some atmospheric haze to that, and there we go...

Assuming, of course, that there does exist a filter system for gathering part of the radiation before it hits the surface or gets reflected back from there, to prevent the heat death and to serve the primary function of the Sphere.

Timo Saloniemi

 

[Forbin]

So, what would the gravity be to someone standing on the outside of a Dyson sphere? That be one hell of a massive structure. But with the mass spread out over all that area/volume, is there enough concentrated mass to make much external gravity?

 

[Christopher]

Rather than a problem, this could be seen as the prime reason for building a solid shell to begin with. If you are not technologically limited to what Dyson was able to imagine, but are at least on level with the 24th century Federation, building a solid shell is a good leap towards the absolute ideal: total collection of everything the star has to offer.

Possibly. But it does mean that the simplistic sci-fi image of a DS as simply an inert solid shell (as in the Bantam Trek novel The Starless World or as the "Relics" DS appeared to be) is woefully inadequate. A DS would have to be a much more complex, dynamic structure.

And a DS that has habitable, terraformed land on the interior is not making maximum use of the star's energy output. Dirt and trees and houses and streets are not optimal solar-power collectors. If your goal in creating a DS is to capture all a star's output, then every last millimeter of the thing would need to be dedicated to that goal. So the fictional conceit of a DS with an inhabited interior is intrinsically abandoning Dyson's original concept of total power collection.

The other problem is that the gravity inside a uniform spherical shell is zero at any point.

Which probably just simplifies things. Artificial gravity, which is notoriously short-ranged when used aboard starships, would be ideal for sticking the inhabitants to wherever they are best placed. The rather feeble pull of the star would not be a factor against such technology.

But that's so inelegant, relying on power generation for artificial gravity. It's more efficient, surely, to build a megastructure that achieves gravity through rotation. Too much sci-fi embraces overcomplicated high-tech solutions when the first principle of engineering is "keep it simple, stupid."

Why would they need to invent anything? They live in a technological construct. Their ancestors probably invented watches millennia before they moved to the Dyson sphere.

Which probably implies that at least some appreciable percentage of the inhabitants have gone feral in the intervening millennia, perhaps regressing all the way back to stone age. The designers might have catered for such a possibility, taking pains in making their Sphere "caveman proof" much like the Stargates are. Depends a bit on what the purpose of the structure is or was.

Heck, at that level of advancement, they'd probably have nanotech integrated into their bodies and wouldn't be able to lose their technology.

So, what would the gravity be to someone standing on the outside of a Dyson sphere? That be one hell of a massive structure. But with the mass spread out over all that area/volume, is there enough concentrated mass to make much external gravity?

To anyone outside, all the mass of the structure would act gravitationally as though it were located at its center of mass. So one would feel an inward gravitational pull equal to the combined masses of the star and the Dyson shell -- which, assuming the DS was assembled from the matter in the star system and not made of something absurd like neutronium, would be trivially greater than the mass of the star. (The Sun contains 99.86% of the mass of the known Solar System.) Essentially, you'd feel the same gravity that you'd feel if you were hovering in open space at that same distance from the star. Since you're standing still on a nonrotating structure, you would tend to be pulled directly inward, but the surface would prevent that.

The mass of the Sun is 2x10^30 kg, its equatorial radius is 7x10^5 km, and its equatorial surface gravity is 28 g. So if you were on a DS around Sol with a radius of 1 AU (1.5x10^8 km), then by the inverse square law, you'd feel a gravitational pull of about 0.0006 g.

 

[Timo]

But that's so inelegant, relying on power generation for artificial gravity. It's more efficient, surely, to build a megastructure that achieves gravity through rotation.

Is it? Disregarding for the moment that a sphere couldn't be "gravitized" through rotation (except at a narrow band at the equator plus perhaps "terraced" surfaces "higher up"), why should we assume that Trek style artificial gravity consumes lots of power? When a starship goes powerless, gravity is always the last thing to go. For all we know, maintaining artificial gravity takes no energy in the ideal case, and the nonidealities aren't any more severe than the nonidealities that would require input of power to keep a Ringworld turning steadily.

Trek-style artificial gravity might be as elegant as it gets - a "solid state" solution requiring no moving parts and thereby trumping the use of even a single gigantic moving part.

In any case, the gravity and its beneficiaries on the inner or outer surface would probably be secondary issues, not issues that would dictate the nature of the construct. I mean, Ringworld might be built specifically to create the habitable surface area, but the solid DS would probably primarily be something else. An energy collector, a stealth measure, a show of force... And secondarily a habitat for everybody involved, with an absurd amount of room to spare.

Timo Saloniemi

 

[Forbin]

Merging the Ringworld with the DS concept: A solid spherical shell, spinning for gravity at the internal equator. A band at the equator, therefore, is the only inhabited area. The rest of the interior surface of the sphere is given to solar power collectors, support macinery, spaceports (at the poles to eliminate lateral velocity?), etc.

 

[Jimmy_C]

The Dyson Sphere in Relics was 200 million km in diameter. It surrounded a g-type star like the sun (Mass = 1.98892 * 10^30 kg, diameter = 1.4 million km). The Enterprise started at an altitude of 150,000 km above the star's surface in the episode. Also in the episode, impulse engines were working at 60% capacity during their accent from the star to the "door," according to Data. According to this web site, the maximum acceleration of the impulse engines on the Enterprise is 10 km/sec^2, so I assume they were pushing the Enterprise at 6 km/sec^2.

I'll fudge a little to make the calculations easier. Assume she started at velocity=0 and traveled in a straight line from the star to the door (which is wrong, she was in orbit, but fudge!). Even taking into account the change in gravity from the star, the final velocity of the Enterprise is about 24,000 km/sec. It looked like she took about a seconds to go through the "doorway", so it is about 20,000 km in thickness! Though that means the Enterprise was huge according to the visuals of the episode.

With a 20,000 km thickness, and assuming it has the density of the Earth (5.52 g/cc), then it has a mass of:

1.38704987 × 10^34 kg

Woa. That's 6973x the mass of the star. Are these calculations logical? Even if the thickness was only 2x the length of the Enterprise (about 1 km for the DS thickness), it would still be about a third the mass of the sun. I guess the saying that if you could build a Dyson Sphere, then you wouldn't need to, is accurate...

As an aside, how thick could you make a Dyson Sphere before it collapses on itself?

 

[Christopher]

You can never take ST spaceship shots literally in terms of their scale and motion. There have been cases where the dialogue has explicitly established two ships as hundreds of thousands of kilometers apart while the FX shots have shown them just a few ship lengths apart. And there have been multiple cases where the proportions of two objects in the same shot have been completely wrong (such as the buoy in "The Corbomite Maneuver" -- said to be over 100 meters wide but appearing a tenth that; the shuttlecraft in "The Doomsday Machine" which was almost the size of a starship; and the Stargazer in "The Battle," which was far larger than it should've been). Not to mention unrealistic elements such as bright lighting (and fill light!) in interstellar space, visible tractor beams, turbulent fireball explosions in vacuum, sound in vacuum, etc. So you can never get any meaningful information on an object's size or speed from a VFX shot. They're not literal depictions, more like visual metaphors. They're meant to look cool and get the idea across, not to be accurate.

 

[Jadzia]

a quick calculation

just how massive would this structure be?

If you took all of the mass of the earth, and recast it into a spherical shell (a Dyson Sphere), at the distance of the earth's orbit, how thick would that shell be?

Volume of earth = 4/3 pi r^3

Volume of dyson sphere = 4 pi R^2 . thickness

working in kilometres,
thickness = r^3 / (3 R^2) = 6400^3 / (3 . 150,000,000^2)

< 4 millimetres


What about forces in the sphere?

Well that can be This Weeks' Maths Puzzle

If we think of the dyson sphere consisting of two hemispheres of mass m/2, radius R, and thickness d, which are stuck together like clam shells, then each hemisphere feels a gravitational force, which along the join, will counter one another.

(1) Assuming that the star has mass M, calculate the force acting on each hemisphere.

(2) As these two forces are balanced, calculate the area of the join, and thus the pressure between the hemispheres.

(3) Show that this pressure is independent of the thickness of the spherical shell.

(4) Ordinary building stone has a safe compression limit of approximately 15 MPa. Beyond this pressure, there is an unacceptable risk that the stone will shatter or explode. Suppose that the sphere is made of such stone. For a star like our sun, what range of sphere sizes would have shell pressures within safety limits?

 

[Shawnster]

While not Dyson Spheres, here are some images of Niven's Ringworld. This might suggest a start as to what the Sphere would look like.

http://adamant.typepad.com/photos/uncategorized/2007/07/03/ringworld.jpg
http://adamant.typepad.com/photos/uncategorized/2007/07/03/ringworld.jpg
http://www.johnstonsarchive.net/spaceart/render/ringworld2.jpg
http://www.timdrussell.com/images/ringworld/ringworld3.jpg

And here are some images when you Google "Dyson Sphere"
http://www.tabletoptelephone.com/~hopspage/DysnSphr.gif
http://www.orionsarm.com/gallery/starlifting_Sirius.jpg
http://www.astronomy.ro/domain/other/img/dyson-sphere.jpg

 

[Forbin]

That first Ringworld image is utterly out of scale. At 1AU radius and 1M Miles wide, the diameter should be, obviously, 186 times more than the width. As Niven puts it, take a Christmas ribbon 50 feet long and lay it in a circle.

 

[Forbin]

Getting back to the 1701-D leaving the DS - what speed would she be traveling as she cut thru the atmosphere layer on her way out? Should't we have seen a plasma fireball engulf her as she blew a conical shockwave thru the air and vaporised a few hundred square miles of surface?

 

[Forbin]

Here's Ringworld rendered in scale, given a ring 1AU in radius and 1M miles wide, and a star the sun's diameter of 800k miles. I've excluded the shadow squares 'cause I can't remember their dimensions offhand.

 

[Christopher]

Personally, I'm more fond of Iain M. Banks' Orbitals, which are like miniature Ringworlds (and are the inspiration for the title structures from the Halo computer game). Ringworlds are seriously unstable, because a Ringworld's center of mass is inside the star rather than orbiting it. Orbitals are much smaller rings that are in orbit of their primary stars rather than surrounding them, but they can still have enormous surface area. And by tilting them a bit relative to the orbital plane, you can have the far side's interior exposed to sunlight for half of the Orbital's rotation period and have a day-night cycle without needing any sort of shadow squares.

The one thing that bugs me, though, is that the gyroscope effect would keep the Orbital's axis pointing in the same direction as it circled the star, so the position of the star in its sky would change throughout the year, and twice a year, the sunward side of the Orbital would totally eclipse the star, possibly for days at a time. I don't think Banks ever addressed this. Perhaps his Orbitals use thrusters to precess their axes, but that would expend a hell of a lot of power.

It might be simpler to use the Stanford Torus approach writ large -- have the Orbital's rotational axis perpendicular to its orbital plane, and instead of having the star shine on its inner surface directly, have a vast, lightweight mirror that angles the sunlight into the Orbital. That way, only the mirror needs to use thrusters to precess, which requires much less power because it's so much lighter. Also, it would protect the inner surface more from stellar flares, although an Orbital's large enough that its atmosphere would do that pretty well.

 

[Meredith]

Here's Ringworld rendered in scale, given a ring 1AU in radius and 1M miles wide, and a star the sun's diameter of 800k miles. I've excluded the shadow squares 'cause I can't remember their dimensions offhand.

Imagine dropping out of warp in that system!!!!

 

[Jerikka Dawn]

This all sounds way too complicated. It's probably why whoever created the universe decided to go with planets instead.

 

[prometheuspan]

Also, I think that the eclipsed areas of the sphere would still be bathed in quite a bit of light, reflected from other portions of the sphere.

To get an idea of that, would any of the resident 3D artists be able to render a quick&dirty image showing the following? Or would that be too much to ask?

* A spherical object with a diameter of about 2AU, with the camera placed inside and at "ground level".
* Views might be: looking straight up, straight up with the sun completely shielded by an object, looking towards the horizon
* One light source in the center of the sphere, light quality and quantity equaling that of our sun.
* Texture of the sphere: some random earth surface imagery, with diffuse reflection set to about 35%.

No. The programs might be able to handle it, but the computers we have
can't do calculations of things so large. I know because I have tried to model very large objects in both google sketchup and autocad. Past a certain size the program freezes and you have to reboot the computer to escape. If you want to freeze your computer, there are simpler ways to do it.

 

[prometheuspan]

For a star like our sun, what range of sphere sizes would have shell pressures within safety limits?

I think you missed the most fundamental problem with a dyson sphere and why its actually impossible to build one out of normal matter.

GRAVITY.

I mean, this is all an interesting thought experiment, but lets get real?

The tension gravity along the curved surface would be thousands of
times more than the gravity pulling you down to the surface.

The only scientifically accurate way to do it is to use some form of exotic matter which doesn't have gravity, or to in some manner use gravitational holomorphics similar to warp fields to cancel it out.

Otherwise, your ribbon snaps and crumples into itself, and your sphere more or less does the same thing somewhat differently.

If you took the earth and turned it into a dyson sphere it would be thinner than paper.

And it would stay in sphere form only so long as you kept the warp bubble on it, otherwise its own gravity would force it to crumple.

It's probably why whoever created the universe decided to go with planets instead.

lol. Well, yeah, the scalar fractal does orbits and valence. There are no known laws of physics that could ever come
up with a dyson sphere. I know this because i was 11 when I invented a dyson "planet" or a hollow world which I explained to exist as hollow via an extremely fast rotational speed. When I presented it to a college prof he was very polite but pointed out that its simply impossible.

The laws of nature don't support such objects and in fact rule them out completely.

This is why a "DYSON" sphere is actually a large number of independent platforms in trojan orbits.
Dyson knew a solid object that size and shape was impossible.

 

[Herkimer Jitty]

Not impossible, simply highly improbable.

By simply hooking the logic circuits of a Bambleweeny 57 sub-meson Brain to an atomic vector plotter suspended in a strong Brownian Motion producer (say a nice hot cup of tea), you can create a finite probability generator. Figure out high of a probablity it is to create an infinite improbability generator, and input that into the finite probability generator. Then, figure out high probable it is to make a Dyson Sphere or a Niven Band stable and input that. Of course, chance of failure is inifnitley probable and activation of the device may simply result in sudden spontaneous massive existence failure.

But seriously, I would think that the only stable sort of massive manmade (alienmade?) structures would be things like orbitals, artifical planets/moons and other objects with their own gravitational center.

 

[prometheuspan]

Not impossible, simply highly improbable.

okay, if you say so...

By simply hooking the logic circuits of a Bambleweeny 57 sub-meson Brain to an atomic vector plotter suspended in a strong Brownian Motion producer (say a nice hot cup of tea), you can create a finite probability generator. Figure out high of a probablity it is to create an infinite improbability generator, and input that into the finite probability generator. Then, figure out high probable it is to make a Dyson Sphere or a Niven Band stable and input that. Of course, chance of failure is inifnitley probable and activation of the device may simply result in sudden spontaneous massive existence failure.

Chance of failure = infinity. Hmm. I think you answered the question
there.
lol.

But seriously, I would think that the only stable sort of massive manmade (alienmade?) structures would be things like orbitals, artificial planets/moons and other objects with their own gravitational center.

right, uhm, a dyson sphere would have a gravitational center. I think you must have meant to say SOLID center.

 

[Herkimer Jitty]

http://i200.photobucket.com/albums/aa155/Wesson_album/LiscombFrisbee.jpg
Quick mock-up of a monolithic space habitat that might work. Big old frisbee with habitable interior towards the edge. The thick interior space would have power systems, and massive amounts of internal technology, with a solid core. If noone else has thought of it, I dub it the "Liscomb Frisbee"