Artificial Worlds

Tom Kalbfus

Mongoose
http://www.popularmechanics.com/science/space/deep/could-we-ever-build-an-artificial-world-17025054
artificial-world-0714-mdn.jpg

Name: Artificial world

Selected Science Fiction Portrayals: The two Death Stars from the Star Wars films and related media; Shellworlds in Iain M. Banks 2008 novel Matter; custom-made luxury worlds in Douglas Adams' The Hitchhiker's Guide to the Galaxy series.

If humans are going to live in an off-world habitat, then it must have the things we’ve evolved to depend on here on Earth: the right temperature range, breathable air, specific gravity, day-night cycles, and plenty more. But rather than gussying up a spinning, tin can space station, wouldn't it make more sense to re-create our planet by building an artificial world?

The term "artificial world" can be interpreted in two ways. The literal interpretation is a planetary replica—a massive chunk of rock fabricated to be essentially indistinguishable from real planets and moons crafted by nature. The other way is to imagine something that merely looks like a world—say, a spherical space station like the Death Star in Star Wars. This second kind of object would not be inherently planet- or moon-like, except in its shape. But through clever engineering, perhaps function might follow form more readily than you might think.

With either approach, engineers would have a hell of a job on their hands. "I don’t want to be a wet blanket, but at least for things we know about today, [when it comes to building an artificial planet,] you run into problems," says Adam Steltzner, an engineering fellow at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

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"That's No Moon"

death-star-0714-de.jpg


Let's start with the second option—the Death Star. It seems more promising than building a true replica planet if only because of size. According to Star Wars lore, the first Death Star in Star Wars Episode IV: A New Hope, had a diameter of 74 miles. That's big, but not when compared to Earth's nearly 8,000-mile diameter. Assuming the approximate density of an aircraft carrier, as the economics blog Centives has done, the mass of a Death Star made mostly from steel works out to about a quadrillion tons—only about one one-millionth of the Earth's mass. Easy!

But acquiring even that amount of material through today's mining technology would be an absurd quest. Given a 2012 world steel production rate of 1.43 billion tons annually, Centives figured it would take more than 800,000 years to acquire all the necessary steel. The price tag? A staggering $852 quadrillion, or about 13,000 times the entire world’s combined gross domestic product. Worse yet: launch costs. Rocketing materials from Earth's surface into space runs on the order of thousands of dollars per pound currently.

The only plausible way to procure materials cheaply is to get them from low-gravity environments, like the Moon and asteroids. "It would be smart … to mine space, rather than try to rocket up a steel I-beam," Steltzner says.

Orbital Construction Site

Next comes fashioning a quadrillion tons of steel into a sphere with a complex internal structure. It would be extremely difficult, but not impossible. Robots would have to (quickly) handle the majority of the work if it were to be completed in a reasonable amount of time; otherwise you’re talking about employing armies of space-suited construction workers for millennia.

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For reference: The world's tallest building, the Burj Khalifa, has a mass of nearly a million tons and took three years to erect, with upwards of 10,000 workers on-site. However, this analogy is not quite apt (though nothing humanity has ever done really compares to building a Death Star). While the artificial world would requires an ridiculous amount of metal, moving those giant hunks around in space could be much easier (with the right machines, anyway) than working in a broiling desert beset by gravity

Also consider the internal structure. The Death Star includes more than 21,000 floors stacked like stories in an office building. This configuration would never be feasible—unless we invented some kind of artificial gravity generators to keep people, furniture, and droids rooted to the floor.

Gravity, the Good and the Bad

Earth-like gravity would be absolutely essential for long-term living. "Our human bodies get all messed up when we don’t have one Earth 'g'," Steltzner says. Astronauts aboard the International Space Station have to deal with bone mass loss and low blood pressure, among other issues, from extended stays in microgravity.

Alas, artificial gravity generators defy known physics. Instead, the artificial lunar megastructure would need to rotate to produce gravity, via centrifugal force, outwardly along its equator. Instead of stacked floors, habitat levels in an artificial moon could resemble layers in an onion. In an inverse of terrestrial reckoning, occupants' heads, instead of their feet, would face "down" toward the megastructure's center. Gravity, too, would be backwards. "At the center of the structure there is no gravity, and you get more as the floors go out," noted Steltzner.

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Getting rotation itself would be simple. Angled rockets could start the whole thing spinning and maintain it at the rate required for Earth-like gravity. The rockets would not need to continuously fire, either. "Because the structure's spinning out in space, there's nothing there to slow it down," Steltzner says.

Yet rotating the artificial moon creates fresh problems. The sections of the structure subjected to one Earth gravity or more would have to possess a high enough strength-to-weight ratio to keep from ripping apart. Steel might not cut it for a 74-mile diameter structure, Steltzner says. A better bet: zylon, a synthetic fiber with the best strength-to-weight ratio known, which is seven times stronger than steel and about twice Kevlar's toughness. Zylon is organic, meaning it contains carbon. So carbon-rich carbonaceous asteroids would be good mining targets for this approach.

Earth, Redux?

For all its engineering challenges, building our Death Star-inspired space habitat would be far easier than constructing a replica Earth. But it could never match a second Earth on one thing: stability.

"All of these structures or ideas for colonies suffer from one sort of inherent, substantial flaw that is summed up in a term: instability," Steltzner says. "Active maintenance is needed for the environment to be maintained, like the exact right orbital parameters. They're much, much less stable than our planet."

Ergo, why not just make another one?

Mark Hempsell, an aerospace engineer who worked for Reaction Engines Limited and has recently started a private consultancy, took a crack at artificial planets in a 2005 study in the Journal of the British Interplanetary Society, of which he is a former editor. He wanted to compare the feasibility of terraforming a planet—that is, geo-engineering it to be like Earth, a painstaking project that would probably take centuries on a world like Mars—versus building one from scratch.

Churning Out a Custom Planet

Hempsell points out that to replicate Earthly conditions, you don’t have to mimic Earth to a "t." For example, mass and distance determine gravitational attraction. So, to get Earthly surface gravity, engineers could cheat by packing just a tenth of Earth’s mass—say, 700 quintillion tons—into a sphere the size of the Moon (diameter: 2,159 miles). That's still an awful lot of rock, but Hempsell explored how engineers might acquire that material and mimic nature's planet-growing, bottom-up process.

Ordinarily, within a disk of leftover material around a newly formed star, molecules aggregate, bit by bit, into larger and larger chunks, and over millions of years develop into a world. To speed things up, Hempsell suggested deploying a futuristic, gigantic super-fusion facility near the Sun—a megastructure to make a megastructure. Using magnetic fields, the facility would harvest abundant hydrogen from the Sun's surface. Onboard fusion reactors would produce desirable heavy elements to comprise the planned faux-Earth.

To squish a Mars-sized mass into a Moon-sized volume, engineers would want the densest elements on the Periodic Table, including osmium, iridium and platinum. Admittedly, these elements can only be made in the thermonuclear explosions of supernovae, and not through conceivable, garden-variety fusion machines. "We're talking about some spectacular fusion technology," Hempsell says. But at least the laws of known physics could still be obeyed.

The facility would launch ingots of these materials out to where the artificial planet would be built up, piecemeal, as ingots collide and bind. All that ingot smashing would generate significant heat throughout the budding world, on par with the 10,000-degree-Fahrenheit surface of the Sun. After a century of cooling to about 3,000 degrees Fahrenheit, ingots of crustal elements, such as silicon, could be layered on top. Another period of cooling would then need to take place, lasting about 10,000 years, until the surface would be cool enough to dump water for oceans and establishment of plant life.

In summary… Hempsell's paper demonstrated that world-making is best left to nature.

"Unless something radically different happens," said Hempsell, "when looking at terraforming things, the paper came to the conclusion that building your own planet is not going to be any quicker."
 

Tom Kalbfus

Mongoose
ShawnDriscoll said:
And this was copy/pasted here because...?
Thought it was interesting. What if you wanted such an artifact in your Traveller campaign, a 1 g world that was size 2, the article tells you what such a world would be made of., Platinum, Iridium, Osmium. To pack one tenth of the Earth's mass into the Moon's volume.
 

Matt Wilson

Mongoose
This raises a question: what's the UWP for an O'Neill cylinder? Do you just use the UWP for the nearest world and assume that the pop code includes space habitats?

That would actually explain type C atmospheres with high pop codes pretty well.
 

Tom Kalbfus

Mongoose
Matt Wilson said:
This raises a question: what's the UWP for an O'Neill cylinder? Do you just use the UWP for the nearest world and assume that the pop code includes space habitats?

That would actually explain type C atmospheres with high pop codes pretty well.
The size for a standard O'Neill cylinder is 0, and an artificial world such as one made out of osmium platinum, and iridium within the volume of our Moon would be 2, but because of its density, it would have an Earth-like G field, escape velocity would still be lower though, so it would be easier to get into orbit from that planet. For an O'Neill cylinder, there is no reason to have anything other than a 5, 6, or 8 atmosphere on its inside. Type 5 atmospheres with high oxygen concentrations are preferred as they produce less stress on the hulls of these space stations.
 

Tom Kalbfus

Mongoose
Another sort of artificial world makes use of grav plating, basically its a hollow artificial planet. Make a sphere with wide holes in the poles.

hollow-earth-euler-300x210.jpg

A world such as this would be possible with grav plating, and insubstantial exotic matter with negative mass surrounding the central sun.

hollowearthbernard.gif

This looks about right, the sun is of course artificial
 

Tom Kalbfus

Mongoose
Infojunky said:
Is a contiguous natural 1g really a requirement?
Well it is an artificial planet. If you were going to build an artificial planet specifically for humans, why wouldn't you have 1g on the surface? You could tell an artificial planet of this kind, is gravity would be way higher than what it should be given its mass. One way to do it is not to actually have an actual ball of plasma for the artificial sun. You have a Sphere inside the hollow world, the sphere is half the interior radius of the shell, since the shell is 800 miles thick the interior radius is 5120 km. 6400 km - (800^1.6) = 5120 km The interior needs to be illuminated at half the illumination the outer surface receives, as there is no night in the interior, so about 700 watts per square meter. The radiating sphere in the center is half this interior radius or about 2560 km in radius, its surface is holographic and it projects an image of a sun in the center and also the surface of the hollow world on the other side of the holographic sphere, thus rendering it effectively invisible to human eyes. The holographic surface radiates visible light at 2800 watts per square meter, about what Venus gets at its cloud tops. The antigrav plating underneath the holographic surface also produces an antigrav field (that pushes outward in stead of pulling inward) of -4g. Both the light and the gravity spread out according to the inverse square law of propagation, so on the inside surface of the shell, you feel a negative gravity of -1g pushing away from the center of this planet, and you get an illumination of 700 watts per square meter, about half what the Earth gets at high noon, but you get it 24 hours a day, because it is alway high noon on the interior surface of this hollow planet. The radiative antigravity sphere is powered by a fusion reactor in its center, there are holes in the poles, each one (1400 *1.6) 2240 km wide, probably in the central sphere oriented toward these poles is 1 giant maneuver drive pointed towards the South Pole, and a giant Jump Drive pointed toward the North Pole. I would give this world a Jump-3 and Maneuver-1. Okay the hull size of this planet starship, if it is the size of the Earth would be what?

There are 14 cubic meters to a displacement ton, a cubic km has 1,000,000,000 cubic meters or 71,428,571 d-tons or 71.43 megatons of displacement for one km cubed, We need a larger unit, the megameter (Mm) will do. 1000 km = 1 Mm, so the tonnage for 1 Mm is one billion times 71.43 megatons. a cubit megameter (Mm^3) has a displacement of 71.43 petatons.

The Earth's radius is 6.4 Mm (Megameters) volume of a sphere is V = 4/3*pi*r^3 = 4/3*pi*6.4^3 = 1098 cubic megameters. Multiply this by 71.43 petatons and we get 78,435 petatons of displacement.
 

Reynard

Cosmic Mongoose
Hollow world as an ancient artifact. Anyone recall if its been done for Traveller?

I see a barren world on the surface, quite unattractive to lower techs and not remarkable to their sensors while not located in the habitable zone. Higher tech can discover anomalies in mass and gravity. Close inspection finds the surface covered in well hidden network of solar absorbers. Extensive deduction finds the planets poles are two huge rings generating the planet's magnetic field which is also a defensive shield against meteor impacts. the rings are just big enough for small ships to pass forming a tremendous mountain ring inside and also holds in the atmosphere to a vast, verdant interior world!

An incredible array of grav systems produce gravity directed to both surfaces while a secondary system of thrusters all over the interior hold the tiny artificial 'sun' in place. The sun produces light and heat and fades on and off cyclically. The atmosphere thins towards the center of the hollow ball. The surface is alive with flora and fauna. No immediate sign of technology. What is this place for?
 

Tom Kalbfus

Mongoose
Reynard said:
Hollow world as an ancient artifact. Anyone recall if its been done for Traveller?

I see a barren world on the surface, quite unattractive to lower techs and not remarkable to their sensors while not located in the habitable zone. Higher tech can discover anomalies in mass and gravity. Close inspection finds the surface covered in well hidden network of solar absorbers. Extensive deduction finds the planets poles are two huge rings generating the planet's magnetic field which is also a defensive shield against meteor impacts. the rings are just big enough for small ships to pass forming a tremendous mountain ring inside and also holds in the atmosphere to a vast, verdant interior world!

An incredible array of grav systems produce gravity directed to both surfaces while a secondary system of thrusters all over the interior hold the tiny artificial 'sun' in place. The sun produces light and heat and fades on and off cyclically. The atmosphere thins towards the center of the hollow ball. The surface is alive with flora and fauna. No immediate sign of technology. What is this place for?
An artificial planet is one step beyond terraforming an existing planet, basically you build you planet at the right distance from a star, as planets often come with inconvenient sizes, gravities and distances from their star.

The lowest tech "artificial planet" is not a sphere but a cylinder which rotates for gravity.
a = v^2/r.
a is acceleration 9.81 meters per second squared
v is the tangential velocity or the rotation of the cylinder
r is the radius of the cylinder which we'll set equal to the radius of the Earth 6,400,000 m.
v = sqrt(a*r) = sqrt(9.81 m/(s^2) * 6,400,000 m) = 7,923.64 meters per second.
To get rotation rate find the circumference of the cylinder and divide by tangential velocity.
2*pi*r = 2*pi*6,400,000m = 40,212,386 meters
divide by 7,923.64 meters per second to get 5075 seconds = 84.58 minutes
This number looks familiar because it is also the orbital velocity and period of an object orbiting at the surface of the Earth, or in low Earth orbit, because in that case centripetal acceleration is counteracting the acceleration due to gravity producing effective weightlessness.

To get a cylinder with the equivalent area of Earth, first find the area of Earth which is the formular for area of a sphere.
A=4*pi*R^2
A = 4*pi*6.4^2 Mm^2 = 514.72 square megameters
The area of a Cylinder is
A=2*pi*R*h minus the end caps
Solve for L
L=A/(2*pi*R)
L=(514.72 Mm^2)/(2*pi*6.4 Mm) = 12.8 Mm

images


The inside of an artificial Earth cylinder when unrolled may look like this:
450px-Lambert_cylindrical_equal-area_projection_SW.jpg
 

Reynard

Cosmic Mongoose
"An artificial planet is one step beyond terraforming an existing planet, basically you build you planet at the right distance from a star, as planets often come with inconvenient sizes, gravities and distances from their star."

Hollowing out a dead planet then building in artificial gravity, an artificial 'sun' and all the other incredible marvels to enable the terraforming of such an interior is a form of artificial world. No one defined artificial worlds as solely metal shells. The one I described would be the analogy of a planetoid ship. As to the one I described, it would have to be determined if the creator(s) did move it to a particular location.

Another interesting detail for that hollow world would be what happened to the matter from the core? Maybe an artificial moon with its own internal secret functions?
 

Tom Kalbfus

Mongoose
Reynard said:
"An artificial planet is one step beyond terraforming an existing planet, basically you build you planet at the right distance from a star, as planets often come with inconvenient sizes, gravities and distances from their star."

Hollowing out a dead planet then building in artificial gravity, an artificial 'sun' and all the other incredible marvels to enable the terraforming of such an interior is a form of artificial world. No one defined artificial worlds as solely metal shells. The one I described would be the analogy of a planetoid ship. As to the one I described, it would have to be determined if the creator(s) did move it to a particular location.

Another interesting detail for that hollow world would be what happened to the matter from the core? Maybe an artificial moon with its own internal secret functions?
To create a hollow world, you don't necessarily have to start out with a planet, the material in the asteroid belt would suffice. The dwarf planet Ceres would probably suffice in making an Earth size cylinder, with Traveller RPG tech, you could make a hollow sphere and install grav plating. And you saw that inverted ringworld surrounding Jupiter in the picture above, that utilyzes Jupiter's gravity at the 1-g radius, the underside as a separate rotating band that pushes up on the underside with magnetic fields transferring upward force against the habitation ring to hold it against Jupiter's gravity. Of course out at Jupiter, you need to focus the Sun's gravity. A rectangular Fresnel lens with 5 times the area of the rings cross section, can focus sunlight at Earth level intensities, or else you'd need an artificial light source.
 

Reynard

Cosmic Mongoose
"To create a hollow world, you don't necessarily have to start out with a planet, the material in the asteroid belt would suffice."

Wouldn't hollowing out a world be easier that building one from loose rocks? They're both a piece of work left to those Ancient tech capacity but seems more intensive to reshape and piece together than scoop out a world. Then again Grandfather gets bored easy.

A lot of the materials for the internal workings could be manufactured from all the core resources and the waste could either be cast off toward the sun or rebuilt such as the before mentioned moon or a ring.
 

Tom Kalbfus

Mongoose
Reynard said:
"To create a hollow world, you don't necessarily have to start out with a planet, the material in the asteroid belt would suffice."

Wouldn't hollowing out a world be easier that building one from loose rocks? They're both a piece of work left to those Ancient tech capacity but seems more intensive to reshape and piece together than scoop out a world. Then again Grandfather gets bored easy.

A lot of the materials for the internal workings could be manufactured from all the core resources and the waste could either be cast off toward the sun or rebuilt such as the before mentioned moon or a ring.

What you got to consider is that we only live on the surface of our world, all that stuff under our feet is not appreciated, the only part we are concerned about is Earth's surface, so we only need the material to create that surface. Hollowing out the Earth is easier said than done. The Earth's mass is 5.976 septillion kilograms (5.976 x 10^24 kg)

Mass is related to volume, The volume of the Earth is 1.087 x 10^12 km^3 according to my book.
The volume of a sphere is given by the formula

V=(4/3)*Pi*r^3
r = 6,378
V=(4/3)*Pi*6378^3 = 1,086,781,292,543 km^3 by my calculator, which is 1.087 x 10^12 km.
Divide Earth's mass by its volume and you get 5,497,700,091,996 kg per cubic km.

Now to find the volume of material to make a hollow sphere in the shape of the Earth you subtract a lesser radius sphere from it. The point on Earth closest to it center is 6,353 km, so we'll carve out a hollow that is 5 km below that point, so I'll calculate the volume of a sphere that is 6,348 km in radius.
r = 6,348 km
V=(4/3)*Pi*6,348^3 = 1,071,517,734,950 km^3 by my calculator
we subtract the lesser volume from the greater one to get 15,263,557,593, which is
1.526 x 10^10 km^3 we'll multiply that by mass per cubic km to get 83,914,461,983,222,344,325,628 kg for this hollow Earth, or 8.391 x 10^22 kg.
Do you know how much mass this is? As I look in my astronomy book, I find that the body that comes closest to this figure is Jupiter's Moon Io, with a mass of 8.94 x 10^22 kg.
So if I wanted to create a hollow Earth, I'd take apart the Moon Io and have to manipulate 8.94 x 10^22 kg of rocky moon instead of hollowing out 5,890,883,150,009,960,544,460,200 kg or
5.891 x 10^24 kg, you would have to move 70.2 times as much material to hollow out the Earth as to make an empty Earth-sized sphere out of the material of Io, seems to me it would be cheaper and cost less energy to make a hollow Earth out of Io than to hollow out the actual Earth.

The acceleration due to gravity on the surface of this hollow Earth is by the way 0.13763845291331 meters per second squared or 0.01403 times the gravity at Earth's surface. Fortunately a cylinder of the same diameter as Earth and same length of that diameter and same thickness as the hollow sphere I described would have the same mass as that sphere due to it having the same surface area. Rotate this cylinder at 7.92 km/sec with a rotation of 84.58 minutes, and with the mass of Io, you could create a hollow cylinder with the same surface area as Earth with mountains, oceans and deep trenches as deep as Earths, a wall 150 km high at each end of the cylinder would keep in the atmosphere. At Jupiter's distance from the Sun you'd need a mirror with 5 times the surface area of the cylinder floor to concentrate sunlight into the cylinder and another bullet shaped parabolic mirror to distribute that sunlight across the interior of the cylinder.

This is the mirror architecture for this hollow cylinder design:
Ch06p086.gif


light paths are shown in this diagram
Ch06p088.gif

the scale of an Earth-sized cylinder is much larger of course.
We don't need the end caps of course, in a cylinder 12756 km by 12756 km we just have the middle part of that cylinder shown, remove the end caps, replace them with 150 km walls and centrifugal force will prevent the atmosphere from spilling out the sides, the cylinder would otherwise be open to space.

With Traveller you have artificial gravity generators, but you would still have to concentrate the light unless you want to move hollow earth to just the right distance from the Sun, the easiest thing to do would be to build it right where you find your construction material, in this case in orbit around Jupiter.
 

Rick

Mongoose
I beg to differ with your opening remark: "all that stuff under our feet is not appreciated" - it is certainly appreciated, without it our world would be too cold for us to comfortably live on. With no molten core, the planet would need to be closer to the sun and the difference between the day and night temperatures would be much greater.
 

Tom Kalbfus

Mongoose
Rick said:
I beg to differ with your opening remark: "all that stuff under our feet is not appreciated" - it is certainly appreciated, without it our world would be too cold for us to comfortably live on. With no molten core, the planet would need to be closer to the sun and the difference between the day and night temperatures would be much greater.
Most of what it does is create gravity, but it takes an awful lot of mass to create a 1-g field, but as Einstein says, gravitational attraction and acceleration are indistinguishable, and a rotation is a form of acceleration, centripetal acceleration. Besides there is an Io's worth of Mass orbiting Jupiter, that creates an opportunity to build another Earth, there isn't an Earth's worth of mass there. The other thing a molten core does is create a magnetic field, I've done that as far back as far grade, all you need is a direct current, insulated wire and an iron rod and you can generate a magnetic field. If you can build on the scale of a planet, you can create a magnetic field on a planetary scale as well.
 

Rick

Mongoose
Begs the question though - if you're living on the inside of a hollow earth, you'll still need to find a way to add heat, but would you still need a magnetic field?
 

Reynard

Cosmic Mongoose
Search for what our magnetic field does for us. From there, imagine the field is used for damage protection both against physical and energy other than just background cosmic radiation, 'force field'.
 
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