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Serious Scientific Answers to Absurd Hypothetical questions

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How much artificial gravity would residents of a ring-shaped Space Station (Stanford Torus) experience if it had a diameter of 12,756 km (circumference of 40,075 km) and it rotated at a speed of 460 m/s (Once every 23.9 hours)?

Edited by WestAir

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18 minutes ago, WestAir said:

How much gravity would a ring-shaped Space Station (Stanford Torus) experience if it had a diameter of 12,756 km (circumference of 40,075 km) and it rotated at a speed of 460 m/s (Once every 23.9 hours)?

About 3/1000 of a g.

http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm

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4 minutes ago, WestAir said:

Wow. I always thought the effects of Earths rotation made a much bigger difference on gravity experienced at the equators. I was so wrong.

People dont fly at the equator.

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1 minute ago, Xd the great said:

People dont fly at the equator.

They do if they run fast enough. :wink:

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1 hour ago, WestAir said:

They do if they run fast enough. :wink:

And miss the ground after throwing themselves at it. 

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On 8/26/2018 at 12:29 PM, Spaceception said:

Would a Ringworld with a diameter of 26,000 km be able to hold, or need that extra mass on the outside? 

It would defiantly need the extra mass, the widest that a rotating cylinder habitat, at 1g, could be is roughly 1,800Km wide, and it would need to use graphene as its structural material (even carbon nanotubes can't cut it at this size). 

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5 hours ago, MinimumSky5 said:

It would defiantly need the extra mass, the widest that a rotating cylinder habitat, at 1g, could be is roughly 1,800Km wide, and it would need to use graphene as its structural material (even carbon nanotubes can't cut it at this size). 

Do you know any equations that could give a rough value for the needed mass given the wanted gee force?

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53 minutes ago, Spaceception said:

Do you know any equations that could give a rough value for the needed mass given the wanted gee force?

Well, most of the mass would likely be the shielding for smaller ones, roughly 10 tonnes per square meter (maybe 15). Eventually, however, the soil and dirt making up the landscape below and the air above effectively shields the occupants. Structural mass makes up a few percent of total mass in smaller structures. More in larger ones. 

You could treat it like a pressure vessel, and find the total force per square meter. For example, if our atmospheric pressure is 50.7 kilopascals (about half sea level on Earth, can have a higher percentage of oxygen), and we can have 10 tonnes per square meter of shielding and soil at 1g, you have a total pressure of 148.7 kilopascals. You can find the pressure for different pseudo- gravity levels by multiplying that mass by the g value in m/s^2. Add some good margins, and then use the pressure vessel equations to find out how thick it needs to be, which can help with volume. Density then gives mass. Add in the total mass of other stuff (10 tonnes per square meter) and figure out the mass of the air, and you've got a decent approximation. 

I think.

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Yeah, except that I just realised something rather important. The pressure vessel approach only works with a true ringworld, as it relies on the gravity of the central star to generate the pressure holding the counterweight against the habitat, which a banks orbital (basically what was suggested) by definition would not have. There is a reason that earthlike banks orbitals are 3 million miles across! 

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On 8/27/2018 at 10:29 AM, MinimumSky5 said:

It would defiantly need the extra mass, the widest that a rotating cylinder habitat, at 1g, could be is roughly 1,800Km wide, and it would need to use graphene as its structural material (even carbon nanotubes can't cut it at this size). 

Why wouldn't a civilization advanced enough to build such a thing just use thrusters at precise locations to counteract the natural stress of the habitat?

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Because, even with advanced fusion drives, that is horribly energy wasteful.

Also, what happens when one of those drives fails? Even if you've mastered fusion, a simple structural beam of any material will be a heck of a lot more reliable than any drive system.

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Isn't an object, once reached certain size and mass goes into equilibrium? Does it means megastructures in space theoretically impossible?

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Yeah, having enough mass to overcome gravity and assume a spherical form is part of the IAU's definition of a planet. That is the case for a large asteroid like Ceres.

As to megastructures, since imo they are just a human fantasy, i can't say much. That is just one argument that they would be too heavy, though the painters of the funny pictures distributed the mass over a whole solar system. So density would probably be too low to force it in a single chunk.

Anyway, no solar system has enough material at all to build a ring world the size of earth's orbit or even a dyson swarm or -sphere. The stuff is unstable, will collide with itself, can't be held above a star's pole, etc. pp. Too much handwaving for my little understanding :-)

 

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17 minutes ago, ARS said:

Isn't an object, once reached certain size and mass goes into equilibrium? Does it means megastructures in space theoretically impossible?

Depend on the stucture, an ring who spins around an heavy object like an ring-world or an ring around an planet could be made if heavy enough. 
Note that gravitational differences could make problems. 

As I understand an doughnut planet can be made stable and hold an atmosphere, it could even be created naturally but that is extremely unlikely as the requirements are very narrow. 

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Re: Dyson sphere/swarm: Solar sails. Sure, you'll need somewhere to vent heat and gasses from, and you'd need to have some fast-acting actuators on the sails to keep them hovering properly, but both of those are trivial problems in the scale we're talking about.

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A Dyson Sphere from inside.

Spoiler

candle_in_the_dark_by_louiseparry-d57ovi

 

Spoiler

The biggest cave to be made.
The apotheosis of claustrophobia, agoraphobia, and megalophobia at once.

Turn the sky into dungeon.

 

Edited by kerbiloid

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On 8/31/2018 at 2:22 PM, kerbiloid said:

The biggest cave to be made.
The apotheosis of claustrophobia, agoraphobia, and megalophobia at once.

Turn the sky into dungeon.

Quote

The car shot forward straight into the circle of light, and suddenly Arthur had a fairly clear idea of what infinity looked like.

It wasn't infinity in fact. Infinity itself looks flat and uninteresting. Looking up into the night sky is looking into infinity --- distance is incomprehensible and therefore meaningless. The chamber into which the aircar emerged was anything but infinite, it was just very very big, so that it gave the impression of infinity far better than infinity itself.

Arthur's senses bobbed and span, as, travelling at the immense speed he knew the aircar attained, they climbed slowly through the open air leaving the gateway through which they had passed an invisible pinprick in the shimmering wall behind them.

The wall.

The wall defied the imagination --- seduced it and defeated it. The wall was so paralysingly vast and sheer that its top, bottom and sides passed away beyond the reach of sight. The mere shock of vertigo could kill a man.

The wall appeared perfectly flat. It would take the finest laser measuring equipment to detect that as it climbed, apparently to infinity, as it dropped dizzily away, as it planed out to either side, it also curved. It met itself again thirteen light seconds away. In other words the wall formed the inside of a hollow sphere, a sphere over three million miles across and flooded with unimaginable light.

 

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Burning Human Flesh.   One of the worst smells I've ever had to endure, and I've done more times than I'd like to remember.    But....  did we evolve to recognize the smell as bad and a possible warning sign of danger, or does it just really smell bad to all animals?    I find the smell of cooking/burning meat to be quite delightful, but burnt people not so much. 

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I guess, the smell of a burning cellulose (tree, paper) is so exciting because it's at once danger (burning forest) and pleasure (food and defence) for our hairy precursors.

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It's probably an inherited trait. We've been using fire for millions of years and evolved in an area known for major wildfires, so it would seem logical that we would associate burning people with bad things. The fact that we can differentiate between cooked antelope and cooked people is likely a unique trait to humans. 

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Yeah, use of fire is very old, connected with Homo erectus ~2my ago. And i would not be surprised if somebody found traces of fire in conjunction with Homo habilis. Use on the one side and control of fire are regarded different things though, the latter being much younger, maybe less than a million of years, that's the official version. But some say that for humans to survive e.g. in European ar Asian climate the control of fire is a prerequisite. This is an open question, though.

Every organism with a proper receptor and processing unit steps, flies or crawls away from a fire. But cannibalism is not rare in nature. In principle, the proteins and nutrients from the same species can be integrated with less energy than that from other species. So some organisms prey on their own species in time of acute need. Nevertheless, in the medium to long run, that's not an evolutionary "success story" for a population if it doesn't multiply very rapidly in times of plenty.

In modern humans, the rare cases of cannibalism are mainly connected with cultural things, like rituals (disposal, conflicts, ...) or simply morbid individuals(*). But you are right, for the average human individual the perception of devouring another human is repellent, if cultural dictate doesn't call for it. Which is very rarely the case despite of horror stories from early explorators !

But, i must say, that there is no evidence that the differentiation is unique to humans.

 

(*) and very few known isolated cases to avoid starving.

Edited by Green Baron

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29 minutes ago, Green Baron said:

In principle, the proteins and nutrients from the same species can be integrated with less energy than that from other species.

If pieces of food were just be being reattached from the food to the eater's body.

But to integrate something from the food the eater's organism should first split complex compounds into simple ones, and only after that integrate some of them.
This splitting requires energy, its products do not necessary match best proportions (say, we can consist of 5 A and 6 B, but our daily needs require 2 A and 1 B due to different rate of their spending), and so on.

So, chemical similarity absolutely doesn't mean better digestability. Otherwise we would be herding monkeys.
Say., trees have little common with animals manure which they prefer.
We have several kg of apatite in our organism, but we don't gnaw apatite pieces. More of that, we never digest calcium directly from stones.
Mostly species better digest what they lack than what they have.

Systematic cannibalism is just energetically ineffective for human species, so it's a marginal event for most of human cultures.

Edited by kerbiloid

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