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Gnargenox
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06 Dec 2017 17:51

Mouthwash wrote:
Source of the post (B) have some part of themselves (atmosphere, solid layer) destroyed by a chain reaction?


All hydrocarbons have a flash point. The point where a substance can ignite or explode without any external form of heating. This value is between the melting point and the boiling point.

You would think you could ignite the entire methane atmosphere of Titan with a single match strike! The problem is that no material on Titan can ever reach that flash point. For methane it's about -178 degrees C, ethane it's about -140 degrees C and for propane it's -104 degrees C. Since Saturn has a roughly circular orbit around the sun and Titan has a circular orbit about Saturn, Titan's surface temperature will never deviate much from about -179 degrees C. So, any hydrocarbon will need to be very strongly heated or have a big enough kick to get it to react. Or you could squirt oxygen into the methane atmosphere and then strike a spark.

The surface temperature of titan is well above the flash point of methane (-178C). Furthermore, we know now that at the surface, the concentration of methane gas is ~5%, this is within the explosion fraction range of methane of 5-15% on earth with an O2 conc. of 20% (the fact that we are dealing with gas at the surface actually negates the relevancy of methane's flash point).

I also suspect that because the pressure of the atmosphere at the surface is higher than at earth's surface, the explosion fraction for methane would actually slightly extend below the 5% lower limit add to this the fact that you'd be burning it with 100% O2 instead of earth's paltry 20% and this probably pushes the explosion fraction limits even wider. The fact that the gas is very cold is irrelevant. What's -180C when you're talking about a flame temperature in the thousands of degrees? Nothing.

It is quite certain that you could light a flame off of a bottle of O2 at the surface and it would self sustain 'till it ran out. Even if you are uncomfortable with the closeness to the lower limit of the explosion fraction at 5%, performing a concentration of methane out of the atmosphere to a slightly higher % would be trivially easy with a semipermeable membrane and a very small amount of energy input (the amount of entropy change you'd need to concentrate it to say, 10% would be very small). The nice thing about the ability to carry liquid O2 instead of liquid hydrocarbon is the high density. a small bottle of O2 would go a long way.

Even if you wanted to run some silly scheme of condensing the methane out of the atmosphere as a liquid using a cryo-cooling loop and then heating and burning off the purified liquid all at once (like for a rocket), this would be VERY easy and energetically inexpensive to do since you're already so close to the boiling point.
Last edited by Gnargenox on 06 Dec 2017 17:56, edited 1 time in total.
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Watsisname
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06 Dec 2017 17:53

Mr. Missed Her wrote:
Source of the post However, I could add better insulation. If nothing else, I could just keep adding layers to keep more heat in.

That is a very nice try. :)  But what you would find is that you still fail to convert the heat into useful power, because you have not actually solved problem 2.  What you encounter again is the undefeatable 2nd law of thermodynamics: the heat still flows outward, and you do not get it back or convert it into useful electric power.

Ah, but why?  

If you add more or better insulation to the shell, then what you're doing is decreasing the rate at which heat can initially flow outward.  But, heat is still transferred outward, and it must, in order to obey the heat equation.  Heat is transferred from regions of high temperature to low temperature, which in this case means outwards, because space outside the sphere of panels is colder than the Earth.

By decreasing the rate at which heat flows outward with insulation, you will cause the temperature on and inside your sphere to increase.  Basically you've put a blanket around the Earth.  So the temperature will go up, but that will then increase the rate at which heat will flow outward (by increasing the temperature difference between Earth and space), and eventually a balance will be re-established between the rate at which the Earth radiates heat and the rate your sphere of insulation radiates heat.  Again, you can't avoid this loss.  The loss just occurs at a higher temperature.

A good analogy is that the Earth with a greenhouse atmosphere still radiates the same amount of energy that it receives from the Sun.  Adding a greenhouse atmosphere didn't decrease the loss of heat. It just increased the surface temperature, and increased the altitude from which the heat ultimately escapes to space.
 
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Mouthwash
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07 Dec 2017 00:43

Gnargenox wrote:
It is quite certain that you could light a flame off of a bottle of O2 at the surface and it would self sustain 'till it ran out. Even if you are uncomfortable with the closeness to the lower limit of the explosion fraction at 5%, performing a concentration of methane out of the atmosphere to a slightly higher % would be trivially easy with a semipermeable membrane and a very small amount of energy input (the amount of entropy change you'd need to concentrate it to say, 10% would be very small). The nice thing about the ability to carry liquid O2 instead of liquid hydrocarbon is the high density. a small bottle of O2 would go a long way.

Wow. Uh, I'm almost sorry I asked. So no colonies on Titan, than.

EDIT: Hold on, do you just mean it would self-sustain until the oxygen ran out? Is it theoretically possible to burn through Titan's entire atmosphere or not?
Last edited by Mouthwash on 07 Dec 2017 05:31, edited 2 times in total.
 
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07 Dec 2017 03:47

Mouthwash wrote:
Source of the post Are there any known celestial bodies that can be (A) destroyed, or (B) have some part of themselves (atmosphere, solid layer) destroyed by a chain reaction?

Considering white dwarfs as celestial bodies: Type Ia supernovae, and novae, respectively.
 
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Mouthwash
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07 Dec 2017 05:24

I meant things that could be set off by human means
 
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07 Dec 2017 05:47

Mouthwash wrote:
Source of the post I meant things that could be set off by human means

Probably not.  It would have to be something already at the extreme brink of catastrophe by chain reaction, only needing a drop small enough for humans to release.  In practice we will never be at the right place or time for that.

Realistically, I think the only celestial bodies of reasonable size that we could practically destroy, though not by chain reaction, would be some asteroids or comets by influencing their orbit to bring them on collision course (with the sun, planet or moon).
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Gnargenox
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07 Dec 2017 10:03

Mouthwash wrote:
Source of the post Is it theoretically possible to burn through Titan's entire atmosphere or not?

I guess you could burn though all of Titan's methane the same way you could burn through all of Earth's oxygen using your own supply of methane.
cc213dbb9976f7e73cdb0c439d46690c.gif
cc213dbb9976f7e73cdb0c439d46690c.gif (772.06 KiB) Viewed 208 times

So, how much Oxygen would you need?
1 CH4 + 2O2 -> CO2 + 2 H2O so you need 4kg of O2 for each 1kg of methane.

Titan's atmosphere is mostly Nitrogen, over 90% actually and very similar to Earth's. Methane makes up around 1.6% in the stratosphere, Hydrogen coming in last place at .1 to .2%. Because methane condenses out of Titan's atmosphere at high altitudes, its abundance increases as one descends below the tropopause at an altitude of 32 km, leveling off at a value of 4.9% between 8 km and the surface. There are trace amounts of other hydrocarbons, such as ethane, diacetylene, methylacetylene, acetylene and propane, and of other gases, such as cyanoacetylene, hydrogen cyanide, carbon dioxide, carbon monoxide, cyanogen, argon and helium. The orange color as seen from space are produced by other more complex chemicals in small quantities, possibly tholins, tar-like organic precipitates.

To destroy Titan, not just scorch it, blow up the atmosphere, or melt the surface, you would have to supply more than its gravitational binding energy. Which is 2.8e29 J. Which would need approximately 5e21 Kg of methane, or, given its liquid density, a global ocean of methane 125 km deep on the surface. And then we would have to add 2e22 Kg of oxygen (200 Zettagrams) on top of that. But Titan doesn't even have a fraction of the required methane, so the point is moot.

But if you are just out to blow up Titan using oxygen, and it doesn't have to be through methane-oxygen combustion, you can do it with far less. Just accelerate a 150 million ton heavy block of frozen oxygen to 99.9 % c and smash it into Titan.
Kablam, Titan gone!
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07 Dec 2017 15:45

Mouthwash wrote:
Are there any known celestial bodies that can be (A) destroyed, or (B) have some part of themselves (atmosphere, solid layer) destroyed by a chain reaction? This occurred to me as I was reading about the theory that Saturn might be turned into a giant fireball by the Cassini probe's plutonium fuel. Of course it's not based on reality, but I was wondering if any such phenomenon is theoretically possible somewhere... it's a big universe, after all.

Something tells me a significant portion of the planet should be fissible material (which is highly unlikely afaik) for that to happen.
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08 Dec 2017 05:21

Gnargenox wrote:
But if you are just out to blow up Titan using oxygen, and it doesn't have to be through methane-oxygen combustion, you can do it with far less. Just accelerate a 150 million ton heavy block of frozen oxygen to 99.9 % c and smash it into Titan.
Kablam, Titan gone!

That would destroy any planet in existence, and probably most stars as well.
 
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08 Dec 2017 10:14

Watsisname wrote:
If you add more or better insulation to the shell, then what you're doing is decreasing the rate at which heat can initially flow outward.  But, heat is still transferred outward, and it must, in order to obey the heat equation.  Heat is transferred from regions of high temperature to low temperature, which in this case means outwards, because space outside the sphere of panels is colder than the Earth.

By decreasing the rate at which heat flows outward with insulation, you will cause the temperature on and inside your sphere to increase.  Basically you've put a blanket around the Earth.  So the temperature will go up, but that will then increase the rate at which heat will flow outward (by increasing the temperature difference between Earth and space), and eventually a balance will be re-established between the rate at which the Earth radiates heat and the rate your sphere of insulation radiates heat.  Again, you can't avoid this loss.  The loss just occurs at a higher temperature.

So, heat still flows outward at the same rate? Then what does insulation do? If Earth was generating energy, Earth would heat up until heat leaked as fast as energy was being made. But with a set amount of heat, insulation definitely slows down escaping heat. And I can ignore any fundamental limit on insulation, because I can just keep adding more layers.
There's a lot of questions with my Earth shell analogy, so let's just get down to the underlying problem: High-entropy heat naturally emits light, which can be converted into orderly potential energy.
This is the principle that I used to create my solar-panel-Earth-shell plan. Even if that plan is completely refuted, I could come up with other configurations of solar panels. I can think of only two possible reasons why solar panels can't reduce entropy.   1: Light is only emitted by heat that isn't 100% entropy. The heat gains entropy in the process of emitting light.   2: Solar panels, like practically every other method of power generation, relies on the uneven distribution of energy to harvest energy. A solar panel in a homogeneous mix of photons is useless.
Space is very spacious.
 
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09 Dec 2017 03:07

Adding insulation initially slows the flow of heat, but does not stop it, nor does it prevent the increase of entropy.  You can go ahead and consider the case where you add infinite insulation.  Does this achieve your goal of stopping the increase in entropy and converting the Earth's radiated heat into useful work?  No.  It replaces the vacuum where the heat radiates away at the speed of light, with a medium where heat flows out more slowly (thermal conduction via atoms bouncing into each other).  But the heat still flows out, and you can't convert it into useful stored energy in your panels.  The entropy increases.


Mr. Missed Her wrote:
Source of the post High-entropy heat naturally emits light, which can be converted into orderly potential energy.

Heat is the flow of energy, and the system which has this flow of energy may be high or low in entropy.  But its entropy implies nothing about light emission.  Thermal emission (blackbody radiation) occurs when a substance has temperature, and the spectrum depends only on the temperature.  

Your idea that the heat energy can be converted into orderly potential energy is partially correct.  Some of it can.  But never to the extent that it reduces the entropy of the system, where the system is defined so that it is closed and no energy gets in or out.  You can try to think of all kinds of clever schemes to try to beat this, but they will always fail.  They will always run into the second law.

Mr. Missed Her wrote:
Source of the post A solar panel in a homogeneous mix of photons is useless.



A sea of photons being homogenous (and we can also add isotropic if we want) does not prevent a solar panel from generating power.  The panel may absorb some photons and convert them to useful power.  

What will prevent the panel from generating power is if the photons do not meet the minimum energy threshold for the panel to generate charge by absorbing them.  Which is the case for the infrared radiation emitted by Earth.

How this relates to entropy is subtle.  That the radiation is uniform does not tell you everything about its entropy.  In fact a uniform sea of thermal photons ("photon gas") has an entropy which depends not only on its temperature, but also its volume.

This suggests that once again you have to think very carefully about how you define the system and its boundary.  Unless the photons are confined in some region, then the volume they occupy is increasing, and therefore the entropy is increasing.  On the other hand, if the photons are confined, then the entropy is constant, except for some inevitable leak of thermal radiation from the boundary, which will increase the entropy globally.
 
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09 Dec 2017 03:19

As an interesting aside, the expansion of a universe containing only photons is isentropic (keeps the entropy constant).  This is because the entropy of the sea of photons is proportional to the volume times the temperature cubed, but the temperature is inversely proportional to the universe's size (scale factor), while the volume is proportional to the scale factor cubed.  So it exactly balances out.
 
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13 Dec 2017 12:20

I have a little question about planetary systems. I'm sorry if it has been asked before, because the thread is very long and I didn't find it, so here it goes:
Do all systems with planets also have asteroid structures like the Oort's clod? Because I'm making a fictional system and I made an asteroid belt for it, as I saw lots of systems that have it in the game, but in the other hand I didn't see any procedural system with something similar to an Oort's cloud. I seem to remember having read that you were working on the procedural generation of such structures so maybe the reason I didn't see them is because they aren't implemented yet. Anyway I would like to know if I should make something similar (I could make a simple program to generate a couple hundreds of asteroids) for my system for it to be more realistic.
Thanks
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Mr. Missed Her
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14 Dec 2017 10:14

A'kast wrote:
I have a little question about planetary systems. I'm sorry if it has been asked before, because the thread is very long and I didn't find it, so here it goes:
Do all systems with planets also have asteroid structures like the Oort's clod? Because I'm making a fictional system and I made an asteroid belt for it, as I saw lots of systems that have it in the game, but in the other hand I didn't see any procedural system with something similar to an Oort's cloud. I seem to remember having read that you were working on the procedural generation of such structures so maybe the reason I didn't see them is because they aren't implemented yet. Anyway I would like to know if I should make something similar (I could make a simple program to generate a couple hundreds of asteroids) for my system for it to be more realistic.
Thanks

First off, I am not a professional astrophysicist (yet), so don't take anything I say here as absolutely certain.
Stars should always have some orbiting bodies, unless another star passed through and threw everything around with its gravity. When a star forms, there will always be some leftovers from the condensing celestial cloud. These leftovers form asteroids and planets. There's no reason to expect that all the asteroids should combine into planets, so there will often be asteroid belts leftover from planet formation. The main and Kuiper belts are these double leftovers in our solar system.
But on the Oort cloud, I'm a little (pun alert) cloudy. First off, it's most accurately described as the Oort void. Second, I'm not certain that it formed with the Sun. It may be homeless asteroids and comets that ended up orbiting the Sun when it formed. The Oort cloud extends out to where it's barely possible to orbit the Sun, so we probably have some foreign asteroids in it, even if it's not purely foreign asteroids.
If the Oort cloud is mainly alien asteroids, then interstellar space probably has a similar density of asteroids for stars to pick up. So any Oort clouds wouldn't really end at the edge of a star system, the asteroids would just be part of the interstellar medium.
Space is very spacious.

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