Author Topic: Predicting Details of Elon Musk's Mars Colony  (Read 54783 times)

Offline cppetrie

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #40 on: 04/01/2018 08:23 pm »
And to your point 3T scanners aren’t even state of the art. 5T and 7T scanners are being used in research hospitals. They aren’t used routinely mostly because their greater expense isn’t worth it for routine clinical needs and also because those field strengths cause disorientation to patients that usually require sedation.

Most MRI machines used in hospitals are slightly under several hundred kilometers in diameter.
Why would it need to be several kilometers in diameter?

Offline speedevil

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #41 on: 04/01/2018 08:24 pm »
You get very, very large currents flowing in the core, which act to cancel your imposed field essentially 'forever'.
Not really. You charge it up over decades. That’s slow enough that the core doesnt cancel out the field.  Additionally, core is above the curie point.

Skin effect means 'slow enough' is many, many thousands of years, not decades unfortunately.

Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #42 on: 04/01/2018 08:43 pm »
You get very, very large currents flowing in the core, which act to cancel your imposed field essentially 'forever'.
Not really. You charge it up over decades. That’s slow enough that the core doesnt cancel out the field.  Additionally, core is above the curie point.

Skin effect means 'slow enough' is many, many thousands of years, not decades unfortunately.
I doubt such a calculation, although I haven’t had time to calculate it myself (Mars core is about 10^6 S/m). But thousands of years is still just fine for stopping erosion. Beefing up the atmosphere is a much greater priority and it’ll make a much bigger difference in surface radiation levels than the magnetic field would.
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Offline speedevil

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #43 on: 04/01/2018 09:22 pm »
I doubt such a calculation, although I haven’t had time to calculate it myself (Mars core is about 10^6 S/m). But thousands of years is still just fine for stopping erosion. Beefing up the atmosphere is a much greater priority and it’ll make a much bigger difference in surface radiation levels than the magnetic field would.
That is - when you turn on your coil around Mars, you induce an equal and opposite current in the surface of the molten core of Mars, which almost perfectly cancels out your induced field.

It takes longer than thousands of years for this cancellation to go away and your imposed field to be visible.
(Local fields that don't touch the core are not affected)

Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #44 on: 04/01/2018 10:57 pm »
I understood your point, I just am not going to accept it as true without doing the calculation myself tonight. Doesn’t make much practical difference, tho, since erosion is only a concern over tens or hundreds of millions of years.
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Offline Alkan

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #45 on: 04/02/2018 06:10 am »
I doubt such a calculation, although I haven’t had time to calculate it myself (Mars core is about 10^6 S/m). But thousands of years is still just fine for stopping erosion. Beefing up the atmosphere is a much greater priority and it’ll make a much bigger difference in surface radiation levels than the magnetic field would.
That is - when you turn on your coil around Mars, you induce an equal and opposite current in the surface of the molten core of Mars, which almost perfectly cancels out your induced field.

It takes longer than thousands of years for this cancellation to go away and your imposed field to be visible.
(Local fields that don't touch the core are not affected)

If it really took thousands of years to become negligible, then all you would have to do is turn the magnet on for a split second and the current induced in the core would keep up a strong enough magnetic field for a long time.

It's kind of absurd, actually. Changing magnetic fields induce currents, steady magnetic fields do not. Currents decay almost instantaneously if nothing is driving it.

https://en.wikipedia.org/wiki/Maxwell%27s_equations#Formulation_in_SI_units_convention

The third one, Maxwell–Faraday equation. The second one is easier to understand (DelXE=-∂B/∂t).
« Last Edit: 04/02/2018 06:18 am by Alkan »

Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #46 on: 04/02/2018 09:59 am »
But the core is really big. Gotta do the calculation.
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Offline TaurusLittrow

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #47 on: 04/02/2018 10:30 am »


So, I'm interested in predicting some of the details of his colony. Each phase is looser and more speculative.

Phase I: Fuel Production

The methane fuel will be created by the Sabatier reaction using CO2 and water.
Welcome to the site.
You're behind the curve here. Substantial Methane deposits have been found.

JS19: Methane deposits?  I missed that.

Are they usable?  What form do they take?  Do you have references?

-----
ABCD: Always Be Counting Down

Elon Musk literally said they're going to use CO2 at ITS presentation, so that comment about me being behind is kind of funny. It's probably easier to find a lot of water.

https://www.youtube.com/watch?v=8unI6KHAocU?t=14m43s

The presentation on radiation on Mars was released before Elon Musk's Mars architecture was outlined. It will be an issue, though I don't think Elon Musk seems to think of it as such a big deal. It is a bigger deal than I think that Elon Musk thinks, but the risk of increased cancer is just going to be part of it.

Agreed. There are serious issues surrounding reproduction in a high radiation environment. Based on measurements by the Curiosity rover in Gale crater, the average dose-equivalent rate of cosmic rays is about 0.64 milliSieverts (mSv) per day on the surface. Day by day, that adds up. One estimate of the annual dose-equivalent of cosmic rays in a regolith-shielded habitat on Mars ranges from 70 mSv (at solar maximum) to 260mSv (at solar minimum). A three-meter deep layer provides the maximum shielding from galactic cosmic rays.

At some threshold, the reproductive organs are at risk. With less protection, chromosomes inside male reproductive cells are more susceptible to radiation damage, especially since the male Y chromosome seems to be more fragile than the female X chromosome. Injury to male reproductive cells could provoke infertility or even change the ratio of girl to boy babies.

Unborn children are at even greater risk than their parents since serious health problems can arise at substantially lower radiation doses. Prenatal radiation can spark structural malformations, growth retardation, sterility, and central nervous system abnormalities, to name a few. The threshold for developmental abnormalities during the period when major organs form is about 100mSv acute gamma rays, and may be even lower for highly energetic neutrons and heavy nuclei in cosmic rays.

The developing central nervous system in the fetus is particularly sensitive to radiation. Statistics from A-bomb survivors exposed in utero at 8 to 15 weeks after conception show decreases in IQ scores of about 21 to 29 points per 1000 mSv. The lifetime risk of cancer also rises following exposure in utero or early childhood—substantially greater than the increased risk in adults.

The most critical health effect for human colonization of Mars may turn out to be infertility in women exposed to radiation before birth. The radiosensitivity of immature eggs in female fetuses—approximately half of developing eggs are killed by only 70 mSv of chronic beta (electron) rays. A female fetus exposed to this level could be born sterile or suffer premature menopause.

Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #48 on: 04/02/2018 10:43 am »
Sorry to interrupt your doomsaying, but you can shield a habitat on the surface to lower than Earth levels of radiation. Heck, a big enough habitat with enough floors will have enough shielding in the structure itself that the lower levels will have Earth-like radiation levels. That’s where children and pregnant families can hang out.
« Last Edit: 04/02/2018 12:18 pm by Robotbeat »
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Offline speedevil

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #49 on: 04/02/2018 01:57 pm »
That is - when you turn on your coil around Mars, you induce an equal and opposite current in the surface of the molten core of Mars, which almost perfectly cancels out your induced field.

It takes longer than thousands of years for this cancellation to go away and your imposed field to be visible.
(Local fields that don't touch the core are not affected)

If it really took thousands of years to become negligible, then all you would have to do is turn the magnet on for a split second and the current induced in the core would keep up a strong enough magnetic field for a long time.

It's kind of absurd, actually. Changing magnetic fields induce currents, steady magnetic fields do not. Currents decay almost instantaneously if nothing is driving it.

https://en.wikipedia.org/wiki/Maxwell%27s_equations#Formulation_in_SI_units_convention

The third one, Maxwell–Faraday equation. The second one is easier to understand (DelXE=-∂B/∂t).
Details matter.
Changing magnetic fields induce currents, steady magnetic fields do not.
But, if you have a conductor a thousand kilometers thick, it takes many, many thousands of years for that current to be 'steady' (the effect of the startup transient to be zero).

https://en.wikipedia.org/wiki/Skin_effect


In practice, the modest shielding of the atmosphere, combined with well shielded living quarters seems to be pretty much adequate, without trying global magnetic field modification.
Modifying the local field is of course possible.


Offline Alkan

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #50 on: 04/02/2018 03:02 pm »
Without being driven and with an extremely high resistivity (which is NOT resistance), each volume element of the planet makes up a resistor. The thing is, there's not even a closed loop inside Mars to induce a current in. Any established potential inside of the planet is what would cause the induced current in the first place, and there isn't a loop - the charge is free to move across the planet's presumably metal core. You need to be thinking about concepts like current density and resistivity before you're thinking about current and resistance.

Quote
Modifying the local field is of course possible.

Putting a magnetic field up near your settlement would do absolutely nothing except for possibly deflecting a few charged particles. EM waves pass right through a magnetic field, which is why you don't see any blurring or any weird effects when you turn on powerful magnets. So, when a gamma ray comes in and happens to be the one that hits a strand of DNA and gives you cancer, that's where an electromagnetic field does nothing to act on the incoming EM-wave. This is because of superposition.

An easy way of modeling this is to imagine a solenoid around an insulating shell with an conducting sphere on the inside. You can assume little magnetization of the material in the insulator, which means you can basically ignore it, leaving a solenoid around a conducting sphere.

If you turn on a direct current, you will induce a small eddy current in the sphere. That will die off as soon as the magnetic field stops changing because the somewhat complicated circular electric potential inside of the sphere will dissipate as soon as the magnetic field running through it stops oscillating. Without a changing magnetic field, there won't even be a current moving in a direction.

Electric fields establish themselves at the speed of light, and the speed of electrons in an actual material is actually very, very slow, on the order of microns per second. Source: https://en.wikipedia.org/wiki/Drift_velocity - see the numerical example at the bottom of the page.

So, really, the decay of this current is going to happen almost instantly.

Magnetic induction stoves use currents that oscillate at 100 Hz to 200 kHz. The skin effect doesn't even make sense as a concept without a driven oscillating electric potential.
« Last Edit: 04/02/2018 03:35 pm by Alkan »

Offline speedevil

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #51 on: 04/02/2018 04:57 pm »
Without being driven and with an extremely high resistivity (which is NOT resistance), each volume element of the planet makes up a resistor. The thing is, there's not even a closed loop inside Mars to induce a current in. Any established potential inside of the planet is what would cause the induced current in the first place, and there isn't a loop - the charge is free to move across the planet's presumably metal core. You need to be thinking about concepts like current density and resistivity before you're thinking about current and resistance.

The core is made of metal.
It is one solid piece of metal, with no insulation.
The loop is formed of the circumference of the core under your coil.

https://en.wikipedia.org/wiki/Dynamo_theory Magnetism can make current move very, very slowly through large conductive bodies, before becoming 'simply' resistive.
This is however off topic here, as no plausible near-term colony is doing global scale geomagnetism attempts.
« Last Edit: 04/02/2018 04:59 pm by speedevil »

Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #52 on: 04/03/2018 01:04 pm »
Speedevil:
I moved my reply (with chris bergin’s help) to this thread: https://forum.nasaspaceflight.com/index.php?topic=45398.0#new

You make a good and valid point BUT... (click that link :) )

Let this discussion continue about the Mars Nation (colony implies subjugation by Earth ;) ).
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #53 on: 04/04/2018 11:31 pm »
Sorry to interrupt your doomsaying, but you can shield a habitat on the surface to lower than Earth levels of radiation. Heck, a big enough habitat with enough floors will have enough shielding in the structure itself that the lower levels will have Earth-like radiation levels. That’s where children and pregnant families can hang out.

Just to follow up: based on my calculations, 900g/cm^2 of Mars regolith (about 6 meters) corresponds to radiation levels of about 3mSv/year, which is lower than Earth (which is about 4mSv/year).

A 10-20 storey building would have about that much vertical shielding just due to structure.
« Last Edit: 04/04/2018 11:36 pm by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline docmordrid

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #54 on: 04/05/2018 12:22 pm »
Plant based meat substitutes tend to have 2 problems: many of the better ones are based on glutens, which make many peoplei ill, and in order to have an acceptable taste they contain ridiculous levels of sodium chloride.

Bioengineered meat; any chef will tell you the animal cell culture isn't near enough.The flavor is from the Maillard reaction, a chemical reaction between amino acids and reducing sugars, and the thermal degradation of a complex brew of animal lipids and collagens. Need to synthesize those too, and in the proper proportions. Some "meats" will need more collagen, as in roasts and stewing meats.
DM

Offline jpo234

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #55 on: 04/05/2018 12:37 pm »
Hi I couldn't find the mars agriculture thread for some reason.. just dumping this here.

https://forum.nasaspaceflight.com/index.php?topic=44465.0
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #56 on: 04/05/2018 12:48 pm »
People forget we actually have a larger forum outside of SpaceX...

General Mars threads should go in the general Mars section, not in the SpaceX Mars section.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline jpo234

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #57 on: 04/05/2018 02:48 pm »
People forget we actually have a larger forum outside of SpaceX...

General Mars threads should go in the general Mars section, not in the SpaceX Mars section.

Actually, there is not really a "general Mars section". The thread Scaling Agriculture on Mars  is under "HLV / SLS / Orion / Constellation", which is not really all that much better than "SpaceX Mars".
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline JesseD

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #58 on: 04/05/2018 03:57 pm »

My theory is that we are going to be living in mars bases one way or another.. even if we stay on earth. This is just another example out of thousands of how the inexorable evolution towards efficient sustainable technology on earth brings mars bases closer.

As foreseen back in the 90s.

Offline Toast

Re: Predicting Details of Elon Musk's Mars Colony
« Reply #59 on: 04/05/2018 11:17 pm »
Plant based meat substitutes tend to have 2 problems: many of the better ones are based on glutens, which make many peoplei ill, and in order to have an acceptable taste they contain ridiculous levels of sodium chloride.

Gluten isn't some boogeyman, the vast majority of the population can eat it just fine. Unless by "many" you mean ~0.5-1% of the population. Plus there's plenty of other plant-based proteins out there for those that can't or won't eat gluten. As for sodium, I'd like to see a source for that because I've never had a problem keeping my sodium intake levels low while on a plant-based diet.

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