Author Topic: Predicting Details of Elon Musk's Mars Colony  (Read 54782 times)

Offline john smith 19

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #20 on: 04/01/2018 06:37 pm »
The one thing that keeps bothering me is the question of power.

What's needed is an estimate of consumption based on the colony plans, a power system concept and design, and then an estimae of mass and manpower that passes a sanity check.

Just saying "solar" or "nuclear" is not enough, and SpaceX hasn't yet anything significant about it.

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I don't think SX have released any estimates for the settlement.

Historical estimates from various groups (which IIRC appeared on the Mars life support or Mars gardening threads) had figures of 6-60Kw/person/day with 60Kw being the number for LED lit greenhouses. 

The other data point is for large space rated solar arrays is that for the ISS at 200Kw.
Note it's not just the size of the array. It's the rate it has to grow as people come to the settlement.

At 6Kw/person well that sounds fairly doable doesn't it? less than 2/3 of a new Kilopower reactor.

But at 60Kw/person/day things get much tougher.  Every 4 people is equal to putting up another ISS array.
I've noted that concentrator PV arrays can hit efficiencies of 43%  (that's about 142 m^2 per person at 60Kw) but people reckon that using thin film PV arrays trade efficiency for low mass per Kw and resistance to dust storms diffusing the sunlight (which can cut insolation by 80% and last for months).

So at 43% every 100 people have to bring another 14200 m^2 with them.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline blasphemer

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #21 on: 04/01/2018 06:46 pm »
I don't think SX have released any estimates for the settlement.

SpaceX Mueller has commented on power requirements for ISRU:

Quote
we’ll need to make about 1000 tons of propellant on Mars over a two-year cycle; bring it back; and that’s a tall order. You need about half a megawatt of energy to <inaudible> that much propellant <inaudible>

Quote
So if you’re taking it to Mars, it’s more efficient to ship reactors than it is to ship solar; it’s just that nobody’s really developed a space reactor yet. We’re working with NASA on that, and hopefully they’ll get funding to develop that. They’ve got a program called kilopower going that’s like, ten thousand watts, a 10 kilowatt reactor. We need a megawatt, but you know, you need to start somewhere.

Eventually, the right way to have power on Mars is fission, but initially, it’ll probably be solar. But in order to get the rockets back, we need a lot of power there to make propellant.

https://www.reddit.com/r/spacex/comments/6b043z/tom_mueller_interview_speech_skype_call_02_may/dhiygzm/?st=jfh5m8bm&sh=81c1cd37

Offline speedevil

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #22 on: 04/01/2018 06:56 pm »
Quote
Mueller: we’ll need to make about 1000 tons of propellant on Mars over a two-year cycle; bring it back; and that’s a tall order. You need about half a megawatt of energy to <inaudible> that much propellant <inaudible>

Half a megawatt times two years is 3*10^13J.
The energy of combustion of 250 tons of methane is around 9*10^12J.
Implying an efficiency of the order of magnitude of 30%.


Offline john smith 19

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #23 on: 04/01/2018 07:04 pm »
Wrong.
The equivalent to having the same radiation protection on Earth is about a 3metre layer of regolith.

I would also like a source for this. Earth atmosphere has mass of 10 tonnes per square meter. Seems to me like equivalent mass of regolith would be significantly thicker than 3 meters. Also, this:
The video I linked talks about radiation at about 42:26. In fact 3m was excessive as Mars regolith is denser than the Moon. The actual figure is 2.67m. Earths atmosphere is non linear. A significant fraction of it supplies no protection. It's when high energy particles hit about 20Km they hit significant density to start cracking molecules and the rest of the atmosphere as an absorber to this "spallation." Start from around 38:00-40:00 for more details.

A couple of boring machines will come in very handy on Mars.
« Last Edit: 04/01/2018 07:07 pm by john smith 19 »
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline speedevil

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #24 on: 04/01/2018 07:13 pm »
Historical estimates from various groups (which IIRC appeared on the Mars life support or Mars gardening threads) had figures of 6-60Kw/person/day with 60Kw being the number for LED lit greenhouses. 

The hardest figure I could find for a reasonable minimum came from cultivation studies on potatoes. You need to carefully look at what's included.
Some, for example, are including in power needs the whole air-conditioning to remove heat from their inefficient light sources to hot florida, as part of the energy budget.

This post outlines some of the results - in short - counting the lighting load only, you can grow 100% of the calories as potatos required by one person in 3kW and 40m^2. (24h/day).
You need somewhat more than this - around double - to do oxygen too.
Other crops are slightly less - around half is common - as efficient as potatos in terms of calories per joule in.
If you want 5% of the diet to be meat, pigs have around 10% efficiency for example, so with some 6kW electrical power into lights, (constant, 150kWh/day) you can get a reasonably varied diet.

This assumes you can do the cooling fairly cheaply, using heat exchange with the outside air, and do not need expensive air conditioning.
But, 60kW is overkill.

Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #25 on: 04/01/2018 07:24 pm »
Presentations on radiation on Mars have been given for decades, the situation has not changed much except that Mars Curiosity has validated that surface radiation levels are much less than deep space and solar events are effectively neutralized (compared to deep space).

Please post a source. Mars has very weak magnetic field and very thin atmosphere. It should therefore receive almost half of deep space cosmic ray dose (like 200-300 mSv per year, other half shielded by the planet itself) and also most of solar flare doses. Not an issue if you only spend a dozen hours per week outside, but more than that and it becomes a serious concern, especially for actual colonists who will hopefully live for many years and decades on the planet, instead of year long missions.
The planet shields half the radiation, and the atmosphere (although "thin") is about 40 grams/cm^2 thick, which dramatically attenuates solar flares and also reduces dosage of GCRs somewhat. It's like a foot or two of regolith.

It only takes a small amount of shielding to make solar flares much smaller in impact.

As far as if it's actually a concern, I was referring to Earth radiation worker doses, not limits.
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Offline blasphemer

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #26 on: 04/01/2018 07:32 pm »
The planet shields half the radiation, and the atmosphere (although "thin") is about 40 grams/cm^2 thick, which dramatically attenuates solar flares and also reduces dosage of GCRs somewhat. It's like a foot or two of regolith.

But isnt low amount of shielding generally even worse that nothing when it comes to GCRs due to secondary radiation? Of course it may depend on exact shielding mass and elemental composition...

Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #27 on: 04/01/2018 07:41 pm »
The planet shields half the radiation, and the atmosphere (although "thin") is about 40 grams/cm^2 thick, which dramatically attenuates solar flares and also reduces dosage of GCRs somewhat. It's like a foot or two of regolith.

But isnt low amount of shielding generally even worse that nothing when it comes to GCRs due to secondary radiation? Of course it may depend on exact shielding mass and elemental composition...
That’s only really for metals or other things with high atomic mass. CO2 per-atom (ie carbon and oxygen) is much lighter than aluminum.

Also, that’s only for thin shields. 40 g/cm2 is getting pretty thick.
« Last Edit: 04/01/2018 07:44 pm by Robotbeat »
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Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #28 on: 04/01/2018 07:46 pm »
As you can see, even aluminum (which is terrible compared to CO2) can effectively eliminate all acute solar flare effects with just30g/cm2. But the Mars atmosphere provides thicker shielding than that.
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Offline docmordrid

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #29 on: 04/01/2018 07:49 pm »
Shield the planet. One of NASAs ideas is a ~1-2 Tesla dipole placed at Sun-Mars L1. 1.5-3 Tesla is about the field strength of a modern medical CT scanner.

PhysOrg...

Presentation video, this starts at 1:36:00

https://livestream.com/viewnow/vision2050/videos/150701155
« Last Edit: 04/01/2018 07:54 pm by docmordrid »
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Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #30 on: 04/01/2018 07:52 pm »
Shield the planet. One of NASAs ideas is a ~3 Tesla dipole placed at Sun-Mars L1. 3 Tesla is about the power of a modern medical CT scanner.

PhysOrg...

Presentation video, this starts at 1:36:00

https://livestream.com/viewnow/vision2050/videos/150701155
Doesnt help for solar flares because solar flare charged radiation doesn’t travel in a straight line from the Sun. Also, that idea is problematic on a few levels. It wouldn’t make hardly any difference to the Mars atmosphere in the near term.
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 docmordrid

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #31 on: 04/01/2018 07:57 pm »
If the plan is colonization then near term could be handled otherwise.

I also wonder about a magnetic 'mesh constellation' akin to StarLink with overlapping zones of influence.
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Offline cppetrie

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #32 on: 04/01/2018 08:01 pm »
Shield the planet. One of NASAs ideas is a ~1-2 Tesla dipole placed at Sun-Mars L1. 1.5-3 Tesla is about the field strength of a modern medical CT scanner.

PhysOrg...

Presentation video, this starts at 1:36:00

https://livestream.com/viewnow/vision2050/videos/150701155
You mean an MR scanner. CT scanners do not generate magnetic fields. 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.

Offline speedevil

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #33 on: 04/01/2018 08:02 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.

Offline docmordrid

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #34 on: 04/01/2018 08:06 pm »


>
You mean an MR scanner. CT scanners do not generate magnetic fields. 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.

Brain fart. Thought MRI, typed CT, but yes.
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Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #35 on: 04/01/2018 08:14 pm »
If the plan is colonization then near term could be handled otherwise.

I also wonder about a magnetic 'mesh constellation' akin to StarLink with overlapping zones of influence.
Just put superconducting cables around the equator on the surface. Bonus: global supergrid with multi-year energy storage (essentially making solar power immune to dust storms no matter how big.
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Offline speedevil

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #36 on: 04/01/2018 08:16 pm »
If the plan is colonization then near term could be handled otherwise.

I also wonder about a magnetic 'mesh constellation' akin to StarLink with overlapping zones of influence.
Just put superconducting cables around the equator on the surface.
You get very, very large currents flowing in the core, which act to cancel your imposed field essentially 'forever'.

Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #37 on: 04/01/2018 08:18 pm »
If the plan is colonization then near term could be handled otherwise.

I also wonder about a magnetic 'mesh constellation' akin to StarLink with overlapping zones of influence.
Just put superconducting cables around the equator on the surface.
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.
« Last Edit: 04/01/2018 08:18 pm by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline Robotbeat

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #38 on: 04/01/2018 08:19 pm »
Remember, we only care about atmosphere erosion over tens of millions of years.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline Elmar Moelzer

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Re: Predicting Details of Elon Musk's Mars Colony
« Reply #39 on: 04/01/2018 08:23 pm »
You get very, very large currents flowing in the core, which act to cancel your imposed field essentially 'forever'.
I am not sure whether I understood your post correctly, but I want to point out that the newer high temperature super conductors such as YBCO do not have the current/magnetic field limitations of low temperature super conductors.

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