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#126 2017-10-17 12:10:14

Terraformer
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From: Lancashire
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Re: Possible Martian Export Products?

Replacing a tonne of Lunar water with a tonne of Lunar food won't require any extra propellent. The stations will be producing water as a byproduct of human respiration, so it might be easier to sell that straight to the depot to make up for the shortfall in Lunar water, and getting the food from Luna.

As I imagine it, depots would import propellent and food from Luna. Stations would then exchange their waste water and CO2 with the depots for food. The water and CO2 would be processed into propellent.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#127 2017-10-17 16:46:10

JoshNH4H
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Re: Possible Martian Export Products?

On the topic of a Martian space elevator, I sort of question the results of our old friend Hop.

Hop has the following to say about Zylon:

Hop wrote:

Zylon has a tensile strength of 580 megapascals or 580 meganewtons per square meter. On earth's surface with it's 9.8 meter/sec2 acceleration, it would take a 591,836,735 kilogram mass to exert that much force.

Elsewhere I have seen a tensile strength of 5.8 GPa quoted, which is probably why Hop chose Zylon.  He seems to have made an arithmetic/transcription error here and I am not sure if it carried over into his calculations.

In his post on a Phobos tether he cites the density as 1560 kg/m^3.  He also correctly cites the tensile strength in that post.  Anyway, using the correct versions of his numbers the specific strength of Zylon is 3.7e6 N-m/kg (3.7 MPa-m^3/kg).

Hop also correctly (well, probably, since I haven't checked his numbers) notes that the taper ratio for a tether with this material will be huge.  What he fails to consider is whether this is a problem or not.  Hop considers factors of safety (of a static tether with no oscillatory loads) of 1, 2, and 3.  I would consider 3 to be a bare minimum factor of safety for this kind of structure.  On top of that, there will be substantial loads caused by vibration and gravitational perturbations.

He gives the required taper ratio for a tether made from Zylon with a safety factor of 3 as 2016.  My question is: What's wrong with that?  The tether material will probably be made from feedstocks derived from an orbiting asteroid (Phobos or Deimos?) and manufactured and extruded in orbit.  A big taper ratio implies more tether mass and a longer time in construction (or more construction facilities), but who cares?

Meanwhile, carbon fibers are getting stronger every year.  T1000G has a slightly lower specific strength than Zylon (3.5 MPa-m^3/kg) but we're seeing rapid growth in the strength of that kind of fiber.

We build 10,000,000,000* kilo bridges to carry 1000 kg cars with a single 70 kg person and don't think this is strange.  Concrete and Steel are cheap and transportation is valuable.  I see no fundamental issue with a taper ratio of 10:1, 100:1, 1,000:1, or even 10,000:1 if the elevator is affordable. Things like throughput, technology development costs, and elevator lifetime are *way* more important than the taper ratio or total mass in governing how much it costs to send a kilo from Mars surface to Mars orbit.  These, in addition to the per-kilo cost of alternatives, should dominate our discussions of what space elevators are practical and which aren't.

Having said that, even if the material for low-taper space elevators on Mars does not exist now it probably will by the time we're actually building one.

*This is a very rough estimate for a large bridge based on a number I saw once somewhere


-Josh

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#128 2017-10-17 17:30:26

JoshNH4H
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Re: Possible Martian Export Products?

Terraformer wrote:

Replacing a tonne of Lunar water with a tonne of Lunar food won't require any extra propellent. The stations will be producing water as a byproduct of human respiration, so it might be easier to sell that straight to the depot to make up for the shortfall in Lunar water, and getting the food from Luna.

As I imagine it, depots would import propellent and food from Luna. Stations would then exchange their waste water and CO2 with the depots for food. The water and CO2 would be processed into propellent.

Ah, you're right about this.  But on the other hand you're basically trading an in-station farm for a small propellant plant, and getting worse quality/frozen food (plus losing out on some greenspace) in exchange.  I don't know how it'll shake out in the end.  I'm sure different facilities will choose once way or another.


-Josh

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#129 2017-10-18 06:51:13

Terraformer
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Re: Possible Martian Export Products?

The bulk of our food is pretty storable, because it's mainly dry carbohydrates that we process (cook) into palatable food when we need it. Besides, the journey from Luna is only going to be a few days by rocket, or months by elevator. Pretty standard for shipping down here. The bigger problem is probably trying to cook in freefall, so don't do that.

A large taper ratio might make the elevator possible, but how do you attach a car to it? Cars going over a bridge don't have to massively change size in order to get over it. I don't think it's going to be practical, unless you can somehow embed gripping points into it and climb up it, rather than gripping opposing sides. On the other hand, just getting a large way out of the gravity field makes a rocket launch far easier. Go far enough, and you can use electric thrusters to enter orbit.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#130 2017-10-18 10:18:43

elderflower
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Re: Possible Martian Export Products?

Elevator could be a tube rather than a cable. Then the climber can go inside it.

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#131 2017-10-18 14:15:15

Terraformer
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Re: Possible Martian Export Products?

That doesn't change the fact that you need to be able to grip it somehow.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#132 2017-10-18 17:24:15

JoshNH4H
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Re: Possible Martian Export Products?

Just off the top of my head, here are a few ways that an elevator car might handle a large-taper tether.

  • Fit the elevator car with an expandable collar

  • Make the cable in the shape of a tube (or square or whatever) with a constant inner size while the outer size is variable

  • Give the cable several notches on the outside, each of which serves as a track with constant size for elevator cars

  • Make the cable flat like a ribbon, with a constant thickness but a variable width.  Cars could travel on the outside.

  • Make a cable structure that is solid at the top but increasingly more threadbare as you get to the bottom

  • Embed magnetic elements in the cable structure that cars can use to propel themselves

There's hundreds of variations on how you could handle a large taper ratio and they're all fun to talk about, but they're all sort of beside the point at the moment. 

This is a basic overview of a technology readiness level scale NASA uses.  The scale goes from 1 to 9, where 1 is "Basic Principles Observed and Reported" and 9 is "Actual System "Flight Proven" through Successful Mission Operations".  On this scale a space elevator is generously a 2, maybe a 1, and very possibly not even at the first level yet.


-Josh

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#133 2017-10-20 09:48:29

JoshNH4H
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Re: Possible Martian Export Products?

Not to belabor the point, but in further reply to Clarke's point about manifest destiny it occurs to me that American Manifest Destiny only really happened because there was an economic incentive for settlers to move West: Land and Gold.  The US did end up controlling and then colonizing the Western portion of the continent (over the objections of various people already living there) but probably would not have done so without the economic incentives we had to go beyond the East.


-Josh

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#134 2017-10-20 11:08:05

IanM
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Re: Possible Martian Export Products?

Regarding your point JoshNH4H, Mars has quite a bit of land; 55.91 million square miles, in fact. That comes out to 35.78 billion acres, or 21.47 billion acres if we assume 40% is below terraformed sea level. In theory this can bring in $214.7 million in gross revenue if sold at merely a penny an acre, or $858.8 million if sold at a quarter an acre, or even a whopping trillion dollars if sold for less than $50/acre, and I believe that is the crux of the argument of the Space Settlement Institute. However, based on various data from http://home.costhelper.com/land-surveyor.html, it costs around $85-150 to survey an acre of land (in bulk, which is what Martian real estate would be) in the tame and developed United States, which would serve as a minimum price for sale if actual homesteading (as opposed to simple novelty values as the SSI suggests) is the goal. This makes the surveying costs alone reach $1.8-3.2 trillion for the entire (above sea level) planet, something that would definitely need some economic raison d'etre.


The Earth is the cradle of the mind, but one cannot live in a cradle forever. -Paraphrased from Tsiolkovsky

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#135 2017-10-20 11:40:50

JoshNH4H
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Re: Possible Martian Export Products?

Hey Ian,

I think it would be a mistake to take terraformation for granted.  I don't have a strong stance on how difficult it would be to terraform (The options as I see it are "really, really hard" and "really, really, really hard") or on the red/green debate.  No matter what ends up happening, though, Mars will remain uninhabitable for a pretty long time.

Until terraformation is substantially underway (e.g. at the least a few centuries from now) empty land on Mars will be substantially more empty than empty land on Earth, and substantially less valuable.  As I'm sure you know, the reason why Americans wanted more land in the nineteenth century was that peoples' livelihoods were basically agricultural, and therefore land+animals=wealth.  As we discussed earlier in the thread that's not really true anymore.  Uninhabited Martian land is nobody's idea of arable farmland, and even if it were it wouldn't be worth very much as such given labor and transportation costs.

Land on Mars is more like land in northern Alaska, Siberia, Antarctica, or Canada's Northwest Territories than the American Prairie: It's cold, not very useful unless it's got an extractable resource on it, inhospitable, and hard to get to.

Terraformation obviously would change that, but that's a many-trillion dollar investment over centuries, and one that is way beyond our current capabilities.


-Josh

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#136 2017-10-20 12:27:16

IanM
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From: Chicago
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Re: Possible Martian Export Products?

JoshNH4H wrote:

Hey Ian,

I think it would be a mistake to take terraformation for granted.  I don't have a strong stance on how difficult it would be to terraform (The options as I see it are "really, really hard" and "really, really, really hard") or on the red/green debate.  No matter what ends up happening, though, Mars will remain uninhabitable for a pretty long time.

Until terraformation is substantially underway (e.g. at the least a few centuries from now) empty land on Mars will be substantially more empty than empty land on Earth, and substantially less valuable.  As I'm sure you know, the reason why Americans wanted more land in the nineteenth century was that peoples' livelihoods were basically agricultural, and therefore land+animals=wealth.  As we discussed earlier in the thread that's not really true anymore.  Uninhabited Martian land is nobody's idea of arable farmland, and even if it were it wouldn't be worth very much as such given labor and transportation costs.

Land on Mars is more like land in northern Alaska, Siberia, Antarctica, or Canada's Northwest Territories than the American Prairie: It's cold, not very useful unless it's got an extractable resource on it, inhospitable, and hard to get to.

Terraformation obviously would change that, but that's a many-trillion dollar investment over centuries, and one that is way beyond our current capabilities.

Of course, I'm simply listing a potential commodity of sorts. The SSI assumes that most Martian land deeds would be simply bought and sold for novelty value, which would probably be right.


The Earth is the cradle of the mind, but one cannot live in a cradle forever. -Paraphrased from Tsiolkovsky

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#137 2017-10-20 12:49:05

JoshNH4H
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Re: Possible Martian Export Products?

People buying land deeds for novelty seems like a pretty bad way to divvy up the planet in the long term.  Having said that if people are only buying a couple of hectares for novelty's sake it would probably add up to a pretty small fraction of the planet.  This is another sort of "auxiliary revenue" in the vein of selling regolith and movie rights.  It's fine to a point and I imagine the Martians will appreciate the revenue*, but it's not a core value proposition for a human civilization on Mars unless we actually have something we want to do with that land.

*This one is sort of sketchy as far as space law is concerned: Who is actually enforcing the ownership of this property?  Is it more like "buying a star" which is basically a scam?  If valuable resources do happen to be found under the land people have bought do they actually have the rights to them?


-Josh

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#138 2017-10-20 13:45:45

louis
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Re: Possible Martian Export Products?

I used to argue for something similar, and I think it could potentially generate a lot of income. 

However, sale of freehold does seem to conflict with the Outer Space Treaty.  I now think that there are so many alternative revenue streams that we don't need to tap this resource directly, although something similar - sale of licences to occupy could follow at a slower rate.

Another approach might be to sell Mars Bonds which would guarantee owners a share in the profits of the Mars Corporation.


IanM wrote:

Regarding your point JoshNH4H, Mars has quite a bit of land; 55.91 million square miles, in fact. That comes out to 35.78 billion acres, or 21.47 billion acres if we assume 40% is below terraformed sea level. In theory this can bring in $214.7 million in gross revenue if sold at merely a penny an acre, or $858.8 million if sold at a quarter an acre, or even a whopping trillion dollars if sold for less than $50/acre, and I believe that is the crux of the argument of the Space Settlement Institute. However, based on various data from http://home.costhelper.com/land-surveyor.html, it costs around $85-150 to survey an acre of land (in bulk, which is what Martian real estate would be) in the tame and developed United States, which would serve as a minimum price for sale if actual homesteading (as opposed to simple novelty values as the SSI suggests) is the goal. This makes the surveying costs alone reach $1.8-3.2 trillion for the entire (above sea level) planet, something that would definitely need some economic raison d'etre.


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#139 2017-10-20 14:11:28

JoshNH4H
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Re: Possible Martian Export Products?

louis wrote:

Another approach might be to sell Mars Bonds which would guarantee owners a share in the profits of the Mars Corporation.

Semi-important distinction: This is not the same thing as the sale or lease of land on Mars.  A Mars Bond is debt for which investors will expect to be paid back with the profits MarsCorp.  Debt is generally only a good thing when you lack liquid assets and plan to invest the money in something that will generate more profits.  On the other hand, leasing or selling land generates actual revenues that (once you've subtracted the relevant expenses) are pure profit.  This is not an earthshattering commentary obviously but selling Mars bonds isn't an export.


-Josh

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#140 2017-10-20 14:23:54

IanM
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From: Chicago
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Posts: 251

Re: Possible Martian Export Products?

louis wrote:

However, sale of freehold does seem to conflict with the Outer Space Treaty.

This might be a ground for revising the OST depending on how advanced colonization becomes. But that is beyond the point of this thread, IMO.

louis wrote:

Another approach might be to sell Mars Bonds which would guarantee owners a share in the profits of the Mars Corporation.

While that is certainly doable, I think bondholders would be mostly Terran, so I doubt it'd have much an effect on the Martian GDP. Though as Josh says, debt might not be the best financing model. Perhaps MarsCorp could issue preferred shares that have priority over common stock in getting profits but without any voting rights.


The Earth is the cradle of the mind, but one cannot live in a cradle forever. -Paraphrased from Tsiolkovsky

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#141 2017-10-20 15:04:35

JoshNH4H
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Re: Possible Martian Export Products?

I think debt is fine so long as it's backed up by a realistic expectation of future revenue.  Selling land gives you cash up front which is good, but it's fine to debt finance some kind of improvement (let's say a space elevator) with the expectation that it will generate future revenue that you can use to pay back the debt.  In this sense, selling Mars Bonds is not a substitute for land sales unless you are using the money you get from the Mars bonds to improve the land and generate more revenue in the future. 

In a Terran context, it's sort of like the difference between funding infrastructure investments with public debt (arguably fine because theycan increase tax revenue in the future and pay for themselves) and funding safety net programs with public debt (not great policy because even though these are important they tend not to increase future tax receipts).


-Josh

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