Privatized Space Travel

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Re: Privatized Space Travel

Postby Zamfir » Fri Jan 21, 2011 4:39 pm UTC

Antimony-120 wrote:Much like North America was colonized AFTER Siberia, the harder it is to get to, the longer it takes us to strat colonizing it. However when the possibility of colonization opens up we tend to begin as soon as it's remotely viable.

Siberia is a large place. There are regions within it that are populated and have been populated for a long time. But huge parts are not populated in any sense of the word, areas where for hundreds of miles there is no human activity at all. Technically, it is viable to live in those places. It's just that no one wants to or has a reason.

http://www.citypopulation.de/php/russia-sacha.php shows the populated places in the republic Yakutsk , roughly a million people in a million square miles. The south of the province is the 'populated' part, where towns are sometimes (though rarely) as close a 20 miles apart. But the northern half only has about 2 dozen settlements (ranging from 100 to 15000 inhabitants) in a several hundred thousand square miles. There is literally not a settlement there that is not at the location of a mine, and when the mine is empty, the settlement disappears. Most of those towns wouldn't exist if the Soviet Union hadn't send its prisoners to them in the first place. As technology gets better, it requires less people to operate mines, and the towns get even smaller.

I'd say that argues against the idea that people behave like a gas, filling all space available. It's a reasonable model for places that are in some sense pleasant to live, but not for distant and unpleasant places.

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Re: Privatized Space Travel

Postby Antimony-120 » Fri Jan 21, 2011 6:32 pm UTC

Zamfir wrote:
Antimony-120 wrote:Much like North America was colonized AFTER Siberia, the harder it is to get to, the longer it takes us to strat colonizing it. However when the possibility of colonization opens up we tend to begin as soon as it's remotely viable.

Siberia is a large place. There are regions within it that are populated and have been populated for a long time. But huge parts are not populated in any sense of the word, areas where for hundreds of miles there is no human activity at all. Technically, it is viable to live in those places. It's just that no one wants to or has a reason.

http://www.citypopulation.de/php/russia-sacha.php shows the populated places in the republic Yakutsk , roughly a million people in a million square miles. The south of the province is the 'populated' part, where towns are sometimes (though rarely) as close a 20 miles apart. But the northern half only has about 2 dozen settlements (ranging from 100 to 15000 inhabitants) in a several hundred thousand square miles. There is literally not a settlement there that is not at the location of a mine, and when the mine is empty, the settlement disappears. Most of those towns wouldn't exist if the Soviet Union hadn't send its prisoners to them in the first place. As technology gets better, it requires less people to operate mines, and the towns get even smaller.

I'd say that argues against the idea that people behave like a gas, filling all space available. It's a reasonable model for places that are in some sense pleasant to live, but not for distant and unpleasant places.


I never said we colonize densely, nor did I suggest that there weren't large tracts of land that have essentially zero people. I am well aware these places exist, I lived in Northern Manitoba at one point (i.e., North of Thompson), which has nigh identical demographics. But lack of dense population does not have the remotest effect on my point. My comment about Siberia was that it was populated by people when there was even less there than there is now, and for no reason other than it was possible to live there. Has it ever gotten much larger than the original inhabitation? No. But that actually only furthers my point. It was colonized to saturation wuite quickly, despite being a generally unpleasant place to live. If I had argued that Mars was going to become a massive metropolis dwarfing earth, then yes I would be in trouble here, but I didn't. I merely suggested that some colonization is likely.
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Re: Privatized Space Travel

Postby Zamfir » Fri Jan 21, 2011 6:52 pm UTC

Isn't it a strange to say that some area is "populated" just because there are people living a few hundred miles away? In such a definition, no place on earth can be unpopulated, because you can always increase the area of the land under consideration until it includes people.

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Re: Privatized Space Travel

Postby Antimony-120 » Fri Jan 21, 2011 7:05 pm UTC

Zamfir wrote:Isn't it a strange to say that some area is "populated" just because there are people living a few hundred miles away? In such a definition, no place on earth can be unpopulated, because you can always increase the area of the land under consideration until it includes people.


Isn't it strange to say an area is "unpopulated" just because the density isn't large enough to match some arbitrary limit? In such a definition, no place on earth has to be unpopulated, because you can always decrease the area of the land under consideration until it no longer includes people.

So that's why I avoided that issue. I asked "If area A was capable, with the technology of the time, of supporting some population density X, did it?" and the answer has, historically, almost always been "yes". So I suspect that as soon as Mars is capable, with the technology of the time, of supporting any population, it will.

Once again: My statement is not that humans have always instantly converted a new area to high population density.

My statement is: Humans tend to fill any given area to capacity, given geographical and technological limitations, regardless of the areas attractiveness.

So would I say that Siberia is filled to capacity? Yes.
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Re: Privatized Space Travel

Postby idobox » Fri Jan 21, 2011 7:37 pm UTC

Sending stuff to LEO with a falcon 9rocket costs about 3000$ a kg, about 5000$ for GTO. I have no idea how much it costs to send stuff to Ceres or other large asteroids, but it will probably be a few times more.

Space tourists are willing to pay a lot of money to get there because it's awesome. But that will never cause any sort of colonization, like cruise boats cannot be considered a colonization of the oceans.

Keeping personnel in space has an horrendous initial cost, and horrendous maintenance costs (ISS will cost something around 100 billions $ over 30 years, for a crew of 6 people). A self-sufficient habitat would have an even higher cost.
If a company decides to built something remotely similar to ISS (a low orbit habitat), it will be only if they find a way to make a few workers earn a few billions a year. There are not many things that can be done only in space, with an annual revenue of 500 millions $ per worker.

Things that will probably not be economically sound in a reasonable time frame:
-space based solar. Solar cells are not economicaly sound on Earth without subsidies. Sending them in space could result in a 300% efficiency improvement, but the cost would be multiplied by much more.
-other forms of energy harvesting. There is a lot of fissile and fusible material down here, and even if we found oil in space, it would consume more energy to get it than what you could retreive.
-colonization. We could have much larger populations in Siberia and Sahara, you have a lot of space, and we master the technology of HVAC. We could build livable megalopoles. We don't do it because the cost would be higher than in other areas, and unless there is a high value natural ressource around, it serves no purpose.

On top of my head, I can think of:
-precious metals mining. Palladium costs about 30 000$ /kg. You could expect a worker to mine much more than the wieght of his craft. But until mines are depleted, it will be much cheper to exploit earth crust.
-extremely high added value manufacturing. If for some reason, someone discovered a way to produce giant graphene sheets, or quantum computers, or cancer medicine, that works only in microgravity, then it might be a sufficient reason to build plants.

If anyone settles to space, it will be scientists, or the army, because they are basically the only ones able to spend thousands of billions on something that is not profitable. If the settlements reach a certain size, they will eventually attract private investors, because it will finally be cheaper to build stuff on site than importing it. Like mining iron or aluminium on the moon rather than importing it to build telescopes, habitats and other stuff.
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Re: Privatized Space Travel

Postby Zamfir » Fri Jan 21, 2011 7:56 pm UTC



Isn't it strange to say an area is "unpopulated" just because the density isn't large enough to match some arbitrary limit? In such a definition, no place on earth has to be unpopulated, because you can always decrease the area of the land under consideration until it no longer includes people.

The situation is not that symmetric. Space in populated areas might not be holding people, but it is still in use by people. As wall or road or farmland or garden or lots of other purposes. In such an area, you cannot deploy some extra space-consuming activity without affecting existing activities. That is qualitatively different from empty space in northern Yakutsk, where people could generate more activities without affecting the space-consumption of existing activities.

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Re: Privatized Space Travel

Postby gmalivuk » Fri Jan 21, 2011 9:06 pm UTC

idobox wrote:Sending stuff to LEO with a falcon 9rocket costs about 3000$ a kg, about 5000$ for GTO. I have no idea how much it costs to send stuff to Ceres or other large asteroids, but it will probably be a few times more.
Once in orbit around Earth, you only need an additional 40% of energy or so to escape Earth's gravity entirely.

Things that will probably not be economically sound in a reasonable time frame:
Define "reasonable time frame". I mean, if you're just going to describe it vaguely like that, you could say just about whatever you wanted...
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Re: Privatized Space Travel

Postby Zamfir » Fri Jan 21, 2011 9:26 pm UTC

gmalivuk wrote:
idobox wrote:Sending stuff to LEO with a falcon 9rocket costs about 3000$ a kg, about 5000$ for GTO. I have no idea how much it costs to send stuff to Ceres or other large asteroids, but it will probably be a few times more.
Once in orbit around Earth, you only need an additional 40% of energy or so to escape Earth's gravity entirely.

Yeah, but reaching escape velocity for the earth is only step 1. That only brings you roughly in solar orbit instead of earth orbit.

You also need delta-v to enter a transfer orbit that goes to Ceres, and then some delta-v more to match Ceres's orbit.

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Re: Privatized Space Travel

Postby Tass » Fri Jan 21, 2011 11:20 pm UTC

idobox wrote:Sending stuff to LEO with a falcon 9rocket costs about 3000$ a kg, about 5000$ for GTO. I have no idea how much it costs to send stuff to Ceres or other large asteroids, but it will probably be a few times more.


Why would you want to go to Ceres? It is way too big and way to far away. It is big enough to have stratified meaning all the good stuff is in the unreachable center. There are Near Earth Asteroids that can be reached with less delta-v than the moon. And from some you can return for as little as 60m/s delta-V using aerobrake in the Earth atmosphere.

idobox wrote:Space tourists are willing to pay a lot of money to get there because it's awesome. But that will never cause any sort of colonization, like cruise boats cannot be considered a colonization of the oceans.


It does one thing, however, drive development of cheaper ways to orbit. Fuels is a very little part of the price to get to orbit. Most of the price is the technology to keep all that fuel working towards its purpose rather than blowing up in your face. This means that there is great potential for improvement. Even if we are still stuck with chemical rockets.

Many private companies are making great progress too.

idobox wrote:Keeping personnel in space has an horrendous initial cost, and horrendous maintenance costs (ISS will cost something around 100 billions $ over 30 years, for a crew of 6 people). A self-sufficient habitat would have an even higher cost.
If a company decides to built something remotely similar to ISS (a low orbit habitat), it will be only if they find a way to make a few workers earn a few billions a year. There are not many things that can be done only in space, with an annual revenue of 500 millions $ per worker.


ISS is horribly inefficient. It is in a highly inclined orbit making it much more expensive to reach than if it was more equatorial. A bigger habitat will be comparatively cheaper. It would be build from material all ready in space, cutting that horrible Earth-to-orbit price. Production of food and other necessities further reduces the need for expensive launches. But you are right, no one is going to build it because it is awesome. They will build it because it is needed. No one will move to space because they can - ocean floor, Sibiria etc. would be cheaper and easier then - they will do it because there is jobs, because there is profit to be made. My thesis is that there is profit to be made on space development:

idobox wrote:-space based solar. Solar cells are not economicaly sound on Earth without subsidies. Sending them in space could result in a 300% efficiency improvement, but the cost would be multiplied by much more.


Try 2000% then you are closer. But you are right, sending them into space is out of the question, they have to be manufactured in space, from material gathered out there (luna or NEA). Only in that way can we avoid the horrible cost of the Earth-LEO step.

Yes, the initial investment is large, but the entire Earths energy consumption is a huge market.

idobox wrote:-precious metals mining. Palladium costs about 30 000$ /kg. You could expect a worker to mine much more than the wieght of his craft. But until mines are depleted, it will be much cheper to exploit earth crust.


Mining planet crust is terribly expensive and inefficient. The interior stratified as the planet formed leaving most of the heavy elements in the center and only trace amounts to be found in the crust. You have to dig far down along veins where the element is slightly less scarce than usual and still you have to move tones of material against gravity, and then process it just to obtain a few grammes of precious metal. M-type asteroids on the other hand are thought to be core parts of a celestial body that stratified, then cooled, and was later smashed by impacts. It is practically pure metal. For construction in space it can pretty much be used as-is. Maybe it would be profitable to extract precious metal first, maybe you could just cut it up into sizable chunks and then de-orbit them. De-orbiting a lump of metal is much easier than it is with a billion dollar piece of fine machinery like the shuttle of course. You don't mind a bit of melting of the surface, and you don't mind a bit of a hard landing, as long as it is small enough that it doesn't make to big a crater.

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Re: Privatized Space Travel

Postby Antimony-120 » Sat Jan 22, 2011 1:26 am UTC

Zamfir wrote:


Isn't it strange to say an area is "unpopulated" just because the density isn't large enough to match some arbitrary limit? In such a definition, no place on earth has to be unpopulated, because you can always decrease the area of the land under consideration until it no longer includes people.

The situation is not that symmetric. Space in populated areas might not be holding people, but it is still in use by people. As wall or road or farmland or garden or lots of other purposes. In such an area, you cannot deploy some extra space-consuming activity without affecting existing activities. That is qualitatively different from empty space in northern Yakutsk, where people could generate more activities without affecting the space-consumption of existing activities.


I used the term carrying capacity for a reason, I have never been to Yakutsk, but at least in Northern Manitoba hunting, fishing and trapping are still major providers of food and income. And a herd of caribou use up HUGE chunks of land. The land may not be directly in use, but you couldn't add more people and not notice a sudden drop in the resources availiable to the people already there. It's wildly unproductive land, and so the few people there are each using up massive amounts of land, despite the fact that it doesn't appear to be in use. You just can't use it very hard at all or the whole thing goes to rat shit faster than you can say "overhunted".
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Re: Privatized Space Travel

Postby idobox » Sat Jan 22, 2011 2:22 pm UTC

gmalivuk wrote:
idobox wrote:Sending stuff to LEO with a falcon 9rocket costs about 3000$ a kg, about 5000$ for GTO. I have no idea how much it costs to send stuff to Ceres or other large asteroids, but it will probably be a few times more.
Once in orbit around Earth, you only need an additional 40% of energy or so to escape Earth's gravity entirely.

This number sounds low, but you to take that additionnal energy to orbit too. So you don't need a 40% bigger rocket.

gmalivuk wrote:
Things that will probably not be economically sound in a reasonable time frame:
Define "reasonable time frame". I mean, if you're just going to describe it vaguely like that, you could say just about whatever you wanted...

A few hundreds years. Of course, it depends on each point, but the idea is that it won't happen until conditions on Earth or technology change a lot, like population reaching 30 billions, or fusion rockets.

Tass wrote:Mining planet crust is terribly expensive and inefficient.

Not that much. Of course precious metals are present only in tiny amounts, and it requires a lot of energy to extract them. But asteroids are not giant nuggets of pure Iridium either, they're mostly made of iron and other common metals. The proportion of rare metals is a lot higher, but you will still need to refine it.
But there are people who really think of mining asteroids in a few decades.

Tass wrote:Try 2000% then you are closer. But you are right, sending them into space is out of the question, they have to be manufactured in space, from material gathered out there (luna or NEA). Only in that way can we avoid the horrible cost of the Earth-LEO step.

Where does that 2000% figure comes from? solar power up there is about 140% of what we have down here, and you can have them exposed all day, so twice as long. If you compare space based to solar panels mounted on motors, you get around 300% increase in efficiency.
And I didn't count all the issues with making large arrays in space, or the cooling of the panels.
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Re: Privatized Space Travel

Postby Pez Dispens3r » Sat Jan 22, 2011 2:53 pm UTC

Antimony-120 wrote:I asked "If area A was capable, with the technology of the time, of supporting some population density X, did it?" and the answer has, historically, almost always been "yes".

Like how we've had boats since forever, and the entirety of the oceans have been colonized.



...Oh.
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Re: Privatized Space Travel

Postby gmalivuk » Sat Jan 22, 2011 5:17 pm UTC

idobox wrote:
gmalivuk wrote:
idobox wrote:Sending stuff to LEO with a falcon 9rocket costs about 3000$ a kg, about 5000$ for GTO. I have no idea how much it costs to send stuff to Ceres or other large asteroids, but it will probably be a few times more.
Once in orbit around Earth, you only need an additional 40% of energy or so to escape Earth's gravity entirely.
This number sounds low
Escape velocity is sqrt(2) * orbital velocity. So I did make a mistake, and was actually talking about delta-V, rather than kinetic energy.

gmalivuk wrote:
Things that will probably not be economically sound in a reasonable time frame:
Define "reasonable time frame".
A few hundreds years.
Are you kidding? The first solar cell was invented less than 130 years ago and the first solar satellite a bit over 50 years ago, and you think another 200-300 years of development won't see additional vast improvements in solar technology?

the idea is that it won't happen until conditions on Earth or technology change a lot, like population reaching 30 billions
If Earth can sustain that many, it only requires two more doublings to reach about 30 billion. That could definitely happen in less than a few hundred years.

solar power up there is about 140% of what we have down here, and you can have them exposed all day, so twice as long.
No, even the most heavily insolated places on Earth get about 7kWh/m^2/day of sunlight, which is less than 292 W, whereas above the atmosphere it's 1372 W/m^2. (Remember, no place on Earth gets *direct* sunlight for a full half-day.) So that's 370% more solar energy in space than in the middle of the Sahara.
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Re: Privatized Space Travel

Postby idobox » Sat Jan 22, 2011 6:39 pm UTC

gmalivuk wrote:If Earth can sustain that many, it only requires two more doublings to reach about 30 billion. That could definitely happen in less than a few hundred years.

The thing is Earth can't support that number. That's why it would make colonisation of space more interresting.

gmalivuk wrote:Are you kidding? The first solar cell was invented less than 130 years ago and the first solar satellite a bit over 50 years ago, and you think another 200-300 years of development won't see additional vast improvements in solar technology?

It doesn't really matter if solar technology improves, it won't change anything to space-based vs ground based solar power. Sending solar plants will probably never be able to produce net energy (I don't have any numbers to support that) and building a solar cell plant in orbit using material mined in space will require a lot of technology and money that would probably be better spent on nuclear power or fusion.

gmalivuk wrote:No, even the most heavily insolated places on Earth get about 7kWh/m^2/day of sunlight, which is less than 292 W, whereas above the atmosphere it's 1372 W/m^2. (Remember, no place on Earth gets *direct* sunlight for a full half-day.) So that's 370% more solar energy in space than in the middle of the Sahara

The integrated total terrestrial solar irradiance is 950 W/m2.
If you put a solar panel flat on the ground, you will get your number. If you mount it on a pole, and track the sun, you will get around 950*12~12kWh/day.
And putting a solar pannel on a motorized pole is a lot cheaper than sending it to space.
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Re: Privatized Space Travel

Postby Antimony-120 » Sat Jan 22, 2011 7:51 pm UTC

Pez Dispens3r wrote:
Antimony-120 wrote:I asked "If area A was capable, with the technology of the time, of supporting some population density X, did it?" and the answer has, historically, almost always been "yes".

Like how we've had boats since forever, and the entirety of the oceans have been colonized.



...Oh.


The ability to cross an area does not denote the ability to live on an area. But actually yes, traditionally coastlines HAVE supported much larger groups than interior areas. So people have been "living off the sea" for as long as we've had boats.
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Re: Privatized Space Travel

Postby Izawwlgood » Sat Jan 22, 2011 8:47 pm UTC

idobox wrote:The thing is Earth can't support that number. That's why it would make colonisation of space more interresting.

Citation Needed. You forget human ingenuity, as well as the sheer amount of untouched terrain on this planet. Spoiler alert: there's a lot of it.
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Re: Privatized Space Travel

Postby gmalivuk » Sat Jan 22, 2011 10:19 pm UTC

idobox wrote:
gmalivuk wrote:If Earth can sustain that many, it only requires two more doublings to reach about 30 billion. That could definitely happen in less than a few hundred years.
The thing is Earth can't support that number.
If that's true, then it will reach the maximum that it can support much sooner than "a few hundred years"

gmalivuk wrote:No, even the most heavily insolated places on Earth get about 7kWh/m^2/day of sunlight, which is less than 292 W, whereas above the atmosphere it's 1372 W/m^2. (Remember, no place on Earth gets *direct* sunlight for a full half-day.) So that's 370% more solar energy in space than in the middle of the Sahara
The integrated total terrestrial solar irradiance is 950 W/m2.
Citation needed. I was unaware that air and clouds only blocked 30% of solar energy.

If you mount it on a pole, and track the sun, you will get around 950*12~12kWh/day.
And if you do that you'll also be shading other areas. If we were only talking about a single 1m^2 panel, then you'd have a point. But we're actually talking about fairly large areas of ground, which means that following the sun isn't actually going to get you a whole lot extra. (Since we were already ignoring issues of whether panels are more efficient for direct or angled sunlight or whatever, and just talking about the total energy hitting the panel.)
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Re: Privatized Space Travel

Postby Solt » Sun Jan 23, 2011 2:08 am UTC

idobox wrote:Things that will probably not be economically sound in a reasonable time frame:
-space based solar. Solar cells are not economicaly sound on Earth without subsidies. Sending them in space could result in a 300% efficiency improvement, but the cost would be multiplied by much more.


It will totally be subsidized in the near future. Think about this: Rail guns, battle suits, and battlefield management software. They are superior fighting technologies, and they run on electricity. So we can't use them unless we beef up our fossil fuel infrastructure or invent magical batteries. Second, fossil fuels are getting more and more expensive and all the cost-saving technologies are being developed for other fuel sources. Also, fossil fuel supply lines have always been a pain in the ass. Eventually these factors will converge in such a way that it will be beneficial for the American military to develop a network of space based solar power satellites that will allow soldiers and vehicles to operate anywhere in the world with increased mobility and decreased reliance on supply lines.

gmalivuk wrote:
idobox wrote:
gmalivuk wrote:If Earth can sustain that many, it only requires two more doublings to reach about 30 billion. That could definitely happen in less than a few hundred years.
The thing is Earth can't support that number.
If that's true, then it will reach the maximum that it can support much sooner than "a few hundred years"


I think calls of overpopulation are way overblown. People have been saying for decades that within the next x years, there will be a catastrophic population explosion. It hasn't happened. No system is truly exponential (http://abstrusegoose.com/218), though parts of the curve can be nicely fitted to an exponential function. Real systems are always logarithmic. Even China is expected to face a labor shortage within the next decade. It's a proven fact that as the standard of living goes up, people start having fewer kids. Why? Because the cost of raising a kid goes way up. They can't be sent to work in the factories anymore, they can't be forced to work the farm all day... instead you have to support them for free until they are 16 and then maybe even send them to college and buy them a car. Not worth it. Economics will drive a family to have 10 kids. Biological need? Maybe 2. Not only is the world population in the process of leveling off, it is very possible that it will shrink in the next half century. Already, the growth rate has been dropping for the last half century: http://www.google.com/publicdata?ds=wb- ... ion+growth. Disclaimer: that graph doesn't nearly explain the whole story, but it's an interesting sign post. There are also factors that were one-off occurrences, such as the introduction of mandatory vaccination and the agricultural revolution. Both caused massive jumps in population, and it's unlikely any life-prolonging event of that magnitude will ever happen again. Will the population increase? Yes. Will it ever reach 30 Billion or some other obscenely energetically impossible number? Doubtful. Even the UN's most agressive estimate is 11 Billion by 2050 (http://en.wikipedia.org/wiki/World_population) and 25 Billion to as low as 3 Billion in 2150.
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Re: Privatized Space Travel

Postby gmalivuk » Sun Jan 23, 2011 8:22 am UTC

Solt wrote:Will it ever reach 30 Billion or some other obscenely energetically impossible number? Doubtful. Even the UN's most agressive estimate is 11 Billion by 2050 (http://en.wikipedia.org/wiki/World_population) and 25 Billion to as low as 3 Billion in 2150.
Um...you do realize that 25 billion is quite close to 30 billion, right? And that 2150 is well within the "few hundred years" time frame we were talking about? I'm not saying it'll definitely happen, either, but it just seems a bit funny that you'd quote a number completely contradicting the point you're trying to make.
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Re: Privatized Space Travel

Postby idobox » Sun Jan 23, 2011 11:40 am UTC

About the figure 30 billions, I have to admit I just used a number that looked big. With only 6 or 7 billions people, we are already screwing up the Earth quite badly. What I meant is at some point, growing food and maintaining a breathable atmosphere will be so dificult on Earth that doing it in space can be an viable option.

About rotating solar panels. If you restrict angle to + or - 60deg, the occupied space will be 3 times the panel, and will still allow 8h of insulation.

The number 950W/m² comes from wikipedia, which cites "2005 ASHRAE Handbooks Fundamentals p.31-14 Table".

Solar and fossil fuels aren't the only power sources. Nuclear is far superior in terms of power density and energy retrieved over energy invested ratio. Apparently, our energy consumption is about 16TW, so about 10% of the solar energy Earth receives. Replacing all of that by solar power will require arrays of areas comparable to Earth itself. This will require massive amounts of materials, no matter if you do it in space or on Earth.

Solt, are you suggesting the use of space-based solar power for off grid applications? It is going to be very complicated to beam energy to a foot soldier with enough accuracy, and without burning him. Ships could use it, but why bother solar when you have nuclear already working?
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Re: Privatized Space Travel

Postby Zamfir » Sun Jan 23, 2011 12:02 pm UTC

idobox wrote:What I meant is at some point, growing food and maintaining a breathable atmosphere will be so dificult on Earth that doing it in space can be an viable option.

If we have the technology to grow food in space and create a livable biosphere from scratch, then we could do those things on earth too, right?

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Re: Privatized Space Travel

Postby idobox » Sun Jan 23, 2011 2:03 pm UTC

Zamfir wrote:
idobox wrote:What I meant is at some point, growing food and maintaining a breathable atmosphere will be so dificult on Earth that doing it in space can be an viable option.

If we have the technology to grow food in space and create a livable biosphere from scratch, then we could do those things on earth too, right?

Of course, but at some point, energy or space will run short. Or maybe the materials will have to come from space, but that won't happen before Earth changes drastically.
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Re: Privatized Space Travel

Postby Technical Ben » Sun Jan 23, 2011 2:31 pm UTC

I wonder. There was hardly any commercialism in Star Trek. What did they sell? :lol:
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Re: Privatized Space Travel

Postby gmalivuk » Sun Jan 23, 2011 5:18 pm UTC

idobox wrote:About rotating solar panels. If you restrict angle to + or - 60deg, the occupied space will be 3 times the panel, and will still allow 8h of insulation.
Okay, so you get 2/3 the insolation (you were previously claiming a full 12h) at 3 times the area, or an efficiency of 2/9 what you were claiming before. Am I supposed to be impressed?

Apparently, our energy consumption is about 16TW, so about 10% of the solar energy Earth receives.
What? How big do you think the Earth is? Your figure of 950 W/m2 over a circle the size of Earth gives 1.2e17 W. So human energy consumption is 0.013% of that.

Edit: and the Wikipedia article on insolation says, "Ignoring clouds, the average insolation for the Earth is approximately 250 watts per square meter." So I'm still not sure what your 950W figure is supposed to mean. Probably it counts everything except the 30% of solar energy that's reflected back into space. But that means it *doesn't* count all the additional energy absorbed on its way down, and it also doesn't count the angle of incidence, meaning both it and the 1366W/m2 solar constant are counted for surfaces perpendicular to the sun's rays.

Because, again, all the actual maps I've seen for insolation at ground level put the maximum at about 300W/m2, in places like the Sahara.
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Re: Privatized Space Travel

Postby BirdMav » Sun Jan 23, 2011 6:24 pm UTC

Sorry, this thread really took off more then I expected to and didn't have time to read through the myriad of posts so if this question has already been answered, please bear with me. Is there technology that is currently available that can store solar energy? We could mix a bit of chemistry, biology, and machinery, to come up with some bio-mechanics that would be similar to how plants store solar energy and use it. I don't know if we have technology capable of doing this but it would be worth some RandD, first sort of organic machine??
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Re: Privatized Space Travel

Postby idobox » Sun Jan 23, 2011 6:41 pm UTC

You get more than 2/3, because after the 8 hours, you still get some energy, and ground space won't be an issue until you have filled every desert with panels.
The actual solar power received from the sun is 170 PW, not TW, so our consumption is, in fact, around 100ppm.

Still, accounting for 24h exposure, and 50% efficiency, which are, even in space and in the future, quite optimistic figures, gives us around 20 000 square kilometers of panels. If the average thickness of the panels is 1 micron, quite optimistic again, you would get a total volume of 20 000 cubic meters of panels. If they are essentially made of silicon, it gives us a mass of around 50 000 tons.
I don't know if there are orbits with more than 12h of exposure a day, or if lagrange points could hold such an array. You also have to take transmission loss into account, as well as maintenance (if a panel has a life time of 50 years, you still have to replace 400 sq km of panels a year). And you have to beam all that down to Earth too, with the associated losses, and risk (it would make a decent death ray)

If you built the same array on Earth, with, let say, 20% (250/1400 ~17%) efficiency of what you get in space, you end up with a 100 000 square kilometers array. A 200x500 km array. If we count the 3 times area thing, we get to 600x500km.
To get worse, imagine the efficiency is, in fact, 2% of what you get in space. You end up with a 1 000 000 square km array.

Now, why would we bother building all that in space, given the incredible initial cost? The Sahara is about 9 millions square km, has virtually no human occupation or wildlife, no economic value and very little clouds.
As a comparison, the current EPR nuclear power plants output 1.6GW of electricity and 4.5GW of heat, and costs at prototype level about 5 billions €. To be competitive, space based solar must be able to furnish the same power for the same money, so around 3€/W.

And we have to keep in mind nuclear power will progress too.

Birdmav.
Energy storage technology hasn't evolved much.
We have batteries, flywheels, dams, and that's about all. There are a number of other technologies, but either the capacity or efficiency is terrible.

ps. Most of the computations are done by head, and I'm a bit sick, so please forgive any mistake.
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Re: Privatized Space Travel

Postby gmalivuk » Sun Jan 23, 2011 7:04 pm UTC

idobox wrote:You get more than 2/3, because after the 8 hours, you still get some energy
Okay, fine. But still 3x the ground area, so 1/3 the efficiency you were talking about before.

idobox wrote:I don't know if there are orbits with more than 12h of exposure a day
Geosynchronous orbits get full sunlight for all but about 2.5 hours a year, at the equinoxes, and *all* orbits get sunlight more than 50% of the time because Earth's shadow covers less than half of any orbit with a larger radius.
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Re: Privatized Space Travel

Postby jmorgan3 » Sun Jan 23, 2011 7:22 pm UTC

gmalivuk wrote:
idobox wrote:You get more than 2/3, because after the 8 hours, you still get some energy
Okay, fine. But still 3x the ground area, so 1/3 the efficiency you were talking about before.

Who cares about land-efficiency? Even at a population of 30 billion, we won't run out of non-arable land. The important thing here is cost-efficiency, and cost of 3 acres of the Sahara will be dwarfed by the cost of 1 acre of solar panels, much less the cost of launching them into orbit.

idobox wrote:I don't know if there are orbits with more than 12h of exposure a day
Geosynchronous orbits get full sunlight for all but about 2.5 hours a year, at the equinoxes, and *all* orbits get sunlight more than 50% of the time because Earth's shadow covers less than half of any orbit with a larger radius.[/quote]
But with a geosynchronous orbit, you're beaming the power from over .1 lightseconds away. How big would the collectors have to be to gather all that energy from so far away?
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Re: Privatized Space Travel

Postby EdgarJPublius » Sun Jan 23, 2011 8:39 pm UTC

Current designs being considered for test deployments call for a ten ton satellite capable of generating 17MW. Unfortunately, I haven't been able to find the size of the collector for these satellites since mass and launch dimensions are much more important for most practical considerations (the ten ton mass is favorable for deployment using existing launch vehicles, power would be generated by a constellation composed of multiple satellites)

However, from some other studies I've read, a 5 GW constellation would require a collecting area of between 10-50 km^2 Though much of that area could be low-cost and low-mass focusing mirrors, meaning that the total area of photovoltaic cells would be much lower.

Personally, I'm curious as to the viability of solar-thermal power satellites using mylar or a similar material for focusing mirrors that are light, cheap and can be folded very small for launch. In the future, the arrangement can also use the focusing mirror array as a solar sail, either allowing the satellite to inject itself into a geosynchronous orbit (meaning a cheaper launch vehicle can be used) or to maintain it's position relative to a surface station at a lower altitude as a statite, which would also reduce the necessary antenna size.
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Re: Privatized Space Travel

Postby idobox » Sun Jan 23, 2011 9:11 pm UTC

jmorgan3 wrote:But with a geosynchronous orbit, you're beaming the power from over .1 lightseconds away. How big would the collectors have to be to gather all that energy from so far away?

Lower orbits will still have very long days without being that far away. Of course, with a non geosynchrnous orbit, beaming the power back to Earth will be more dificult.
EdgarJPublius wrote:Current designs being considered for test deployments call for a ten ton satellite capable of generating 17MW. Unfortunately, I haven't been able to find the size of the collector for these satellites since mass and launch dimensions are much more important for most practical considerations (the ten ton mass is favorable for deployment using existing launch vehicles, power would be generated by a constellation composed of multiple satellites)

SpaceX falcon9 can bring a 10t payload to LEO for 44M$, which gives us an orbiting cost of about 2.6$/MW.
With an efficiency of 40% (multi junction cells have efficiency much higher than I thought), you get 560W/m², and thus need 30 000m². If we consider 8 tons are devoted to cells made of GaAs (5.3t/m^3), it gives us a thickness of 50µm.

That's credible. But it is still far from being a credible competitor to nuclear.

EdgarJPublius wrote:Personally, I'm curious as to the viability of solar-thermal power satellites using mylar or a similar material for focusing mirrors that are light, cheap and can be folded very small for launch. In the future, the arrangement can also use the focusing mirror array as a solar sail, either allowing the satellite to inject itself into a geosynchronous orbit (meaning a cheaper launch vehicle can be used) or to maintain it's position relative to a surface station at a lower altitude as a statite, which would also reduce the necessary antenna size.

Apparently, heat dissipation is one the worst headache you encounter in spacecraft design. I doubt it would be very efficient.
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Re: Privatized Space Travel

Postby gmalivuk » Sun Jan 23, 2011 10:32 pm UTC

Yes, but you're using current infeasibility to predict continued problems 300 years in the future. I just don't buy that.
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Re: Privatized Space Travel

Postby idobox » Sun Jan 23, 2011 11:12 pm UTC

We can look at it another way.
What is the advantage of building solar panels in space rather than on Earth. Longer exposition, higher power. So basically, you need less surface, and less materials. Given that solar panels are made of relatively easy to find materials (if they use iridium or paladium, I'm not aware of it), and we have plenty of available space on Earth, why would we bother?
Building stuff in space is, and will be for a long time, more difficult and expensive.

We have land on Earth that is practically free (deserts), with much easier maintenance and access to the grid. If solar power ever becomes an economically sound alternative to nuclear power, it will still be more cost efficient to do it on the ground. Building a huge factory in space, with the habitat for the workers, mining kilotons silicon or germanium from asteroids, building huge arrays of thin panels in space, with no solid support, maintaining them, all of that will be more difficult and costly than doing it on Earth.
That is, of course, until we approach Kardasev 1 level, because free land will start to be in short supply.
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Re: Privatized Space Travel

Postby jmorgan3 » Sun Jan 23, 2011 11:20 pm UTC

gmalivuk wrote:Yes, but you're using current infeasibility to predict continued problems 300 years in the future. I just don't buy that.

Is this thread about private space travel in 300 years? If so, then it is impossible to rule out the practicality of any technology that doesn't violate the laws of physics.

A much more sensible approach would be to limit our predictions to time frame of 50-100 years, or to our own predicted lifetimes.
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Re: Privatized Space Travel

Postby gmalivuk » Sun Jan 23, 2011 11:26 pm UTC

jmorgan3 wrote:Is this thread about private space travel in 300 years?
This particular bit of it is, yes.
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Re: Privatized Space Travel

Postby Solt » Mon Jan 24, 2011 7:14 am UTC

gmalivuk wrote:but it just seems a bit funny that you'd quote a number completely contradicting the point you're trying to make.


25 Billion is the high estimate produced by the UN. They also estimated as low as 3 Billion. I think if you actually took that snippet in context you would have seen that it supports my argument, which is that population growth is unlikely to be that dramatic.

idobox wrote:Solt, are you suggesting the use of space-based solar power for off grid applications? It is going to be very complicated to beam energy to a foot soldier with enough accuracy, and without burning him. Ships could use it, but why bother solar when you have nuclear already working?


Well, the "without burning him" part is simply wrong. These systems work on resonance and so only a correctly sized antenna will pick up a significant amount of energy. The soldier could be bathed in the beamed energy and only the receiver on his back will actually pick up any of it.

As for being accurate enough to only hit your guys but not give the enemy power, that's certainly a problem but it doesn't sound intractable. I'm not an EE but you could probably use some kind of transmitting array on the satellite (with multiple transmitters, each with a very narrow area of effect, as opposed to a point source) that would have the ability to shut down power to some areas of the battlefield. Maybe you could periodically tell all your guys to shut off their receivers and then try to overload any bad guys' receiver. Maybe if there's a way to change antenna geometry a little bit you can change the transmission frequency and antenna geometry continuously so anyone who doesn't know the pattern ahead of time will be able to pick up much less power.

I can think of more methods but the point is, the system is feasible and the need is justifiable. Nuclear is great for ships but not really feasible for foot soldiers (even wearing power suits). Fuel cells have the same problems as fossil fuels, and batteries just don't have the capacity. As for fossil fuel, every gram of fuel used by your soldiers has to be shipped to the battlefield, and these battlefields are usually really shitty terrain such as the mountains of Afghanistan. Not even dirt roads are guaranteed. Convoys are open to attack (as has been happening to NATO supply lines going to Afghanistan), fuel is expensive as hell by the time it reaches the destination, and even when it is near your soldiers and vehicles, it still must be protected, and your units have to stop their activity periodically to return to the forward operating base and resupply. Plus they have to carry that extra fuel around with them in preparation to use it, adding tons of weight and driving power requirements up even further. In contrast, all you have to do is figure out how to defend a satellite from ground based lasers and you can avoid all of these problems. And in the process you subsidize commercial space power production and launch, just like the military subsidized the development of transistors and satellites for the initial wave of commercial applications.

Incidentally, I do think nano-scale nuclear power plants will play a big role in the future, but this thread is about space.

idobox wrote:We have land on Earth that is practically free (deserts), with much easier maintenance and access to the grid. If solar power ever becomes an economically sound alternative to nuclear power, it will still be more cost efficient to do it on the ground.


Not exactly. You still have to build underground superconducting conduits to major population centers, including under oceans, which will be expensive as all hell. Space based solar power needs almost no transmission infrastructure, just receivers at key points in the already existing distribution grid.

idobox wrote:I don't know if there are orbits with more than 12h of exposure a day


There are plenty. You can craft a sun-synchronous orbit such that it is continuously in sunlight, day round and year round. A Molniya-type orbit could be created that spends the vast majority of its time (8 hours) on one side of the planet, and flings itself around the night side in less than 4 hours. A Molniya orbit can also be tuned to be constantly in view at a single point on earth for those 8 hours, meaning 3 satellites can completely cover a point (in fact, a whole country) with transmissions, while in sunlight the whole time, and without having to be in geosynchronous orbit. This is the orbit Russia uses for satellite TV, given that geosynchronous orbit, which must be over the equator, is practically below the horizon for a large part of their country.

BirdMav wrote: Is there technology that is currently available that can store solar energy?


The reason hydrogen is probably the way of the future is that, unlike gasoline, it can be made from electricity. No one can make gasoline economically from electricity, it has to be mined. So, hydrogen can be made from (or, can act as a battery for) solar power.
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Re: Privatized Space Travel

Postby Zamfir » Mon Jan 24, 2011 7:39 am UTC

You still have to build underground superconducting conduits to major population centers, including under oceans, which will be expensive as all hell.

Why superconducting? Undersea dc cables are by now pretty much standard tech. Cables under the North Sea usually cost a few hundred million euros each. That's a lot in earth-terms, but in space such money buys you a single, perhaps two communications satellites, with a power in the kw range. Sure, future-tech might make satellites cheaper, but why should it not also make cables cheaper?

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Re: Privatized Space Travel

Postby Technical Ben » Mon Jan 24, 2011 11:29 am UTC

Can you compare it to oil digging in Alaska? For most of the time it's only economical to tap wells. Then when the prices rise it's economical to dig it out of the soil and refine that.
However, Not until space travel is the same cost as a bicycle can I see it being economical to get materials from space.
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Re: Privatized Space Travel

Postby idobox » Mon Jan 24, 2011 11:59 am UTC

Solt, about the overpopulation thing, I have already admitted I used a random number that looked large.

About the buring soldier, I am actually an EE engineer, specialized in antennas. High power microwaves are dangerous because of thermal effects. Your frozen lasagna are not tuned to 2.4GHz, but they heat up when you put them in a microwave oven.
Beaming energy via microwave is difficult because:
-generating microwaves with a good efficiency is difficult. 80 to 90 % efficiency is about the best you can get.
-microwaves have long wavelength, which means you need large arrays to get narrow beams. I didn't put any numbers, but km scale both on ground and satellite seem reasonable. I'm at work right now, but I'll do some calculations tonight.
-atmosphere absorbs quite a lot of microwave. There are some frequencies at which it is more transparent, and they are currently use for satellite communications. using these bands for energy transfer will likely forbid them for communication, but that is not such a big issue.
-beaming microwave over a large zone with mobile unit catching a part of it is actually very very inefficient. Energy beamed to places where no one catches it will be lost. If you want to transmit power to foot soldiers, or even to vehicles, you're going to have transfer efficiencies of a few ppm at best. You would probably make a better use of that energy by powering an orbital laser.

About transporting energy: Sahara is about 1000 to 2000km (depending on the points in Europe and Sahara, otherwise Gibraltar strait is a few km only). Geosynchronous orbit is 36000km.
If you have technology to beam energy from space, you have it to beam from Sahara to Europe or US.
But still good'ol cables are not very expensive and very efficient
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Re: Privatized Space Travel

Postby Tass » Mon Jan 24, 2011 12:26 pm UTC

Zamfir wrote:
You still have to build underground superconducting conduits to major population centers, including under oceans, which will be expensive as all hell.

Why superconducting? Undersea dc cables are by now pretty much standard tech.


Distribution is a major problem for solar power. Most deserts are far away from the places where the power is needed.

Zamfir wrote:Cables under the North Sea usually cost a few hundred million euros each. That's a lot in earth-terms, but in space such money buys you a single, perhaps two communications satellites, with a power in the kw range. Sure, future-tech might make satellites cheaper, but why should it not also make cables cheaper?


Actually a few hundred million euros buys you like five launches of a russian Proton rocket or about a hundred ton in LEO or maybe twenty ton in GEO. That is way more than the kW range. The Falcon 9 that the US is developing is expected to do much better. The VASIMR technology can be expected to greatly reduce transfer cost from LEO to GEO (or anywhere). But you are right, launching the satellites straight is prohibitively expensive at the moment. That is why we should make them in orbit.

Technical Ben wrote:Can you compare it to oil digging in Alaska? For most of the time it's only economical to tap wells. Then when the prices rise it's economical to dig it out of the soil and refine that.
However, Not until space travel is the same cost as a bicycle can I see it being economical to get materials from space.


Have you been reading the thread? The materials could be extremely useful IN space, because they don't require the expensive launch. Initially for things like SSP and the building of a more attractive space resort than the cramped ISS for rich tourist, eventually for all kinds of things. Exporting material from space to earth is not ideal, as it loses the advantage of having stuff in orbit in the first place, but some resources are so scarce and hardly accessible on Earth and so much more abundant in space, that it may make up for the expenses of heavy launch to get it.

Edit:

idobox wrote:If you have technology to beam energy from space, you have it to beam from Sahara to Europe or US.


Except for the little caveats that the earth is curved blocking direct transmission, and that you need antennas with a cross section of kilometers perpendicular to the beam path. Oh, I know! Lets put a giant reflector in space - oh wait.

Making a kilometer wide antenna in space is not that hard, due to micro gravity, and as the power comes straight down the ground one can be lying flat on the ground. As the rectenna mesh is transparent and blocks the microwaves, the area underneath can be used for grazing.

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Re: Privatized Space Travel

Postby gmalivuk » Mon Jan 24, 2011 12:59 pm UTC

idobox wrote:About transporting energy: Sahara is about 1000 to 2000km (depending on the points in Europe and Sahara, otherwise Gibraltar strait is a few km only). Geosynchronous orbit is 36000km.
If you have technology to beam energy from space, you have it to beam from Sahara to Europe or US.
But we're talking about completely different methods of transmission. You can't "beam" energy from the Sahara to Europe, so your comparison of distances makes about as much sense as me saying my roommates are only about 20 feet away and my dad's more like 900 miles away, so surely it'll be easier to communicate with my roommates. Except, there are a couple doors between us so I'd have to yell to do that, whereas I can call my dad on the phone and talk at a completely comfortable volume.
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