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A stored heat engine is another option that might beat Li-ion battery power in terms of performance. Molten silicon can store up to 1MWh of thermal energy in 1m3. Charging would involve the use of heating elements and is not rate limited in the way that batteries are. As a working fluid, we could use liquid CO2, compressed to at least 5.1 bar. With a conversion efficiency of 30%, 300kWh of mechanical power would keep your digger going for 6 hours before recharging.
The enthalpy change of boiling of CO2 is relatively poor, so you would need to keep a bowser of compressed liquid CO2 close to your digger and refill regularly. You would need more liquid CO2 than the equivalent volume of diesel here on Earth, because heat transfer rates will limit the peak temperature of the CO2 in the engine. But again, this is not rate limited in the way that recharging batteries is. Liquid CO2 can be produced by compressing and refrigerating Martian air and stored in carbon steel tanks indefinitely at ambient Martian temperatures. So this is a good way of storing intermittent energy that can then be used to power diggers and air tools when needed. Not suitable for powering transportation due to the relatively low energy density, but it would work for applications close to a base.
If a rover could carry a flexible solar array and a compressor, it would be interesting to compare the performance of a stored heat engine to Li-Ion batteries. An RTG might be useful in this way. During the night, the RTG could power a small heat engine that could compress CO2 into a cylinder where it would liquefy. During the day, the vehicle would use direct heat from the RTG to boil the CO2 in a heat engine, generating propulsive power.
Good post from GW. It is always useful when someone puts extra time in to do arithmetic on these concepts.
A small mobile PWR reactor would work well for water mining. Something the size of a road tanker, that can be towed to different locations between uses. The heat exchanger can be a single loop design with the boiler on its side and vertical steam separator. Decay heat removal can be accomplished by radiating through the skin of the towed reactor. If the vehicle is 3m wide and say 10m long and radiates at 200C, then using steffan-boltzmann with an emissivity of 0.9, gives a maximum decay heat dumping capability of 177kW. If sustained decay heat levels are about 1% of operating power, that would mean a mobile reactor of this type would have maximum operating power of 17.7MW.
That is about enough to melt and warm up about 30 litres of water per second. The reactor would be partially shielded by a water blanket, which would also serve as a reflector. It would generate relatively high levels of external radiation while active, so should only be activated remotely. Since refuelling would be extremely difficult on Mars and fuel is only a modest part of system mass, it would make sense to design a system that uses an elongated core with a movable reflector, such that core life can be decades.
If the base is relatively close to the glacier, we could pump the water back using polypropylene/polyethylene pipes that can be rolled up and dragged to new drilling points.
As far as general use I do like exergy but it's not a universally valid metric because sometimes you actually want low-quality energy. As rare as this is I'm mostly with louis on this one, unsubsidized production prices (probably also accounting for environmental damage and human health effects) are the best metric by which to evaluate energy sources. EROI is baked into that since energy consumption is included in production costs.
To a degree. I think the problem with EROI is that there is no clear cut off as to where one should set the boundaries of the analysis. The EROI (and rate of return EROI) will inevitably influence the price of energy from a source. However, prices are influenced by economy of scale. It is not clear how this is factored into EROI. Low economy of scale and poorly developed build processes is why some new nuclear projects appear relatively expensive.
Excellent post Josh. I don't disagree on any particular point. One way of assessing the EROI when heat is involved, would be to convert the heat into exergy equivalent. The exergy equivalent of electricity is close to 1, whereas for heat, it can estimated using the Carnot equation.
Here is a link to the EROI study that generated the chart: https://festkoerper-kernphysik.de/Weiss … eprint.pdf
Wow! This thread is screwed up!
Mearns gives a good introduction to EROI and the net energy cliff.
Different people carrying out EROI analysis do use slightly different methodologies, which complicates matters. For this reason, if you cannot trace the logic behind an analysis, it isn't worth spit. There is always difficulty in knowing where to set the boundaries of the analysis. Some institutions, when calculating the EROI of renewable energy sources, will multiply the EROI value by 3, on the basis that three times as much 'primary energy' would need to be burned to produce the same amount of power in a thermodynamic power plant. But this is really a dishonest practice, designed to big up something that they advocate. Also EROI calcs don't usually account for the energy losses and embodied energy in storage for intermittent energy. So EROI analyses often end up comparing completely different things and pretending that they are the same. To really compare solar power with nuclear power say, one has to assume that solar is equipped with enough storage to provide exactly the same product as the nuclear power reactor.
When erroneous claims are removed and the true energy cost of storage is accounted for, intermittent renewable energy sources tend to do badly in EROI studies. This is well reflected in economic studies. In this study produced for Euan Mearn's website, the strike price of offshore wind was found to be six times higher when sufficient energy storage was in place to remove the effects of intermittency.
http://euanmearns.com/the-real-strike-p … hore-wind/
This is why places like Germany and Denmark, for all their talk of a 100% renewable energy economy, are actually nowhere near it. Both meet about a third of electricity demand using renewables (in Germany, a big chunk of which is hydro). In terms of total energy, renewables are about 10%. Not very impressive, when you consider the efforts that go into making it work. But both are able to maintain an approximate 30% production of electricity from renewables, because relatively cheap coal and gas power plants are used as back up. If this didn't exist and storage was required on a massive scale, the costs would rapidly become unaffordable.
It's kind of hard to see anything that Mars could produce that couldn't be better done either on Luna (manufacturing, tourism), asteroids (mining for metals/volatiles), or even in free space (food production? We need to recycle the air anyway...).
I am inclined to agree. The best place to send factories and food production facilities would be high Earth orbit. Here they are ideally positioned to manufacture solar power satellites, space hotels, food and interplanetary transport vessels. Relatively small mining bases will be established on Lunar and NEAs, to supply the orbital facilities with raw materials. This is the most sensible strategy because: (1) The mass ratio is much better shipping to GEO or L5 than to Mars; (2) Space manufacturing equipment is heavy; (3) The markets for manufactured goods are in Earth orbit.
With this in mind, and given that we are colonizing space as a permanent venture, how much sense does it make for Mars to be the first target for human colonisation? Earth orbit would appear to be a much more sensible target.
We could build boiling sodium reactors on Mars that produce power using MHD generators without the need for argon cover gas or boilers. The Martian atmosphere is so thin and so inert, that sodium leaks would be non reactive. About 100 times the power density of Earth-based PWRs, few moving parts and many times cheaper. With a comparative advantage like that, maybe a Mars colony can manufacture refined metals for export to Earth?
Mars might have a competitive advantage in manufacturing processes, especially those that use vacuum.
https://en.m.wikipedia.org/wiki/Vacuum_deposition
Also, Mars could have a competitive advantage in heavy industry, if it can unlock nuclear energy without the bureaucratic straight jacket that it faces on Earth.
You do have to "go" to Mars to take up-close, dramatic photographs of the landscape and be there using all the photographers' tricks of the trade to get the pic perfect. No one on Earth can replicate that, not even Rover cams. You have to have humans there to have humans in the pics as well. You also have to be there to write about the experience.
If you really think a Mars colony couldn't sell huge numbers of books on Earth, there really isn't much I can say is there? I guess you think no books on the lunar missions were ever bought either.
Terraformer wrote:Sure, but you don't have to *go* to Mars to write a book about Mars.
Okay, that's the most ridiculous suggestion I've heard you've make, and pretty much all suggestions you make are ridiculous, louis.
This is a joke though, isn't it? No one makes much money out of books. Music, software, films, are a little more lucrative. But still wouldn't be more than small change for a Mars colony.
Exports need to be something a bit more lucrative. Is there something valuable that can be made under Martian conditions that would be much more expensive if we tried to make it on Earth?
Food is not energy for the purpose of this discussion and even if you see it as the source of human energy output, its EROI must be pretty stable in and of itself. War, taxation, cultural conflict, migrations, disease and invasions are all much better explanations of the decline and fall of the Roman Empire. I have never read of EROI being cited as a cause by any reputable historian.
That's probably because few if any historians have a scientific background. They would probably say the same thing in a different way.
The EROI of food supply is clearly important if most of the work in an economy is carried out by human and animal labour, as it was until the industrial age. If more human time and energy are spent gathering food, and less fodder is available to animals, it would have a deleterious effect on other areas of a pre-industrial economy, including defence, high culture, maintenance of roads, etc. Eventually, the food supply is incapable of supporting the population at any achievable level of human labour input. That sort of scenario describes the Maya collapse, in which corn yields declined due to soil erosion, triggering civil wars and a catastrophic decline in Maya population. The civilisation was well past its peak by the time the Spanish arrived in the Yucatan. Most historians don't describe it in terms of EROI, but it certainly could be explained in those terms.
Incidentally, growing food on Mars is an activity that will be more energy intensive than on Earth, as it will need to take place in pressurised, heated structures, under controlled conditions, maybe even using artificial light. Under those conditions, expensive energy will mean expensive food. Not a very sustainable situation for a growing colony.
Pigs will fly south for the summer. One thing we can be pretty much sure of is that China's economy won't collapse because they are moving into green energy - any more than Germany's has. A banking crisis, an investment crisis, huge financial corruption, a US trade embargo or an internal political crisis, perhaps but not EROI.
Antius wrote:Falling EROI of China's domestic fossil fuel production, will result in economic collapse of the country unless it swiftly transitions to other sources of energy. This could happen very soon, as the Chinese debt-GDP ratio is already one of the highest in the world. A global peak in oil production is now not very far away.
I don't see how Louis can profess to know that. Renewable energy is bleeding Germany dry:
http://fortune.com/2017/03/14/germany-r … rgy-solar/
It is scaling back it's feed-in tariff.
http://www.pes.eu.com/renewable-news/ge … ariff/234/
As of yet, it provides about a third of German electricity consumption and a much smaller proportion of other energy. And Germany's carbon dioxide emissions are rising!
https://www.technologyreview.com/s/6015 … enewables/
So far, some $4trillion have been poured into this white elephant with little to show. Global investments have tanked since the last financial crisis. What was the point of any of it? How much more money must be poured into this white elephant? When will the Green Gods be appeased?
Falling EROI of China's domestic fossil fuel production, will result in economic collapse of the country unless it swiftly transitions to other sources of energy. This could happen very soon, as the Chinese debt-GDP ratio is already one of the highest in the world. A global peak in oil production is now not very far away.
At the moment, the sheer administrative and legal ball ache of trying to get a nuclear power reactor from Earth to Mars, has forced Musk to rely on a solar based solution. Maybe Musk can get a reactor from a non-US source ajd launch it from outside the US?
I have been looking into options for building reactors on Mars using local resources. Crude reactors could be built using natural uranium, but this requires that Musk brings a supply of heavy water with him. It would be very difficult to make that on Mars. But assuming the ability to make steel tanks and aluminium tubes, a crude pressurised heavy water reactor (or boiling heavy water reactor) would not be beyond the capabilities of a small Martian base. It would always be easier to build it on Earth and ship it to Mars. Maybe he could launch a non-fuelled reactor and natural uranium separately? Until it is assembled on Mars, it is just a steel tank full of heavy water.
Graphite moderated reactors are a much more challenging prospect, because the minimum critical core size is about 25 feet in a diameter. Calder hall was 30' in diameter and the graphite core weighed about 2000 tonnes. The power plant consisted of 4 units, each generating 200MW heat and 50MW of electrical power. The UK built this in 1956. It generated for nearly 50 years. If Musk intends to build a city of a million people on Mars, then native built Magnox reactors are something that could be produced relatively quickly using native resources and burning natural uranium. But you would need a sizable city to make a 50MW reactor a worthwhile investment. I wondered if it would be possible to build simpler, lower pressure units using graphite powder moderator and natural uranium metal bars houses in aluminium tubes. But there is no way around the minimum critical radius limit, aside from using heavy water. I think a small CANDU type reactor would be more practical.
No, I don't think you right. You put in 1 unit of energy to get the 4 units of energy (the "return") you can freely use for things other than making energy systems. So you have 5 units of energy in total and your one unit of investment is 20% of the total energy produced.
I think the problem with your analysis is that you appear to assume we will be operating at Earth average outputs, or perhaps American style averages. Why?
You list essential outputs like steel. World production of steel is about 250 kgs per person per annum. The people on Mars will easily be able to outproduce that per capita figure. A 1000 strong Mars community with full access to robot machines and automated processes will probably be closer to 50 tonnes per person per person, which - after all - is only 137 tonnes per day (about a thousandth of the UK's large steel works at Port Talbot in South Wales).
The point I am making is that the Mars community is already starting from such a high base that it will easily outperform Earth economies even if energy is more of a constraint on growth than on Earth.
Why would you assume that Mars colonists will be able to automate their processes to a greater extent than we do on Earth? They will essentially have the same technology that we do. They will be working with less than we have, not more. And they won't have the economy of scale that we do here on Earth. Economy of scale is key to increasing productivity.
Although it may be possible in the early days to subsidize a colony with automated factories that some Earth government or billionaire will pay for, that won't be the case for a city of millions, which is after all what Musk is looking to establish on Mars.
A Mars colony will not have any magic advantages over a community of equivalent size on Earth. It will face a lot of difficulties that we do not face on Earth - specifically, a cold, airless environment, with no natural foods or fuels and huge import and export tariffs. What magic ingredient is going to allow these people to greatly outperform equivalent groups on Earth? If there is such a magic ingredient, then you can be sure Vladimir Putin would have established thriving economic power houses in Siberia. Siberia is after all a lot like Mars in many respects. It is cold, isolated and full of untapped resources. It even has air. If Mars is destined to be an economic power house because of some magic 'hyper capital' ingredient, then why has the same thing not happened in Siberia or Antarctica? We could establish solar powered communities in these places, equipped with solar powered solar panel factories. By Louis' logic, they should have a competitive advantage over the rest of Earth and should have higher GDP. Yet it doesn't happen. The reasons are actually quite obvious. The environments are less productive than the warmer and more clement regions of the Earth. Nor do people living in these places get round that problem with hyper intensive capital supported by subsidized solar panels. They are more dependent on fossil energy just to stay warm and achieve the most basic level of survival. They are less capable of affording expensive energy, not more.
Suffice to say, the Russians do have long-term plans for settlement of Siberia. They involve fast breeder reactors and district heating systems.
https://en.m.wikipedia.org/wiki/Akademik_Lomonosov
Not exactly what Louis had in mind. Reality has a cruel habit of crapping all over utopian dreams.
The Roman empire collapsed because its physical resources (especially food) were no longer sufficient to maintain it's supply lines and armies and defend it against external invasion. The collapse of Rome was a direct result of declining EROI.
Hall suggests that the minimum EROI for sustaining present day civilisation is 12-14. No doubt it will vary from place to place.
http://energyskeptic.com/2016/lambert-h … y-of-life/
Ahmed presents solid evidence that declining EROI in fossil fuel extraction is leading to declining prosperity in Western economies. The situation appears to be particularly severe in the UK, presumably because we have depleted our oil and gas reserves, closed our coal mines and trashed our initial technological lead in nuclear power.
https://medium.com/insurge-intelligence … 7344fab6be
I have presented plenty of evidence and reasoned arguments as to why low EROI energy won't work on a planet that is much harsher than any environment on Earth. Perhaps I have overlooked something?
None of what you say is very controversial in and of itself - it's the conclusions you draw in relation to Mars that are heading in the wrong direction.
If we assume an EROI of 4, that means 20% of energy generated over the lifetime of the system must go into replacing the energy system - we can assume that's 20% of energy use constant for the sake of simple calculations.
In the USA the energy consumption level is about 9KWs average constant per capita. Let's assume an EROI of 19 across the board. That would mean that 5% of the energy consumed would have to go into replacing the energy system - so 0.45 Kw, leaving 8.55 Kws
So, if the Mars residents energy consumption/generation is 20 Kw per capita, with an EROI of 4 as suggested earlier, then that would mean you had to use 4 Kws to replace the energy system, leaving you 16 Kws...still way more energy per capita than available in the USA on a per capita basis.
In reality, lower EROI does not lead to arithmetic reductions in disposable wealth. What I mean to say by that, is that reducing EROI from 100 to 4, would not lead to a 19% reduction in disposable income. It doesn't work that way. Because of the need for unavoidable energy investments in infrastructure and base living standards, an EROI beneath a certain critical value will eventually lead to societal collapse. It has happened plenty of times before in human civilisation - the primary energy source declines and the society can no longer afford to maintain the infrastructure that it previously built or minimum living requirements for the population that has grown up. On Earth, the result is usually civil wars, increasing political oppression and genocide. In fact, the economic problems that we have here on Earth, I.e. the ongoing Financial Crisis, has it's roots in the falling EROI of our energy sources. This is especially true of oil and gas. For coal, not so much. Basically, industrial civilisation grew and prospered on the back of almost free energy. The fact that we now need to resort to fracking and offshore drilling to obtain that energy (which is much more expensive and has lower EROI than giant onshore fields of old) is a clear sign that the era of cheap energy and with it high rates of economic growth, are over. Soaring levels of debt represent the widening gap between what we need and what we can afford. Worryingly, our own civilisation may be close to collapse.
We do not know what the minimum practical EROI for Martian civilisation will be. A low EROI may manifest itself in poor rates of growth or the need for continuous subsidy from Earth. The fact that even air is not available for free on Mars, would seem to suggest that minimum EROI for a Martian city or colony, will be higher than equivalent settlements on Earth. It takes a lot more energy just to provide the basics like air, food and water on Mars. So in all respects, a civilisation on Mars will be far less tolerant of high energy costs.
On Earth, we have been able to integrate small amounts of intermittent renewables into our electricity grids, without collapsing our economic systems (at least, so far). But this has only been possible because renewable energy is essentially subsidized with fossil fuels. Fossil fuels are used to reduce the iron and silicon that makes wind turbines and solar cells. And fossil fuel power plants provide backup for the renewable energy sources, which negates the need to store energy, but also limits the proportion of renewable energy in the mix. If we had to store electricity in batteries or some other means, there is no way intermittent electricity could ever be affordable.
http://euanmearns.com/the-real-strike-p … hore-wind/
There is no doubt that on the Musk plan (he advocates solar energy, let's not forget) with a 300 tonne cargo delivery, there will be no problem with delivering an energy system that could produce 20 Kws average per capita for say a 10 person crew. Might be a lot more. They could be unpacking 50 tonnes-100 tonnes of energy equipment. Who knows at this stage? With a hundred tonnes of solar energy equipment you could be averaging 1500 Kws or a 150 Kws per person (assuming 10 persons) - over 16 times the US average.
I would also add that there is not a one for one match between energy use and production. We know improved energy efficiency has been exerting quite serious downward pressure on energy usage.
I think Musk understands some things better than others. What you are describing is a subsidy. The cost of the energy source supporting a 10 man crew, is affordable, because Musk is prepared to subsidize its cost and the cost of shipping it to Mars. That could work when things are essentially small in total scale. It starts to break down as the scale of the society increases beyond what any Earthbound entrepreneur or government can support. Trade balance then becomes more and more important. It is already a severe problem for a developing Mars colony, because of the high cost of transportation between Earth and Mars. Under that burden, it really is important for a Mars colony to become as self-sufficient as possible, as rapidly as possible and to maximise the productivity of local industry. The worst thing you could do is hamper it with a low EROI energy source for some silly ideological reason.
Of course, Mars does not have fossil fuels that we know of, nor any air to burn them in if it does. I will post again the chart showing energy source EROI. Which ones offer both high EROI and are available for use on Mars? I will give you a hint. The list is extremely short.
The per capita person question is one of through put to equipment capable to make the product and that is related to energy available to run the process.
Correct. Globalisation has fooled many people into believing that economic production can somehow be decoupled from consumption of energy and other resources. At a local level, this appears to be true.
http://scottishsceptic.co.uk/wp-content … c8ea1b.png
But it has only worked in the western world because it was possible to outsource energy intensive industry to China. At a global level, GDP is a direct function of energy use.
https://gailtheactuary.files.wordpress. … o-2016.png
http://scottishsceptic.co.uk/wp-content … 263661.gif
The economy is a thermodynamic machine. It takes energy and other resources, and converts those inputs into goods and services that human beings value and consume. The volume of goods and services produced is a direct function of the total energy available to support production.
Artificial energy is also a way of leveraging human labour. We do this using machines that process matter using artificial energy into goods that we then consume. Capital is basically the stock of machines and supporting infrastructure that allow human beings to leverage their labour in the production of goods. But that 'capital' is only effective in leveraging human labour so long as there exists an energy source capable of powering it. A factory, a furnace, a loom, a machine of any kind, is simply a means of using energy to process matter into something that human's can consume. This is why in the final calculation, GDP is an almost linear function of exergy - of thermodynamic work.
This is why the EROI (energy return on investment) of the energy sources of a society is important. Out of the energy produced by society, a certain amount must be reinvested just to maintain the energy supply. After that, some must be invested to maintain infrastructure. Some is then invested in the production of consumables and luxuries. Anything left over, supports growth. If EROI is poor, a much larger share of energy produced must be invested in maintaining the base energy supply. After maintaining infrastructure, less is available for manufacture of consumables and luxuries. And less is available to support new growth. And that smaller margin reinvested in new growth of the energy supply, will yield a smaller return, because EROI is lower.
This is why, for so many centuries before the industrial revolution, human numbers and living standards did not increase. It was only after human kind developed ways of unlocking the high EROI, almost free energy of fossil fuels that modern culture and high living standards developed. We could never have done this using renewable energy, because there was never sufficient surplus energy to make the capital investments necessary, so long as we lived off the land. And there would have been too little surplus energy to power the machines, had we been able to construct them.
A Mars colony needs a high EROI energy source. For a Mars colony to be successful, it must rapidly convert inert materials into new infrastructure - new factories, new mines, new food production and new energy sources to power it all. You cannot do that if a large part of the energy supply of your colony is consumed simply replacing itself.
This one chart explains why it will be so difficult to build a prosperous society using solar power, even on Earth.
http://large.stanford.edu/courses/2015/ … /f1big.gif
Earth based civilisation has developed a huge surplus of wealth thanks to the almost free energy provided by fossil fuels. Whereas the steady income of renewable energy is like earnings, fossil fuels are like a windfall inheritance. The only cost associated with extracting them is the cost of going to the bank.
In the centuries before human kind gained access to this energy, human numbers and wealth increased at a very gradual pace. Between 1000BC and 1500AD, numbers roughly doubled from 500m to 1bn. Then human beings began exploiting fossil fuels. Within 2 centuries of starting that process and reinvesting the wealth gained, human numbers increased about 6 times and total material wealth about 100 fold.
Such is the power of high EROI energy. Understand that and you should also understand why it is not practical to build a society on Mars using low EROI energy.
Mars is not going to have a population in the billions. Achieving very high productivity and supertechnology in a small community is far more doable.
Terraformer wrote:Plus, if technology was such a great multiplier, we'd apply it here on Terra and get those benefits. After which we'd terraform Mars for a lark, because that's what powerful post-scarcity societies do to stave off boredom.
No it won't have a population in the billions and that is a big part of the problem. It won't have economy of scale in any industries. It will need to either make a huge variety of products at very small scale, which is inefficient, or make a few at large scale with enough profit to overcome the huge import costs of the rest of what it needs to import. Some compromise will no doubt be reached. If there is something very valuable it could mine or make that cannot (or cannot easily) be produced on Earth, then perhaps making almost everything will be unnecessary. The only thing I can imagine in that category are manufactures and raw materials destined for Earth orbit. Since Mars has only a tenth the Earth's mass, it is not inconceivable that it would be cheaper to make an item on Mars and ship it to Earth orbit than to launch it from Earth. Even so, I think the sheer complication of that sort of triangle trade makes it a long shot.
Josh,
I don't disagree that a close to 100% working age population will be a benefit to a Mars colony. But I think there is a severe case of rose tinted glasses in Louis' analysis. A few points:
1. The Mars colony will not have superior technology to an Earth based nation. Its technology sets will be about the same. Its research capabilities will lag those of any Earth nation until it achieves comparable population. Why would we expect superior technology?
2. Capital is basically the stock of factories, machines and other infrastructure available to support mining, manufacturing, services, transportation, etc. These things have to be made or imported. The US and other nations, didn't just materialize these things over night. Capital investment in developed nations is an iterative process, with new investments building on older ones. The high incomes of the developed world are the result of centuries of accumulated capital. A Mars colony will not only need to start from scratch, but must import capital infrastructure at enormous cost.
3. One of the great historical advantages that the US had as an industrial power was economy of scale. This allows higher productivity. It is a big part of China's cost advantage today. A Mars colony will be a relatively small affair for a long time to come. Small nations can dominate individual industries if they have export markets. But it is progressively more difficult for a nation to manufacture all of the goods it consumes if it is small and lacks scale economies in internal markets.
4. It is not at all true to say that material resources will be virtually free on Mars. Mining will require substantial investments in heavy equipment, energy and labour, just as it does on Earth. A sizable portion of this must be imported and this will be the case for a long time to come. What's more, Mars is an altogether more difficult environment to work in. It is colder, subject to large temperature swings and without air. Expecting materials to be cheaper than they are on Earth would appear to be optimistic.
5. The assumption that energy will be cheap because colonists can make solar panels is unsupportable in my opinion. There are some things we can turn to our advantage on Mars. But overall, solar power on a planet with 2/5ths the sunlight intensity is not going to be any cheaper than it is on Earth. In fact the energy return on investment for solar panels, will inevitability be weaker than on Earth. The equipment used to manufacture the panels must of course be imported at enormous cost. Problems relating to power storage will not be any easier.
All in all, it is important to remember that wanting something to be true will not make it so. When one is enthused with an idea or concept, it is all too easy to bend facts to support the conclusions we want to hear.
Many happy returns! In another 10 years, this might not be a theoretical exercise!
Regolith samples would be valuable initially, but as more are accumulated and scientific questions are answered, the value would decline rapidly.
To successfully export a product to Earth, it's sale price on Earth must be competitive with equivalent products made on Earth. If transport costs are upwards of $1000/kg, that does severely limit what a Mars colony could make and sell. As Louis has pointed out, high value novelty items could have a competitive niche. Some precious elements might have export potential, but then again the cost of operating on Mars will be much higher as well. The problem with high-end manufactured goods is that they also tend to require high-capital investments in equipment. A Mars colony would have difficulty affording those sorts of infrastructure investments. Deuterium would be problematic for the same reason. The small cost advantage of a factor 8 increase in concentration relative to Earth, would likely be swallowed by the much greater cost of operating on Mars.
Food might be something a Mars colony could export. If space tourism gets going in a big way, it may be cheaper to grow food on Mars and ship it to LEO than to launch from Earth. The same could be said of water, radiation shielding and maybe some basic manufactured products. Earth orbit would be a much more competitive export market than the Earth itself.
Solar power satellites or orbital nuclear power plants are another possibility. Could Gerard O'Neill's vision be made to work with Mars as the hub, instead of the moon? The advantages Mars has are a much improved availability of material resources. The disadvantages are an atmosphere (cannot easily use mass drivers); substantially greater gravity and distance from Earth. The latter would make it much more expensive to establish a mining operation on Mars compared to the moon. Launching components from the Martian surface to orbit will be more expensive and transporting finished satellites from Mars orbit to high-Earth orbit will take longer than simply assembling them in HEO. So probably not.
It doesn't seem to me that any variant of the Nuclear Saltwater Rocket would have conditions that are favorable for fusion. What makes you think it would occur?
Fusion will occur because the plasma will have temperature in the millions of kelvin. The fusion will contribute no more than about 10% of the total energy of exhaust. Too much fusion fuel will start to add an unacceptable level of moderation to the mix. Most of the energy from deuterium tritium fusion is released as super fast neutrons, which will boost the fission yield and reduce critical mass. So the fusion is there to produce neutrons, rather than energy.
