Various accounts of what happened to Japan’s Akatsuki Venus orbiter continue to come in, but it seems clear that the craft failed to achieve orbit. Sky & Telescope has been keeping a close eye on things and reports that errant thruster firings evidently caused an unexpected rotation that resulted in an on-board computer putting the vehicle into standby mode. The result: Too short a burn to ensure orbital capture, with Akatsuki now in a solar orbit that won’t take it back to Venus for another seven years. Are course changes possible for another go then? We’ll see.
Supply, Demand and Near-Earth Space
In an unaccustomed way, the Venus news has me in an inner system mode this morning, which means it’s probably a good time to talk about Dana Andrews’ thoughts on supply and demand when it comes to space colonization. Andrews (Andrews Space, Seattle) and colleagues Gordon Woodcock (Space America Inc.) and Brian Bloudek have been putting together a scenario for near-term commercialization of space, one that takes a hard-headed look at the economic drivers that humans need to make their presence beyond Earth sustainable.
A space-based infrastructure is the ultimate goal here, and if we ever build one, it will have to be because we’ve found a compelling reason to do so, one wrapped up in economics and, perhaps, species survival as we face dwindling resources. Andrews made the case at this year’s International Astronautical Congress in Prague that mining scarce resources on the moon and Near Earth Objects could be the key to commercial development that will become critical as we face future shortages. It will also offer us a chance to move past our dependence on oil:
Our hypothesis is that if we add lunar resources, we can afford to maintain the switch to plug-in hybrids throughout the world, thereby increasing productivity and reducing persistent pollution. Even though the flow of lunar resources is relatively small, these critical metals have a large impact on productivity, resulting in a potential soft landing for the world population.
What kind of resources are we talking about? Andrews enumerates quite a few, a list on which items like rhenium — used in fuel-efficient aircraft engines — stand out. The price of rhenium is now over $11,000 a kilogram, twelve times what it was just four years ago. Reserves of indium, which is used in solar cells and LCDs, are forecast to run out within ten years, and so is the hafnium we use in computer chips and nuclear control rods. Such shortages and accompanying price increases can be the driver for space commercialization. Andrews proposes moving the mining and smelting of key non-renewable resources to the Moon, providing access to high grade ores and transferring potentially polluting mining operations away from our planet.
What Space Offers
So let’s look at space resources. Two-thirds of known meteorites are iron/nickel in composition, containing mostly iron but about 5-30 percent nickel and a few tenths of one percent cobalt, along with high concentrations (at least by standards on Earth) of strategic metals, from the platinum group to gold, gallium, germanium, iridium and others. Says Andrews:
Interestingly enough the lower the Fe-Ni metal content in the meteorite, the more enriched the Fe-Ni metal is in these rare and precious metals and elements. These elements readily dissolve into the metal that exists, and the less metal that exists, the less diluted they are. Many asteroids are richer in most of these precious metals than the richest Earth ores which we mine. Further, these metals all occur in one ore when it comes to asteroids, not in separate ores.
We don’t know how abundant rare Earth elements that can be mined actually are on the Moon, but Andrews wonders whether there are parallels between craters on the Earth and the Moon. The impact crater at Sudbury, Ontario is rich in iron, nickel, cobalt, copper and platinum group metals. Are these metals debris from an ancient impactor, or did they well up from within our planet after the impact? A study of impact craters on the Moon may give us some answers, for all asteroid impacts on the Moon should have left their debris on the surface, since the Moon lacks plate tectonics. What we need to learn is whether they are found there in concentrations we can mine.
What We Need to Know
Lunar prospecting, then, is a first step in determining the existence of asteroidal metal containing nickel, cobalt and platinum-group metals on the surface. We have much to learn, including not just the quality and location of ores, but also the location of volatiles like water. We also need to learn what happens when asteroidal nickel/iron is made into metal products, and to what extent we will have to rely on engineered alloys to get the desired result. At present, of course, we cannot test the processes we might use on the lunar surface, requiring a preliminary manned base there to work through these contingencies.
Andrews works out a simple cost model exploring mining, processing and shipping operations, comparing these to existing costs. With platinum, for example, selling at close to $40,000 per kilogram, a price that is itself escalating, the case for lunar mining is clearer than that for more plentiful products like cobalt. Even so, working in the lunar environment poses huge challenges:
A very important lesson learned is that most resource production equipment must be made on the Moon. Shipping it is unaffordable. For example, we assumed 90% of the mining and hauling equipment was made on the Moon. Even though this equipment is very productive (our estimates were that a miner or hauler could process on the order of 100,000 times its own mass in a year) so much of it is needed that indications are about 90% must be made on the Moon. That probably means electronics, electric motors, gears and bearings made on Earth and everything else on the Moon.
Getting from Here to There
Andrews proposes a lunar sling for launching metal products to Earth, but goes into greater detail on what any space infrastructure requires going out of the gate: A simple and inexpensive way to get to Earth orbit, what he calls FRETOS — Fully Reusable Earth-to-Orbit Systems. A fleet of five launchers supporting a flight rate of 1000 launches per year using four tethers is at the heart of the proposal. On the space side, a Skyhook capture device located at 300 kilometers orbital altitude is part of a picture that also includes a Low Earth Orbit station at 1000 kilometers, a powered winch module at 1700 kilometers and a counter-balance at 2400 kilometers. The total mass of the space segment is estimated at 190 metric tons, including 2100 kilometers of tether lines, high-speed winches, power generation arrays, counter balances and station-keeping components, all to be launched separately and docked together for assembly.
Image: Fully Reusable Earth to Orbit Stage (FRETOS) combined with Tether Upper Stage (TUS) provide cheap access to orbit. Credit: Dana Andrews/Roger Lenard.
As for getting to orbit, the launch segment is envisioned as a first stage subsonic carrier/aircraft with onboard hybrid rocket motor to achieve altitude for release of a second stage at 12.6 kilometers, with the second stage delivering a 13-ton payload to the capture point at the bottom of the 2100 kilometer long tether system. After payload capture, the second stage re-enters and glides to a landing at the launch and recovery base. Andrews’ assessment is that the entire recovery, turn around, launch and tether lift cycle could be completed within 24 hours, which works out to 1000 missions a year with the proposed fleet of 5 launchers and four tethers.
To get equipment to the Moon, outgoing payloads are released from the tether every day or so and transported to a lunar transfer station at L1, where they are assembled into lunar lander packages and then delivered to individual mining sites or research centers. The L1 station also collects and processes propellants for lunar landers and, possibly, deep space exploration missions, its operations almost entirely automated but allowing for the presence of a small crew as needed.
Economics of the Infrastructure
Will it pay for itself? The economic model Andrews built of the entire infrastructure as operational over a twenty year period shows the cost of rare metals brought back to Earth at about $2600 per kilogram, an investment he notes is ‘fairly lucrative’ given current costs, and while a flow of materials from the Moon will lower the price, demand should also increase assuming we find momentum to reduce our use of fossil fuels, leaving a sizable potential for profit.
There is more detail in the paper than I can squeeze into this post, but I’m struck by a couple of things. Andrews is working on the practicalities involved in commercializing space, and in doing so points to a model that should be economically sustainable, and one that should produce a permanent human presence not only on the Moon but other space venues. We don’t often look at near-Earth issues on Centauri Dreams, but of course the development of a Solar System-wide infrastructure is more or less a given if we are ever to produce a true interstellar probe, one that will tap the expertise and resources that infrastructure has made available.
I’m also struck by the potential of tether methods for moving large payloads around near-Earth space, and reminded of Michel van Pelt’s book Space Tethers and Space Elevators (Springer 2009) as a great introduction and backgrounder for those of you unfamiliar with the variety of tether concepts out there. You’ll find my earlier thoughts on this book here. As Andrews makes clear in his paper, getting out of the gravity well at minimal expense (and he believes his methods, if fully operational, could drop that cost to $250 per kilogram) is step one in getting the needed infrastructure built. A profitable space market must grow to make it happen.
The paper is Andrews et al., “Space Colonization: A Study of Supply and Demand.” I’ll pass along the full reference when it’s published.
Comments on this entry are closed.
The Fed just handed out 3.3 trillion to various corporations in 2008
There is the trip to Neptune. Neptune would have been far more worthwhile
Sorry to hear about Akatsuki—sounds like Nozomi all over again. That said, ISAS/JAXA can be pretty ingenious—let’s hope they can work something out (and avoid solar flares).
Excellent Article Paul, With China planning on cutting mining of ‘rare’ earth metals by 2012, and the toxic by-products and environmental impact of mining those metals. What might be needed is to factor in those costs as well, making near earth resources even more attractive.
One possible way to exploit asteroid resources is by using reusable light sails to capture small NEO asteroids (200 tonnes or less) and transport them to one of the Earth-Moon Lagrange points for processing. The oxygen and hydrogen continent of the asteroids would already be extremely valuable for fueling reusable tugs for transporting communications satellites from low Earth orbit to geosynchronous orbit. Asteroid material might also be a cheap source of radiation shielding for manned space stations and interplanetary vehicles. Cheap extraterrestrial oxygen and hydrogen would also be valuable for the emerging space tourism industry, if such journeys extend to visiting hotels on the lunar surface.
A dramatic reduction in the cost of space access is the one big step we need to take, that will never happen using the chemical rockets all the way methods we use now. Over the last few months tethers have climbed to the top of my list of how it’s likely to be done.
If it comes down to “species survival as we face dwindling resources” space colonization probably won’t happen unless it’s already well underway, resource scarcity will lead to economic recession first, which means that money for things other than basic needs won’t be available, we’ll just end up fighting over the resources that are here on Earth.
H G Wells had put it (in A Modern Utopia) that all Earth imports are meteors. Scarcity due to consumption has been treated in several recent articles such as this one http://io9.com/5664078/humanity-will-need-two-earths-to-sustain-itself-in-just-twenty-years
io9.com often suffers poor journalism, but the warnings about upcoming scarcities have been around since the 1960’s… that I personally recall. Asimov had also written that petroleum reserves should be significantly depleted later in this century. He had also written that the Moon could become a 21st Century Japan, as a productive economic entity…
As probes continuously reveal the wealth in our neighborhood worlds, there come suggestions that these resources be used. One does not live in a cradle forever.
Do we really need to mine the materials on the moon at all? NEAs may prove easier since the materials are not in gravity wells and can be shuttled back to the earth tethers using local resources for propellants, or solar sails. The asteroids are somewhat more difficult.
For 1000 launches a year, what is the likely impact rate of space debris on the vehicles and likely consequences. What about material sent back from the moon that misses the target?
Having said that, I think that seriously thinking about the economics of the uses of space is given less time than it should be. For a lasting space presence, the economics need to be favorable, even if it turns out that humans remain limited in this arena.
Found this at NASA: “a ten meter-sized near-Earth asteroid from the undiscovered population of about 50 million would be expected to pass almost daily within a lunar distance, and one might strike Earth’s atmosphere about every ten years on average. ”
So finding small NEO’s wouldn’t be a problem, the problem would be catching them.
A 10 metre diameter asteroid would mass about a thousand tonnes, or more if it’s Fe-Ni.
We have nothing w/o inexpensive access to Earth orbit.
Single stage to orbit. Single stage to orbit. Single stage to Orbit.
“What I tell you three times is true.” – Robert A. Heinlein.
My suggestion, send a small ore processor and a 3-d printer to the moon and use it to make everything else needed for mining.
“Reserves of indium, which is used in solar cells and LCDs, are forecast to run out within ten years…”
If this comes to pass, I’ll eat my hat. It’s London to a brick that someone has made the classic mistake of simply dividing ‘reserves’ (a term which has specific commercial meaning, and does NOT connote total available substance) by forecast demand and/or current consumption to arrive at the ‘ten years’ figure. This completely ignores the capacity of exploration to discover more reserves, and the fact that the threshold for material to be considered ‘reserves’ falls as the price rises. You can also be sure that exploration efforts (which hitherto have been minimal to non-existent for most of the elements mentioned) will ramp up in concert with the price. These are the reasons why “warnings about upcoming scarcities… since the 1960s” (thank you Carl Keller) have been way off beam, and will continue to be.
True there is no shortage of fossil fuels . We have 400 years of coal, enough to turn us into Venus Our lazy dependance on old fuels and technologies traps us in a stagnant economy and a stagnant society
Our greatest economic growth came form all the post WW2 technolgy expansion -the jet age and the space age . Other than the internet what new do we have in the last 20 years? We need space. We need new energy. We need to grow.
One hopes you are joshing about turning Earth to Venus by burning all the coal. That carbon was in the atmosphere once without making surface temps higher than the melting point of lead.
To paraphrase Freeman Dyson (or was it Russell Seitz?), “to return the planet to the state it was during the Carboniferous you would not only have to burn all the coal and oil but you’d also have to disassociate the CO2 from all the limestone.”
I just had to jump into this great discussion.
Mining the moon and asteroids for precious rare Earths and exotic metals should be persued with great governmental and commercial enthusiasm at this point.
Solar concentrators would work for the purposes of directly heating ore or by using electro-resistive elements powered by solar PV systems.
My brother John and I have lots of IP related to many types of extremely high mass specific solar concentrators which can be manufactured in theory very, very cheaply, and mass produced very, very cheaply with appropriate tooling. These devices are so cheap in principle that even loosing and needing to replace half of them in a solar concentrator facility would be almost trivial in cost once we obtain single stage to orbit and routine transport to the moon and NEOs.
I am sure that lots of other potential solutions that do not involve photo-thermal-solar concentrators can avail themselves also. However, someone got to grab the ball and run with this. There are just to many interplanetary resources not to grab them.
Mining outposts will need lodging, medical facilities, retail outlets, recreational facilities and security. The point being that the commercial market for interplanetary resources can drive the commercialization of interplanetary space.
We will then set up space based laboratories and R&D facilities and the wonderlust to leave the solar system will lead us eventually to our stellar neighbors and then further outward.
This is just to great an opportuinity for our era and our times these very next two decades to miss out on.
Elton John’s “Rocket Man” may become an iconic song for the commercial space flight frieghter business.
Can we not afford to make this all happen!
One point I want to challenge is the “400 years of coal” claim. At what rate of use? There really isn’t that much. Estimates are presently between 600 billion and 1200 billion tonnes of accessible coal – there’s a lot more inaccessible carbon mixed in a lot of rock. If we rely on coal for ~100% of the 15 TW.year currently used for all energy sources, then that’s ~40-80 years worth of global energy in coal. Of course only 40% of world energy is from coal burning, so at present usage we’re looking at just ~100-200 years of coal.
@David: though I agree with your conclusion, you make a classic mistake: we do NOT have 400 years of coal reserves, in fact not nearly so. Global coal consumption doubles about every 16 years. The coal reserves, which are hardly or not growing anyway (contrary to natural gas), that were sufficient for 200 – 300 years around 1980 and sufficient for some 140 years (1995 estimate) are now sufficient for about 70 – 80 years. And with continuing consumptive growth that will even be less in the (near) future. Even China has become a net coal importer since a few years.
BTW: the CO2 content of the Venus atmosphere is about 200 thousand times as much as the earth atmosphere, so no comparison. In the worst case scenario (using up all exploitable fossil fuels, carbon sinks getting saturated) the earth atmospheric CO2 content could increase to 700 – 1000 ppm, more likely it will stabilize between 600 and 700 ppm.
Venus runaway greenhouse effect is really a consequence of its proximity to the sun and resulting insolation/heat plus photolytic loss of water.
A great article! There is no doubt that gravity drives up the cost of mining on Earth. Before now, we had no other choice. I bet we still have a few more decades of Earth mining discoveries here . This is a big rocky planet.
Near Earth asteroids are next though.. First we’ve got to do more prospecting the NEAs. Mining companies and consortia must stake out and prove resources in space. And own them. Today no one can do that, by the Cold War era Space Treaty. So no one bothers to try.
And our long range remote robots will have to improve too. They’ll have to make more of their own fast on-the-spot decisions. AI functions req’d. Human controllers are too far for quick adjustments. As JAXA knows all too well. Perhaps less AI needed if we have human engineers living Ceres, Vesta, etc .. And Mars seems like the natural HQ for that Belt mining industry.
Also, don’t overlook the military economics for going ‘higher’ and higher into space. The USAF certainly hasn’t overlooked it. Their secret X37 just landed at California last week after 284 days up there , doing something or other. The high ground is always better. Military superiority can get you profits in more indirect ways. You make the rules, collect the rent. Luna will not be overlooked by the military powers of US, China, Japan, India. That’s also a nice ‘local’ market for the commercial groups operating in the Inner System.
BTW If we factor in exponential growth, then ALL fossils fuels will be gone in ~100 years. However about half of those are probably unreachably diffuse within the sediments, so the actual burn-up time is somewhat less.
Coal produces ~30 MJ/kg burnt. Call it a “Watt-year”. Thus a Terawatt-year needs 1 trillion kg of coal, or 1 billion tonnes. Thus 600-1,200 billion tonnes of cheap(-ish) coal is ~600-1200 TW-years of energy. Currently we (all humanity) consume ~15 TW-year of energy from all sources. There’s not a huge amount of oil left – about 300 TW-years is economically reasonable to extract, while quite a bit more (estimates vary, about x2-x5 the cheap stuff) is accessible for rapidly diminishing net-energy returns (eg. oil-sands, shales etc.) Gas is a bit trickier to estimate, but ~1500-3000 TW-years isn’t too far off the mark. Overall we’re looking at 4,500 – 9,000 TW-years of extractable fossil-fuels. Past a certain concentration level there’s no NET energy gain from extracting it – if it takes more energy to get it out than it can generate, then it’s useless. Technology might make up for that with efficiency gains in extraction, but even that begins looking pointless if – for example – we’re putting more energy in than it takes to make oil/gas from carbon dioxide in the air. Why that might obtain is if nuclear reactors are used to heat up oil-fields to improve extraction – at some point the energy is best used in other ways.
Thus, at best, we’re looking at ~9,000-18,000 TW-years in fossil-fuels. Demand for energy is rising. People in underdeveloped nations rightly expect to match developed nations for consumption. If power-supplied increases at ~2.5% on average globally, then usable fossil-fuels run-out in just ~108-136 years. With efficiency gains in usage we might go from ~25% to 50% efficiency. That extends the usable life-span of fossil fuels by just 24 years. Thus by ~2170 they’re all gone. There will still be plenty of carbon in the ground and lots in the atmosphere, but it won’t be worth extracting to burn the stuff for energy.
Of course the carbon in the biosphere is available to burn, but there really isn’t very much in that. We would be limited to what can be grown each year, which stores just ~0.1% of the total amount of energy poured on the Earth from the Sun, a mere 122 TW-year/year. We might actually want *some* of that to eat and for other members of the biosphere to eat too.
FYI if everyone of the estimated 9 billion, by 2050, member human species ate the 2,000 dietary calories per day recommended then our bio-energy needs would be ~0.875 TW-year. As there are several million other species we consume a rather large share.
Of course, we could also start mining our garbage and electronic trash for precious metals etc.
ant6n has it exactly right. We need to mine our old landfills for society’s discards, particularly those landfills that filled and closed before anyone was actively recycling. Of course, those old landfills are filled with toxic waste and the dangers of reopening them wouldn’t be small, but the benefits of both cleaning up the sites and reclaiming all kinds of discarded resources would make it worthwhile, particularly as the prices for metals continue to soar. I could easily imagine the landfills being sorted and emptied by robots, under sequestered human control, to minimize the dangers. Another problem with landfills- besides the obvious problem of migration of hazardous liquids into underground water sources- is that they tend to get lost over time. You wouldn’t think something as large as a landfill would ever be forgotten, but poor record keeping and a “out of sight, out of mind” mentality has resulted in a surprising number of old landfills being built over, turned into recreational areas, etc., with few people (if anyone) aware of the ticking time bomb under their feet. Even with those landfills where the general location is known, boundaries become fuzzy and the amount of discarded materials they actually contain become nothing better than someone’s “guesstimate.” We need to get a better handle on where our landfills are and develop a strategy to mine them both for their resources and to prevent any future “Love’s Canal” type scenario.
Yes, I know this isn’t sexy or as awe-inspiring as boldly mining asteroids for their raw resources, but it’s a serious problem that can’t continue to be ignored.
$00 years at current usage
Are you counting all the methane hydrates?
You cant be because we dont know how much methane could enter the atmosphere from the permafrost or the oceans. It might not be a problem or it might very well be .
Venus is hotter than Mercury While teh sun makes Venus worse. CO2 has heated Venus beyond Mercury
@Denver: the quote from Dyson (or Seitz) about CO2 requirements to return the earth to the Carboniferous is simply and blatantly wrong, that is to say that it is a very wrong idea that all the carbon now stored in all fossil fuels was once all in the atmosphere at the same time. It has accumulated over long periods of time.
This is even much (MUCH) more so for limestone and other organic rock formations: the total C content of all organic rock, particularly limestone and related, is about 10,000 to 20,000 times as much as that in all fossil fuels (!). It was not all in the earth atmosphere at the same time, but but gradually added to it by volcanic eruptions, incorporated by (partic. marine) organisms and deposited in sediments. Most of this actually took place after the Carboniferous, particularly during the Cretaceous.
@Adam: if our energy consumption keeps growing at a realistic 3%, we will have cumulatively used up all easily accessible (conventional) fossil fuels (assuming a generous 4500 TWY) by 2080, and all fossil fuels (incl. coal, oil sands, gas hydrates, assuming 9000 TWY) by 2100.
In fact, growing at that modest 3% rate, we will also have consumed all exploitable uranium well before 2150, all deuterium in the earth oceans plus all He-3 from Uranus by 2800, all He-3 from all four gas giants by 2900, and all deuterium of all four gas giants just before 3300.
We would need the entire output of the sun by 3050.
That is what exponential growth does.
I know. There may well be a point when we’re using enough for long-term stability, but we’re far from that level yet. K1 energy usage is a mere 360 years away at 2.5% growth. Beyond that the planet needs active cooling. I would hope the human race resident on Earth finds a happy energy usage level before we need to cover the planet in radiators.
Mark Wakely, your description of robots sorting old toxic landfills is the first really good setting I’ve come across for humanoid robots, shaped just like us who could walk and climb in tight situations and grasp and pull with onf root balanced on something. Four legs is too clumsy. Wheels and crawlers would be useless.
Maybe just add the prehensile tails of our ancestors!
Stan, I don’t think any of our ancestors actually had prehensile tails. (Prehensile tails evolved in New World Monkeys after they split from the lineage that eventually produced us).
Not to say that a humanoid robot with a prehensile tail might not be a bad idea for certain applications….
Robotic New World Monkeys with prehensile tails would make very adroit space-farers as well. It would be interesting to see how an actual monkey would react to a zero gravity flight, with ropes and branches.
“The Economics of a Space Infrastructure”
Do we have any realistic costs for tether infrastructure? Is it even feasable at the moment, or would we need more research first. Basically if Bill Gates decided to drop 5 billion on a tether, could it happen?
Indeed, this is very relevant to my interests. I’ve been saying in comments here and elsewhere that the next necessary step to colonizing space is space economy. Economics will be the engine that drives expansion into space. Helium-3 on the moon and maybe gas giants, metals in asteroids, etc. Mercury, while often seen as a no mans land, has great potential solar power and may have great quantities of iron and minerals. Space mining will become important, especially as earths resources dwindle and become more difficult to extract.
I’ve probably said this before, but space colonization is roughly analogous to European settlement of america. They made difficult voyages across the ocean, an unfriendly medium, and couldnt get back home without trouble. At first there were scientific/exploration missions such as Lewis & Clark, followed by fur trappers, traders, ranchers, miners etc. looking for economic profit from the natural resources. From this, you had trading posts, which grew into forts and towns, and eventually the wilderness was colonized.
While space is not exactly the same, the historical model paints a very good picture of where things will go as we go further into space.
By the way, I’ve recently picked up a book called Turning Dust to Gold by Haym Benaroya. I haven’t gotten far, but so far it’s great. It lays out alot of info about colonizing the moon and beyond.
Do you know this for a fact? You seem to be arguing that it could not have all been in the atmosphere because there is 10,000 times more organic minerals (limestone) than fossil fuels. That does not make sense to me. Indeed I believe it is quite plausible that the carbon in fossil fuels AND the limestone was once in the atmosphere, making it much like that of Venus.
Where else would the carbon have been, before there was life? Are there any carbon minerals that are not of organic origin? Because carbon will take oxygen from silicon, it will quickly end out as CO2 and make its way into the atmosphere, all of it. The only way it gets back into the ground is through organic processes. If there is no life, all carbon will be in the atmosphere. That’s why there is so much carbon in the atmospheres of Mars and Venus.
I suspect if you added up all the carbon in Venus’ atmosphere, you would find as much or more than in all of the limestone and fossil fuels on Earth combined.
Great that lunar mining has been planned that much. But… maybe that plan with skyhooks and all is too complicated: investing the money into Skylon single-stage-to-orbit-shuttles and VASIMR-powered lunar tugs would be simpler, cheaper and more effective, I guess.
There is one thing that can be mass-produced, quite easily, in space and transported down into the Earth’s gravitational well without any costs, and that thing is energy.
Solar panels can be easily made from lunar regolith. I’ve read that it is possible with current technology to make a simple robot that bakes the lunar sand into solar panels. It is much cheaper to kick the panels into a geostationary orbit from the Moon than to send them there from the bottom of the gravitational well with massive rockets. The panels modules could carry lunar-made propulsion gases (oxygen or hydrogen from the lunar ice) for the solar-powered VASIMR-tug which carries them to the power plant under construction.
With a Moon-based solar panel factory we could make the space-located solar power plants profitable and thus also open the Moon for other commercial purposes. The factory could (and must, to be profitable) be fully automated/radio controlled, but eventually the profit it makes could be invested into turning it into a manned lunar base (and its premises could be, for example, rented for NASA) .
Eniac: as I mentioned, much if not most of the limestone was deposited during the Cretaceous. Obviously all this carbon was not in the atmosphere all at the same time before the Cretaceous, because atmospheric conditions would have been almost Venusian. There are reasonable estimates of atmospheric CO2 levels through earth history, at the most CO2 level may have been some 20 to 30 times present level during the history of life, not 10,000 times !
Carbon is not only present in the atmosphere, but also within the earth, and it is replenished through volcanism. The limestone rocks are a sink, until they are ‘recycled’ again through volcanism. The atmosphere is actually a relatively small reservoir, the oceans contain about 50 times as much dissolved CO2, but the earth rocks even vastly more.
But limestone is organic in origin, so I think you have not answered my question: Where was the carbon before there was life?
And another: How can we possibly know (or even have “reasonable estimates”) that the atmosphere was NOT Venusian billions of years ago?
Eniac (sorry for my late answer, but I have been quite busy finishing some work);
what I meant to say the whole time was that all that carbon which is now locked up in liemstone and related organic rock was very gradually released from the inner earth by volcanism.
The atmospheric CO2 content through the ages is reasonably well-known, see for instance the graph of phanerozoic atmospheric CO2 content in:
Though sometimes significantly higher than today, it was never even near Venusian through the age of life on earth.