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Gerard O'Neill's Island 1 was intended to present an appealling image of a space habitat so that people could become emotionally invested in the project. But if our goal is to set up space manufacturing capabilities and the purpose of the space habitat is to house the workforce, we do not need to begin with such large habitats. They are things that we can build up to over time. Starship is designed to house up to 100 passengers in a habitable volume of 1000m2 for at least 6 months. That is a 10m3 volume for each passenger.
If we used Starship as a guideline for the required habitable volume of a minimal space habitat, then a workforce of 1000 people would require 10,000m3 of habitable volume. That is a sphere some 26.7m in diameter. We can be more generous without the space habitat becoming unrealistically huge. Lets assume 10x the Starship volume per worker. That is 100m3 each, or 100,000m3 in total. That is equivelent to a spherical habitat some 57.6m in diameter. Say 60m.
Let us assume that such a habitat rotates to produce artificial gravity. Human beings can endure about 3 rotations per minute before inner ear problems start to become problematic. There is some evidence that humans can adapt to higher rates over time. But lets assume for the time being that 3 rev/min is what we will design to. That is 0.314rad/s. Centripetal acceleration can be calculated as:
A = w^2 × r.
Solving for r = 30m, gives a centrifugal gravity of 2.96m/s2 at the outer edge of the sphere, or 0.3g exactly. This is slightly less than Martian gravity. The closer one gets to the centre of the station, the shorter the radiys of rotation and the lower the centripetal acceleration. Lunar levels of gravity (1.635m/s2) would be experienced some 16.58m radius from the centre. This means that about 60% of the internal volume of the sphere would have gravity greater than lunar. Habitation areas will be concentrated around these outer sections.
The total volume of a 60m diameter spheres is 113,097m3, or 113.1m3 each. Some of this volume will need to be apportioned to life support functions. Food will be produced using a mixture of hydroponics, algaeculture and extracted chloroplasts. Using acetate salts, food can be produced in very compact volumes without sunlight. Gone is the need for the extensive agricultural areas that O'Neill anticipated in the 1970s.
Such a habitat would not have any wide open spaces. But there is sufficient volume for every crew member to have their own small bedroom, equipped with a personal ensuite. A cubic room with dimensions 2.4m aside, would have internal volume 13.8m3. If every crew member had such a room, they would collectively account for 12.2% of internal habitation volume. There would be canteens within such a habitat, as well as lounges, gym and cinema. There could even be small green spaces beneath artificial lighting.
How much would such a habitat weigh? This is difficult to estimate. For Island 1, mass was dominated by cosmic ray shielding. This amounted to 5000kg of silicate slag per square metre of hull area. For a sphere 60m in diameter, this equates to a total shielding mass of 56,500 tonnes. This is only 1.44% of the 3.9 million tonnes of shielding that would have been required by Island 1. As our habitat will be constructed for the workforce of a lunar ore processing facility, it is reasonable to assume that this mass will be derived from lunar materials. We could either use the first 56,500 tonnes of lunar ore as shielding or just work without shielding until we have 56,500 tonnes of silicate wastes from the ore refining itself. Much will depend on the mass that can be provided by an initial lunar mining operation.
I am going to call this 60m, 1000 person habitat concept, Island 0.1. Back in the 1970s, O'Neill had assumed that the colonists in Island 1 would be working families, with children attending school in the habitat, with both parents working. This seems less realistic for an early habitat supporting space manufacturing, though it isn't impossible. I think it more likely that individual workers would sign up for a 2 year contract, which would include transport to and from the habitat, food and accomodation, in addition to wages. The habitat would be attached to the ore processing and manufacturing areas. These would mostly be low or zero gravity. Operations would either be automated or controlled remotely from within the habitat. Only maintenance that cannot be carried out robotically, would require humans to leave the safety of the shielded habitat. This allows exposure to cosmic rays to be minimised by limiting exposure time. So the majority of the space factories will not require cosmic ray shielding.
Isaac Arthur has released his latest video on space based data centres.
https://youtu.be/iLNrYwx0th0
The neat thing about this is that it obviates the need for transmission of power from an SPS to the ground. Power is used where it is generated. This is a product that can realistically be sold to Earth based customers for profit. There is huge and growing demand for it. The downsides are transmission delay - 0.1s to a satellite in GEO. Such a satellite would also probably need a manned presence.
I am presently looking into buying a computer with enough capacity to handle fire modelling CFD applications. The cost is likely to be $5000 - $10,000. The problem is that for a 3-Dimensional geometry, especially structures, the number of cells increases very quickly, which eats up a lot of memory. To run a simulation in a reasonable amount of time, a high end Intel Xeon W-series processor is needed. A minimum of 1TB of free memory space per simulation and preferably, 64 cores to be able to run the simulation in hours rather than days. It gets expensive very quickly. But it is such a significant advantage to me as an engineer, that I am minded to take the hit and make the investment.
I read the Space.com article. The thing that really put the boot in Gerard O'Neill's concepts, was the failure of the space shuttle project to deliver a low cost, reusable launch service. Maybe Starship will ultimately do what the Space Shuttle couldn't.
There were other problems, such as failure to develop a reliable mass driver that could lift the required megatonnes of ores into high Earth orbit from the lunar surface. This failure had more to do with the mass driver being something of a bespoke application for lunar mining. There weren't really any other commercial drivers for it. It was too bulky to be useful to the military. For research of high velocity impacts on Earth, the light gas gun is a lot more compact. The real benefits of the mass driver are very specific to offworld mining applications, where propellant is not available in large quantities.
Although O'Neill's vision was not achieved during his lifetime, events are unfolding in a way that brings it closer to reality. The Artemis programme and the commitment to developing a lunar base. The development of Starship with its promiss of rapid reusability. Whilst O'Neill's colonies have always generated excitement, the reality is that the mass budget of these space stations, makes them impractical in the near term. We need to be focusing more on the problems of lunar mining and space manufacturing of products that we can sell to customers on Earth. We will need a workforce in space. But their initial accomodations will be a lot smaller than Island 1 and will likely be attached to factory complex that they are working within. As the scale of operations expands alongside revenues, at some point Islands 1, 2 & 3 will become affordable. How long that will take is anyones guess.
Wave power and tidal power are two different things. Both are worthy of consideration. But they need to be discussed seperately. The energy available from tidal power at a particular site is a function of tidal range.
https://www.researchgate.net/figure/Ran … _334235446
The higher the tidal range, the greater the potential energy available to exploit. Tidal range will determine both the volume of water flowing and the difference in head height between high and low tides. So the energy available per metre of coastline will be proportional to 0.5 x R^2, where R is the height difference between high and low tide. The energy available at a particular site will depend upon regional tidal range but is also influenced by local geography, which can funnel the tide.
There are other factors that may come into play when considering the site for a tidal power project. Environmental considerations have halted development in the UK, despite the UK having the worlds best resource. Tidal lagoons may provide side benefits, such as storm protection of the coast, protection from erosion and marine aquaculture in the lagoon itself. These other benefits may encourage development in places where the resource is otherwise marginal. The longevity of lagoons once created, makes the concept attractive as a longterm investment.
In places where coastal development is impractical, tidal stream power generation is possible as well. These draw energy from tidal water flow, rather like underwater wind turbines. But like wind turbines, the power output is proportional to the cube of flowrate. When this is factored in, the tidal stream resource tends to be quite limited. For example, the straights of Gibraltar experience tidal flow as Atlantic water flows in and out of the Mediteranean. The average power is a few hundred MW. This is not nothing. But compared to the electricity needs of a large nation (a few to several hundred GW) it is a small resource.
TH, this may be of interest.
https://en.wikipedia.org/wiki/Woodbridge_Tide_Mill
There were quite a few tidemills in Britain during the 19th century. But as with windmills and watermills, the steam engine put them out of business. With coal in decline and electricity increasingly expensive and unreliable, it may be time for a comeback of these old technologies. With hydraulic power transmission, a modern mechanical tidemill would be far more efficient. But as I have learned from my own wind power project, simplicity has value in itself. If systems are simple enough that they can be built by a cratsman with modest skills and simple materials, they are accessible to people who are prepared to commit their time and don't necessarily have a lot of cash to spare.
Spacenut, that is an interesting concept. It would appear to allow hydropower generation without too much disruption to the river. It would also be cheap and relatively easy to set up. For repairs it could be hauled up onto a slipway, allowing people to work on it outside of the water. Another advantage is that this device is simple and cheap enough to be built locally by craftsmen. It doesn't need to be a commercial product. That may be important in the years ahead, as supply chains come undone.
I have occasionally wondered about the potential for a small asteroid mining vehicle. This would target NEAs <10m in diameter. Such bodies would be completely disassembled. Useful metals and volatiles would be extracted. The remaining slag would be a mixture of iron, magnesia and aluminosilicates. These could be used as propellant by heating them into plasma with radio frequency heating. Small vehicles equipped with solar electric propulsion working on this principle, could ship the valuable materials back to high Earth orbit. The same propulsion tech would then be used to shift the orbit of the asteroid mining vessel to intercept the next NEA.
We have examined how we would mine such objects in previous work. One method would be to surround the body with a rotating ring. The ring would carry a set of arms equipped with enclosing shovels. These would grab chunks of surface material and drop it down chutes also mounted on the ring. The whole arrangement would be enclosed in a thin polymer bag to prevent loose material from escaping and contaminating the local space. The chutes would empty into ore processing. How we seperate recovered materials into useful elements needs more consideration.
The kite sail concept looks very promissing. This is something that can save fuel when the wind speed and wind direction is sufficient and be wound in and packed away when not needed. And it doesn't eat into hull volume and cargo space. Definitely something that deserves wider application.
Liquid air could be deployed as part of a hybrid propulsion system. The waste heat produced by the diesel engines is high quality heat at a temperature of up to 500°C. It would allow for efficient energy recovery from the liquid air. But on the plus side, the ship still functions on diesel if liquid air isn't available. So again, this is something that can save fuel over the lifetime of the ship. In the medium term, we don't necessarily need to phase out diesel altogether. If we can use it more efficiently then we extend the lifetime of the resource base. But things that add a lot of additional hardware cost only make sense if diesel is physically unavailable.
The low energy density of liquid air would appear to be less of a problem for inland or coastal freight transport. Maybe rail could make use of this tech as well.
The low efficiency of an atmospheric pressure steam engine (5-15%) makes the concept unsuitable for most power applications. But as part of a combined heat and power system, in which the rejected heat has practical use, the economics of the system look better.
It has been a while since anything was posted in this topic. But I found this today, which is interesting.
https://www.sciencedirect.com/science/a … 8112007082
The atmospheric steam engine uses heat at temperature <100°C, to raise steam in a boiler under vacuum. The condenser has a temperature of 30°C and a pressure of 4KPa. The low temperature difference between hot a cold side, mean that this heat engine is relatively inefficient. At 100°C boiler temperature, theortical efficiency is 25%. This drops to 10% for a boiler temperature of 69°C. Real efficiency in a practical device would be lower than this, perhaps 6-15% in a steady flow turbine system. This has led to relatively little interest in the atmospheric steam engine.
However, this concept deserves further study. Whilst it is relatively inefficient and bulky, it is easy to build. All of the pressures involved are beneath atmospheric. This means no expensive pressure vessels are required, as forces act inwards. Concrete shells capable of resisting implosion forces are easy to cast insitu. As the differential pressures are low, components are not under a great deal of stress. It should be possible to make use of low alloy steels, polymers or even wood for moving parts.
The low efficiency is also less of a problem if the abundant waste heat at 30°C can be used. This is where district heating becomes attractive. We could use water in this temperature range to heat houses and other buildings. Or we could store this heat with the ground during summer and extract it as input heat for a district heat pump for winter heating. A solar thermal powerplant built in the UK would generate some electrical power during the summer. The waste heat it produces could be stored in boreholes ready to supply district heating systems during winter.
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Additional: The addition of a small biomass fuelled boiler would increase the capacity factor of the powerplant. Solar power would preheat the water entering the boiler, with the boiler then heating the water to a consistent 100°C. Using solar power in this way, allows us to stretch the benefits of a limited fuel supply.
A while back, someone proposed building a rotating statite. This would gradually accumulate rotational energy that could then be used to launch payloads.
I wondered about building such a device in the asteroid belt. A while back we discussed mining ice from Ceres and then firing ice packages onto an orbit that intersects the orbit of Mars. As the ice packets explode in the upper atmosphere, they would saturate the Martian ionosphere with water vapour. This would have a global warming effect. Additionally, solar UV would break down the water vapour into hydrogen and oxygen. The hydrogen would escape and the oxygen would accumulate within the atmosphere.
It would take many centuries to build a breathable atmosphere in this way. We would need something like 700,000km3 of ice to do it. But patience is essential for terraforming. To do the job in 700 years, we could need to deliver 32,000 tonnes of ice every second. That means either a very big statite or more likely, lots of smaller ones.
Void, that is interesting. It is worth remembering that most of the mass of a space habitat will be cosmic ray shielding. Ice can be used for this purpose. It doesn't need to rotate. The metal shell of an Island 1 colony was estimated to mass around 100KT. But the shielding would mass at least 3MT. The mass of the air within it is also not trivial.
Using KBOs as starships makes no sense. These bodies have huge mass and the energy needed to dV them by any practical amount is just enormous. The only caveat is if we find a rogue object that is already travelling in the direction we want to go at a respectable speed. That is possible.
Isaac Arthur is without a doubt, one of the greatest futurists of our time.
Void spent some time researching the use of water ice as a building material. The colder ice gets, the stronger it becomes. On icy moons and dwarf planets, ice could serve as a structural material for buildings and dugouts. Insulation would be needed to prevent heat from habitable spaces from draining into ice walls. For free space habitats, cosmic ray shielding dominates the total mass budget. Ice is one of the most efficient shielding materials that we know.
Turns out Makemake has an atmosphere, albeit a very thin one.
https://www.space.com/astronomy/dwarf-p … scientists
This is surprising, because methane is a light gas and a world as small as this should not be able to hold it. The very low temperature this far from the sun no doubt reduces the vapour pressure of methane. So escape is a slow process.
Interesting topic. As the study notes, there are a number of ways to power a tug. Liquid air is promissing, as the water surroundingbthe tug can provide a heat source. Stored thermal energy in a phase change material could work as well. In the case of liquid air, the heat pump producing the air could dump heat into a district heating system. Liquid air has the advantage of being storable in underground tanks. A well designed system could avoid the need for cryogenic pumps by allowing liquid air to be distributed by gravity. Seperating the air into LN2, LOX and noble gases, would allow other revenue streams. Air liquefaction also allows CO2 capture from the air.
Bennu is technically easier to reach than the surface of Mars, or indeed, the moon. Its mass of 70 million tonnes, is sufficient for 20 Island One habitats and several hundred 10GWe solar power satellites. It is known to contain water, carbon, nitrogen and phosphorus, in concentrations much greater than we are likely to find anywhere on the moon. Whilst Mars is scientifically more interesting, Bennu offers better near term commercial prospects. The two goals are not mutually exclusive of course. But if I were in Musk's position, I would probably prioritise near earth asteroud settlement and mining, for the simple reason that they are more likely to offer a return on investment in a reasonable window of time. For space settlement to be sustainable, it needs to pay. The biggest hurdle that space colonisation faces is developing a business case for it.
This calculator provides the Jean's escape parameter for an atmosphere around a body of known radius, mass and temperature.
https://agentcalc.com/jeans-escape-parameter-calculator
If the parameter is less than 3, gases escape rapidly. If the value is greater than 10, an atmosphere can have a long lifetime by human standards.
I have been reading about superheavy gases, specifically sulphur hexaflouride. This gas is extremely dense ~6kg/m3 at room temperature. This makes the gas ground-hugging. It remains trapped in a tank with open air above it, because its high density limits the rate of mixing. It occurs to me that sulphur hexaflouride introduced onto a small rogue planet like Pluto, would tend to result in a strong thermal inversion within the atmosphere. The SF6 close to the ground could be much warmer than nitrogen above it, because gaseous nitrogen remains less dense than SF6 is at room temperature, even when the nitrogen is close to its boiling point. Any SF6 diffusing into the cold nitrogen layer, would rapidly freeze and fall back into the SF6 gas layer as snow. Any nitrogen entering the SF6 layer, would absorb heat, making it less dense and causing it to rise back about the SF6. The two layerswill therefore remain seperate, even if the lower SF6 layer is much warmer than the N2 above it.
Provided that colonists are able to provide an artificial heat source, and are able to locate sufficient flourine (a big if), ground conditions could remain warm, even with a cryogenic atmosphere above the SF6. The SF6 functions as a kind of blanket.
Isaac Arthur's latest video concerns clusters of space habitats.
https://youtu.be/jEWRL-6BR0A
One great benefit of tethering large numbers of space habitats and industrial facilities together is that transportation between them can be carried out without need for propellant. That offers sustainability advantages.
Ultimately, thousands of habitats, factories and ore refining facilities, could be located within a thin metal sphere. The sphere would serve as a transportation conduit, a waste heat radiator and a means of collecting volatiles that escape from space habitats. Each facility would have its own (non-rotating) cosmic ray shield, on the underside of the metal sphere.
In deep space, spheres would also house fusion reactors, providing the individual habs with light and power.
Void, that is an excellent find. On Mars, we won't be able to afford thousands of acres of pasture land for cattle. An energy efficient process for manufacturing fats in a compact facility will be essential for survival on Mars.
Another excellent video from Dami Lee.
https://youtu.be/8GbHWY0roOY
This one examines Lord of the Rings architecture. Both hobbits and dwarves live in underground structures, but there is a vast difference between them. The hobbits build small, individual underground borrows, which conserve heat and protect them from the weather outside. The dwarves carved out entire mountains, building great underground cities with great halls and art deco architecture. They specifically wanted to leave an eternal mark upon the Earth.
Future Martians, will build both kinds of structure. This will be a civilisation built underground.
Back in my university days, I attended a short course detailing the production of nuclear graphite. From memory, magnox graphite was made from petroleum coke. This was ground into powder, which was then bound with a glue and compressed into moulds. The green bricks were then baked at very high temperature, resulting in the particles fusing together and the glue undergoing pyrolysis. AGR graphite was produced differently. It was made from graphite that was mined in the US. This had a desirable microstructure.
Natural carbon is about 99% C12 with 1% C13. It would be desirable to seperate the C13, as this absorbs neutrons and creates C14, a long lived radioactive waste product. Concentrated C13 can be inserted into sample tubes within reactors in order to breed C14 if there is a specific use for this isotope. But bulk seperation of C13 would be desirable, as it would greatly reduce the volume and activity of waste upon reactor decommisioning.
Hopefully it isn't carrying protomolecule :-)
The object appears to contain nickel with far less iron than a sol comet. CO2, but little CO or water ice. Strange indeed. But it did form in a different environment to the solar nebula. Different is to be expected. Maybe in the future we will find comets with different isotope ratios or comets full of gold or uranium?
NASA bans Chinese nationals from working on projects.
https://www.zerohedge.com/geopolitical/ … y-programs
The Chinese intend to annex the moon as a national possesion. The free nations of the world should unite to ensure that it is not taken by the hostile flag of conquest.
Electricity offers the benefit of being easily transmissible. On the demand side, electrical machinery is also very compact and allows high power density. In factory environments, electrical machines have the advantage that changing factory layout is easy and machinery can be positioned for maximum productivity.
The disadvantages of electricity are inherent complexity in generation, transmission and use. Electrical systems are complex, not suitable for local manufacture and typically require exotic materials and programmable controls. Electric grids are also demand driven. This makes them unsuitable for energy sources that have naturally intermittent supply. Energy storage and backup power tend to be counterproductive, as both impose substantial additional capital and operational costs that makes delivered power very expensive. This problem is clearly evident in European countries that have embraced wind and solar power.
Rolling blackouts have sometimes been suggested as solutions to these problems. Unfortunately, this introduces problems of its own. Firstly, businesses dependant on electrical power lose all productivity when it is cut off. In some cases, loss of power can actually cause damage. Secondly, when power is shut off and breakers fail open, these must be manually reset. This is costly and time consuming.
A potential solution to these problems is to remove certain applications from dependance on the electric grid. Hydraulic and compressed air power systems, are somewhat more cumbersome to install than electrical systems. But they have the advantage of being simpler, similar in terms of efficiency and offering the same benefits of flexibility and power density as does electrical power. Hydraulic systems do not need exotic materials or complexity inmthe ways that electrical systems do. Most components can be made from steel, with limited use of polymers for seals and flexible couplings. This makes hydraulics more suitable for local manufacturing. It is somewhat less practical to use hydraulics to transmit power over long distances. But for local power networks it is straightforward. Power can be switched on and off by opening and closing valves.
In a small hydraulic network surrounding a mechanical windmill, intermittency is easier to manage. With only a handful of different users for the power in close proximity, it is possible to switch off certain loads quickly, by closing valves. Hydraulically powered heat pumps and air compressors can serve as dump loads that will not be active unless wind power is above certain thresholds. Swimming pool heating, heat for cooking, warm water for district heating, cooling for large underground freezers, are all systems that can be engineered with large thermal inertia through thermal mass and insulation. Other more direct mechanical applications, like a laundry and power to a machine shop, need power to be more reliable. Grinding is an application that can be switched on and off, provided that aggregate productivity is maintained across a whole year.
In this way, I can see applications for mechanical windmills providing services for a town. Intermittency is a problem that we can work around at a small scale in ways that is not practical in a large scale electric grid. Hydraulic power transmission allows flexibility and local manufacture of machines in ways that are not possible with electricity.