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It turns out that Ryugu is a mixed carbonaceous and G-type (clay) asteroid; probably a rubble pile consisting of coalesced debris from both.
https://en.wikipedia.org/wiki/162173_Ryugu
This has important implications for mission architecture. If Ryugu contains a lot of carbon and oxygen (in silicate clays) then it has most of the feedstock necessary for CH4/LOX propellant manufacture. Carbon is also a reducing agent in the production of iron.
If the transit between Ryugu and Earth/Mars is relatively short (days - a week), then passengers can be housed in small jet-aircraft type fuselages with little requirement for space or consumables. Most or all of the fuel needed for transfers between the asteroid and Mars/Earth can be produced on the asteroid. The small chemically fuelled transfer vehicle would presumably need to rendezvous with other vehicles in Mars/Earth orbit, whose purpose is specifically to ferry people and materials between LEO/LMO and the surfaces of both respective planets.
Ultimately, this should make the transit between Earth and Mars both cheaper and safer, at the expense of developing the asteroid into a viable cycler in the first place.
baseline mission architecture:
1. Ryugu is developed into a combined asteroid mine / cycler, whose task is to deliver minerals to Earth orbit and convey passengers between Earth orbit and Mars orbit. The cycler material will be processed insitu to produce oxygen for crews and propellant, and possibly to grow food using native carbon and oxygen. A huge investment will be required to convert the asteroid into a workable cycler - probably several tens of billions of dollars. This is partially amortised by export of materials back to Earth orbit and Earth surface.
2. Missions to Mars will use a reusable starship type rocket to rendezvous with a reusable transfer vehicle in Earth orbit. The transfer vehicle will take on passengers and extra propellant and will carry passengers to the cycler (dV ~6km/s?), whilst the starship upper stage returns to Earth surface;
3. Passengers will live in the cycler using its materials to supply all consumables for the duration of the trip and using propellant derived from the asteroid to refuel the transfer vehicle.
4. Upon Mars approach, passengers will board the transfer vehicle once again, and complete the short trip to Mars orbit, burning propellant to complete orbital injection.
5. The transfer vehicle will rendezvous with a reusable Mars SSTO that cycles between Mars surface and low Mars orbit. It will transfer people and payload and take on some fresh propellant. Ultimately, fresh propellant may be produced on Phobos, but this implies more capital investment.
6. The transfer vehicle will then transfer people and payload from low Mars orbit back to the cycler.
7. Upon Earth approach, the transfer vehicle is refilled with propellant from the cycler and achieves Earth orbital injection with a propulsive burn.
8. The cycle repeats again.
If the orbital characteristics are reasonably close to what is needed, we could use mass drivers to optimise the orbit. Mining the asteroid and hollowing out internal spaces will generate a lot of rubble that could be used as reaction mass. This might be feasible if the delta-v required to adjust the orbit is no more than 100m/s, say. Where this may prove impractical is for bodies whose orbit is not well aligned to the plane of the solar system.
I believe that Ryugu is one of the best candidates for an Earth-Mars cycler and that probably has a lot to do with why the Japanese are so interested in it. I would propose that this should be considered as the baseline for further discussion. It is also close to spherical in shape, making it an efficient option for enclosure in a pre-stressing restraining bag.
I previously calculated that the zylon restraining bag for a 100m spherical asteroid would weigh 98 tonnes, if rated to contain a 50KPa pressure with a sufficient safety factor. Given that the mass of a pressure vessel scales with volume, a similar but larger restraining bag for Ryugu (900m diameter) would weigh 71,442 tonnes.
This sounds like an unachievable mass to consider launching from Earth. However, Musk believes that his reusable starship will be capable of lowering launch costs to $200/kg in regular operation. If we could divide the restraining bag into smaller hexagonal sections that can subsequently be clipped or stitched together; some 240 starship launches would be needed to deliver the bag to Low Earth Orbit. Total cost would be $14.4bn. If we want to spin Ryugu to produce lunar levels of gravity at its equator, the required mass of the bag would roughly double and so would launch cost. If an electrically propelled transfer vehicle could be used to deliver the bag sections to Ryugu, then the project might be accomplished at a cost of ~$50bn.
Whilst this is a large sum of money, it may be a good investment. Ryugu weighs 450 million tonnes. If it can be mined, much of this material could be returned to Earth orbit to support space manufacturing, or even to Earth surface for relatively valuable elements. The volume of the asteroid is 380million cubic metres. If the asteroid is mined to excavate roughly half of its volume, this would ultimately allow sufficient space for tens of thousands of passengers travelling between Earth and Mars. The capital cost of the project can also be offset against the reduction in cost of spacecraft needed to transfer colonists between Earth and Mars, which would be much smaller if a cycler is used, as it only needs to house the colonists for a shorter period of time.
We would ideally attempt to engineer the bag segments such that they easily clip together; are covered in solar cells to generate power; contain heat transfer channels allowing them to be used to dump waste heat; and include an internal void that can be filled with compacted dust to protect the tensile material from meteorite impacts.
A few candidates for Mars cyclers, none of them ideal. I haven't looked at orbital inclination, which may disqualify some candidates. Ryugu looks like the best mars cycler candidate from an orbital mechanics point of view. Do you suppose that the Japanese picked it for that reason?
Aphelion slightly too small for Mars, but perihelion is good for Earth. Diameter is slightly too large.
https://en.wikipedia.org/wiki/(529366)_2009_WM1
Orbital characteristics look good – but at 20m diameter, the body is on the small side.
https://en.wikipedia.org/wiki/2009_DD45
Aphelion is 0.3AU beyond Mars orbit, but perihelion is good for Earth. Diameter is too large at 370m.
https://en.wikipedia.org/wiki/(292220)_2006_SU49
Orbital characteristics look good. I knew there was a reason that the Japanese were interested in this asteroid. Quite large at 900m diameter.
https://en.wikipedia.org/wiki/162173_Ryugu
Aphelion falls 0.3AU short of Mars orbit and it is small at 30m across.
https://en.wikipedia.org/wiki/1998_KY26
Perihelion is good for Earth, but aphelion is 0.2AU beyond Mars, though perhaps a tolerable orbital parameter. Another asteroid specifically targeted by the Japanese. Dimensions are too large for bag enclosure – it is 500m long and 200m wide.
https://en.wikipedia.org/wiki/25143_Itokawa
Perihelion is good for Earth, but aphelion is 0.5AU beyond Mars orbit.
https://en.wikipedia.org/wiki/4660_Nereus
Perihelion and aphelion are both more than 0.1AU from either planet. Much too large for bag enclosure, though interestingly Eros mass is high enough that natural gravity may balance internal pressure in excavated volumes if they are deep enough.
https://en.wikipedia.org/wiki/433_Eros
Much too large for bag enclosure (2km) and aphelion is 0.3AU beyond Mars orbit.
https://en.wikipedia.org/wiki/1943_Anteros
For a cycler, there are many possible candidates. For Mars missions, we would ideally choose an asteroid that is <100m in diameter and is both Earth crossing (or grazing) and Mars crossing (or grazing). An orbit that grazes the orbits of both planets would appear most desirable, as it suggests minimal dV needed to match the orbit of the cycler at both ends and of course, it increases the frequency of useful transits. Wiki has a huge list of minor planets that I am gradually interrogating.
https://en.wikipedia.org/wiki/List_of_minor_planets
Essentials in selecting a candidate cycler are:
(1) Correct orbit (as discussed);
(2) Composition – there is flexibility here, but metallic asteroids probably aren't what we want.
Bonuses:
(1) Presence of water and organics (ideally), but as a minimum, iron oxides in stony asteroids can be reduced to yield oxygen, which dominates propellant mass;
(2) Size: Too small and the asteroid does not warrant a long term investment; Too large and the initial investment is excessive. About 50-100m across appears to be in the correct range;
(3) Presence of exportable mineral groups (to Earth and Earth orbit) would be a valuable bonus. For this to be viable, we are probably interested in asteroids with perihelion close to 1AU.
A tether (rotating skyhook) would presumably be used to boost a spacecraft tangential velocity such that it reaches orbital velocity. What sort of boost to dV is likely to be achievable? If a rocket were to fly straight up to 100km say, could a tether provide all of the tangential velocity increment?
If this is achievable, then a rocket at takeoff would only need to achieve about 3km/s dV (1500m/s altitude, 500m/s drag, 1000m/s gravity loss) to reach orbit. That is within reach of a single stage Kerosene/methane oxygen stage, or even a large nuclear powered lower stage using water propellant, taking off and landing on the ocean. A single stage booster could be heavy enough to have a long fatigue life and its economic model would be closer to that of an aeroplane. An upper stage that needs to reach orbital velocity could never work like that.
Some variation of the nuclear pulse option that GW refers to would allow take off from Earth surface and landing on Mars; all with a good payload fraction. The ship can be built on the Earth's surface and can be loaded with fuel, passengers and supplies on a planetary surface at both ends.
The ion propulsion concept would presumably require multiple chemical rocket launches to allow assembly of the vehicle, fuelling, victualling and delivery of passengers. That implies a lot more capital and operational costs. And the vehicle would have a shorter lifetime. I think a reasonable estimate would put the cost of a seat on an ion driven ship at least an order of magnitude greater than a nuclear pulse ship.
The implications are clear; mankind will not colonise the solar system until we get much cosier with radioactivity in the environment. We are prepared to tolerate substantial human health consequences from fossil fuel air pollution. We need to be comfortable with radioactive pollution is much the same way.
Tahanson, thank you for your feedback and support on this topic – I am aware that I have not contributed for a while. My situation is very much as you imagined it to be; three children – all teenagers. My job is eating more of my time than it usually does and I have been on holiday for a week.
When I started this discussion it was to explore an idea, hopefully with the intent of developing it into something that others will find useful. I haven't abandoned that intention, but keep in mind that I did not set any timescales as such. I hope that you have not incurred any expense in support of this; I certainly did not ask you to.
The original concept involved using a polymer bag to stabilise a small asteroid such that internal tunnels could be pressurised without exploding the body and (potentially) to allow the asteroid to spin up to produce artificial gravity; although this proved to be more challenging. The concept is raised under terraforming, which would be a natural consequence of the project, as we are attempting to recreate an Earth-like environment within excavated spaces. But the real potential here is to support asteroid mining to deliver materials to Earth orbit and valuable substances to Earth surface. It allows mining to take place in gravity and in a shirt-sleeve environment; basically using tools that we are familiar with here on Earth.
The original concept involved manufacturing the bag on Earth and delivering it to Earth orbit by heavy lift vehicle. The bag would be transported to the asteroid using either a chemical stage or some form of electrically propelled transfer vehicle. The original concept concluded that a spherical asteroid 100m in diameter would require a vectran bag weighing 100te to safely contain internal pressure (assuming 0.5 bar) but this would roughly triple if the asteroid were spun up to produce 0.3g gravity at its equator. On this basis, a 100m diameter spherical asteroid is probably about the largest we could terraform without using ISRU to produce the bag, given that Musk's starship has a reusable lift capacity of 300te.
One useful topic that we have discussed recently is cyclers. This adds a new application to the concept. Cyclers only appear to be useful if a sizable portion of the consumable (especially propellant) for a mission can be derived from the body of the cycler itself. They also work best if multiple destinations are of interest (i.e. Mars and asteroids). If the concept can be adapted to cyclers and used to support Mars missions, then Musk could be a key interested party.
Well, building a huge habitat may or may not require going to a cycler. You are just building the equivalent of an ocean liner that flies in space. There really is a way to do that: nuclear explosion propulsion. That has its own limits or restrictions on use. But we have known since 1959 that it would work. It just works best at gigantic scales, which is really why we have never used it.
Look for yourself at the mass ratio and delta vee capability for something in the 10,000-20,000 sec Isp range with a vehicle thrust/weight in the 2-4 gee range! Yep, it's hard to hold it down to 2-4 full gees! I think you will really like what you see. These are built out of heavy steel plate the same way armored warships are, and can be launched from Earth's surface, starting with fractional-kiloton devices. The yield goes up as you fly up into vacuum.
There are side effects to nuclear explosion propulsion. Everybody thinks about nuclear fallout, but that is NOT the big one. EMP is. These have to built and launched from very isolated locations, and flown into space such that the ground track stays very isolated. And you can't stop in low Earth orbit, you must park it higher up to dilute the EMP with distance squared.
I'd caution against notions of building these or any other structures out in space from asteroid materials. No one yet knows how to make real engineering materials out of rocky debris. Those who say we know are lying to you. So far, stones are for masonry, and such cannot serve as pressure vessels or take anything but a compressive load. Sorry, that's just where we humans are.
GW
NASA are developing a Z-pinch based fission-pulse device, in which much smaller masses of fissile material are compressed to enormous density using electric fields. The advantage here would seem to be that fission takes place at much lower explosive yield without sacrificing efficiency. The reaction takes place within a magnetically lined thrust chamber and thrust can be augmented by feeding hydrogen propellant into the chamber. The concept is still inherently pulsed, but this would appear to take care of the EMP problem and at least partially mitigate the radioactive contamination issue, given that fission energy is more efficiently used to produce thrust.
Clearly there are pros and cons with the use of cyclers. Using a cycler inevitably results in higher mission dV requirements, because fuel must be burned matching the cycler orbit and adjusting orbit again upon approaching destination. Additionally, using a cycler implies waiting for its orbit to align such that it makes a close pass at Earth followed by a close pass at Mars. This would make journeys to and from Mars irregular; you may need to wait years for the orbits to line up in a way that makes the cycler a viable tool.
Some advantages I can see with this approach:
1. The bulk of an asteroid shields the crew from radiation and thermal cycles for at least part of the journey.
2. The cycler may be a destination in itself. If asteroid mining can be carried out for minerals that can be delivered to Earth orbit, then building the cycler can be subsidised by the profits made from those materials.
3. Most asteroids contain silicates; some contain carbon and water. It may be possible to manufacture some consumables for the mission using material mined from the cycler. This might include oxygen, propellants and maybe even food grown on the cycler.
4. Using a cycler reduces the requirements placed on the interplanetary transfer vehicle. Instead of being suitable for an entire journey, it need only be sufficient to transfer people to and from the cycler, which are presumably much shorter journeys than the entire trip. If transfer times are no more than a week say, it might be tolerable for people to endure cramped conditions, like the interior of an airliner cabin. No one could survive that for eight months, but a week might be tolerable without driving people nuts. The accommodations on the cycler could be far more comfortable - more like a small town than a spaceship. Tahanson, SpaceNut and I have discussed a scheme for structurally reinforcing small asteroids to allow tunnels to be pressurised. There is even the option for artificial gravity, though this is more difficult.
5. Whilst alignments between the cycler and individual planets are irregular, the use of the cycler would be more optimised if we are interested in multiple destinations. If a cycler allowed close approaches to main belt asteroids, that would be a valuable bonus. If we can refuel from the cycler, using propellants derived from the cycler, it might even be possible to use it as a springboard for journeys to Jupiter and the Trojans. These sorts of things imply that the cycler would have a limited useful life as we use it up.
Gail Tverberg provides an interesting counter perspective here as to why Trump tariffs do make sense.
https://ourfiniteworld.com/2019/05/22/w … e-tariffs/
https://ourfiniteworld.com/2019/06/12/s … rom-china/
I would also add that the trade war has little to do with boosting the wealth of American workers and Trump probably knows this. It is aimed at delaying and blunting China's ability to emerge as a geopolitical rival to the US.
Algae is the most productive food crop in terms of harvested energy and volumetric efficiency. The challenge is to produce algae based foods that are appealing to eat. Wheat is the overwhelming contributor to western diets. If we could develop an algae product that resembled flour when dried, then a large percentage of human food requirements can be met in this way.
https://www.businessinsider.com/algae-i … ?r=US&IR=T
Alternatively, we might feed algae based fodder to livestock or fish.
Interesting. The problem with 3D printing is that molten material is bonded to a solid substrate. This makes it unsuitable for construction of structures the need to take tensile forces, such as pressurised structures, but generally works fine for compressive structures. The problem is even more intractable if ceramic materials are used.
One solution would be to use pre-stressing cables or tendons to provide a compressive force on the structure that balances the pressure within. A cylinder shaped ceramic structure could be reinforced by internal, longitudinal, pre-stressing cables. These would provide enough longitudinal force to balance radial atmospheric pressure through frictional forces between the compressed ceramic materials. Further reinforcement could be provided by external steel locking brackets.
The cables could be made from low carbon steel, glass or basalt fibres or polymers. It would be wise to choose materials that did not creep, although internal cables would be easy to replace.
China is building new coal burning plants with supercritical boilers. These have efficiency of 45% and are replacing older units with efficiency less than 30%. The Chinese economy is built on the premise of manufacturing of bulk commodity grade products at a lower price than the rest of the world; something that requires a lot of cheap electricity. The economy is therefore intolerant of high electricity prices.
In recent years, Chinese coal mines have been closing because coal prices have been too low for them to remain profitable. Higher labour costs and depletion are eating away at the profitability of the industry.
https://ourfiniteworld.com/2016/06/20/c … s-problem/
They are mining as much coal as the rest of the world combined, but have only 13% of global reserves. Somethings got to give. I seriously believe that the only reason the Chinese are bothering to build new coal burning power plants, is that they cannot expand their nuclear power capacity rapidly enough. I think they understand the net energy problem all too well and are doing everything they can to move away from a fossil fuel energy base.
If someone here can access the paper, please could you tell me what's in it? Junkyard battery.
Okay, so more information is available without access here. The brass was 67% Cu/33% Zn, and the batteries achieved 20 Wh/kg. What I want to know is how much copper and zinc is needed per kWh of storage. It's very exciting, since we have on the order of a billion tonnes of recoverable copper according to the USGS, though only ~250 million tonnes of zinc, so that gives us 750 million tonnes of brass for the batteries. World energy consumption is ~15 TW, so 18 billion tonnes of battery would be needed. Eh, it might work, depending on how much they need and whether they can be improved (probable).
Batteries are a poor solution for large-scale energy storage. They are poorly efficient, have limited cycle life and significant embodied energy. Maybe the solution is to ditch the batteries all together. The most successful electric vehicles in the world are grid connected. It would appear improbable that the battery electric car is a scalable solution.
https://www.lowtechmagazine.com/2008/01 … s-o-1.html
https://www.lowtechmagazine.com/2009/07 … trams.html
For long-term energy storage, heat is a good option. Deposit heat in rock or gravel using heating elements and convert it back to electric power using a boiler working on an S-CO2 cycle. Efficiency is about 50% but embodied energy and capital cost per unit power are low.
A novel idea. For this to really be workable, we would need to mine the southern polar cap and use a heat source to melt the dry ice at a pressure of several bar and temperature of about -50C. This would allow the CO2 to be pumped. Maybe geothermal power could be used as the heat source. If we were clever, we could use CO2 phase change to power the mining equipment.
A pipeline 1m in diameter, with flowrate of 10m/s could carry thousands of MW of power. Liquid CO2 would be pumped to cities closer to the equator, where solar heat would be used to generate high pressure CO2 to power gas turbines for electricity production or to generate direct mechanical power, such as for compressed air tools or mining equipment.
The absence of intervening seas and oceans allows for the development of global grids on Mars, transporting power using CO2, as well as electricity; and water harvested from ice deposits and pumped to cities thousands of km away. It is also possible to transport physical goods and raw materials by pipeline, by encasing them within floating hydraulic capsules in either brine solution or liquid CO2. Kind of like an enclosed canal network.
Of course, pipelines represent a significant investment in infrastructure. A pipeline from the southern cap to the equator would require tens of thousands of tonnes of steel or plastic. Not something that would be done until significant settlements existed on Mars.
Every time this ridiculous "limited pie" theory rears its ugly and ignorant head, it turns out not only to be wrong, but absurdly wrong in every sense of the word. How the cretins who peddle this nonsense continue to get anyone to buy into it is beyond my comprehension. Humanity has been advancing in living standards, some societies faster than others, but this requires more energy and better energy usage efficiency to continue doing it. Even so, we're in no danger at all of ever running out.
Some of what I read in that is profoundly ignorant, but I attribute that to stupid people with stupid ideas coming to stupid conclusions to further their own stupid agendas. The notion that America was most economically productive in the 1930's, for example, is mind-blowingly dumb. It's almost as if the idiots who wrote that hit every branch on the stupid tree before they nose-planted into the mountain of their own brain droppings. It's also why we tend to ignore such cretins until they seize power and begin implementing their stupid agendas.
Quote from the article covering the idiocy of these two idiots- Victor Court and Florian Fizaine:
Insight: The US economy, he shows, appears to have reached "the peak in productivity in the 1930s, the same period in which the EROI of fossil fuels reached an extraordinary value of about 100."
People were starving to death in the 1930's because they had no jobs and no food. Nobody starves to death in the US today, except by choice. To this day, we still can't fix stupid. The people I see begging for change on the roadside today have beer guts. Good luck finding photos of poor people from the 1930's who were morbidly obese. Yes, these morons are as derp-tastic as they come.
The authors are talking about productivity growth rates, not productivity per se. They are not arguing that life is harder now than in the 1930s; something that is clearly not true. Productivity was growing more rapidly throughout most of the 20th century than it is today. Average productivity is the integral of the productivity growth rate curve. This makes sense when you consider that our ability to perform useful work depends upon investments of energy embedded within infrastructure made in previous times. Ahmed should have been clearer about the difference between productivity and productivity growth rate when he discussed their work. The difference in this case is far from trivial - because of his gaffe you completely misunderstood the article. It shows the importance of proof reading.
Productivity growth rates hit record high values in the two decades between 1920 and 1940. This was the period in which abundant, storable and portable energy in the form of oil products; allowed rapid growth of low-cost road and rail transportation. This improved the mobility of labour and finished products and the large US population, allowed huge economy of scale to be realised in factory production. Factories were able to take advantage of cheap coal based electricity and the growth of hydropower. Steel and refined materials also became cheaper as they exploited oil based energy in mining and coal based energy in their manufacture and cheap transport allowed them to develop their own economies of scale. Ultimately, America grew into the world foremost industrial power by exploiting a solid resource base of fossil energy. That is the source of the wealth that you and I enjoy to this day. The UK did the same thing in the previous two centuries by exploiting coal based energy. These facts are uncontroversial, but economists don't generally talk about the economy in physics terms, so it sounds a little unfamiliar to consider it in this way.
The problems that Ahmed alludes to stem from the fact that the quality of our energy resource base is now degrading, in that for each unit of energy we get out, a growing proportion must be invested in the extraction process. The most striking example is shale oil, which requires very high drilling rates to maintain production and produces lower quality crude that must be blended prior to refining. It is the continuation of a trend that has been growing since at least the 1960s; but had not reached levels that would choke economic growth until the early years of the 21st century. It is noteworthy that even though oil prices have tripled since 2000, shale oil producers are unprofitable and have run up hundreds of billions of dollars of debt. The situation is mirrored across the globe; it is now impossible to find a price that is both affordable to consumers and profitable for producers. If Court and Fizaine are correct, then EROI will soon decline to the point where productivity growth rate will become negative.
Globalisation allowed the effects of fossil fuel depletion to be mitigated for at least a couple of decades, by allowing energy intensive industry to relocate to Asian countries (especially China) with low cost coal production and cheap labour. This aggravated problems of inequality in western countries. The effects of energy resource depletion are aggravated by depletion of other resource sets, such as metal ores.
I don't think there is anything ignorant or moronic about thermodynamic models of the economy; that is simply the way it works. What we call wealth is simply the effects of surplus energy (that is energy harnessed, minus the energy used in its production) transforming or manipulating matter into things that we want. It is a giant machine that we are all part of and the laws of physics govern it in the same way they govern any other machine. The problem in a nut shell is that it takes a certain amount of energy to produce a unit of GDP. If you want a cup of coffee, it takes 100KJ to boil the water. If you want a tonne of steel, you need 30GJ to heat the ore and reduce it. There are certain irreducible energy requirements that need to be input to generate goods and services. Hence an energy intensity to GDP. So there are limits to what we can afford to pay without going into debt.
The question ultimately is what, if anything, we can do about this. Since the 2008 recession, global debt burden has more than doubled. Interest rates in all major economies have been beneath inflation for a decade. Quantitative easing has flooded the world with cheap money that has so far failed to stimulate economic growth, because the crisis has nothing to do with a shortage of money. It results from physical resource depletion. The solution, so far as I can see is to expand humanity's resource base. We can start by rapidly expanding the use nuclear power and bringing in new sources of rare elements from near earth asteroids. But ultimately, we need to leave the Earth behind.
For Calliban re #35 .... both books have arrived here. They are both well used library copies, perfect for marking up as I like to do.
I invite you to consider how we might use these resources (and others along the way) to create a series of posts which would (or could) provide guidance for a student working on a paper, or (on the high end of the spectrum) for someone thinking about bending education toward a career in the asteroid mining or related fields.
As mentioned previously, GW Johnson is a potential resource for designing a series of posts with educational value.
(th)
Thanks Tahanson. I have been away from my electronics this past week, so apologies for the late reply. I will try and devote some time to this now.
I agree with your proposal. A series of posts would be a good start, ultimately culminating in some papers or perhaps an online book. Most people here have a scientific or engineering background, so it is a good place to develop ideas on every aspect of 'Near earth asteroid colonisation' concept. Ultimately, we need something equivalent to the 'Case for Mars' directed towards NEOs.
My original concept of using a polymer net to reinforce an asteroid to allow pressurised tunnelling and artificial gravity, is a tiny subset of a much larger topic. I therefore suggest keeping this topic close to its original intent and raising others to explore other aspects. SpaceNut has pointed us towards posts that indicate that there has already been a lot of discussion on individual elements that can be built upon.
Enjoy the books. I have an old copy of Mining the Sky which I am going to track down. I am going to see if I can get the other books through my library.
Correct me if I'm wrong here. There would appear to be fundamental limits to the height of a rocket vehicle. Ultimately, engine pressure would need to be proportional to height, as increasing height means more mass per unit of cross sectional area, and hence, the need for higher engine pressure to enact enough force to allow acceleration without intolerable gravity losses. Higher engine pressure means higher pumping power and higher rates of heat transfer within the combustion chamber, throat and engine cone. I'm not sure at what point engine pressure would become a limiting factor, but doubling rocket height would appear to be less straight forward than doubling diameter.
For Calliban #30 ...
https://www.amazon.com/Colonies-Space-T … way&sr=8-1
A used hardcopy is available. I recommend it over the small paperback, for greater ease of reading and color illustrations (I think (not certain)).
If you decide to invest in a copy, I'll pull mine out of the archive and have it available to compare notes.
The paperback is going to a freshman headed off to college. It was published in 1977, but much of the technology seems as fresh as the day it was printed. The computer capabilities have improved of course, but physics hasn't changed much in that time.
Heppenheimer was part of the Stanford Torus summer study.
(th)
Thanks tahanson, I will buy a copy. I cannot seem to get a copy of Asteroid Mining 101 for less than $100. It appears to be out of print, not sure why.
At somepoint when I would say the internal is 80 - 90 % of the planetoid has been removed we will want to switch over to having men there to help in finishing out the internal construction of wiring, plumbing and much more. The bore hole for the initial entrace and exit on the oposite side would need to have a docking means attached for crews to have a mainway to traverse inward and to have an airlock chamber made possible.
I think the process is likely to be incremental. We would start with a minimal bag structure to allow the beginning of mining activities. As time proceeds and mining produces more silicate waste material, we would use it to progressively reinforce the bag and allow the tunnel network to expand and gradually increase spin gravity. This allows us to do more as we earn more money by selling the mined material.
The destination for any mined material will be Earth orbit. We will need a certain amount of reaction mass to transport valuable metals from the asteroid to Earth orbit where they can be processed into other valuable products or exported to Earth's surface. I would imagine that reaction mass will account for a lot of the bulk silicates, though some may remain available for the production of basalt fibres.
It is enormously advantageous for manufacturing operations to take place in Earth orbit. It requires less delta-v to ship equipment into Earth orbit than it does to ship it to the surface of the asteroid. Repairs and communication are easier and most important of all, operations in Earth orbit can be teleoperated from Earth, with only a minimal crew needed to address problems if anything malfunctions. This has the potential to significantly reduce costs and would be cumbersome if attempted at more distant targets.
The idea of using thin bags of loose material to shield against micrometeorites is a good idea. In the absence of this, the safety factor of the pressure restraining bag has to be over-specified in order to accommodate micrometeorite damage. It would also likely have only a limited design life.
Declining EROI has been exerting an increasing drag on the global economy since the turn of the century. Soaring commodity prices, especially energy, were an important contributor to the 2008 great recession. The more complex, wealthy and energy intensive an economy is (and those three things do tend to go hand in hand) the more vulnerable the economy is to declining net energy. However, EROI of fossil fuels has now declined to the point where developing countries are encountering problems too. The Chinese economy is stalling largely because its domestic coal production has levelled off.
Tim Morgan explains in this primer exactly why 21st century economic problems can be directly traced to declining EROI of the world's energy sources.
https://surplusenergyeconomics.files.wo … onomy2.pdf
Gail Tverberg on why renewable energy sources are unlikely to replace the energy provided by fossil fuels:
https://ourfiniteworld.com/2019/07/31/r … -mandates/
Global fossil fuel average EROI remained high until the 1990s, because new technology and globalization was developing previously inaccessible resources. But we ultimately hit limits around the turn of the century when all of the best global resources were already under development.
Well worth a read. If this assessment is correct, then none of the ambitions for space colonisation that this board was founded upon, have any hope of being achieved.
https://www.resilience.org/stories/2017 … -collapse/
The world economy is basically a thermodynamic machine. What we call wealth, is really just the result of energy used to transform matter into valuable products and services. The problem is that most of this energy comes from fossil fuels and with each passing year, the Earth's stock of high grade fossil fuels is progressively depleted. This suggests that we are ultimately heading towards economic collapse in the not too distant future, because increasing proportions of refined energy must be reinvested in the extraction process. This leaves less available to power the production of goods and services that aren't related to primary energy. Given that GDP is really just a function of energy use; declining profitability of fossil fuel energy will increasingly crush human prosperity in years ahead.
No ethical issues, just practical ones. A 1MT thermonuclear warhead would release 4.4E15 joules of energy. That's the same amount of energy as released by sunlight over 1 square kilometre for 1 year in the UK. Doesn't sound like much when you look at it like that. What's more, if the desire is to avoid generating radioactivity, then the bomb would need to air burst and most of the heat would be delivered by thermal radiation. This would be a relatively inefficient means of transferring the heat, as half of the heat radiates into the sky and much of the other half would be reradiated due to the poor thermal conductivity of frozen ice and CO2 and the short duration of the flash. You would need a lot of bombs to vaporise the Martian cap and the cost would be huge.
If the intention is to colonise Mars, then a better option would be to set up a nuclear powered CFC factory on the surface of Mars. Or better still, to start mining the dry ice and using it as a source of power. That way, vaporising the ice is a by-product of human operations, rather than something we must specifically pay for.
For Calliban re #28 ...
Would you be willing to revise your "first visit" plan for Apophis so that the actual encounter is performed by a combination of AI and telepresence? The probe that recently visited Ceres (and another remote object) was able to function without direct human control, although telepresence (with time delay) was used to program the behavior of the systems on the probe.
A (relatively) light weight vehicle could accelerate from GEO (as just one example of an approach) to match orbit with the asteroid as it passes close to the Earth, well inside GEO itself. However, due to the proximity of Earth, high data rate telepresence would be possible for a short period of time, followed by reducing data rates as the body recedes.
Multiple missions are possible and perhaps even likely, if the idea of landing on the asteroid becomes popular.
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By any chance, do you have Heppenheimer in your library? I was reviewing my yellowed copy of the paperback today, while waiting for an appointment, and found on (about) page 135 a detailed discussion of the procedure for smelting lunar rocks in a free flying "construction shack". I was struck by the similarity of those 1977 musings, and your more recent posting about how materials would be differentiated in space.Not much has changed over the decades, it would appear.
Edit: In particular, I was struck by Heppenheimer's description of sputtering of aluminum mist onto a fabric balloon, to make the walls of a habitat cylinder.
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There are no doubt many possible mission proposals that could yield valuable results.
I do not have Heppenheimer's work, but his proposal for vacuum plating is interesting and similar to a proposal that I can remember reading in Gerard O'Neills 'The High Frontier'. One possible issue with this idea is the use of aluminium, which takes about 20kWh of power to produce a single kg and takes place in super high temperature electrolysis cells, using carbon electrodes. I can't see it being an easy thing to make in space. If the same thing could be done using iron, it would be technically much easier.
The design referenced by Spacenut is interesting in its use of magnetic fields to deflect charged radiation, thus avoiding the need for heavy shielding. However, I note that it consists of 900 modules each weighing 40-50 metric tonnes. That is a lot of mass if it needs to be launched from Earth. Maybe there is a way to develop this on a slightly smaller and more incremental scale?
Peroni's estimate of 740mSv per year surface doses on Mars seem rather excessive. That is representative of cosmic ray doses in interplanetary space. The data I have seen for mars surface dose rates of about 200mSv/year (20 rems). But I digress.
I think any real spacecraft that we send to an asteroid will probably be far more weight constrained than this. If we reach the asteroid relatively quickly, perhaps we could use surface materials for shielding, or set up a magnetic ring that shields the surface? If we choose Apophis as the baseline for the mission concept, and it takes only a day or two to reach it's surface; is it realistic to assume that the spacecraft itself will not need special shielding for such a short trip?
PS. I recalculated the amount of basalt fibre needed to reinforce Apophis to allow it to spin up to provide lunar gravity (0.17g) at its far ends (it is an oblique spheroid). It works out at 46,500 tonnes, assuming a fibre stress of 1GPa. I also came to the realisation that an asteroid that is reforced in this way may not need any separate provision for pressure containment, because the weight of the rock above will tend to stiffen the walls of the tunnels, so long as they aren't too far from the axis.
Apophis' gravity is so weak (40 micro-g) that a rotating habitat massing a thousand tonnes on its surface would weigh only 40kg. This could easily to tethered to the asteroid and supported by magnetic bearings. The hab could contain both living space and a factory complex and would house a construction crew until they had manufactured and installed the restraining bag, at which point pressurised tunnels could be created. The hab would immediately be sheltered from 50% of incoming cosmic rays by the bulk of the asteroid.
Spinning up the asteroid would take considerable time and would require a lot of reinforcement even to achieve lunar levels of gravity - some 4 times more than would be needed for pressure containment alone. Building rotating habitats within voids dug out within the asteroid would appear to be a more cost effective choice. However, some amount of gravity would assist mining and would allow excavated voids to be used as habitats without the need to create rotating habitats in void spaces, which would require motors and bearings and would generally be cumbersome. The best solution would ultimately need to be arrived at by cost-benefit analysis.
I like the idea of Apophis as a colonisation target, as it comes close enough to the Earth that journey times to reach it in 2029, will be measured in hours. Colonists will not have to endure months of space travel before reaching the target. Those months can be spent setting up greenhouses, digging tunnels that take them away from space radiation and of course, manufacturing the restraining bag. Given that Apophis regularly makes close approaches to Earth; returning home and returning mined minerals would appear to be much easier than it would be for other targets.