Colonies in Space: Mirrors vs Artificial Lighting

[chimericoncogene]

Your suspicions don't add up to me. Like, literally, have you done the math? Gerrard O'Neill was an engineer, and designed these things with an eye towards materials strengths and mass, and given that his smaller designs do in fact have mirror arrays that wrap around the entire structure, I would expect that the Island 3 and Model One use three mobile structures rather than a single static one for good reason. If the structure is an array of independently moving mirrors, then the structure gets heavier due to the required machinery for independent tracking. That's the trade-off for using independent tracking.

Agreed. I didn't do the math, no, and I have no problem taking your word for it. Rosinante's array is static in the short term (the mirrors don't track the land segments in real time). I guessed from the book that they eat the extra thermal load and wasted light from light hitting the underside of the cylinder floor. It has many disadvantages.

Plus you have to consider the effects of micro-meteor impacts over time on the structure. A lighter structure is also more fragile. So you could make a mirror array that is as light as a solar sail, but it will be easily punctured and torn. That means it isn't a practical method for lightening the structure.

Are a few holes and rips in your habitat solar mirror necessarily unacceptable? It's just a habitat, and the mirrors are outside, hidden from casual visitors. They don't need to be 100%. I can totally see people skimping on repairs and accepting degradation and maintenance for lower startup cost. OTOH, you might be correct that space colonies will not accept a need for frequent maintenance and replacement, but that seems more like a preference to me, albeit a logical one (you shouldn't skimp on life support, but someone will anyway).

Something that lasts two years and costs ten bucks may well be considered better than something that lasts ten years and costs fifty bucks (the colony can pay for a mortgage/maintenance, it's the upfront costs the bean counters worry about).

I suspect that short-termist thinking will follow us into space, especially if SpaceExxon, SpaceFoxconn, and the SpaceMansonFamily follow SpaceX, SpaceMormons, and the SpaceLibertarians into space. Good enough is good enough. Also, industrial accidents are great for storytelling.

HA! Ha ha. Hahahahahahahahahaha. That isn't how the real estate market works at all, dude. If you look at the actual economic status or income levels of people living in inner cities, you quickly find that rent prices can actually be a predictor of poverty, as counter-intuitive as it sounds. No, at least in the US the rich don't live in the inner city. They get as far as fucking possible from it as they can, as often as they can, while balancing that against the need to visit the city for business reasons.

Thank you for educating me on urban dynamics in North America, with application to large chunks of the world. What you say about itinerant rich people does make some sense, since a lot of rich people anywhere have multiple homes. But like I said, I live in a weird city-state. Not much room for middle-class suburbs and mansions, and a lot of opportunity for middle-upper class rich people to pack themselves in next to a Trump Tower equivalent and live there full-time, with a 300-store luxury shopping mall, glitzy IMAX theater, public transport, and skating rink an elevator ride away (basically a glitzier version of my apartment complex, with marble flooring, wood paneling, and an overpriced, overdecorated supermarket). Both models may be useful in modelling pressures in space colonization. This sort of thing is why multiculturalism and different perspectives are good.

I said its not free, not that its expensive. You still have to move it from place to place in the solar system, which isn't free. Oxidized compounds aren't the same thing as oxygen, you first have to chemically change them to be breathable atmosphere, and that isn't free. And once a habitat has filled its atmosphere to capacity, it needs to balance that atmosphere constantly with some sort of recycling system (like, say, actual plants recycling the CO2). You have to remember that it isn't free in the sense that you have to balance the production of CO2 and other unwanted gasses because you don't want to cause ecological problems in miniature, because you don't have the support systems of an entire planet to fall back on. Its for that reason that a space colony would likely do well to consider controls on industrial activity and possibly even population cap (well, it has to cap the population at some point anyway because of the limited room inside the ship). That's what I mean.

You just admitted yourself that life support isn't cheap. Why add to the costs during the construction phase when proper economic planning can limit the problem to begin with? Why, for instance, should we be treating plastic as a disposable resource? Tell me one good thing that has come about because of that short-sighted attitude towards petrochemicals

I tend to be rather cynical. I think people will always go for the cheapest, simplest option, even in a space colony, even if the long-term costs add up. I suspect there will be demand for lot more imports, and a lot of casual dumping of waste, than we expect. When energy is cheap, rockets are cheap, and materials are cheap (and that's kinda what you need if you want to attract people to colonize space on a large scale), people will end up horribly wasteful. Who cares about the sewage and refinery byproducts? Import more ammonia from Titan, mine the tar out of the next million-tonne rock, dump the crap and vent the waste gas! There's no environment to pollute, and if the vacuum-works are annoyed, well, they can move, or we can just extend the waste pipe!

Of course, if rockets are expensive and bioengineering/ecological management cheap, the inverse will be true. As to where the balance will fall, you view is probably much closer to the mark, since rockets have never been cheap. Nonetheless, it is a contextual decision to a certain extent, and I believe there to be room for discussion (especially in a PMF space boom/land rush, where, since space activities are apparently economically viable, something is cheaper to do in space than to make on the ground).

[Formless]

By the way, back on the subject of lighting, I've been doing some more research and found that there is the option of doing away with mirrors entirely and just relying on a window facing the sun. You've probably seen artwork of O'Neil cylinders that look like that, giving the interior a "light at the end of a tunnel" feeling. Without a diffusion cone or similar construct in the middle of the cylinder it may not make much sense, but you know how you fix it?

The famous Russian rocket scientist Konstantin Tsiolkovsky had this figured out back in 1933. Don't make the station a cylinder or a torus or a sphere at all. Make it a cone or teardrop shape. Then light will fall evenly on the whole floorspace of the station due to the station's geometry alone. His own sketches of the concept are crude, but instructive, while the second, more elaborate drawing came along sometime later, and became the go-to design among soviet artists referencing his idea. Tsiolkovsky's Greenhouse concept would later be forgotten as later Soviet artists started favoring torus designs and moon bases, and I think I've even seen Soviet art that just steals O'Neil's Island 3 design like Gundam did (the most sincere form of flattery, as they say).

Of course, a tapering object will have some similar issues to a sphere with regards to people walking the length of it. On one hand it will feel like walking uphill, but on the other as you do so the gravity will get progressively lower because you approach the center of rotation. The Coriolis effect will also become progressively more and more noticeable. The rear end of the station will also still see less light, and while people have called the later artists out for mistakenly showing the trees grow at the wrong angle, plants do in fact grow towards their source of light, which in this case is always the same direction. So its not totally wrong. The answer of course is to truncate the cone and place a domed mirror on the opposite end to redistribute light that would have hit the end of the station anyway. A cone will also have similar advantages to a cylinder, as you can adjust its length at the cost of changing the degree to which it tapers. But as shown in the soviet elaboration on the concept you can embed the cone within a cylinder or series of toroids to get some extra habitat space with no loss in G-forces for the inhabitants of the cylindrical part of the station. like the Island 3, stabilizing such a design should be as simple as pairing up two cones to counter rotate relative to one another.

Are a few holes and rips in your habitat solar mirror necessarily unacceptable?

The issue is that if the material is too thin like a solar sail, then it will in fact act like a solar sail. Radiation pressure and solar wind will want to take it away from the habitat as well as pulling on any rips that develop in it should the mirrors be attached to the station. Holes aren't a problem for a solar sail because sails aren't meant to be stationary, nor redirect light for the purpose of lighting a colony. They are meant to be a propulsion system, so normally the effect of punctures is measured in a reduction of thrust, which is apparently minimal. But this is a colony mirror we are talking about, so we have to think about it differently.

Something that lasts two years and costs ten bucks may well be considered better than something that lasts ten years and costs fifty bucks (the colony can pay for a mortgage/maintenance, it's the upfront costs the bean counters worry about).

I suspect that short-termist thinking will follow us into space, especially if SpaceExxon, SpaceFoxconn, and the SpaceMansonFamily follow SpaceX, SpaceMormons, and the SpaceLibertarians into space. Good enough is good enough. Also, industrial accidents are great for storytelling.

I doubt the analogy holds up once you account for the size of the mirrors we are talking about. Some damage is expected, but anything that could suddenly leave a colony without sunlight isn't just costing you repairs, but dead crops as well. Think about how much time it will take to replace a shattered or ripped mirror of the sizes we are speaking of. Catastrophic failures in this regard must be avoided. The best insurance is building things to last. Even the stupidest bean counter isn't going to allow a space colony to be built in the first place if it could just fall apart due to structural flaws. Real life isn't like Babylon 5. After Babylon 1 fell apart the engineers responsible would all be fired (possibly out an airlock) by whatever corporation or government hired them. The show should have been named "Babylon 2," but I guess the name wouldn't have caught on.

Thank you for educating me on urban dynamics in North America, with application to large chunks of the world. What you say about itinerant rich people does make some sense, since a lot of rich people anywhere have multiple homes. But like I said, I live in a weird city-state. Not much room for middle-class suburbs and mansions, and a lot of opportunity for middle-upper class rich people to pack themselves in next to a Trump Tower equivalent and live there full-time, with a 300-store luxury shopping mall, glitzy IMAX theater, public transport, and skating rink an elevator ride away (basically a glitzier version of my apartment complex, with marble flooring, wood paneling, and an overpriced, overdecorated supermarket). Both models may be useful in modelling pressures in space colonization. This sort of thing is why multiculturalism and different perspectives are good.

From the sounds of it... do you live in Hong Kong? Don't answer if you don't feel comfortable answering. Even if so, mind you that the very richest people even in that city are still itinerant. They can afford to leave Hong Kong entirely and have summer homes in Canada if they want. Or literally any other place where they can afford the housing. Seriously, there is a surprising trend for Chinese businessmen to own houses in Canada for some reason, although much of that is for the purpose of renting it out, but not in all cases.

Hong Kong is as packed as it is because geography makes it impossible to expand the city any further. This was not the case in North America, and it is not really the case in space either. Many space colony designs are made to be expandable, whether by adding more rings to a torus or adding additional modules to a beaded habitat. The only restriction is materials, not space, and possibly not even energy. Maybe rocket propellant. That's it. That's why I apply the North American model, because it predicts perfectly what happens any time there is still room to expand outward. Look at the urbanization of China right now and you see a pretty similar pattern. China has built dozens of cities the size of New York that no one has heard of because they are twenty years old or younger. Its insane how fast they've expanded their infrastructure to meet the demands of their population growth. But its not surprising either.

[Formless]

Oh, and here's another Soviet use of the Tsiolkovsky Greenhouse, this time with a spaceport going through the whole length of the cylinder, and the surface is apparently covered in what looks like reused fuel tanks (much like how some Nasa proposals reused fuel tanks to build ring stations). Slightly different form factor, same basic concept. Its a wonder that western sci-fi authors and space colony entheusiasts like Gerrard O'Neil never considered teardrop and conical shapes as the basis for a space station. You would think that as its a geometric primitive people would realize it, well, exists, but somehow it gets completely overlooked outside of Russia.

[chimericoncogene]

"Tsiolkovsky Cone Snip"

Interesting design, and certainly ahead of its time, but it has radiation shielding issues (unless you really fill that glass with a huge water tank, or flip the design (pointy end to sun or something) and use a mirror to send light in. Also people will probably need sunglasses for comfort at low sun angles. Another reminder that creativity can do wonders for habitat geometry.

The issue is that if the material is too thin like a solar sail, then it will in fact act like a solar sail. Radiation pressure and solar wind will want to take it away from the habitat as well as pulling on any rips that develop in it should the mirrors be attached to the station. Holes aren't a problem for a solar sail because sails aren't meant to be stationary, nor redirect light for the purpose of lighting a colony. They are meant to be a propulsion system, so normally the effect of punctures is measured in a reduction of thrust, which is apparently minimal. But this is a colony mirror we are talking about, so we have to think about it differently.

Thank you for pointing that failure mode out. The extension of rips and tears leading to catastrophic failure rather than graceful degradation is a doubly problematic issue for rotating mirrors (which may or may not be harder to repair). But IRRC, the classical heliogyro and solar sail had to transmit substantial force to payloads via rigid members or tethers, so these problems are not necessarily insurmountable (not that anyone has ever built a full-scale one to find out). But you're right - that is a huge problem and probably needs to be designed around with increased durability or modularity or something.

is as packed as it is because geography makes it impossible to expand the city any further. This was not the case in North America, and it is not really the case in space either. Many space colony designs are made to be expandable, whether by adding more rings to a torus or adding additional modules to a beaded habitat. The only restriction is materials, not space, and possibly not even energy. Maybe rocket propellant. That's it. That's why I apply the North American model, because it predicts perfectly what happens any time there is still room to expand outward But its not surprising either.

I agree completely - once the space economy matures and habitats get really cheap, the North American model will dominate. Capital, labor, and raw materials costs will all affect habitat construction, and there seems to be a lot of room for fluctuations in these costs, depending on the distance into the future (e.g. 2050 vs 2200), maturity of the interplanetary economy, technology (particularly the nearly-self-replicating kind), and location in the Solar System (e.g. L5, where all asteroids need to be shipped in or shot from the lunar catapult, vs an orbit around Psyche, vs. Pluto-Charon L1, with easy access to Nix and Hydra and the Pluto-Charon tether). If materials and capital costs dominate (especially in the early days around Earth Orbit), it may not be cost-effective to sprawl your space habitats, and you will get more compact habs. If you're already shipping self-replicating factories out to the Trojans at , then by all means go crazy with Island Threes filled with wildlife parks. Also, different people have different amounts of capital and labor. SpaceMormons might be able to afford an Island Three; SpaceMansonFamily gets a mostly prefabbed third-rate habitat.

[Formless]

Interesting design, and certainly ahead of its time, but it has radiation shielding issues (unless you really fill that glass with a huge water tank, or flip the design (pointy end to sun or something) and use a mirror to send light in. Also people will probably need sunglasses for comfort at low sun angles. Another reminder that creativity can do wonders for habitat geometry.

Filtering out x-rays isn't necessary since glass absorbs them anyway. Filtering UV is more essential, but something we already know how to make glass do as well. Shielding the colony window against charged particles emitted by the sun is a more pressing issue, but you know what material is really great at absorbing charged particles while saving on weight AND is transparent? Polyethylene. No, really. I mean, sure, water between glass works to, but I suspect it would make for a heavier window. Perhaps even heavier than lacing a mesh of wiring that elctrostatically repells charged particles, a form of active shielding. But if you want to get really fancy, this could be an ideal place to try out plasma shielding as a form of active shielding, since the plasma is unlikely to be opaque to sunlight. Really, the radiation you most worry about with a colony is cosmic rays, since they have the kinetic energy to punch through most forms of radiation shielding and create a secondary radiation hazard. However, I suspect this design has an advantage here in that its window is so small relative to the surface area of the entire colony, unlike the long strips of glass in an O'Neil cylinder. The rest of the cone can be made of thick concrete, and if you embed it within a cylinder, that only adds to the overall radiation shielding of the colony, effectively doubling it.

I also don't know why sunglasses would be necessary. It would just look like a constant sunrise, and we're filtering out the UV (or most of it). While I suppose its true that other colony designs discourage you from looking directly at the sun by orienting the sun "up" relative to the colonists, most people learn not to look directly at the sun as children. And also, colonies are unlikely to rely on automobiles for transportation, so the risk of drivers getting blinded by the sun is sidestepped. Its not hard to imagine consciously designing walkways and railways to spiral around the cone so you never have to look directly at the sun just getting around. It would also limit the feeling of walking up and downhill whenever you walk the length of the cone by making you go the long way.

But IRRC, the classical heliogyro and solar sail had to transmit substantial force to payloads via rigid members or tethers, so these problems are not necessarily insurmountable (not that anyone has ever built a full-scale one to find out). But you're right - that is a huge problem and probably needs to be designed around with increased durability or modularity or something.

Not really. The classic solar sail has a very small payload relative to the truly massive area of the sail. The thrust is real, but quite small, just like an ion engine. Of course all things orbiting the Sun will experience this pressure, but the simplest solution happens to be the counterintuitive one-- increase the mirror array's inertia. I know people often talk about mass payload being important to spacecraft, but when we start talking about colonies 30km+ in length, its not that problematic to make the mirrors a proper thickness like terrestrial mirrors. At that point the thrust from solar radiation moves it so little that its easily compensated for with the same maneuvering thrusters that you use to make stability adjustments.

[chimericoncogene]

I also don't know why sunglasses would be necessary. It would just look like a constant sunrise, and we're filtering out the UV (or most of it).

Eh, just my personal experience. I never need sunglasses in my tropical city because sunsets are dim and the hot afternoon sun is always near zenith. In my travels to Canada, I need sunglasses at mid-afternoon because the sun is near the horizon, or my eyes get uncomfortable. As usual, the place should be designed for the average person, not for the anecdotal me. Your experience may count for more.

when we start talking about colonies 30km+ in length, its not that problematic to make the mirrors a proper thickness like terrestrial mirrors. At that point the thrust from solar radiation moves it so little that its easily compensated for with the same maneuvering thrusters that you use to make stability adjustments.

I agree with your point. I was just thinking in terms of economics rather than mass savings. Commercial/kitchen-grade aluminium foil (10-20g/sqm or so?) may be cheaper than 1mm sheet aluminium, and still work well enough (my understanding from reading the old Space Studies Institute article on solar sails to drag asteroids is that kitchen foil is unfavorable solar sail material because it is too heavy per unit area for useful payloads). Solar sail ultralightweight material might be another grade of material. Obviously, this is all dependent on exact habitat design.

[chimericoncogene]

Filtering out x-rays isn't necessary since glass absorbs them anyway. Filtering UV is more essential, but something we already know how to make glass do as well. Shielding the colony window against charged particles emitted by the sun is a more pressing issue, but you know what material is really great at absorbing charged particles while saving on weight AND is transparent? Polyethylene. No, really. I mean, sure, water between glass works to, but I suspect it would make for a heavier window. Perhaps even heavier than lacing a mesh of wiring that elctrostatically repells charged particles, a form of active shielding. But if you want to get really fancy, this could be an ideal place to try out plasma shielding as a form of active shielding, since the plasma is unlikely to be opaque to sunlight. Really, the radiation you most worry about with a colony is cosmic rays, since they have the kinetic energy to punch through most forms of radiation shielding and create a secondary radiation hazard. However, I suspect this design has an advantage here in that its window is so small relative to the surface area of the entire colony, unlike the long strips of glass in an O'Neil cylinder. The rest of the cone can be made of thick concrete, and if you embed it within a cylinder, that only adds to the overall radiation shielding of the colony, effectively doubling it.

I've seen NASA studies for spacecraft magnetic shielding (big loops of superconductors) good enough to repel GCRs, and my understanding is that GCR doses in LEO below the magnetosphere are lower than cislunar GCR doses (the whole Apollo sparks-in-closed-eyeballs Fe ions thing).

Do electromagnetic shielding or mini-magnetospheres (if those work at all) mostly work against GCRs too? Or would those ultra-high-energy Fe particles still ruin everything and still leave tracks of cancer cells and dead neurons in our brain?

EM shielding has major attractions for both space and surface installations; if lightweight and cheap, you can actually build those big cool-looking glass/metal domes on the Moon. I don't think you could get ~ten tonnes of air per square meter under those like you could on an O'Neil cylinder - the biggest partially-pressure-supported dome I've seen was ~25km across and a few (5?) kilometers tall by structural strength limits. Not that those would be super-economical - rows and rows of dirt-covered arches seem cheap and scaleable - but those can be pretty cool.

Also useful for vehicles and personnel on the inner Jovian moons, especially if you can rig a mini-magnetosphere to cover a whole continent on Io (or the whole planet), or string up some superconductors over a temporary camp or research installation (before the lava and shifting surface gets you). I don't think the mini-mag would work near planetary surfaces, but I still wonder whether it could be used in some way (stick it on top of a ten-kilometer-tall rubber pole?). Has anyone had any ideas on outdoor work on the inner Jovian moons, other than teleoperation of rad-hardened robots while staying safely on Callisto like that HOPE study?

[Formless]

Eh, just my personal experience. I never need sunglasses in my tropical city because sunsets are dim and the hot afternoon sun is always near zenith. In my travels to Canada, I need sunglasses at mid-afternoon because the sun is near the horizon, or my eyes get uncomfortable. As usual, the place should be designed for the average person, not for the anecdotal me. Your experience may count for more.

Hmm, there seems like there are two things that could be going on here. One is a matter of the city itself. If there is significant smog, that would account for dimming and help make it easier on your eyes at sunrise or sunset. Again, I don't know where you live, so I can't confirm that this is the cause. The other possibility is altitude. I live in Colorado, a mile above sea level. One effect of this is that we get more UV light coming through because we're that much closer to space. Obviously, UV light is bad for your eyes, and the primary reason you shouldn't stare directly at the sun. Even WITH sunglasses on. That's why they sell special glasses just for looking at solar eclipses.

But there are other possibilities, of course. Personal tolerance, the degree to which the sun is obscured by terrain, etc.

I agree with your point. I was just thinking in terms of economics rather than mass savings.

Mass IS economics. Since mass is part of the rocket equation, transporting mass over a distance becomes a major economic factor to take into account. However, the largest habitats are so massive by default that that is why I say it isn't much of a factor overall compared to the mass of the rest of the structure. You almost certainly build these things around (or even inside, some would argue) large asteroids, comets, moons, and dwarf planets to have the easiest access to the necessary building materials, and limit the need to transport building materials around the solar system. But of course, that depends on what kinds of propulsion technologies have become avaliable when they get built.

Do electromagnetic shielding or mini-magnetospheres (if those work at all) mostly work against GCRs too? Or would those ultra-high-energy Fe particles still ruin everything and still leave tracks of cancer cells and dead neurons in our brain?

Strong electromagnetic fields (besides requiring very heavy superconducting loops to create) are potentially unhealthy to be around, because it turns out that both water and DNA have magnetic properties. A high enough tesla magnetic field can straighten out your DNA, which is a baaaad thing. NASA's studies on EM shielding mostly focus on either combining weaker magnetic fields with static shielding* or ring/toroidal spacecraft where you can safely wrap the field lines around the living area. That's why I mentioned electrostatic and plasma based alternatives, as they are both lighter and lack those health risks. The plasma based alternatives still require electromagnetic fields, but they are either farther away from the spacecraft, or weaker, so they aren't as much of a danger. Keeping an electrostatic or plasma based shield up does still consume non-trivial amounts of power, though.

* polyethylene, parrafin, water, liquid hydrogen, etc.-- all low density materials rich in hydrogen. It turns out you are unlikely to be hit by a GRC directly, but the secondary radiation from aluminum or iron atoms spalling off your own spacecraft hull is the real issue.

But we're getting off topic, and besides, you've inspired me to do so much more research on space colonization that I'm thinking of making a new resource thread on this and other space colonization issues. That's why I've been taking days to get back to you between posts. For now, I want to get back to the issue of lighting re: natural VS artificial lighting.

The real killer for artificial lighting, IMO, comes down to this. Lightbulbs don't last long before they need to be replaced. Certainly they don't last a human lifetime. This is especially true of those lighting technologies that offer the highest brightness, like metal halogen bulbs and Xenon arc bulbs (both of which come pretty close to having the same spectral properties as the sun-- right down to emitting high amounts of UV). Now, you can increase this lifetime by using induction bulbs and eliminate the electrodes in the bulbs (the electrodes erode away fast on arc lighting), but they still won't last forever. Even LED lighting, while it has a longer lifespan than many of the technologies that came before it and higher efficiency, has a limited lifetime, and has limited brightness besides. Its also a fairly heavy technology once you account for heat sinks (I could hurt someone by throwing an LED bulb at them. Not so much with an incandescent). Its also easy to focus too much attention on the lighting needs of the colonists while forgetting that their crops have different lighting needs. LED grow lights are a thing, but we're still experimenting with them, and you will notice that to make them work they can't be too far from the plants (about a meter away, but no closer than 30cm either). You even need UV, at least in a colony, because many species of birds and insects that pollinate these plants see in UV. Really, there is no clear and obvious winner when assessing the technologies available for grow lighting... except natural sunlight, of course, because that's what they evolved with. That's what all life on Earth evolved with, except that which lives in the deep sea and caves.

By the way, there are at least two more methods of getting sunlight into a colony that has not been discussed so far because one didn't exist in O'Neil's day (so he couldn't have known it would someday exist) and the other... I don't know, no one thought of using it? I guess? It could be the difficulty in installing it, because I'm talking about light tubes. Its not entirely clear how to integrate these into most of the traditional colony designs, but would definitely help bring light into colony designs that didn't put much thought into lighting, like the almost forgotten space city design by Darrell C. Romick that predates O'Neil's cylinders. But even more flexible (literally) are fiber optic cables, which enable us to gather light wherever its most convenient and bring them into even deeply buried asteroid stations like this mining town concept. We don't have to restrict our imagination to just those lighting schemes imagined by engineers back in the 70's (even if they still hold up as valid designs), technology has moved on and created this new option. I can definitely see the Stern cylinder design benefiting from using fiber optics or light tubes to vastly simplify the mirror system, for instance. Now instead of a secondary set of mirrors bouncing light into the rear cylinder, you just have the parabolic mirrors focus light onto the center of the cylinder where light tubes or fiber can then take sunlight and shine it directly through the two diffusing tubes running through the centers of the cylinders. I bet the kids who designed it didn't think of this only because fiber optic lighting is still rare, especially outside of Europe, apparently.

[chimericoncogene]

Hmm, there seems like there are two things that could be going on here.

Yeah, it might just be air pollution or urban canyons - but I've never had similar problems in the countryside, either. Tell me your experience if you ever go to the tropics. I still think the latitude effect is real.

https://space.nss.org/shackleton-dome-i ... -possible/
Found a secondary source for the 40-km, 2,000m lunar dome I was talking about. 16 billion tonnes of silica glass, two meters thick, apparently. That's how they did the radiation shielding - no need for fancy mini-magnetospheres or superconducting wire. I guess that you could build a much bigger dome with thinner material, but radiation shielding requirements would differ.

I've always been a fan of the covered-over lunar rille myself. Easy to expand, if you can get the endcaps to work. I've never been a huge fan of stations buried deep inside asteroids - at the present time, it seems that tunneling down is more expensive than building up (which is one of the reasons we don't have underground cities). But building up a kilometer-tall radiation-shielding structure on an asteroid probably comes with another set of problems.

But there are other possibilities, of course. Personal tolerance, the degree to which the sun is obscured by terrain, etc.

That's why I mentioned electrostatic and plasma based alternatives, as they are both lighter and lack those health risks. The plasma based alternatives still require electromagnetic fields, but they are either farther away from the spacecraft, or weaker, so they aren't as much of a danger. Keeping an electrostatic or plasma based shield up does still consume non-trivial amounts of power, though.

But we're getting off topic, and besides, you've inspired me to do so much more research on space colonization that I'm thinking of making a new resource thread on this and other space colonization issues. That's why I've been taking days to get back to you between posts. For now, I want to get back to the issue of lighting re: natural VS artificial lighting.

Thank you very much for your effort and patience. I'm glad you've found this discussion stimulating.

I know of mini-magnetosphere and plasma magnet based shielding; but I've never been totally convinced that they work. I love love love the concept, but lack an understanding of physics to evaluate it (I know Van Allen belts exist, but do they scale down as described?), and it sounds too good to be true.

You get efficient beam-powered propulsion, fast transits to the Outer Solar System at at least 20km/s (and no apparent limit for plasma magnets; if you can tap the propulsion beam for plasma and use multiple beams to lengthen the acceleration track!), and offload system complexity onto fixed installations... and you get radiation shielding within a kilometers-wide bubble at barely a few kilowatts of power?! What can't plasma magnets do? Also I think I read somewhere (Centauri Dreams I think) that M2P2 doesn't work as a propulsion system (shielding only), but plasma magnets do. So I was wondering about that a little. You know much more than I do, so I will defer to your opinion.

https://www.dartmouth.edu/~sshepherd/re ... report.pdf

Also, I'm not sure how those mini-magnetospheres will interact with planetary surfaces, dust, and atmospheres. My guess is that they probably wouldn't work on Mars, what with all the dust in the air and air currents, unless you lifted the whole apparatus high above the atmosphere. Because the plasma would get discharged fast and lose heat or something (high school physics and observation of the aurorae from starfish prime is all I have to go on here). Similar problems may exist on Io (but probably lesser ones).

Back on topic (sorry).

Well, you can always produce and replace light bulbs, and optimize different sections of the station for different tasks. You don't necessarily need to grow all your food in the main habitat section. It's a different set of headaches, and as you say probably a bigger set of headaches, but we'll just have to wait for the real thing in three to five hundred years.

[John Done]

As for me, it is impossible to build colonies on Mars or Moon. There are no resources on them and transferring them there is a waste of time. I'd say it is better to use those resources in order to save the earth and make it live as long as possible.

[Formless]

What are you talking about? There is plenty of raw material on the moon and Mars with which to build colonies. And if you have a problem with the gravity of Mars making it expensive to launch spacecraft from its surface to orbit, you just build the colony out of its moons, Demos and Phobos (and of course remember not to summon the armies of hell while you are at it ). And if you want to preserve those bodies for whatever reason, capture some friggen asteroids and hollow them out! If you need volatilizes, capture a passing comet. None of these are new ideas. You build in space with materials that are already in space. You build on planets with materials that are already on the planet. You DO NOT send materials from space back to Earth unless they are very rare elements because if you fuck up re-entry, your lander becomes a giant hole in the ground. Any Gundam fan will know the words "colony drop" and understand what I mean.

Plenty of smart people have looked at Mars and found all the elements we need to make a living there. Personally the only reason I favor space colonies over planetary colonies is the issue of low gravity and its effects on human health. But if you think resources are the problem you simply haven't done the research.

[TommyJ]

What are you talking about? There is plenty of raw material on the moon and Mars with which to build colonies. And if you have a problem with the gravity of Mars making it expensive to launch spacecraft from its surface to orbit, you just build the colony out of its moons, Demos and Phobos (and of course remember not to summon the armies of hell while you are at it ). And if you want to preserve those bodies for whatever reason, capture some friggen asteroids and hollow them out! If you need volatilizes, capture a passing comet. None of these are new ideas. You build in space with materials that are already in space. You build on planets with materials that are already on the planet. You DO NOT send materials from space back to Earth unless they are very rare elements because if you fuck up re-entry, your lander becomes a giant hole in the ground. Any Gundam fan will know the words "colony drop" and understand what I mean.

Plenty of smart people have looked at Mars and found all the elements we need to make a living there. Personally the only reason I favor space colonies over planetary colonies is the issue of low gravity and its effects on human health. But if you think resources are the problem you simply haven't done the research.

Hey! I found a like-minded person. Indeed, there is enough material on Mars. The only thing you need is the tools to work with them. But this is no longer as destructively expensive and difficult as delivering all the materials to a neighboring planet.
The speed of technology development will only grow now. I don’t think it will be any difficulty at all. When it becomes clear that the project can be profitable, it will give us an impetus into a new era. The era of space technology in the truest sense of the word. Not all the same to engage in the launch of more and more satellites into low orbit)