A lot of stuff not about Orion boosters, split from another thread.

[magnemoe]

On 3/26/2022 at 5:25 PM, JoeSchmuckatelli said:

Serious question: why, after scratching the surface of Orion do people retain the fascination with it? 

I looked at this after reading Niven and Pournelle's Footfall - and even in the book it's such a desperation move, and IRL clumsy and inefficient. 

This isn't a dig at @Spacescifi

   

It's that Orion is kind of a trope thing... And I don't understand the continued interest 

Further - it's likely to be part of KSP2... And one might hope that the way they present it is as a very early tech that gets quickly obsolete 

It the torch ship we could build today. Yes its obviously 2-3 order of magnitude harder than starship who in this contest is easy. 

Use SRB to get the booster out out the fireball and delay the first blast, no reason to launch it manned after all. 
Later ones are build at your orbital shipyard. No not the big one one at Jool , the LKO one.
And yes Musk:

This is an starship. Here is another 

You are simply building an fully easy reusable heavy lift orbital rocket who is the most awesome thing this decade unless some create an generic cancer vaccine or cold fusion. 
 

[kerbiloid]

The red-hot radiator panels next to the heat-proof (cryo?) spheres look good.

[magnemoe]

58 minutes ago, magnemoe said:

It the torch ship we could build today. Yes its obviously 2-3 order of magnitude harder than starship who in this contest is easy. 

Use SRB to get the booster out out the fireball and delay the first blast, no reason to launch it manned after all. 
Later ones are build at your orbital shipyard. No not the big one one at Jool , the LKO one.
And yes Musk:

This is an starship. Here is another 

You are simply building an fully easy reusable heavy lift orbital rocket who is the most awesome thing this decade unless some create an generic cancer vaccine or cold fusion. 
 

 

[Nuke]

18 hours ago, farmerben said:

It is a massive advantage to be massive with an Orion style drive.  I see it as something you can build out of asteroids and then use for interstellar colony missions.

The  crazy part of the idea are the giant springs.  The more massive we make the entire thing the less need for springs.  

I mean we just need to save up enough deuterium... then we can hollow out Vesta and go for a spin around the galaxy.   

thats always bugged me. you need a mechanical contraption to sit idle for hundreds of years before you use it, and if it doesn't work, you liquify your crew during a critical breaking burn. 

i always figured a practical way of asteroid deflection would be poor mans orion drive. rather than ablating the pusher plate as your main source of remass, you ablate the surface of an asteroid with a non-contact nuclear detonation. this would apply a uniform force to the surface of an asteroid and can in theory even work with rubble piles. this could be used to build an asteroid ship, though i think this would be inefficient.

i think a better way would be to construct an artificial asteroid entirely out of the materials you need for the colony to be used at a later date. you would have a core hab module (hab centrifuge, industrial area, the works). this would be surrounded by spherical insulated double hull pressure vessel. outside that you would have water ice storage, other ices (like ammonia or hydrocarbons) separated by bulkheads. within the ice can be storage containers for various useful metals and other materials, cold storage for biologicals like seeds and embryos. also this would be your warhead magazine and nuclear reactors. another pressure hull would surround this, followed by insulative material and then an armored outer hull layer. out side that would be remass material to be ablated by warheads. such a craft could be relatively large, support a healthy human population, and be self sufficient for some time in the target system in the event that any suspected biosphere be unviable. this maximizes colonization options, you could set up terrestrial colonies and/or use the ship as a permanent station in an astreroid belt or moon system. at the destination the bulk of the ship can be cannibalized to kickstart colonization. 

Edited April 1, 2022 by Nuke

[magnemoe]

28 minutes ago, Nuke said:

thats always bugged me. you need a mechanical contraption to sit idle for hundreds of years before you use it, and if it doesn't work, you liquify your crew during a critical breaking burn. 

i always figured a practical way of asteroid deflection would be poor mans orion drive. rather than ablating the pusher plate as your main source of remass, you ablate the surface of an asteroid with a non-contact nuclear detonation. this would apply a uniform force to the surface of an asteroid and can in theory even work with rubble piles. this could be used to build an asteroid ship, though i think this would be inefficient.

i think a better way would be to construct an artificial asteroid entirely out of the materials you need for the colony to be used at a later date. you would have a core hab module (hab centrifuge, industrial area, the works). this would be surrounded by spherical insulated double hull pressure vessel. outside that you would have water ice storage, other ices (like ammonia or hydrocarbons) separated by bulkheads. within the ice can be storage containers for various useful metals and other materials, cold storage for biologicals like seeds and embryos. also this would be your warhead magazine and nuclear reactors. another pressure hull would surround this, followed by insulative material and then an armored outer hull layer. out side that would be remass material to be ablated by warheads. such a craft could be relatively large, support a healthy human population, and be self sufficient for some time in the target system in the event that any suspected biosphere be unviable. this maximizes colonization options, you could set up terrestrial colonies and/or use the ship as a permanent station in an astreroid belt or moon system. at the destination the bulk of the ship can be cannibalized to kickstart colonization. 

For an astroid redirection you only use the orion charges as in the shape charged nuke on an probe, you will launch multiple of them, think MIRV but from an deep space capable rocket, space them out a bit so they don't run into fragments from the previous and you can measure changes in orbit. 
If its deflected you can just detonate the rest of the charges in deep space. 

For an reusable first stage, well they thought of using an Saturn 5 and also to capture the first stage, 18 m Starship would also be an good platform. 
However I say this is something you rather build in orbit and you assemble the charges in orbit. No you can not detonate an nuke by accident like crashing it, but its still an Chernobyl style dirty bomb if you get an magazine explosion during an failed launch. 

[farmerben]

41 minutes ago, Nuke said:

 

i think a better way would be to construct an artificial asteroid entirely out of the materials you need for the colony to be used at a later date. you would have a core hab module (hab centrifuge, industrial area, the works). this would be surrounded by spherical insulated double hull pressure vessel. outside that you would have water ice storage, other ices (like ammonia or hydrocarbons) separated by bulkheads. within the ice can be storage containers for various useful metals and other materials, cold storage for biologicals like seeds and embryos. also this would be your warhead magazine and nuclear reactors. another pressure hull would surround this, followed by insulative material and then an armored outer hull layer. out side that would be remass material to be ablated by warheads. such a craft could be relatively large, support a healthy human population, and be self sufficient for some time in the target system in the event that any suspected biosphere be unviable. this maximizes colonization options, you could set up terrestrial colonies and/or use the ship as a permanent station in an astreroid belt or moon system. at the destination the bulk of the ship can be cannibalized to kickstart colonization. 

We haven't had much success yet with self sustainable colonies even on Earth.  It would take a small world worth of supplies to colonize another star system.  

Vesta is 500 km in diameter of iron ore.  You could use quite large fusion explosions and still have impulsive forces less than the gravity of the body itself.  Ice and so on would stick to the outside by gravity.  And the pusher plate could be rigidly attached to the entire vessel.   For crew comfort ( not necessity) use sprung chairs or bunks for the crew.

[Nuke]

54 minutes ago, farmerben said:

We haven't had much success yet with self sustainable colonies even on Earth.  It would take a small world worth of supplies to colonize another star system.  

Vesta is 500 km in diameter of iron ore.  You could use quite large fusion explosions and still have impulsive forces less than the gravity of the body itself.  Ice and so on would stick to the outside by gravity.  And the pusher plate could be rigidly attached to the entire vessel.   For crew comfort ( not necessity) use sprung chairs or bunks for the crew.

well the idea is you get rid of the slag and keep the good stuff. rather than iron ore, the have steel hull panels that can be scrapped and recycled at the destination. steel is very easy to recycle, and you dont have to carry a bunch of dead mass (only a fraction of the ore is iron). having a lot of steel ice compartments and storage bays for consumables. when i say a manufactured asteroid, i mean something asteroid scale but made with refined materials.

life support experiments have had their share of failures. the whole biosphere 2 experiment i think was far too ambitious. it was a bad experiment because what it tried to do was far too broad. the whole thing was plagued by unforseen consequences, concrete eating up all the oxygen as it cured, bug infestations, and a low biodiversity ecosystem prone to various cascade failures. the goal for long term life support is not to maintain an engineered ecosystem but to keep the crew alive for an extended period of time. all you really need to do is scrub co2, provide oxygen, heat, water, food and recycle waste materials. the ultimate life support experiment is actually the iss, which has thus far been successful. we probibly need to get our consumable consumption rates down low enough before we do an interstellar colony mission, try to maximize our recycling and really start developing space agriculture technologies. 

 

[kerbiloid]

A small colony can't be self-sustainable.
It requires various resources and thus a lot of industrial equipment, but this equipment needs operators to operate.
Especially the agriculture and its chemindustrial part.

So, a self-sustained colony should either be an expensive pet project of a rich society (and not so many people need it), or be enough large to provide full technological chains.
On the Earth the civilisation started since 10k cities, when the division of labour got effective.
The self-sustained full-featured societies, afair, begin from 300..500 mln people.

The Earth is already colonized by such societies..

The Mars is the only place in the Solar system except the Earth, which can provide enough illuminated territory and heat sink to support tens or maybe hundreds of millions with food and industry.
And it's by order of magnitude less capable.

So, the best thing we can expect, is a conserved Martian backup Earth colony for 100 mln of potential survivors in case of a global cataclysm, and various bases totally depending on the cargo ships from the Earth.

[farmerben]

Living inside an O'Niell cylinder might be more pleasant than living on the surface of Mars.   Most O'Niell cylinders would attempt to create a stable, desirable ecosystem.  In our solar system they could resupply or reset the ecology in special cases.   Producing most of their own food is probably not their biggest problem.  

On an interstellar mothership mission we would want to bring the largest possible seed bank.  And hope to find worlds where any type of ecosystem can take hold.  In the timescales it takes to travel between the stars with lots of mass, evolution will take each fertile world in its own unforeseeable directions.  

 

[darthgently]

1 hour ago, kerbiloid said:

A small colony can't be self-sustainable.
It requires various resources and thus a lot of industrial equipment, but this equipment needs operators to operate.
Especially the agriculture and its chemindustrial part.

So, a self-sustained colony should either be an expensive pet project of a rich society (and not so many people need it), or be enough large to provide full technological chains.
On the Earth the civilisation started since 10k cities, when the division of labour got effective.
The self-sustained full-featured societies, afair, begin from 300..500 mln people.

The Earth is already colonized by such societies..

The Mars is the only place in the Solar system except the Earth, which can provide enough illuminated territory and heat sink to support tens or maybe hundreds of millions with food and industry.
And it's by order of magnitude less capable.

So, the best thing we can expect, is a conserved Martian backup Earth colony for 100 mln of potential survivors in case of a global cataclysm, and various bases totally depending on the cargo ships from the Earth.

Maybe.  Maybe not.  The jury is still out.  I don't think that the required population to be self-sustaining is necessarily a static quantity.  With advancing molecular techniques, other technological advance, and more and more labor automated (the term "division of labor" gets disrupted quite a bit here) a viable self-sufficient colony may be had with a much smaller population. 

A colony of 100 people with access to an egg/sperm bank of billions of individuals is not the same as an isolated population of 100 homo sapiens 10k years ago.  The more we understand how elements are cycled in an ecosystem, the more we can replace thousands of square miles of emergent ecosystem with much smaller, more condensed, ecosystems augmented with control processes at understood and pivotal points. 

If anything, such advances will likely make the supply/support from Earth (and later Mars) less frequent over time, with less payload, and less urgent.  O'Neil cylinders that are fairly self-sufficient are not ruled out yet.   It is a wait and see kind of thing because there are so many unknowns.

But it wasn't long ago that the Earth was supported by a stack of turtles, then later when we thought we were smarter, epicycles controlled the path of planets.  I would never bet against anything that depends on knowledge and technology for its outcome as we constantly underestimate the perennial growth of both of these

Edited April 1, 2022 by darthgently

[Nuke]

3 hours ago, kerbiloid said:

A small colony can't be self-sustainable.
It requires various resources and thus a lot of industrial equipment, but this equipment needs operators to operate.
Especially the agriculture and its chemindustrial part.

So, a self-sustained colony should either be an expensive pet project of a rich society (and not so many people need it), or be enough large to provide full technological chains.
On the Earth the civilisation started since 10k cities, when the division of labour got effective.
The self-sustained full-featured societies, afair, begin from 300..500 mln people.

The Earth is already colonized by such societies..

The Mars is the only place in the Solar system except the Earth, which can provide enough illuminated territory and heat sink to support tens or maybe hundreds of millions with food and industry.
And it's by order of magnitude less capable.

So, the best thing we can expect, is a conserved Martian backup Earth colony for 100 mln of potential survivors in case of a global cataclysm, and various bases totally depending on the cargo ships from the Earth.

more bigger is definitely the way to go.

[magnemoe]

10 hours ago, farmerben said:

We haven't had much success yet with self sustainable colonies even on Earth.  It would take a small world worth of supplies to colonize another star system.  

Vesta is 500 km in diameter of iron ore.  You could use quite large fusion explosions and still have impulsive forces less than the gravity of the body itself.  Ice and so on would stick to the outside by gravity.  And the pusher plate could be rigidly attached to the entire vessel.   For crew comfort ( not necessity) use sprung chairs or bunks for the crew.

As I know we had one serious try as I know, biosphere 2, it failed because concrete curing ate something and they gave up. 
Think they was a bit of an cult or something. on an moon or Mars base its no issue adding more co2 or o2 if needed. 
You fly in biff and chocolate but fresh salad an tomato are just as important. 

[magnemoe]

5 hours ago, kerbiloid said:

A small colony can't be self-sustainable.
It requires various resources and thus a lot of industrial equipment, but this equipment needs operators to operate.
Especially the agriculture and its chemindustrial part.

So, a self-sustained colony should either be an expensive pet project of a rich society (and not so many people need it), or be enough large to provide full technological chains.
On the Earth the civilisation started since 10k cities, when the division of labour got effective.
The self-sustained full-featured societies, afair, begin from 300..500 mln people.

The Earth is already colonized by such societies..

The Mars is the only place in the Solar system except the Earth, which can provide enough illuminated territory and heat sink to support tens or maybe hundreds of millions with food and industry.
And it's by order of magnitude less capable.

So, the best thing we can expect, is a conserved Martian backup Earth colony for 100 mln of potential survivors in case of a global cataclysm, and various bases totally depending on the cargo ships from the Earth.

We kind of evolved for earth, any stone age tribe was self sustaining. 
Mars or other places require an very high order of magnitude more technology like space suits and workshops to make space suits and workshops to make the tools for the previous ones. Same for solar panels.

Farming is easy and we have 10K year experience, the hard part is to have the technology you need to operate in space self-sustainable from earth. 
More so in that it does not make economical sense, lots of specialized parts it would be expensive to set up and maintain an production line for in case earth was cut off. 



 

[darthgently]

50 minutes ago, magnemoe said:

As I know we had one serious try as I know, biosphere 2, it failed because concrete curing ate something and they gave up. 
Think they was a bit of an cult or something. on an moon or Mars base its no issue adding more co2 or o2 if needed. 
You fly in biff and chocolate but fresh salad an tomato are just as important. 

One of the problems biosphere 2 had (among many) was that they couldn't keep the outside environment outside.  It made things far more complex.  The main problem it had was that it was mostly emoto-politically driven instead of scientifically driven.  The nail in the coffin was that we simply didn't (and still don't) know enough to make something like that work.  I think it will be easy someday.  As a last resort, we turn the problem over to a big neural net machine to solve and manage; I'd rather not go there though

[JoeSchmuckatelli]

11 minutes ago, darthgently said:

One of the problems biosphere 2 had (among many) was that they couldn't keep the outside environment outside.  It made things far more complex.  The main problem it had was that it was mostly emoto-politically driven instead of scientifically driven.  The nail in the coffin was that we simply didn't (and still don't) know enough to make something like that work.  I think it will be easy someday.  As a last resort, we turn the problem over to a big neural net machine to solve and manage; I'd rather not go there though

Yeah - rather than a 'let's make a self sustainable habitat' for designing towards future space exploration... It became a weird "what if we had a desert and a ocean and a rainforest biome inside the building and see what happens!" 

Total design by committee failure. 

[darthgently]

20 minutes ago, JoeSchmuckatelli said:

Yeah - rather than a 'let's make a self sustainable habitat' for designing towards future space exploration... It became a weird "what if we had a desert and a ocean and a rainforest biome inside the building and see what happens!" 

Total design by committee failure. 

A lot of the failure was that the occupants were not suited to the task.  They could have been put through the same screening that astronauts go through for example.  Not everyone is cut out to be confined like that and still be a good team member.  They were sneaking things into the hab, bickering a lot, making really unscientific decisions on how to "fix" things, fumbling chores that caused imbalances.  All this in a system that was based on some kind of eco-faith that simply having a lot of "nature" in a box would magically make things work out ok.  Nature can be a very harsh mistress, especially when caged and cornered

[kerbiloid]

7 hours ago, farmerben said:

Living inside an O'Niell cylinder might be more pleasant than living on the surface of Mars. 

Living on the surface of Mars in great amounts is impossible in any case, due to the low gravity, low magnetosphere, low insolation, and so on.
They will preven any healthy children development.

While the magnetic field and the insolation can be artificial in small amounts inside the habitats, the 0.4 g is a no-go even for long-term adult living, let alone the child growth.

The orbital habitat with artificial gravity is the only way to live in/on.

7 hours ago, farmerben said:

Most O'Niell cylinders would attempt to create a stable, desirable ecosystem. 

8 hours ago, farmerben said:

Producing most of their own food is probably not their biggest problem.  

It IS their biggest problem.

The O'Neill cylinder is a harmful, purely pseudoscientific fantasy, having nothing common with dull reality and elementary physics.
They should be blamed and degraded like a kind of perpetual motion machine.

Humans need food.
The food is O,C,N,H combined into molecules. This needs energy. The energy comes either from the Sun, or from an artificial energy source like a nuclear reactor.

The process of the food molecule appearing is highly ineffective in sense of energy, and this can't be changed for purely thermodynamic reasons,
because you can't change the total enthalpy and entropy of the chemical reactions turning CO₂, N₂, and H₂O into polysaccharides, fats, and proteins.
Using reactors instead of Sun also changes nothing in this sense. 

So, the energy conversion efficiency of the chain will stay same low as now, and the "entropical" waste heat will always prevail over the useful energy stored inside the food molecules in form of atomic bonds.
But even the food-stored energy gets released when a human digests the food, because it's the main purpose of the food.
Most of the digest-released energy dissipates as waste heat when an ATP molecule splits to ADP, then to AMP one.
Some small part  of energy gets stored as the human body molecular bonds, but gets released later, when the body tissue in some form decays.

So, all energy, coming from the energy source nto the food production, finally (and mostly immediately) gets turned into waste heat, requiring a heat sink.

The whole food chain and life support is a thin gasket between the heater and the cooler, as any other useful thermodynamic process.

Here, on the Earth, the cooler is the huge planetary body, and especially the large amount of cool water in the ocean.
So, the people remember only about the heater, which is usually the Sun.
But rarely they have to care about the cooler, because their amount and total power is too negligible to warm the oceanic cooler. Only last few decades they start thinking about this at all.

The waste heat washed from the human farms and habitats into the ocean, gets radiated into space as IR photons.
Because any kind of orbital habitat, including such large one as a planet, has to release the same amount of energy as it had gotten from the energy source, and the only way to do this in vacuum is radiation.

So, any orbital habitat needs as much energy income per human as it has on the Earth, and enough large radiator panels to radiate this total power into space.

If it works on the Sun energy, it needs as much solar income area as on the Earth, and the plants should be splattered all over this insolated area as a thin layer, because the light can't infiltrate deep.
Any light passing below the leaves (or algae) is not caught by them.
The Earth radius is 637 km, but the useful humus layer is just about a meter thick, and the biosphere if press it down is just several inches of organics more.
Becausse the sunlight can't go deeper, and the chemical reactions are thinly splattered over the plowland/greenhouse area.

On the Earth a humanrequires about 1 hectare (10 000 m²) to fulfil all his needs (food, clothes, basic medicines, etc) and 0.1 hectare to barely survive.
A Sun-powered orbital (or cloud balloon) habitat needs same.  Maybe even several times less if produce fertilizers and optimize the plant structure, but this doesn't change the game.

This means than either the orbital habitat should be a enormously huge thin plate(thus forget about rotation, but face the problem of coolant pumping through the enormously long pipes),
or it should be a compact cylinder (like the O'Neill's one) of ridiculous cross-section area. And the  large is the cylinder, the lower is the insolated/living area ratio.

As you can easily calculate, the classic ~10 km sized O'Neill cylinder has the insolated area to support just several tens (optimistically - hundreds) thousands of people.
This certainly looks absolutely silly to seriously plan.

 

They may decide to use fusion reactors instead of the sun light, and increase the insolated area by using pipes with algae around light bulbs.
This indeed a soltion to the problem of the insolated plowland area, and can pack many millions of people inside the cylinder.

But this still needs a heat sink, and the amount of energy to be sunk stays same.

When you use the sun-powered food chain, the productive layer is so thin that the light receiver itself (plowland+water pool) is enough large to be a radiator panel.

In the reactor-powered habitat they need to have radiator panels of similar total area like they need for the plowland.
So, the problem stays same, just instead of enormous flat solar receivers they still need enormous flat radiator panels of comparable total area.

This in turn again forces to limit the total power of the internal power source with same tens-thousands of people per cylinder.

So, the only way to colonize anything beyond the Earth is to separate the habitat and the food production completely.
The habitat can be only orbital, rotating at 1 g.

The food production doesn't require anything of that if use algae.
The algae are always in zero-g due to timy size and hydrostatic balance, they hardly need magnetic fields for same reason, they can use a pool of any shape to grow, either a thin layer of glass pipes under sun, or the same glass pipes around a light bulb.

But the waste heat still needs to be utilized. So, orbital greenhouses for millions of people should face the sane problems of cooling and coolant pumping like in O'Neill case.
All you gain is absence of rotation, so your orbiatl plowland won't be torn aparn by centrifugal force.

So, the only thermodynamically reasonable way of the agricultural mass production is a thin layer of sunlighted greenhouses covering a planetary surface.
In this case they are cooled same way like on the Earth, by the panetary body to redistribute the heat, and the planet surface are to receive enough power from Sun and the radiate it then as waste heat.

You can locally enforce this by adding reactors, but their total power shouldn't be comparable to the solar income,  as in such case they will overheat the system over the plants critical temperature and kill the agriculture at all.

***

Thus, the only viable way to colonize some place in the universe is to have a massive planetary body inside the habitation zone of the star, cover it with thin layer of algae-pipe greenhouses, and make this the source of food for you colony.
The colony itself should be only orbital, in rotating habitats (though not the huge cylinders, which is a loss of volume, but bunches of smaller cylnders attached to a zero-g central module).

The population of the orbital colony is limited by the food production of the planetary surface, and as unlikely it can be comparable to the Earth one, the colony capacity can be only much lower than the Earth population.

In the Solar System the only colonizable place is Mars.
The Moon is too small and too close to the Earth to bother.
The Ceres is too small, receives much less solar energy than even Mars.

The Venus could be potentially turned into a greenhouse, if remove the atmosphere and let the light pass to the ground, but it doesn't rotate, so the  on-ground greenhouses would face monstrous problems with cooling in the eternal midday, as they had to pump hot water to another part of the planet.
Cloud balloon greenhouses are also not a variant, because they require same total are, and  thusabsolutely enormous size of balloons making them fully unstable mechanically, in the windy upper atmosphere.
So, in any case the whole Venus could produce much less food than it may seem based on its size and gravity.
Actually, a totally useless place in sense of colonization. Maybe some minerals can be mined, but also unlikely due to lack of long-term liquid water in its visible history.

***

So, the Mars is the only place to be colonized, but its maximum food productivity is many times lower than the Earth have, due to much smaller size and twice lower insolation.
It can support a hundred million or several times more, but this is not what makes it reasonable for demographic migration at all.

Thus there is no reason to keep hundreds of millions there,

It can be just a backup multimillion-capable colony, populated by small amount of scientific and industrial personnel.

***

The interstellar colonization is absolutely the same.

For the reasons above they can widely colonize only a water-rich planet in habitation zone, with small amount of people in orbital habitats.

It makes sense to colonize only a star system of not less than ~0.5 bln capability, otherwise they can't be self-sustauned. Seed or not, doesn't play a role.

[Nuke]

i always figured an under ground centrifuge on low grav worlds would be optimal for a colony. all you need is a tbm and several kilometers of maglev track (or even conventional rail would do). the colony would exist on a bunch of train cars, more or less, though somewhat bigger. the track would be angled such that the centrifugal force adds to the gravitational force to a magnitude of 1g. perhaps the hab modules would be on trunions. its probibly better to pressurize the tube than the cars themselves, though the cars could provide secondary atmospheric containment in an emergency. a smaller spindown rail could be used to enter/exit the hab, as some people will need to venture into the tubes for maintenance and can provide emergency gravity in the case you need to spin down the main ring. aside from the investment in casement for the tunnel and the track itself, the hab cars need not all be installed immediately with the installation, you can add cars as your population grows until the full ring is used. beyond that build another ring concentric to the first one, with the spindown rail acting as an interchange between the rings. being underground provides ample radiation protection. this would probibly be of better use just outside the habitable zone so you can groundsink the surplus heat. you would still be fairly dependant on some external nuclear power of some sort. insulating the tunnels would be critical i think as the warming from the interior environment could cause them to shift. the trans alaska pipeline has a problem with the hot oil melting the permafrost and you need a combination of ground sinking the surplus heat over a wider area and flexible pylons that can handle expansion. you would have something similar especially if you set up shop on an ice moon. 

[kerbiloid]

1 hour ago, Nuke said:

an under ground centrifuge on low grav worlds would be optimal for a colony. all you need is a tbm and several kilometers of maglev track

The problem is capacity and ability to withstand a power loss.

The rotating orbital habitats are more sustainable in both senses.

Edited April 2, 2022 by kerbiloid

[JoeSchmuckatelli]

5 hours ago, kerbiloid said:

For the reasons above they can widely colonize only a water-rich planet in habitation zone, with small amount of people in orbital habitats

Well, except if the planet found proves panspermia and we discovered that we can eat virtually all of the animals and many of the plants, and have the ability to defend ourselves from being eaten by most of the animals and many of the plants (along with the fungi, microbes and viruses, etc.) 

We could very easily overpopulate that place, poison its air and oceans and then need to start looking for a 3d goldilocks planet 

[kerbiloid]

58 minutes ago, JoeSchmuckatelli said:

Well, except if the planet found proves panspermia and we discovered that we can eat virtually all of the animals and many of the plants, and have the ability to defend ourselves from being eaten by most of the animals and many of the plants (along with the fungi, microbes and viruses, etc.) 

The natural biosphere is totally based on the sunlight, so it's just a less productive version of the planet fully covered with algae greenhouses.

[farmerben]

 

It seems like the reflectors offer plenty of adjustability to control temperature throughout the habitable zone and maybe beyond.   People who live there will want a variety of plants.   For strictly industrial use (algae farms), etc simpler structures will work.  

This approach is very efficient at creating habitable space with a minimum of mass.   On planets, most of the material gives you nothing but gravity.   On Earth land is already quite expensive.  

 

 

 

 

 

 

[kerbiloid]

1 hour ago, farmerben said:

It seems like the reflectors offer plenty of adjustability to control temperature throughout the habitable zone and maybe beyond. 

Calculate their area and put on google maps.

 

Upd.

https://www.statista.com/statistics/196106/average-size-of-farms-in-the-us-since-2000/

Average US farm = 428 acre = 1.7 km².

Average O'Neill cylinder: d = 8 km, L = 32 km.

S_side = pi * 8 * 32 = 804 km².

Swindows = 804 / 2 = 402 km².

236 average US farms, if the surface totally consists of plowland.

https://www.nass.usda.gov/Publications/Todays_Reports/reports/fnlo0220.pdf

2 million farms in US.

O'Neill cylinders per USA needed = 2 000 000 / 236 ~= 8 500

Number of US humans per O'Neill cylinder = 330 mln / 8 500 ~= 39 000.

I.e. O'Neill cylinder can provide with food ~40 kiloamericans.

Or, if count the exported food, ~ 100 kAm.

(Exactly like I had calculated before).

Edited April 5, 2022 by kerbiloid

[darthgently]

On 4/1/2022 at 9:56 PM, magnemoe said:

any stone age tribe was self sustaining

Not really, without intermarriage with other neighboring clans and tribes they'd reach a genetic dead-end relatively quickly unless the population was fairly large.  Even stone age tribes needed to intermarry, even if it was with Neanderthals it was better than death by inbreeding.  People like to consider "nation states" as some kind of artificial thing, but really it is likely just a manifestation of small clans and tribes allying for the genetic and economic betterment of all.  And yet the idea of just having one, big, global "nation" is not ideal as then one disease or one bad administration's policies can wipe out the whole thing.  Big enough to not have genetic bottlenecks and to enjoy the economic efficiencies, with some boundaries between parallel "nation experiments" to prevent monoculture and decelerate wipeout events caused by disease or bad policies is the sweet spot.  Sometimes the world is working the best it can and maybe we just don't understand it.  If stone age tribes were self-sustaining nations would not have formed

[magnemoe]

30 minutes ago, darthgently said:

Not really, without intermarriage with other neighboring clans and tribes they'd reach a genetic dead-end relatively quickly unless the population was fairly large.  Even stone age tribes needed to intermarry, even if it was with Neanderthals it was better than death by inbreeding.  People like to consider "nation states" as some kind of artificial thing, but really it is likely just a manifestation of small clans and tribes allying for the genetic and economic betterment of all.  And yet the idea of just having one, big, global "nation" is not ideal as then one disease or one bad administration's policies can wipe out the whole thing.  Big enough to not have genetic bottlenecks and to enjoy the economic efficiencies, with some boundaries between parallel "nation experiments" to prevent monoculture and decelerate wipeout events caused by disease or bad policies is the sweet spot.  Sometimes the world is working the best it can and maybe we just don't understand it.  If stone age tribes were self-sustaining nations would not have formed

Who is correct, and yes I  implied as an extended families living together most of the time, as seen with hunter gatherers in modern times. Not an culture like say the Cheyenne or Apache. But its just that you need multiple tribes for long term survival. 
http://freefall.purrsia.com/ff800/fv00718.htm

Now in space you need an very high order of magnitude more. Probably doable in some hundred years if pressure for it and an optimistic expansion into space.