Author Topic: Worldships  (Read 5188 times)

Offline lamontagne

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Re: Worldships
« Reply #20 on: 02/13/2017 05:12 PM »
A Worldship is going to be a lot more leaky than Earth, so new resources are probably required much faster.

Indeed. Every few hundreds of years, it will need to stop in a suitable Oort Cloud :D

why stop "in" the Oort Cloud
with thousands of years between stops
the technology they start with will not
necessarily be the ones they have even
with the first stop...

Cities in Flight, by James Blish might be a good primer to read...
I really liked Cities in Flight :-), probably some influence there :-)
Indeed.  the very concept of worldships requires that a number of technologies not happen:  no FTL, no inertialess propulsion, no uploading, no singularity, probably no hibernation (although it was neatly woven into the narrative of Aurora, by Kim Stanley Robinson).  BTW Aurora was too small.

Offline sghill

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Re: Worldships
« Reply #21 on: 02/13/2017 05:24 PM »
In light of this discussion, I thought I'd post the 1970's space art library from Ames Research Center.

Many of us grew up (sort of) dreaming about these stations....

Too many paintings (in poster quality resolution) to poster here, so just follow the link.

https://settlement.arc.nasa.gov/70sArtHiRes/70sArt/art.html

Bring the thunder Elon!

Offline lamontagne

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Re: Worldships
« Reply #22 on: 02/13/2017 09:38 PM »
In light of this discussion, I thought I'd post the 1970's space art library from Ames Research Center.

Many of us grew up (sort of) dreaming about these stations....

Too many paintings (in poster quality resolution) to poster here, so just follow the link.

https://settlement.arc.nasa.gov/70sArtHiRes/70sArt/art.html

These are great.  I also loved a national geographic article by Isaac Asimov, July 1976, the next frontier.  Paintings by Pierre Mion, about Oneil colonies.

https://www.flickr.com/photos/42665617@N07/sets/72157626987734175/

« Last Edit: 02/13/2017 09:41 PM by lamontagne »

Online Coastal Ron

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Re: Worldships
« Reply #23 on: 02/13/2017 09:51 PM »
[Perhaps the journey is the reward?  ::)

That's OK to say once the Worldship is built, but I can't see that as the primary reason for why someone or some group would provide the funding to build such an vessel (or the fleet of 4 for that matter).

Elon Musk's goal is to make humanity multi-planetary, and starting that by setting up a human colony on Mars.  That is a very specific goal, and Mars is a pretty well known commodity (i.e. better than any other known planet, though not anywhere as comfy as Earth).  So potential investors have, I think, enough information to make a decision on what to spend their money - and they may see their money going towards the potential survival of their progeny.

I'm just trying to imagine what the pitch would be to investors for a Worldship, and how many potential investors would be likely to buy into the vision.

Quote
But seriously, my thinking, ever since coming up with the spiral space station concept (video below), is that any kind of interstellar Worldship will never be "complete".  They will set off on their journey with whatever minimum viable population/agriculture is, and by harvesting materials along the way, the ship size would grow as the colony does.

The spiral space station design is interesting, but I'm not sure the structure is robust enough to scale up for human use.  The design seems to be limited by the strength of any one link, and when you scale that up it becomes problematic.  Just my $0.02, but I'm not a structural engineer.

As to a Worldship never being complete, that gets back to what the purpose of the vessel is, and what the inhabitants want it to be.  And depending on the design, they may not have the manufacturing capability to expand their vessels, or the design may not scale.  10,000 person communities on Earth don't have a lot of manufacturing capabilities that are independent of the global ecosystem.

Quote
I actually tend to think that any Worldship that was truly successful might reach the "destination" star and have cause to wonder what was so great about planetary surfaces, anyway?  Go down a deep gravity well, only to deal with all this uncontrolled weather and seismic activity.  Why would you bother?  ::)

That could happen.  But there needs to be a vision that investors buy into in order for the Worldship fleet to be built and launched in the first place, which could influence what their choices are.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline lamontagne

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Re: Worldships
« Reply #24 on: 02/13/2017 10:02 PM »
[Perhaps the journey is the reward?  ::)

That's OK to say once the Worldship is built, but I can't see that as the primary reason for why someone or some group would provide the funding to build such an vessel (or the fleet of 4 for that matter).

Elon Musk's goal is to make humanity multi-planetary, and starting that by setting up a human colony on Mars.  That is a very specific goal, and Mars is a pretty well known commodity (i.e. better than any other known planet, though not anywhere as comfy as Earth).  So potential investors have, I think, enough information to make a decision on what to spend their money - and they may see their money going towards the potential survival of their progeny.

I'm just trying to imagine what the pitch would be to investors for a Worldship, and how many potential investors would be likely to buy into the vision.

Quote
But seriously, my thinking, ever since coming up with the spiral space station concept (video below), is that any kind of interstellar Worldship will never be "complete".  They will set off on their journey with whatever minimum viable population/agriculture is, and by harvesting materials along the way, the ship size would grow as the colony does.

The spiral space station design is interesting, but I'm not sure the structure is robust enough to scale up for human use.  The design seems to be limited by the strength of any one link, and when you scale that up it becomes problematic.  Just my $0.02, but I'm not a structural engineer.

As to a Worldship never being complete, that gets back to what the purpose of the vessel is, and what the inhabitants want it to be.  And depending on the design, they may not have the manufacturing capability to expand their vessels, or the design may not scale.  10,000 person communities on Earth don't have a lot of manufacturing capabilities that are independent of the global ecosystem.

Quote
I actually tend to think that any Worldship that was truly successful might reach the "destination" star and have cause to wonder what was so great about planetary surfaces, anyway?  Go down a deep gravity well, only to deal with all this uncontrolled weather and seismic activity.  Why would you bother?  ::)

That could happen.  But there needs to be a vision that investors buy into in order for the Worldship fleet to be built and launched in the first place, which could influence what their choices are.

The question of motive is fundamental and not very clear.  Rather like space colonization in general.
My idea on this is that these would be preceded by space colonies, and build by societies used to live in space colonies.  If the asteroid belt ever gets a little crowded, then colonies might invest into moving to the Oort cloud, and from there it's not that much of a stretch to moving first to rogue planets and finally to other stars.

The drive needs to be fairly cheap to operate.  That is why I like deuterium, that is simple to mine, and carries its own energy, as opposed to anti matter that requires a humongous production facilities.






Offline spacenut

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Re: Worldships
« Reply #25 on: 02/13/2017 10:06 PM »
I could see O'Neal colonies around our solar system.  They would use the moon, Mars, moons of Jupiter and Saturn for resources, as well as the asteroid belt.  The O'Neal colonies would need resources to build new colonies, make replacement parts, etc.  That way, people could avoid the gravity wells and atmospheres to overcome landing and launching.  The only landing and launching could be raw materials and mining equipment.  Moons and asteroids without atmospheres might be better for raw material accessibility.  An O'Neal colony could be accessed in space, zero g, in their center sections on the ends. 

Offline mikelepage

Re: Worldships
« Reply #26 on: 02/14/2017 04:48 AM »
Would recommend this documentary on Thorium and molten salt reactors to anyone here who hasn't seen it.  I came across it a couple weeks ago - I didn't intend to watch the whole thing, but it drew me in :)  It's very well presented, and makes the case for Thorium nuclear in space.  The levels of Thorium on the moon and Mars do make me think this is a viable solution for having energy when we go beyond the range where solar power is useful.

Suffice to say, any kind of worldship is going to need serious power, and Thorium MSR is a concept that already has proof-of-principle demonstration.

https://www.youtube.com/watch?v=0BybPPIMuQQ&feature=youtu.be

Perhaps the journey is the reward?  ::)

That's OK to say once the Worldship is built, but I can't see that as the primary reason for why someone or some group would provide the funding to build such an vessel (or the fleet of 4 for that matter).

Elon Musk's goal is to make humanity multi-planetary, and starting that by setting up a human colony on Mars.  That is a very specific goal, and Mars is a pretty well known commodity (i.e. better than any other known planet, though not anywhere as comfy as Earth).  So potential investors have, I think, enough information to make a decision on what to spend their money - and they may see their money going towards the potential survival of their progeny.

I'm just trying to imagine what the pitch would be to investors for a Worldship, and how many potential investors would be likely to buy into the vision.
(snip)
The question of motive is fundamental and not very clear.  Rather like space colonization in general.
My idea on this is that these would be preceded by space colonies, and build by societies used to live in space colonies.  If the asteroid belt ever gets a little crowded, then colonies might invest into moving to the Oort cloud, and from there it's not that much of a stretch to moving first to rogue planets and finally to other stars.

Because we can.

I don't mean to be trite with that.  If you think about what a species has to go through to get to the stage where they have so much excess energy to play with that they can even contemplate trying to escape the gravity well of their home planet, much less do it enough times to transport up the extra mass required for that initial beachhead required to live in space, you start to realise how exceptional "because we can" is, as a statement.

Life has been on the planet for ~4 billion years, with photosynthetic cyanobacteria for most of that.  These became the source of our fossil fuel industry of today, for which we have arguably used as much as half of them, or will have soon, in the last 250 years or so, and will probably continue using them at our current rates for some time to come.  The sun will expand through Earth's orbit in only another 4 billion years or so.

Which means that in the entire history of Planet Earth (past and future), we humans, in this ~200 year window, are probably the only species on the planet that will ever be able to say "we can".

My personal opinion is that settling Mars isn't actually enough.  Even supposing we set up a full million-person colony on Mars, if the ships that move us through space fail to become self-sufficient in their own right, any catastrophe that destroyed, say, the ability to launch/manufacture such ships, would just leave Earth and Mars, trying to survive independently.  Sure, two is better than one, but for long term survival, you'd still have to put your money on Earth.  It's only if the ships which go between worlds become fully independent and self-sufficient colonies in their own right: true "worldships" that we hedge against planetary catastrophes. 

If those ships go interstellar, that becomes a hedge against solar system-level catastrophes, which we know will happen in 4 billion years, but could also happen at any time in the form of nearby gamma ray bursts, supernovae, etc, or even something as mundane as an influenza pandemic.

Offline Katana

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Re: Worldships
« Reply #27 on: 02/14/2017 05:29 AM »
A colony on a small asteroid with low gravity could be fully lifted to space as a worldship.
If colonization of Mars could happen, colonization of asteroids is straightforward.
Pressurized and shielded hab on Mars is already virtually pressurized and shielded hab in vacuum.

That's OK to say once the Worldship is built, but I can't see that as the primary reason for why someone or some group would provide the funding to build such an vessel (or the fleet of 4 for that matter).

Elon Musk's goal is to make humanity multi-planetary, and starting that by setting up a human colony on Mars.  That is a very specific goal, and Mars is a pretty well known commodity (i.e. better than any other known planet, though not anywhere as comfy as Earth).  So potential investors have, I think, enough information to make a decision on what to spend their money - and they may see their money going towards the potential survival of their progeny.

I'm just trying to imagine what the pitch would be to investors for a Worldship, and how many potential investors would be likely to buy into the vision.

Offline Nascent Ascent

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Re: Worldships
« Reply #28 on: 02/14/2017 05:44 AM »
Back in the early 1960s there was a book entitled Beyond Tomorrow.  About the future of spaceflight through the lens of those optimistic days.  A relative of mine, Roy Scarfo did the artwork and I remember his depiction of a hollowed out asteroid way back then. I believe well before Rama.  You can see many of the illustrations here..

http://www.royscarfo.com/

http://www.allentium.com/playground/royscarfo_site/index.cfm?section=visions&fuse=prints

http://www.allentium.com/playground/royscarfo_site/main.cfm?section=visions&fuse=prints&id=33

http://www.allentium.com/playground/royscarfo_site/main.cfm?section=visions&fuse=prints&id=34
« Last Edit: 02/14/2017 05:45 AM by Nascent Ascent »
“Why should we send people into space when we have kids in the U.S. that can’t read”. - Barack Obama

Offline Rei

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Re: Worldships
« Reply #29 on: 02/14/2017 01:41 PM »
I don't see worldships travelling at semi relativistic speeds. 1 or 2% of light speed is fully enough to go 10 or 20 light years.

That is what I would call "semi-relativistic speeds".

Quote
I also don't see a need for replenishing on the way.

My whole point is that closed ecosystems are not anywhere nearly as simple as presented on that graph.  They tend to inherently go out of balance unless you're talking something the size of a planet that has a lot of inertia going for it.  Meanwhile, every system has consumables / needs maintenance over time. 

Think of it like battery chemistry.  You have a given set of reactions on charging and discharging.  On charge, certain compounds change into others, and on discharge they change back.  Why doesn't any battery chemistry last forever?  Because of side reactions. No process proceeds perfectly.  Eventually everything ends up locked up somewhere where it's not participating in the desired reactions, and you're out of luck.

I already mentioned Biosphere 2 as a concrete example, and recommend reading about it.  Or for a more mechanized example, look at hydroponics recycling.  In a basic hydroponics system, you add in every mineral your plants need at appropriate levels and monitor electrical conductivity, to see how much of the minerals plants have taken out of solution.  You then add minerals back until EC is restored to the original levels.  Good, right?  Nope.  The pH will swing badly and eventually kill your plants.  Okay, so  you monitor pH too and add in various nutritive acids and bases as well as EC monitoring, and now you're good, right?  Nope.  After a while the various anion and cations go all out of balance, and ultimately kill your plants. Attempts to close the loop have gone so far as to burn all plant matter at high temperatures, creating a mix of oxides and hydroxides with all of the cations, then dissolving them in manufactured acids to restore the anions (mainly nitric, since nitrates are the most in demand).  Guess what?  That doesn't work either.  The only way to keep the solution in balance is to do ion-by-ion analysis, such as with mass spec, and add them ion-by-ion (such as taking your incineration outputs and running them through fractional crystallization).

Soil doesn't stay in balance.  Air doesn't stay in balance.  Pollinators don't stay in balance.  Nothing stays in balance unless you make it.  The Earth only stays in balance because it's so utterly massive that it takes a long time for things to change in a relevant manner, during which time species can adapt, and because species have adapted to the Earth over the course of billions of years.  None of this applies to a small isolated biosphere.  Ultimately, whatever aspect you're talking about, something vital ends up getting broken down or locked up somewhere inaccessible over time.  Even the structure of the ship can do this - in Biosphere 2, for example, the carbon dioxide ended up becoming locked up in the concrete of the greenhouse.

In space you have to be able to make everything.  Which means incredibly long dependency chains. It's not a trivial task. That doesn't mean it's not a task worth working on - it absolutely is.  Not does it mean that it's unachievable - it absolutely is. But graphs that credit things to generic terms like "industry" bring nothing to the table.  The concept isn't even new; it's called a generation ship and it's been around for ages; Goddard proposed it in 1918. 

I'm just trying to figure out what is being proposed that's new here.

Offline guckyfan

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Re: Worldships
« Reply #30 on: 02/14/2017 04:32 PM »
Soil doesn't stay in balance.  Air doesn't stay in balance.  Pollinators don't stay in balance.  Nothing stays in balance unless you make it.  The Earth only stays in balance because it's so utterly massive that it takes a long time for things to change in a relevant manner, during which time species can adapt, and because species have adapted to the Earth over the course of billions of years.  None of this applies to a small isolated biosphere.

That's why it is a good idea to start on Mars and not start with a O'Neill space habitat. A nearly closed circle ecology is needed but some losses are permissible because there are still resources around. After a few hundred years the knowledge will be gained to make a nearly closed circle ecology with minimal losses that enables O'Neill habitats. Add another few hundred years of experience and improved propulsion a worldship can be sustained for a few hundred years until it reaches another sun to replenish its resources.

Offline envy887

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Re: Worldships
« Reply #31 on: 02/14/2017 05:09 PM »
I don't see worldships travelling at semi relativistic speeds. 1 or 2% of light speed is fully enough to go 10 or 20 light years.

That is what I would call "semi-relativistic speeds".

You can for all practical purposes ignore relativity at those speeds. There's no noticeable length contraction or time dilation.

Offline lamontagne

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Re: Worldships
« Reply #32 on: 02/15/2017 01:52 AM »
I don't see worldships travelling at semi relativistic speeds. 1 or 2% of light speed is fully enough to go 10 or 20 light years.

That is what I would call "semi-relativistic speeds".

Quote
I also don't see a need for replenishing on the way.

My whole point is that closed ecosystems are not anywhere nearly as simple as presented on that graph.  They tend to inherently go out of balance unless you're talking something the size of a planet that has a lot of inertia going for it.  Meanwhile, every system has consumables / needs maintenance over time. 

Think of it like battery chemistry.  You have a given set of reactions on charging and discharging.  On charge, certain compounds change into others, and on discharge they change back.  Why doesn't any battery chemistry last forever?  Because of side reactions. No process proceeds perfectly.  Eventually everything ends up locked up somewhere where it's not participating in the desired reactions, and you're out of luck.

I already mentioned Biosphere 2 as a concrete example, and recommend reading about it.  Or for a more mechanized example, look at hydroponics recycling.  In a basic hydroponics system, you add in every mineral your plants need at appropriate levels and monitor electrical conductivity, to see how much of the minerals plants have taken out of solution.  You then add minerals back until EC is restored to the original levels.  Good, right?  Nope.  The pH will swing badly and eventually kill your plants.  Okay, so  you monitor pH too and add in various nutritive acids and bases as well as EC monitoring, and now you're good, right?  Nope.  After a while the various anion and cations go all out of balance, and ultimately kill your plants. Attempts to close the loop have gone so far as to burn all plant matter at high temperatures, creating a mix of oxides and hydroxides with all of the cations, then dissolving them in manufactured acids to restore the anions (mainly nitric, since nitrates are the most in demand).  Guess what?  That doesn't work either.  The only way to keep the solution in balance is to do ion-by-ion analysis, such as with mass spec, and add them ion-by-ion (such as taking your incineration outputs and running them through fractional crystallization).

Soil doesn't stay in balance.  Air doesn't stay in balance.  Pollinators don't stay in balance.  Nothing stays in balance unless you make it.  The Earth only stays in balance because it's so utterly massive that it takes a long time for things to change in a relevant manner, during which time species can adapt, and because species have adapted to the Earth over the course of billions of years.  None of this applies to a small isolated biosphere.  Ultimately, whatever aspect you're talking about, something vital ends up getting broken down or locked up somewhere inaccessible over time.  Even the structure of the ship can do this - in Biosphere 2, for example, the carbon dioxide ended up becoming locked up in the concrete of the greenhouse.

In space you have to be able to make everything.  Which means incredibly long dependency chains. It's not a trivial task. That doesn't mean it's not a task worth working on - it absolutely is.  Not does it mean that it's unachievable - it absolutely is. But graphs that credit things to generic terms like "industry" bring nothing to the table.  The concept isn't even new; it's called a generation ship and it's been around for ages; Goddard proposed it in 1918. 

I'm just trying to figure out what is being proposed that's new here.
Nothing is new.  I'm not proposing anything.  I'm just exploring the idea a bit, revisiting a classic, if you want. 

I think people forget just how powerful a worldship is, and I expect that power could be used in interesting ways to help the ship survive.

I am annoyed by stories where agrarian societies live on  broken down worldship and have no idea where they are.  I agree that worldships are incredibly complex.  I've read Kim Stanley Robinson Aurora, that describes in excruciating detail how these ships can/would go wrong.

I think it would be interesting to determine if there is a size that is large enough that the stability can be a few thousand years.  And if reaching a solar system after a trip could provide sufficient ressources to enable the worldship to rejuvenate itself.  I would have though that small Islands, for example, provide examples of working ecologies that could be applied to worldships.

There is the whole social side of things that would be fun to explore as well. 

I also think it would be interesting to determine that the worldship is unworkable.

I am mainly an illustrator; I would like to improve what I draw, and am limited in what I can do on my own as my ignorance it vast and limitless.

Offline mikelepage

Re: Worldships
« Reply #33 on: 02/15/2017 06:32 AM »
I also find this topic interesting, but I do think the illustrations earlier in the thread are unworkable.  Mainly it's those vast internal chambers where only the circumference is used.  It's an insane waste of pressurised space, and my mind immediately jumps to nightmarish scenarios of what a large chamber like that looks like when an explosive decompression occurs. 

Much more realistic to have an interconnected set of smaller chambers, and nature has already shown us how to do this.  This is where the spiral space station concept came from in the first place:




Quote
My thinking, ever since coming up with the spiral space station concept (video below), is that any kind of interstellar Worldship will never be "complete".  They will set off on their journey with whatever minimum viable population/agriculture is, and by harvesting materials along the way, the ship size would grow as the colony does.

The spiral space station design is interesting, but I'm not sure the structure is robust enough to scale up for human use.  The design seems to be limited by the strength of any one link, and when you scale that up it becomes problematic.  Just my $0.02, but I'm not a structural engineer.

Interesting that this was your impression, but I probably should have prefaced that video with the pic of the nautilus shell above. Far from being weak, the log spiral is one of the strongest natural structures that exist.

The only modification is to make it a dual-log spiral, so as to allow it to stay balanced while spinning. Here's a different (earlier) depiction of the concept, a cross section of a series of solid chambers, rather than a framework for inflatables.



Each segment covers 30 degrees of the circumference, but includes an increase in radius and width by a factor of ~1.031 (or more exactly, a 1.2x increase in size over 180 degrees).  Your first stage of construction is to build out until you reach a radius that supports 1xg, and then the spin rate will slow down as the radius grows ever larger.

Of course this means that the "prime" real estate is towards the circumference, and with a range of lower g areas towards the axis.  I also like to imagine that one of the two spirals would be isolated as agriculture/botanical garden, while the other one would be living space/workshops (although no special need to stick to this, since each segment will be isolated by airlock from those pro-spin, anti-spin, above and below).  Construction of the ever bigger segments would occur close to the axis and then be lowered down via crane to be installed in place.

Offline guckyfan

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Re: Worldships
« Reply #34 on: 02/15/2017 09:19 AM »
O'Neill cylinder type structures would not be a model for a worldship. Those are designed for using incoming natural sunlight. A worldship would use completely artificial light as there is no sun near. So it could have a large number of concentric volumes. It would not be sensitive to hits as they could be compartmentalized.

Assuming that people adjust well to martian gravity, 60% of the radius at least could be habitats. The 40% inward would represent only a quite small percentage of the total volume. That area could house plants. As ISS tests prove there are plants that don't mind even microgravity. A worldship could grow by stretching the cylinder or by adding another shell outward. Outward would have more gravity or it needs to spin slower which would reduce gravity in existing shells.

Offline high road

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Re: Worldships
« Reply #35 on: 02/15/2017 10:29 AM »
Soil doesn't stay in balance.  Air doesn't stay in balance.  Pollinators don't stay in balance.  Nothing stays in balance unless you make it.  The Earth only stays in balance because it's so utterly massive that it takes a long time for things to change in a relevant manner, during which time species can adapt, and because species have adapted to the Earth over the course of billions of years.  None of this applies to a small isolated biosphere.

That's why it is a good idea to start on Mars and not start with a O'Neill space habitat. A nearly closed circle ecology is needed but some losses are permissible because there are still resources around. After a few hundred years the knowledge will be gained to make a nearly closed circle ecology with minimal losses that enables O'Neill habitats. Add another few hundred years of experience and improved propulsion a worldship can be sustained for a few hundred years until it reaches another sun to replenish its resources.

That's why it's a good idea to start by gradually upgrading a space station in LEO. Extracting resources to produce consumables and equipment with a limited lifetime (that's everything) requires a scale that is already far beyond our current activities in space. Better to postpone that until the station/colony grows to that scale by itself. ;-)

Offline Katana

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Re: Worldships
« Reply #36 on: 02/15/2017 02:58 PM »
Soil doesn't stay in balance.  Air doesn't stay in balance.  Pollinators don't stay in balance.  Nothing stays in balance unless you make it.  The Earth only stays in balance because it's so utterly massive that it takes a long time for things to change in a relevant manner, during which time species can adapt, and because species have adapted to the Earth over the course of billions of years.  None of this applies to a small isolated biosphere.

That's why it is a good idea to start on Mars and not start with a O'Neill space habitat. A nearly closed circle ecology is needed but some losses are permissible because there are still resources around. After a few hundred years the knowledge will be gained to make a nearly closed circle ecology with minimal losses that enables O'Neill habitats. Add another few hundred years of experience and improved propulsion a worldship can be sustained for a few hundred years until it reaches another sun to replenish its resources.

That's why it's a good idea to start by gradually upgrading a space station in LEO. Extracting resources to produce consumables and equipment with a limited lifetime (that's everything) requires a scale that is already far beyond our current activities in space. Better to postpone that until the station/colony grows to that scale by itself. ;-)
Or EML2 space station + ARM mining.

Offline lamontagne

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Re: Worldships
« Reply #37 on: 02/16/2017 01:13 AM »
O'Neill cylinder type structures would not be a model for a worldship. Those are designed for using incoming natural sunlight. A worldship would use completely artificial light as there is no sun near. So it could have a large number of concentric volumes. It would not be sensitive to hits as they could be compartmentalized.

Assuming that people adjust well to martian gravity, 60% of the radius at least could be habitats. The 40% inward would represent only a quite small percentage of the total volume. That area could house plants. As ISS tests prove there are plants that don't mind even microgravity. A worldship could grow by stretching the cylinder or by adding another shell outward. Outward would have more gravity or it needs to spin slower which would reduce gravity in existing shells.
There is a problem with concentric volumes if they are used for agriculture.  In such a case, each floor receives an average of 250 W/m2 via lighting.  But as there are floors above and bellow there is no way to remove this heat. The bottom floor of a 4 floor structure would receive 1000 W/m2 of heat and be unlivable.
The answer to this problem is to add cooling, and to remove the heat as fast as it is added.  So your vessel will end up with radiators and pipes and systems to remove heat.  Kalplana 1 is an interesting space colony design that addressed this problem.
In fact, the soil and ship wall are so insulating that it is impossible to remove the heat directly through radiation.  So even a single wall worldship required extra cooling and radiators, as per the image joined.

The space even a single floor of habitation provides is colossal.  For the 5km x 15 km ship, 230 km of habitation, at 100m2 per person, is space for over 2 million people.  As the biome will have difficulty more than a few tens of thousands, you would need to create much denser and much more artificial food production facilities, that risk breaking down sooner.  But the ship inhabitants would have the power to run them if they decided to go that route.

There is also the question of the mass of the floors. There may not be all that much gain in having dozens of floors, versus having one enclosed area. Rather like a sheet on a bed vs a folded sheet in the cupboard, it has the same area, and the same mass but it is more compact. If there is one thing that is not expensive in space, it is volume...
I agree the unused gas in the middle of the vehicle can be seen as a waste; that is why the design I have is more of an extended torus, and the center is filled with fuel, stores, and zero g spaces.




Offline lamontagne

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Re: Worldships
« Reply #38 on: 02/16/2017 01:19 AM »
O'Neill cylinder type structures would not be a model for a worldship. Those are designed for using incoming natural sunlight. A worldship would use completely artificial light as there is no sun near. So it could have a large number of concentric volumes. It would not be sensitive to hits as they could be compartmentalized.

Assuming that people adjust well to martian gravity, 60% of the radius at least could be habitats. The 40% inward would represent only a quite small percentage of the total volume. That area could house plants. As ISS tests prove there are plants that don't mind even microgravity. A worldship could grow by stretching the cylinder or by adding another shell outward. Outward would have more gravity or it needs to spin slower which would reduce gravity in existing shells.
I think stacking rings is the way to go.

Offline cro-magnon gramps

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Re: Worldships
« Reply #39 on: 02/16/2017 03:02 PM »
http://www.cbc.ca/news/technology/toronto-student-s-space-colony-design-wins-nasa-contest-1.821777
I was reminded of this by your mention of layered rings. As has been mentioned, this might be a useful interim step...

To the left side of the news article is a link to a detailed pdf (11mb) of the student's project...

Gramps
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