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PraedSt
2008-Sep-29, 10:18 PM
Just curious to know what the population of this (excellent) forum thinks.

As an economist I think the colony's Balance of Payments, and thus its chances of survival, might be in better shape if it were situated on a planet.

But as a space enthusiast I'd have to say the lack of a gravity well for an orbital sounds extremely appealing.

So: Planet or free floating?

Thanks,

Dabs

cjameshuff
2008-Sep-30, 01:34 AM
Just curious to know what the population of this (excellent) forum thinks.

As an economist I think the colony's Balance of Payments, and thus its chances of survival, might be in better shape if it were situated on a planet.

But as a space enthusiast I'd have to say the lack of a gravity well for an orbital sounds extremely appealing.

So: Planet or free floating?

How about free floating, on a planet?
Given a good way to turn CO2, water, and H2SO4 into UV and H2SO4-resistant polymers and rocket fuel, Venus is not a bad choice. At the right altitude, you have Earthlike pressures and temperatures, allowing lightweight protective gear to be worn "outside" and greatly reducing the danger of a breach. Air is a lifting gas, the atmosphere gives you a way to both keep temperatures stable without relying on heavy, complex, power hungry machinery, and shielding against particle radiation and meteorites, and there's no shortage of sunlight for growing crops. And, though the atmosphere is mostly CO2, Venus has more nitrogen overall than Earth, and is about the only other source for it closer than Saturn. Venus could be a good source of supplies for a colony on Mercury or inner-system asteroids. And given the above way to turn atmosphere into building material, you could quickly build enormous volumes of habitat space.

The superrotation of the upper atmosphere might even make a beanstalk possible. At high altitudes, a floating habitat would circle the planet every 4 days or so, and Venus' gravity well is shallower than Earth's.

Then there's Mercury, oddly enough with more easily available water than Venus, which could be shipped out on solar sails if what's in the Venusian atmosphere isn't enough, and a handful of asteroids. I like the inner system...short communications and transport distances, and you can ship things around in reasonable times with solar sails. Mars is cold, dim, has an atmosphere that's almost worse than useless in being substantial enough to need reentry shielding, too thin to be much help for landing, and variable enough to make aerobraking difficult to predict, and enough of a gravity field to be a pain. It does have those useful polar deposits of water and CO2, though...

There's also Earth's moon. A lunar space elevator might be more practical than an Earth one, though even more demanding in sheer quantity of material. The lack of an atmosphere would make mass drivers useful for moving bulk material into orbit, too. A few inconveniences like the long nights, but nothing really a huge problem.

ravens_cry
2008-Sep-30, 04:02 AM
Yeah, I like Venus aerostat colonies too. With carbon based composites as building materials, and telerobotics and cargo balloons from the surface, about the only thing Venus would lack would be water. And even that could be gotten in certain quantities, especially if cracked from sulfuric acid.

PraedSt
2008-Sep-30, 05:53 AM
(cjameshuff) Yeah, I concur with your inner system/Mars observations...for the reasons you mentioned.

Must admit, I hadn't considered Venus aero-colonies. Intriguing. Think I'll read up on it, especially those polymers you mentioned.

But playing devil's advocate here, wouldn't you have the worst of both worlds? Expensive raw materials (metals) and an annoying gravity well? You could fall off!

JonClarke
2008-Sep-30, 10:31 AM
Gravity wells have their uses. A lot of industrial processes use gravity to separate and store materials

PraedSt
2008-Sep-30, 10:44 AM
True! But those useful properties can be obtained on a rotating habitat. The annoying thing about planets is getting on and off them. We're still stuck on this one! :)

PraedSt
2008-Oct-01, 12:47 PM
Whoever moved this thread to Q&A: Thanks!

cjameshuff
2008-Oct-01, 03:01 PM
But playing devil's advocate here, wouldn't you have the worst of both worlds? Expensive raw materials (metals) and an annoying gravity well? You could fall off!

If you can make ripstop, airtight fabric and buoyant fill gas from the surrounding atmosphere, raw material for expansion is practically unlimited. We can make formic acid from CO2, water, and electrical power, which seems like a good first step to making polymers, or algae or other plants could produce the raw materials. Biggest problem is that plants require more than air, light, and water...

It may be practical to get minerals and metals from the surface. It's only at the melting point of lead, after all...extremely hot in human terms, but simple machinery could operate there, with the brains staying up in the clouds. Wind power would be plentiful as well...my understanding is that probes determined surface winds were very constant, and while slow, the high density atmosphere means you could get a lot of power from a relatively small turbine. And there's some very interesting indications of mineral processing by the supercritical CO2 atmosphere...metallic or semiconducting snow on mountains, for example.

Alternatively, it may be economical to import material from Mercury using solar sail propulsion. Particularly hydrogen in the form of water ice, or perhaps first converted to methane...more hydrogen for the same amount of mass, and easier to transport than elemental hydrogen.

And yes, you could fall off. Look on the bright side...you wouldn't have to worry about the sudden stop at the end. It really *would* be the fall that kills you.

PraedSt
2008-Oct-01, 03:05 PM
Lol.

I like that turbine idea.

This is new to me: 'interesting indications of mineral processing by the supercritical CO2 atmosphere...metallic or semiconducting snow on mountains'

Know where I can read up on it?

Thanks

cjameshuff
2008-Oct-01, 03:18 PM
This is new to me: 'interesting indications of mineral processing by the supercritical CO2 atmosphere...metallic or semiconducting snow on mountains'

Know where I can read up on it?

This is the best source I could find with a quick search.
http://sse.jpl.nasa.gov/news/display.cfm?News_ID=7459

Andrew Barton
2008-Oct-01, 04:01 PM
How about free floating, on a planet?
Given a good way to turn CO2, water, and H2SO4 into UV and H2SO4-resistant polymers and rocket fuel, Venus is not a bad choice. At the right altitude, you have Earthlike pressures and temperatures, allowing lightweight protective gear to be worn "outside" and greatly reducing the danger of a breach.
<snip>


The 'right altitude' is inside the sulphuric acid cloud layer. What 'protective equipment' would be necessary in there?

Andrew

PraedSt
2008-Oct-01, 04:10 PM
cjameshuff: Thanks for the link. And yeah, due to surface temp and pressure it's going to have to be robotic extraction.

Andrew Barton: The colony would be enclosed. So 'lightweight protective gear' would be normal clothing I presume.

cjameshuff
2008-Oct-01, 04:40 PM
The 'right altitude' is inside the sulphuric acid cloud layer. What 'protective equipment' would be necessary in there?

For working outside, a hazmat suit, not even necessarily airtight, positive pressure would probably do. Erect a working tent to keep the sulfuric acid aerosols away and block UV from the sun, and shirtsleeves and a mask to supply air and protect the eyes might be enough. Make *that* positive pressure, and you might be able to use a simple lightweight filter mask, and brief activity with no protective gear whatsoever would probably not be harmful (though certainly not recommended).

PraedSt
2008-Oct-01, 04:49 PM
For working outside, a hazmat suit, not even necessarily airtight, positive pressure would probably do. Erect a working tent to keep the sulfuric acid aerosols away and block UV from the sun, and shirtsleeves and a mask to supply air and protect the eyes might be enough. Make *that* positive pressure, and you might be able to use a simple lightweight filter mask, and brief activity with no protective gear whatsoever would probably not be harmful (though certainly not recommended).

You don't recommend enclosing the colony? Would be 'relatively' cheap given the mild conditions. How about those high winds? I know we'll be moving along at the same speed; but still. The turbulence would be a killer I think.

cjameshuff
2008-Oct-01, 05:04 PM
You don't recommend enclosing the colony? Would be 'relatively' cheap given the mild conditions. How about those high winds? I know we'll be moving along at the same speed; but still. The turbulence would be a killer I think.

I'm not sure how you could maintain buoyancy in an "unenclosed" habitat. Maybe a bubble of nitrogen under a bell? By "outside" I mean "outside the habitat". An enclosed habitat does still have an outside, and work will periodically need to be performed there.

Winds would not be an issue, I think. There's a high differential in winds at different altitudes, but the habitat would be drifting with it for the most part. You could tether two modules at different altitudes to get wind power and control the habitat's motion around the planet, in which case wind would be an issue, but you could bring them to the same altitude and thus reduce the airspeed when work must be done outside.

PraedSt
2008-Oct-01, 05:23 PM
Sorry!

Ok..so it's enclosed. Then the hazmat, mask, etc is for breaches?

To be honest, the more I think about planets, the more I find rotating orbitals habitats appealing. Everything just seems simpler.

samkent
2008-Oct-01, 05:44 PM
And when mom says "Don't go outside of the fence!" she has a darn good reason. That first step will be a doosey.

ravens_cry
2008-Oct-01, 05:45 PM
Sorry!

Ok..so it's enclosed. Then the hazmat, mask, etc is for breaches?

To be honest, the more I think about planets, the more I find rotating orbitals habitats appealing. Everything just seems simpler.
Orbiting as in space? or Orbiting as in balloon filled with breathable air at high altitude in a carbon dioxide atmosphere? That is what I call simpler.

cjameshuff
2008-Oct-01, 06:00 PM
Ok..so it's enclosed. Then the hazmat, mask, etc is for breaches?

And for work outside the habitat...

PraedSt
2008-Oct-01, 06:09 PM
Orbiting as in space? or Orbiting as in balloon filled with breathable air at high altitude in a carbon dioxide atmosphere? That is what I call simpler.

I think it's the high altitude. My spanking new forebrain is going 'yeah, ok, that seem's logical', but my ancient brainstem is going 'aaaaaaaaaaaaaaagh!'

ravens_cry
2008-Oct-01, 06:38 PM
I think it's the high altitude. My spanking new forebrain is going 'yeah, ok, that seem's logical', but my ancient brainstem is going 'aaaaaaaaaaaaaaagh!'
Yeah, it sounds crazy, until you look at it. The only place in the solar system that has Earth temperature range and pressure, besides earth. It won't be simple, nothing about outer space colonization is, but it certainly removes a lot of barriers, albeit with some new ones,such as a higher gravity well then say Mars or the Moon.

PraedSt
2008-Oct-01, 06:52 PM
We could give the concept a trial run right here couldn't we? Helium cells, small pressurised living quarters, UAV delivered cargo, etc?

We'd have to dodge aircraft though...

cjameshuff
2008-Oct-01, 08:09 PM
Yeah, it sounds crazy, until you look at it. The only place in the solar system that has Earth temperature range and pressure, besides earth. It won't be simple, nothing about outer space colonization is, but it certainly removes a lot of barriers, albeit with some new ones,such as a higher gravity well then say Mars or the Moon.

Not the only place. Saturn, and I think Jupiter have similar regions (though they also have the minor difficulty of a huge gravity well should you ever want to leave, and the hydrogen/helium atmosphere makes buoyancy a bit harder to achieve...nothing usable as a lifting gas, so you'll need hot air balloons), and the moon is a quite stable and comfortable temperature once you get enough dirt and rock above you to smooth out the day/night cycles...about 24 C/75 F.

ravens_cry
2008-Oct-01, 09:44 PM
Not the only place. Saturn, and I think Jupiter have similar regions (though they also have the minor difficulty of a huge gravity well should you ever want to leave, and the hydrogen/helium atmosphere makes buoyancy a bit harder to achieve...nothing usable as a lifting gas, so you'll need hot air balloons), and the moon is a quite stable and comfortable temperature once you get enough dirt and rock above you to smooth out the day/night cycles...about 24 C/75 F.
True, your right, my mistake. The moon, no matter how much rock you pile, still has no air, so decompression is a much more serious problem, though alavated mostly by having a series of bulkheads.

PraedSt
2008-Oct-01, 10:05 PM
Ha! Give me a year, and I'll convert you all. Orbital habitat. Orbital habitat. Orbital habitat. :)

ravens_cry
2008-Oct-01, 10:06 PM
Ha! Give me a year, and I'll convert you all. Orbital habitat. Orbital habitat. Orbital habitat. :)
Give me six months and I'll convert you to Breathable Air Aerostats.
Starting. . .now.

eburacum45
2008-Oct-01, 10:43 PM
Venus Express results suggest that the atmosphere of Venus is uncomfortably turbulent, so aerostat balloons would be an uncomfortable ride- unless you could make them so big that turbulence just washes over them. Not sure how big that would have to be.

Saturn, Uranus and Neptune also have winds which would make hot hydrogen habitats challenging. I'd like to think that those challenges could be overcome, however.

Jupiter is a different case; lots of updrafts and downdrafts, high gravity at the cloudtops, high escape velocity when you want to leave the planet; Jupiter might not be quite so welcoming.

And remember that an air-filled habitat in a hydrogen atmosphere could be a fire or explosion risk.

PraedSt
2008-Oct-01, 10:52 PM
Eburacum45: What are your views on orbital habitats?

cjameshuff
2008-Oct-01, 10:52 PM
Ha! Give me a year, and I'll convert you all. Orbital habitat. Orbital habitat. Orbital habitat. :)

Orbital habitats are great for their own reasons (you get to choose your own gravity, for one, and you can build huge mirror arrays for powering heavy industry), but they need material. The moon, Venus, Mercury, and inner system asteroids are good sources for it.

My proposal would be get established on the moon and get some basic infrastructure going...not a touch and go, not an extended visit, but going there to stay. Land some nuclear reactors, set up solar furnaces and mass drivers, and start turning out basalt fiber, glasses, and asteroid iron (if you can still call it that after it's blasted itself all over the moon), and try to get aluminum and titanium refining going.

Send ground probes to Mercury and nearby asteroids, ground and atmosphere probes to Venus, and re-evaluate where to go from that point. If the aerostat idea works out well enough that an aerostat can build more aerostats from the surrounding air with relatively small amounts of machinery and minerals from the ground and from above, Venus could be an enormous source of polymers and atmospheric gases, food, and living space for the inner system.

PraedSt
2008-Oct-01, 11:06 PM
Yeah, my personal (jaundiced) view is use System bodies for mining/manufacturing, but use an orbital for living.

By the way:


My proposal would be get established on the moon and get some basic infrastructure going...

Has mining/construction on a low gravity-no atmosphere body been discussed on this forum? I think it just might be the messiest thing we've ever done. :)

cjameshuff
2008-Oct-01, 11:31 PM
Has mining/construction on a low gravity-no atmosphere body been discussed on this forum? I think it just might be the messiest thing we've ever done. :)

Yeah...there's vacuum, little to no water, and with the asteroids, a lack of gravity, which is one other reason I think the moon's a good first step. We know the environment a little better, and can apply more of what we know. It'll be hard enough when you can make piles of stuff on the ground and move it around on conveyor belts and wheels.

timb
2008-Oct-02, 12:45 AM
Yeah, I like Venus aerostat colonies

That's balloon colonies. Aerostats are tethered to the surface, which would obviously not be likely on Venus. Choosing a word because it sounds cooler is rarely correct.

Van Rijn
2008-Oct-02, 01:00 AM
That's balloon colonies. Aerostats are tethered to the surface, which would obviously not be likely on Venus. Choosing a word because it sounds cooler is rarely correct.

Aerostats are usually tethered, but I don't see from the definition that they absolutely must be tethered. A lighter than air structure might be able to hold to a stationary position without a surface tether.

ravens_cry
2008-Oct-02, 01:03 AM
That's balloon colonies. Aerostats are tethered to the surface, which would obviously not be likely on Venus. Choosing a word because it sounds cooler is rarely correct.
The book I read described an aerostat as merely the general term for a lighter then air craft, including balloons, both tethered and not, blimps, dirigibles, and semi-rigid's. Admittedly this book is from 1972, so is by no means recent. It cited the (whatever this is) British Standard 185 Part 1 as its source.
Besides, a certain amount of tethering just may be useful, not to the ground obviously, but tentacles reaching down into deeper and thicker layers to provide a keel effect to allow a balloon to sail and or gather energy from the winds. I picture it as being rather lens shaped, with the a miles long cable reaching down into the Venusian hell, This would provide electricity from the temperature differential, as well as being the keel. Up top, a sail along each pie section of the craft, could furl and unfurl to catch the wind, something balloons wouldn't normally be able to do.

timb
2008-Oct-02, 01:14 AM
The 'right altitude' is inside the sulphuric acid cloud layer. What 'protective equipment' would be necessary in there?

Andrew

The right altitude doesn't really exist. From wikipedia (http://en.wikipedia.org/wiki/Atmosphere_of_Venus#Circulation)


alt. T P
50 75 1.066
55 27 0.5314
60 -10 0.2357

So if you want 1 bar you get about 70o C (which kills 100% of people), and it you want room temperature you get less than 0.5 bar (which causes altitude sickness in many people). As you point out the altitudes that are close to ntp are deep in the sulfuric acid cloud layer that covers altitudes from about 45km to 65km. This would not only impose materials constraints, but mean that the ambient light is quite dim and the environment likely turbulent.

Venus is an attractive target for a long-duration high altitude rover (balloon, airship or even aircraft). That might make for an interesting discussion. Planning vast floating cities is fantasy.

timb
2008-Oct-02, 01:26 AM
The book I read described an aerostat as merely the general term for a lighter then air craft, including balloons, both tethered and not, blimps, dirigibles, and semi-rigid's. Admittedly this book is from 1972, so is by no means recent. It cited the (whatever this is) British Standard 185 Part 1 as its source.
Besides, a certain amount of tethering just may be useful, not to the ground obviously, but tentacles reaching down into deeper and thicker layers to provide a keel effect to allow a balloon to sail and or gather energy from the winds. I picture it as being rather lens shaped, with the a miles long cable reaching down into the Venusian hell, This would provide electricity from the temperature differential, as well as being the keel. Up top, a sail along each pie section of the craft, could furl and unfurl to catch the wind, something balloons wouldn't normally be able to do.

According to Wikipedia, an aerostat is a lighter than air object that can stay stationary in the air. It then goes on the include every class of lighter than air craft as an aerostat! I concede defeat. Anything that floats is an aerostat whether it remains stationary or not.

Wind power or "aerothermal" power would be unusual possible energy sources for a Venusian airship, I agree. The dynamical effects of a keel at an altitude with much different winds might take some coping with. If you give up spending most of your time in the cloud layer then solar power would be a simpler alternative.

PraedSt
2008-Oct-02, 01:26 AM
Planning vast floating cities is fantasy.

Good fun though :)

But, as I keep telling anyone who'll listen, orbital habitats...less variables, more control.

PraedSt
2008-Oct-02, 01:30 AM
According to Wikipedia, an aerostat is a lighter than air object that can stay stationary in the air. It then goes on the include every class of lighter than air craft as an aerostat!

Wikipedia is correct. Any lighter-than-air object, if left alone, is stationary relative to the airflow.

In piloting terms, you're confusing airspeed with ground speed.

Think of a balloon blown along by a 1mps wind. Ground speed 1mps, Airspeed 0mps.

timb
2008-Oct-02, 02:01 AM
Wikipedia is correct. Any lighter-than-air object, if left alone, is stationary relative to the airflow.

In piloting terms, you're confusing airspeed with ground speed.


Wikipedia are failing to distinguish the two. In common use speed means relative to (the local) ground. That unpropelled floating bodies remain at rest relative to their medium is a fairly trivial observation. Such a body is just doing what you would expect, so it doesn't really need a fancy term to describe its behaviour. They also say airships are free flying aerostats that can be propelled and steered. If they're being propelled then their airspeed is non-zero, surely? I think aerostat just sounds too cool to retain a precise meaning. Let's start calling all manner of water craft hydrostats.

Van Rijn
2008-Oct-02, 02:10 AM
If they're being propelled then their airspeed is non-zero, surely?


And so is a tethered airship, if the wind is blowing.

PraedSt
2008-Oct-02, 02:10 AM
Lol. Everyone knows what everyone else means.

I also know that this thread is drifting relative to my intent.

Sorry. Bad joke.

cjameshuff
2008-Oct-02, 02:18 AM
Besides, a certain amount of tethering just may be useful, not to the ground obviously, but tentacles reaching down into deeper and thicker layers to provide a keel effect to allow a balloon to sail and or gather energy from the winds.

More than that...with two modules, a tether, and some aerodynamic surfaces, you could use changes in buoyancy and the differential in the winds at different altitudes to propel yourself in any direction.

Which would make it non-stationary from the point of view of everything but orbital habitats, of course...



So if you want 1 bar you get about 70o C (which kills 100% of people), and it you want room temperature you get less than 0.5 bar (which causes altitude sickness in many people). As you point out the altitudes that are close to ntp are deep in the sulfuric acid cloud layer that covers altitudes from about 45km to 65km. This would not only impose materials constraints, but mean that the ambient light is quite dim and the environment likely turbulent.

The graph just above the table puts it at closer to 0 C. Other sources I've seen put it in the range 0-50 C. One abstract for a paper on VeRa results from Venus Express refers to a 30K variation at the 1 bar level at different latitudes, but I don't have the subscriptions needed for the full papers with the actual temperatures...

The range of acceptable pressures is quite high, though. Human inhabited areas would be at a slight positive pressure anyway, to make leaks easier to detect...CO2 leaking into the human living areas unnoticed would be bad. Some fraction of an atmosphere of internal pressure would also help give structural rigidity to those portions. Altitude is something the body can acclimate to within a wide margin, changes in the oxygen content of the air can expand that range, and you can design machinery to operate in and breed plants to thrive in pressures where humans can not live comfortably.

Even assuming the Wikipedia table is the more accurate, all the other advantages still hold, the only advantage reduced is the low difference in pressure between the inside and outside. And even then, a breach would not be as big of a problem as it would be on Earth.

Turbulence appears to vary widely with latitude and altitude. This type of habitat may only be possible in the mid latitudes, it may simply require good monitoring of the surrounding conditions, or it may not be a problem at all at certain altitudes.

ravens_cry
2008-Oct-02, 08:41 AM
More than that...with two modules, a tether, and some aerodynamic surfaces, you could use changes in buoyancy and the differential in the winds at different altitudes to propel yourself in any direction.

Which would make it non-stationary from the point of view of everything but orbital habitats, of course...
Even better. Venus was made for balloons. So many ideas I would like to see tried out.
Well like I said, 'The only way to find out, is to go there, and find out.' the gravity is a bummer for leaving the place, but it is a bit less then Earths, enough to add a spring in your step. And the near-earth gravity means you don't have to worry about bone loss and other low g problems as much or at all. Interestingly, I have read that Venus is actually a better place to access the the asteroids then Earth is. That, and telerobotic mining of the surface, would provide what materials can't be gotten from in atmosphere. As thick a blanket as Earths to protect you from radiation, though almost no magnetic feild. Some people want to see Mars, and I think Mars is great, but I want to live on Venus, or at least in the sky thereof.

PraedSt
2008-Oct-02, 09:25 AM
Alright you Venus balloon lovers, you've had your fun. My turn. :)

Orbitals. I'll get the two major disadvantages (as I see them) out of the way first, so no-one can accuse me of excessive bias. Heh.

Both stem from a lack of atmosphere.

1. Temperature control. No fluid for convective heat rejection. A big pain.

2. Impact risk. No idea what to do about this one. I suppose, theoretically if not practically, it's possible to move the entire structure in order to avoid catastrophic impacts. But for smaller objects: ??

Please note, some planetary/satellite sites share these disadvantages (eg lunar colonies).


Some advantages. I'm sure there are more!

1. The external environment is less variable than those on planets/satellites.

2. Orbitals can be located anywhere.

3. They can start off small, and expanded over time.

4. There is no upper limit to their size. They can end up huge.

5. Artificial gravity.

6. No gravity well.

7. No earthquakes, volcanoes, hurricanes, tsunamis.


Ok. Now someone please tell me what other solar system location can beat all of that.

No wag say 'Earth' please :)

Thanks!

ravens_cry
2008-Oct-02, 09:44 AM
If you look at pictures of Mir near the end of it's life span, it looks like someone took a .22 to it, lots and lots of times. A habitat will have to last much longer. Another trouble I see, is that you have to drag all your materials along. An advanced lunar outpost could get quite a bit, if not all, from the moon itself, empty space is well, empty. Everything would have to be dragged from a comet or asteroid or out of a moon or planets gravity well. Just my 2 credits on the matter.

eburacum45
2008-Oct-02, 12:00 PM
O'Neill expected that orbiting space habitats would be constructed mostly from lumar materials, so we need mining facilities on the Moon before we can start building space islands.

I think the Moon will eventually hold a large population, exporting aluminium, iron, oxygen, silicon and titanium to create habitats and spacecraft. We are very lucky to have such a large source of materials so close by.

One thing the Moon is short of is water (more precicely hydrogen)- this could be supplied from water rich objects beyond the snow line; it could be cheaper to mine water in the outer solar system and import it to the dry inner zone than dragging it up from Earth.

Carbon is in short supply too, on the Moon; Venus has an awful lot of carbon, which we might like to try removing at some point- yes, it s at the bottom of a gravity well, but solar power (and wind power) are abundant there.

What emerges is a picture of a soar system-wide civilisation, trading materials and energy from place to place. Few location in the solar system have everything we require; Earth is one of them, and it is far from full, no matter what the pessimists say. But we don't really want to fill the Earth to capacity with humans, as that would make our planet into a huge hothouse filled with people.

Everything required for life is available in space, if not necessarily all in one location. A system of trade between the various locations in the system could ensure that space based habitats are suplied with the resources they need .

eburacum45
2008-Oct-02, 12:21 PM
But what would an orbiting habitat have to trade? They can be used to grow crops, for one thing; food which doesn't have to be lifted off Earth (or up from the Moon, and Mars, for that matter). They also represent locations where manufacturing can occur- a space habitat can include large solar power collection arrays, and facilities in microgravity or rotation-induced gravity of arbitrary value. But most of all they will contain people- people who will be alble to use the resources found in space to the best advantage. Since resources will be moving from location to location in the solar system once trade takes off, the people in orbiting habitats will have easier access to those resources than the inhabitants of planet-based colonies.

Carbon and hydrogen may arrive into the Earth-Moon system for consumption on the Moon, but the orbiting habitats would also benefit from this trade; it is cheaper to deliver these materails to a habitat than to the surface of the Moon, for example.

In the long run, I can imagine the Moon, and the other smaller bodies of the Solar System, will be partly or wholly disassembled to make orbiting space habitats of increasing size; the asteroids, the moons of the outer planets, Mercury... such habitats could support trillions of people, more. But that is a very long term consequence of what will at first be just a trade in resources.

PraedSt
2008-Oct-02, 12:26 PM
Finally, someone who agrees with me :)

ravens_cry
2008-Oct-02, 12:35 PM
Finally, someone who agrees with me :)
Hey, if I had my way we would do it all. And logically, it looks like we may have to if we are going to truly do it at all. Trade is one of the basic ways of generating wealth, buy stuff where it's cheap, sell it where it's not. I was looking at the comparison between an O'Neill habitat, and the ISS, and it struck me how big we once dreamed. Will it always be a dream?

Ronald Brak
2008-Oct-02, 01:45 PM
An increasing amount of trade this days is in carefully arranged ones and zeros. Nowadays there are quite a few people who arrange ones and zeros and use the income they derive from it to live in a wide variety of stupid places. (Such as on earth.) I see now reason why people couldn't do something similar in the future to fund living in stupid places in space.

PraedSt
2008-Oct-02, 01:48 PM
:)

cjameshuff
2008-Oct-02, 02:04 PM
An increasing amount of trade this days is in carefully arranged ones and zeros. Nowadays there are quite a few people who arrange ones and zeros and use the income they derive from it to live in a wide variety of stupid places. (Such as on earth.) I see now reason why people couldn't do something similar in the future to fund living in stupid places in space.

Finite bandwidth would make such traffic more expensive...but a communications network could support much greater bandwidth than a single direct link and would not be that expensive to set up, so it might not be an issue.

It feels like selling my soul to say this (not a sports fan), but look at what gets invested in ground-based sports stadiums...billions of USD up-front, just for the stadiums. Consider the possibilities of freefall or low-gravity sports...especially when the stadium goes overhead every 90 minutes. And the ads...deploy a billboard 3 km across, and from the ground it'll be the same visual size as the moon.

PraedSt
2008-Oct-02, 03:20 PM
Consider the possibilities of freefall or low-gravity sports...

That...is one hell of an idea.

Except swimming maybe? I read somewhere that fluids form one big glob in low/no gravity.

NEOWatcher
2008-Oct-02, 03:27 PM
...Except swimming maybe? I read somewhere that fluids form one big glob in low/no gravity.
Swimming might work, especially since you can swim around the circumference. (I think).

Diving might be really interesting though.

PhysBrain
2008-Oct-02, 07:03 PM
Here's just a few other things that you might want to consider in your discussion here.

- For high-altitude floating stations, who ever said that the displacement volume had to be a bag filled with a gas. Imagine a semi-rigid, air tight structure assembled in a high orbit. The interior volume would be a vacuum. Lower this structure into the upper atmosphere by means of skyhook (e.g. tether). The structure need only be sufficiently strong enough to resist the ambient pressure at whatever altitude you decide to sink it to and support whatever habitats or instrumentation you choose to hang from it.

- As an alternative to spinning colonies in free space, consider a station with two segments separated by a long tether, such that the tether is aligned with the gravitational gradient. Assuming both ends were the same distance from their common center of gravity, the stations at both ends of the tether would experience equal and opposite forces (the lower station due to the planet's gravity, the upper station due to centrifugal acceleration). For such a station, there is a somewhat fixed notion of up and down directions which are relative to the planetary body. Such a distinction might be appreciated by the inhabitants of the station. Docking with the station is as simple as matching orbital elements with some part of the station. If not docking to the center of the station, then the docking apparatus must be capable of supporting the weight of the incoming payload. There are also some potential advantages regarding the ability to efficiently transfer orbits simply by releasing a payload at different points along the tether.

- Google for stratostation or go visit the website of JP Aerospace (jpaerospace.com). They've been working on developing these technologies for several years now. They also have an idea for a lighter-than air craft which may be capable of flying to space. I have my doubts as to the feasibility of such a vehicle making it all of the way to orbit. However, if one of these ships were able attain a significant altitude and velocity then one could conceivably launch a payload on a short suborbital trajectory that could then be captured by the lower end of the tethered station mentioned above.

- Once you include rotating tethers into the mix, a whole universe of interesting possibilities open up.

PraedSt
2008-Oct-02, 07:14 PM
As an alternative to spinning colonies in free space, consider a station with two segments separated by a long tether, such that the tether is aligned with the gravitational gradient.

Yep. Heard of this. It's a good idea. Useful to start, get experience, that sort of thing.
Thanks for the link too.

cjameshuff
2008-Oct-03, 03:25 PM
- For high-altitude floating stations, who ever said that the displacement volume had to be a bag filled with a gas. Imagine a semi-rigid, air tight structure assembled in a high orbit. The interior volume would be a vacuum. Lower this structure into the upper atmosphere by means of skyhook (e.g. tether). The structure need only be sufficiently strong enough to resist the ambient pressure at whatever altitude you decide to sink it to and support whatever habitats or instrumentation you choose to hang from it.

Supporting large hollow structures against outside pressure and keeping the shell mass low enough that the result is buoyant is...difficult. Such a craft would have to be extremely high altitude to not be crushed, extremely large to have any useful lift at that altitude, and the larger it is the more unstable and fragile it will be. You will also have trouble keeping it impermeable to gases and still lightweight enough to float.



- Google for stratostation or go visit the website of JP Aerospace (jpaerospace.com). They've been working on developing these technologies for several years now. They also have an idea for a lighter-than air craft which may be capable of flying to space. I have my doubts as to the feasibility of such a vehicle making it all of the way to orbit. However, if one of these ships were able attain a significant altitude and velocity then one could conceivably launch a payload on a short suborbital trajectory that could then be captured by the lower end of the tethered station mentioned above.

JP Aerospace claims it's possible to accelerate a huge hypersonic airship to orbital velocity with solar powered ion engines. I am extremely skeptical about anything they say they're working on...

But yeah, as I mentioned, the upper atmosphere moves around the planet over the course of about 4 days. With the somewhat shallower gravity well, an elevator might be practical. Venus is lower density as well as lower mass, so the elevator is further out of the gravity well to begin with. Even if the elevator doesn't work out, there's other tether arrangements that might be practical.

Tidal gravity would work for things attached to elevators and near-elevator-length tethers, but I think "bola" habitats consisting of two tethered masses rotating for gravity are more practical. Put a nuclear reactor on one mass, and the habitat at the other...a few hundred or thousand meters of tether and the inverse square law are likely the lightest and cheapest radiation shielding possible.

PraedSt
2008-Oct-03, 03:45 PM
but I think "bola" habitats consisting of two tethered masses rotating for gravity are more practical

I was thinking that bolas might be best if you want a habitat that you can slowly enlarge. You have to coordinate the distribution of habitat mass as you go about it...as you obviously want to keep the centre of mass fixed.

So bolos: add living space on one side, simultaneously add any lump of mass onto the counterweight side.

Anyone know of any other way of increasing the mass of a rotating body, without sending it tumbling? If so, please let me know!

mugaliens
2008-Oct-03, 09:14 PM
There are also some potential advantages regarding the ability to efficiently transfer orbits simply by releasing a payload at different points along the tether.

Only if your payloads are small compared to the mass of the stations. Sand wouldn't affect things much...

Such as setup, however, would be sensitive to either the capture or the release of any object. Furthermore, releasing any object at any point other than the zero-G point would result in that object entering an elliptical orbit.

ravens_cry
2008-Oct-04, 06:08 AM
Hmm, the Zero G point would be the center of the line connecting the two modules, right or wrong? Well, how about, you have the docking area right at the center, when you dock, send an astronaut massed lego block(with some kind of release mechanism) b to lock into the other other side. Same with cargo, send an identical massed block to dock with the other blocks. climb hand over hand,or along rungs, or something, to get to the habitation/service end. BYOB (Bring Your Own Block) would mean transport to the station would be twice as expensive.
Does this sound workable?

eburacum45
2008-Oct-04, 10:01 AM
- As an alternative to spinning colonies in free space, consider a station with two segments separated by a long tether, such that the tether is aligned with the gravitational gradient. Assuming both ends were the same distance from their common center of gravity, the stations at both ends of the tether would experience equal and opposite forces (the lower station due to the planet's gravity, the upper station due to centrifugal acceleration).

This is a new idea to me. Hmm; how big could we make it? A circumplanetary ring, in three parts, with the outermost and innermost rings dependent from the middle ring. These two rings would have a low gravity environment, one facing inwards, one facing outwards.. Place this triple ring in geostationary orbit and you could hang space elevators from it.

This is a very big construct, if in Earth orbit; but we could make it bigger, by moving the ring out further than geostationary orbit, or by placing it in orbit around a gas giant.

PraedSt
2008-Oct-05, 12:19 PM
mugaliens
You're right; I think the effect of adding or subtracting mass from the colony would be very dependant on its initial mass, and its distribution. Active station-keeping and rotation management is probably in order.

ravens_cry
Sounds complicated! (But workable, I'm sure.)
And I think it will always be complicated until you expand the station enough to form an enclosed ring.

eburacum45
Three circumplanetary rings! What if they start rippling?! Don't ask me about the physics of this, but I have a hunch that unless the rings have freedom to move in relation to one another (like Saturn's), you're going to get rippling. :)

eburacum45
2008-Oct-05, 03:26 PM
The innermost ring and the outermost ring would be pulling away from the central (orbiting ) ring, so would send to keep the structure in tension, especially if there is slightly more 'weight' pulling outwards than inwards. It could ripple up and down with respect to the orbital plane, though.

Some interesting effects might be noticed if there were large moons nearby...

ravens_cry
2008-Oct-06, 12:47 PM
While Googling to see if anyone else had thought of the idea of a starship made of ice, I found this. The basic premise seems to be a ring space station made of ice.
http://www.neofuel.com/iceships/
Certainly seemed to have some interesting possibilities.

PraedSt
2008-Oct-06, 12:56 PM
Lol!

On the thin line between 'spoof' and 'hang on a minute...'

cjameshuff
2008-Oct-06, 02:09 PM
While Googling to see if anyone else had thought of the idea of a starship made of ice, I found this. The basic premise seems to be a ring space station made of ice.
http://www.neofuel.com/iceships/
Certainly seemed to have some interesting possibilities.

Look up "pykrete"...plain water ice is pretty terrible as far as structural strength goes, but when reinforced with fibrous material, it becomes rather tough stuff. Easy to recycle, repair, and reshape, too. It might be quite a good option, for habitats at least.

PraedSt
2008-Oct-09, 11:57 AM
Sorry lads and ladies, I've just discovered that this topic was covered, and covered well, last year. Here's filrabat's thread:
http://www.bautforum.com/life-space/65282-orbital-habitats-flexible-solution-humanity.html

I've got one more thing to do before closing this thread.
I want to work out the size limits of a rotating orbital, based on the structural limits imposed by rotation. All the literature I've come across so far address the structural problem from the point of view of maintaining internal pressure, so I'm starting to think that pressure is the more relevant issue...if the habitat is strong enough to maintain 1atm, it's strong enough to resist rotational stress. Still working on it!

And eburacum45, from filrabat's thread:

Fibre optics are a good way to illuminate the habitat
I agree! Don't like windows either..

eburacum45
2008-Oct-09, 09:10 PM
While Googling to see if anyone else had thought of the idea of a starship made of ice,
Did you find Jonathon vos Post's ice ship concept?
Hydrogen Ice Spacecraft for Robotic Interstellar Flight (http://www.magicdragon.com/ComputerFutures/SpacePublications/STAR.html)
One of the best concepts I've seen.

ravens_cry
2008-Oct-09, 09:25 PM
No I hadn't, so thank you.
My Google-fu must not be as strong as I thought.
The website is a little screwy on my computer, in firefox the lines warp after only about 20 characters. In IE, it isn't quite so bad.

PraedSt
2008-Oct-13, 11:05 AM
I've got one more thing to do before closing this thread. I want to work out the size limits of a rotating orbital, based on the structural limits imposed by rotation

Maximum radius of a Banks-type Orbital made out carbon nanotubes.

Assumptions were made to simplify analysis. Answers vary widely with assumptions and values used. These are mine:

1. Orbital is 'Banks-type'. A rotating ring that is open on the inside. The atmosphere is retained by the artificial gravity generated and huge side walls.
2. The thickness of the ring is small relative to its radius.
3. The rotation speed of the Orbital is such that the value of artificial gravity generated at the inner surface is 1g.
4. The ring can be decomposed into two layers. The outer is the structural layer, made out of carbon nanotube. The inner is the habitat layer, made out of a mixture of materials, air, soil, water, etc.
5. The mass of the inner ring is the same as that of the outer ring. In other words, the structural outer ring has to be able to support exactly twice its own weight.
6. There is no 'safety factor'. The radius is thus the theoretical limit given assumptions above and the material values given below..

Variables, Parameters, Values:

r= radius of Orbital in metres
S=tensile strength of carbon nanotube=63 thousand million Newtons per metre squared (63GPa)
D=density of carbon nanotube=1,400 kilogrammes per metre cubed
g= standard acceleration due to gravity, 9.8 metres per second squared

Formula:

r = S/2Dg

The tensile strength of the material has to be able to withstand the hoop stress generated by the rotating ring. You can work out the hoop stress by either: using a non-rotating thin walled pressure vessel as your model, or by using a thin rotating ring as a model. Both methods give you the same result, the same formula. Full derivation is available on request.

So, with the formula and figures given above, the maximum radius of a Banks-type carbon nanotube orbital works out to:

r = approx =2,300km, or a diameter of 4,600km.

Also:

1. A radius of 2,300km means that the Orbital will rotate approximately once every 50 minutes.
2.Hoop stress is the limiting stress. Hoop stress does not depend on cross-sectional area. In other words, you can expand the Orbital 'lengthwise', and make a structure that looks somewhat like a bracelet.
3. If this bracelet had a radius of 2,300km and a width a tenth of that, 230km, it's surface area would be about 3 million square kilometres, which is a third of the size of the entire US.

Still, not as large as I hoped. Banks Orbitals, with radii of 1 million kilometres, cannot be made with carbon nanotube. Nor can they be made with anything, I'm given to understand; theoretically impossible. Boo hoo.

eburacum45
2008-Oct-13, 11:55 AM
r = approx =2,300km, or a diameter of 4,600km.
That is assuming that you have no extra load; no landscape, no cities and towns, no water. Which is why the Orion's Arm rings are generally half that size.

One way to make them bigger is to lower the gravity requirements. Martian gravity might suffice; I suspect that plenty of people will live on Mars, and the Moon, and in other lower gravity environments. The Earth turns out to have the highest gravity of any solid object in the Solar System; we will have to adapt to lower gravity to live elsewhere, and we might as well build our habitats with lower gravity too.

Don't get confused by the fact that human body doesn't adapt well to microgravity and freefall; microgravity is a completely different problem to Martian or Lunar gravity.

One problem with lower gravity rings is that you need higher side walls.

PraedSt
2008-Oct-13, 12:08 PM
I like that gravity idea. But you're right...more than right actually...I am worried about humans adapting to low gravity :)

Wouldn't adaptation be limiting? For example, could we travel back to Earth for a visit? A trivial questions I know but...
How about dangerous? Bones, etc? I should read up about it I guess...

As for load on the Orbital, I gave it some (points 4,5 at the top). But your point is valid because in reality the load would be much higher than what I used. Also, unlike the design for Orion's Arm, mine doesn't incorporate a safety factor. So 2,300 is really the upper limit.

Ara Pacis
2008-Oct-13, 02:39 PM
Would the walls really hold in the atmosphere by centrifugal force? Wouldn't the solar wind constantly knock some of it off?

mugaliens
2008-Oct-13, 02:40 PM
This is a new idea to me. Hmm; how big could we make it? A circumplanetary ring, in three parts, with the outermost and innermost rings dependent from the middle ring. These two rings would have a low gravity environment, one facing inwards, one facing outwards.. Place this triple ring in geostationary orbit and you could hang space elevators from it.

This is a very big construct, if in Earth orbit; but we could make it bigger, by moving the ring out further than geostationary orbit, or by placing it in orbit around a gas giant.

Sadly, while stupdendous, it's also dynamically unstable.

A simple two-section construct, on the other hand, one multi-floored cylinder at LEO and the other beyond geostationary orbit, would allow for a geostationary couple, but at significantly less stress, and with significantly reduced problems we would encounter with an Earth-bound tether.

Because of the forces, the pair could be made to orbit once / 24 hrs, or by adjusting their positions, at any interval one desired such that the interval > that for LOE.

A 36 or 48-hour interval might be interesting.

We would still have the problem of a space tether having to counter massive amounts of space junk.

PraedSt
2008-Oct-13, 02:54 PM
Would the walls really hold in the atmosphere by centrifugal force? Wouldn't the solar wind constantly knock some of it off?

Solar wind...yes you're right. You'd loose atmosphere. I don't know the rate at which this happens, but I suspect time-scales are long (I'll look it up). You could always put a roof over it if you wanted, or some sort of magnetic shield replica, so I suppose the issue would be one of cost.

Atmosphere...kept in on the top of the surface/inside of the ring/hubwards by artificial gravity, much like our atmosphere is kept in by the real thing. The walls are for the sides of the ring...

timb
2008-Oct-13, 10:09 PM
Or, if you prefer things that might happen this century, put a couple of tin cans like skylab in LEO and join them with a steel (sorry, no unobtainium required) cable.. Put some flooring in and spin it up, and hey presto, you have two space apartments! You'd need a lift that rides the cable and a docking port in the middle to make it accessible. At our current rate of progress I'd rate the odds of something like this being built before 2050 as about one in three.

PraedSt
2008-Oct-13, 10:30 PM
Or, if you prefer things that might happen this century, put a couple of tin cans like skylab in LEO...

Very true. Just planning ahead!

Ara Pacis
2008-Oct-14, 10:41 PM
Solar wind...yes you're right. You'd loose atmosphere. I don't know the rate at which this happens, but I suspect time-scales are long (I'll look it up). You could always put a roof over it if you wanted, or some sort of magnetic shield replica, so I suppose the issue would be one of cost.

Atmosphere...kept in on the top of the surface/inside of the ring/hubwards by artificial gravity, much like our atmosphere is kept in by the real thing. The walls are for the sides of the ring...

But as a field effect, gravity can grab at air as it bounces around trying to escape. With spinning, once it sloshes over the wall, it's gone for good. I wonder if the delta-v would be different too.

eburacum45
2008-Oct-15, 12:21 PM
This thread contains a useful formula for calculating air pressure on a rotating habitat
http://www.bautforum.com/space-exploration/77433-centrifugal-artificial-gravity-2.html
note that the 2000km ring basically needs to be entirely enclosed, if only by a membrane above the 50km mark.

PraedSt
2008-Oct-15, 04:52 PM
This thread contains a useful formula for calculating air pressure on a rotating habitat...

After all that, I went and forgot air pressure. :wall:

Thanks eburacum45. And Grant.

timb
2008-Oct-15, 08:19 PM
This thread contains a useful formula for calculating air pressure on a rotating habitat
http://www.bautforum.com/space-exploration/77433-centrifugal-artificial-gravity-2.html
note that the 2000km ring basically needs to be entirely enclosed, if only by a membrane above the 50km mark.

I'm a little uncomfortable if the ceiling is lower than about 2.5m. I still haven't fathomed what the additional 49,997.5m is for, other than boosting the material requirements by a factor of 20,000.

PraedSt
2008-Oct-15, 08:54 PM
I'm a little uncomfortable if the ceiling is lower than about 2.5m. I still haven't fathomed what the additional 49,997.5m is for, other than boosting the material requirements by a factor of 20,000.

Birds of course. Can't not have birds...

timb
2008-Oct-15, 09:00 PM
http://heartthreads.typepad.com/photos/uncategorized/2007/11/14/birdcage.jpg

PraedSt
2008-Oct-15, 09:03 PM
Lol...
That just cruel

Ara Pacis
2008-Oct-16, 05:48 PM
At least he didn't give you the other bird. :-D

eburacum45
2008-Oct-17, 01:51 AM
I'm a little uncomfortable if the ceiling is lower than about 2.5m. I still haven't fathomed what the additional 49,997.5m is for, other than boosting the material requirements by a factor of 20,000.
One way to use that perception is to make your rotating habitat into a series of concentric shells, with a nice comfort zone between them. The floor of one shell would be the roof of the next shell outwards, and so on.

You could even make the roof high enough so that clouds could form; that would add a nice homely touch. Add a gently glowing blue sky behind and you have a comfortable Earth-like environment. There are lots of tricks you could probably pull to make such a large space feel like the great outdoors, given a large enough budget.

One little problem would be access between the decks. If you just have an open lift shaft you would lose all the atmosphere in the 'upper' levels, as it would all pass down the shasft, congregate in the 'lower' levels and make the air pressure there uncomfortably high. The lifts and lift shafts would need to be sealed and pressurised - in fact the lifts might be better off outside the habitat altogether, in the vacuum of space.