In the end, your own underlying philosophy behind building construction also plays a role.

As alluded to above, I prefer a "Lego blocks" approach: start with small discrete "compartments" (or "cells"), adding cells to increase the size of the orbital as desired.

I think this model is more efficient because it's easier to add onto "existing" habitats than to build totally new ones from scratch. Furthermore, if desired, we can cannibalize the walls of old cells for new outer shell construction material (think home improvement on a magnitudinally larger scale). Cells can be of any size, of course, but I modeled my assumptions on a near-perfect cube, with 16 meters each in all three spatial dimensions (the cell shells are 2 meters thick in all dimensions, for at cubeoid of 20 meters to each edge).

Time to human habitation is reduced even more if we elect to have lower orbital gravity (say, mars-like). At 2 RPM, we only have to have a floor-to-axis radius of about 90 meters, which reduces the material requirements by around 60% by my estimate.

Result: much quicker investment for our money (especially important if a private company is paying the bills), plus by the time we add enough compartments to get to the "1G line" (224m), we'd have enough construction experience to know how to build safely and with high quality. This, in turn, makes for more satisfied immigrants (DEFINITELY NOT a trivial matter!)

It's the same area. Or more accurately, the same volume. The outer shell shape doesn't need to match the shape of the internal floors which are occupied. A spherical outer shell simply provides extra "bonus volume" in the equatorial bulge and endcaps which can be used for hydroponics, storage, or whatever.

If length=diameter, then you're already building a habitat which is roughly spherical. You can't have flat sides because air pressure would bulge them outward. In order to keep the length roughly the same as the diameter, the outer floor is reduced to an equatorial band between the two bulging endcaps.

This is inefficient because the bulk of the outer shell's mass is required for radiation shielding. You'll have internal partitions which are horrendously over-engineered. Note that you can have radiation shielding that does double duty as hydroponics also. This only works with the outer shell, and not internal partitions.

If you want to inhabit a partially completed habitat, start with the outer shell and fill it with air. Then, build the internal floors from the outside in.

Point conceded.

I didn't think of air pressure; specifically conflating it with mere air mass in kg. Just as as party balloon on earth filled to 2 ATM air pushes outward on that ballon's interior surface, so a 1 ATM pocket of air pushes outward on a habitat surface (possibly even more so, given that the baloon-to-earth atmosphere pressure difference is tremendously less than the habitat-to-almost-vacuum of space is. I don't know if the pressure difference is a matter of x / y or if its x - y). You got me there.

I was thinking in terms of "terrorist attack" (and safety in general) when I wrote this. Yes, it'll definitely raise material requirements, but on the other hand it'll be a relatively cheap form of life insurance - more "cells" present means more protection against a massive hull breach of some sort.
No doubt you can argue that 16 - 20 meters is too much of a good thing. Furthermore, on second thought, Lego Blocks might make it easier for terrorists to disassemble the habitat, esp. if each cell is designed to be unhooked easily from the habitat.

Regardless, it seems we both agree on compartmentalization. How do you reconcile this with the statement I quoted ?

My idea of internal compartmentalization is that the internal partitions are strong enough to hold in partial atmospheric pressure, and that a combination of flexing and safety valves will ensure graceful degredation. In the case of an outer breach, the nearby cells will expand and vent until the pressure is reduced to, say, one third pressure. The surrounding cells will expand and vent until the pressure is reduced to two thirds pressure. Then the cells around that can have full pressure.

What the internal partitions don't need to do is provide radiation shielding. The increased cancer risk from the radiation exposure will be minimal compared to the radiation exposure of an interplanetary trip anyway.

Hi, Basically, you can think " airliner fuselages" . They are designed to support
at least 10 pounds per square inch, and since they will be cycled only once,
I expect they will endure 15 lbs. with no problem. Build them and boost them.
Connect them in a ring, and cable stay the assembly. Standard parts, cheaper price. If you get the cost down, you might even go to space with such a system.
Best regards, Dan

Sounds good for a small station, but unless we cure cancer there's a question of radiation shielding. I'm reminded of ideas to build a space station out of Space Shuttle fuel tanks.

This rotating habitat is imagined to be made from reused heavy lifter fuel tanks
http://www.orionsarm.com/civ/Habitats.html#ringhabitat
if reusing heavy lifter fuel tanks is a realistic option, I am aware of many potential uses for these things.

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Orion's Arm . The Starlark . Voices: Future Tense . OA Flickr set

Hi, The shuttle fuel tanks would indeed make a good cell. Even if only "some"
of the cells were fuel tanks, they would be strong enough and already boosted
into LEO. There may yet be merit in that scheme.
Dan

Early prototype stations would likely be placed in Low Earth Orbit, both because they can be reached easily in an emergency, and because it's inside the Earth's magnetosphere, providing a good deal of radiation protection. Later stations, which will very likely be built using at least partly space-mined materials (from asteroids and/or the Moon), and will be able to use the nonstructural leftovers and slag as an effective layer of shielding mass. It need not even rotate, just place it in a shell around the station. O'Neill proposed using metal reflectors like a periscope, to let in sunlight and keep out ionizing radiation

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

I think asteroids should be used as raw materials--and perhaps chopped up using cables/tethers that would loop around the asteroid--much like how Kursk was cut up. Explosive/gas formed spheres with liquids layering up the width of the structure might work.

I fondly remember all the comic book representations of asteroids as flat on one side and bumpy on the other. With cutting cables, this might actually be the case with layers.

A sphere would be cut in half, then layered one atop the other, and melted into the flat surface of the asteroid. The gap between would be filled with a blue gel, to simulate a blue sky...artificial g from spinning surface habs away from the dome.

The main advantage of Mars is the public will probably pay for a manned mission to Mars. They won't pay for another space station nor a manned mission to a tiny asteroid. That perception could change in 5 or 10 years. NASA can't do much better than another space station oriented to space colony, unless there is a large change in leadership. My guess is tiny asteroids will get us to space colonies sooner. Second best is a tiny unsafe colony that costs a lot less than the space station, but my views are shared by few.
MY plan is telescoping tubes which can be carried to an altitude of about 500 kilometers in the cargo bay of the space shuttle. These tubes of thin metal and/or carbon fibers, extend to about 100 meters long. About 4 meters in diameter at the big end and 1.4 meters in diameter at the small end. Three to seven such tubes are nested with shock absorbers a few centimeters apart. with an air lock to each adjacent tube. Each should be equipped for survival in case the other tubes fail. A massive radiation shield binds the tubes at the big end where the colonists can huddle during a solar flare. The shield is shaped like a giant bottle cap. The big end normally points into the maximum dangerous radiation. This likely is not sufficient radiation protection, but is the best we can do near term. The colonists will have a short average life expectancy, unless we can genetically alter them for improved free fall and radiation tolerance. Neil

My question is--what's actually "inside" the tubes? It seems to me more straightforward to launch modules that already have equipment installed. Inflatable or telescoping portions, or maybe a spent Shuttle tank may be good for a place for the astronauts to stretch out and relax, of course.

That might be better as a design for extended missions, but probably not for lifelong colonization. No gravity plus high radiation would be especially bad for pregnant women and babies. I suspect we aren't going to be able to start a true permanent colony using only Earth-launched materials, unless someone decides to build a huge fleet of heavy-lifters dedicated to nothing but launching building materials. Which won't happen anytime soon.

(I suppose some apocalyptic religious group with a charismatic leader and fanatical followers could take over a small but wealthy nation and channel all its resources into leading his people "into the heavens", but I'm not betting any money on that scenario.)

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

I'm thinking the telescoped tube will barely fit out the door of the Shuttle cargo bay, and is close to the weight limit, unless we think less altitude than 500 kilometers. Weight permitting, each tube needs a plastic liner somewhat like a swimming pool, so it will be airtight. The folded liner will possibly fit inside the 1.4 meter diameter of the smallest tube.
I'm also thinking the colonist need to adapt to 2 psi oxygen partial pressure to reduce the stress on the tubes and reduce the violence of blow out, should that occur. People in Tibet live long lives on 2 psi oxygen partial pressure, so that should be do-able.
I think we should do this on or before 2020, as later may mean no one can leave Earth, because we are back in the dark ages. There are several reasons to think the good times won't last much longer.
At present, external tanks are released in an eliptical orbit which decays quickly. Releasing them higher in a more circular orbit with significant stuff inside will halve the payload of the shuttle. At present we don't have an inexpensive way to get the tanks back together even if they stay in orbit. Some people think we need space tugs (like tug boats) but I'm a bit doubtful space tugs will work well.
There is also a problem getting my 3 to 7 tubes (delivered separately) together.
Hopefully there would eventually be a way to to move unhappy and/or unhealthy colonists to a larger colony, but we can't wait in my opinion for that to happen. I think we will get voluteers, even if the projection is 10% of the colonists will be dead in ten years.
If you choose "go advanced" your edit or post is more likely to succeed on bautforum. Neil

Yes, I noticed that too, and mentioned it on the New Software thread. What's up with the Quick Reply buttons?

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

I'm just saying...what you've described is a just hollow shell devoid of any equipment. There still needs to be some "stuff" inside a habitat which actually keeps the inhabitants alive.

I think in the short term, the best we can do is haul used fuel tanks to the ISS, attach them to the outer shell, and construct a ring that's 150 to 175 meters in radius. Then, rotating the ring at 2 rpm, that should get us tolerable gravity. If we want Mars-type gravity, we can go down to 90 meters in radius. Regardless, it seems that without mass produced carbon nanotubes (1/3 the mass of steel per cm^3, but dozens of times stronger), all our grand schemes will be just that - grand schemes.

Not so. The designs for the Bernal sphere, Stanford torus, O'Neill cylinder, and other designs calling for nothing but ordinary metals and glass, would be capable of supporting tens of thousands. Carbon nanotubes may make construction of space habitats easier, but they aren't necessary.

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

In the very short term, we'll HAVE to take them from Earth's gravity well. Together with the current high expense per gm of nanotube, it'll probably be necessary - possibly as long as the next several decades. On the other hand, it's only 1/3 the mass of steel (don't know about aluminum). However, I'm apparently alternating between short term and long term. So in the end, nanotubes are the long-term optimal solution, IM