in what way (that doesn’t reference the facile conceits of science fiction authors)?
Stranger
But… but… where would we geeks be, without the facile conceits of science fiction authors?
Would it/they “stick” without a magnetic field? The solar wind stripped the last atmosphere it had…
Didn’t it take life quite a few million years to change Earth’s atmosphere?
I’d stick with domes, they’re cheaper.
The idea of living inside of Mars makes more sense.
Or we could pressurize just a canyon and live in the cliffwalls.
But, Stranger is right in one respect: orbital habitats make more sense as long as we posit some sort of artificial gravity. From what I understand, the human body doesn’t handle long-term microgravity very well at all.
Simulated gravity is almost trivial, especially with a large structure, which can be spun not only to experience centrifugal radial force on the inner surface but also to enhance structural rigidity. This may be technically challenging in developing the ability to apply and maintain spin, but doesn’t require an understanding beyond gyroscopic dynamics.
Stranger
I assume that one of the problems with using this for a small structure would be that people would get nauseated walking around inside. What would be the minimum diameter needed for people to be able to lie down, stand up, and more around without getting sick?
If you don’t wanna live under a dome, you could bioengineer people more easily than you could terraform Mars. There’ve already been some sf stories about that.
To breathe Carbon Dioxide at 1% atmospheric pressure? 
What about tourists?
Those books were a great read. I don’t for a minute believe that terraforming Mars will or even can happen but, still, it’s fun to think about.
One thing that Robinson did that made it believable was that terraforming Mars was not a concerted, centuries-long effort to give humanity more breathing room. It was done bit-by-bit by individuals and groups that went there to do research, make a living, or just make money.
Even if we had the technology to accomplish the task it would be a horrible investment. It would require an incredible expenditure of capital and resources over a long period of time for…a small area of living space with too-low gravity, far from the sun, with an environment that would have to be constantly maintained to stay livable. It would be a far better investment to terraform the Sahara, the Australian interior, Antarctica, etc.
Colonies will not exist in space until it pays to put them there. And it must pay big enough to overcome the huge capital “activation energy” of building the first habitats. The only thing I can think of that might suffice is discovering an asteroid with huge concentrations of some extremely valuable element.
Assuming off-Earth colonies happen, I’m with Stranger in believing they will be in off-planet habitats.
Since always. All the articles saying we have even the materials and know-how to build a space elevator on Earth or Mars are full of misleading and outright false claims.
They all make exaggerated claims (to the point of being absolute BS) about what is feasible with existing technology.
For example, they tend to assume the strength of nanoscale (or even microscale) carbon nanotubes is maintained when scaled up to millimeter or centimeter scales. As of right now, we can’t scale up the small fibers we CAN create while maintaining the tensile strength we need to support the structure, even under Mars gravity. A similar analogy would be to assume a 600 foot man could even support his own weight (easy for an average 6 foot man). A scaled up human like that couldn’t even get enough oxygen, much less support his own weight.
Also, they all tend to use the lowest cost estimates for the amount of material necessary. The problem is that if a company estimates they can deliver X amount of carboon nanotube material for $Y, they usually mean they can only generate so much of it. They can’t create the huge volumes of necessary material at any price. But the blue-sky space elevator concepts all assume relatively cheap production of massive quantities of as-yet unrealistically strong nanotubes.
Beyond that, there are the simple (but not easy) engineering challenges involved in an inherently unstable design.
The elevator will sway. We have no real way of controlling it right now. There’s an inherent instability so the elevator won’t be rigidly locked in place during construction. We can’t control that. Even after completion, it’ll sway a bit, and that creates some issues for the elevator system.
Also, there’s a power issue. A space elevator will necessarily need an accessible power supply running along its entire length. While carbon nanotubes provide a reasonable conductor, we really have no good way of running such a long power line and a power plant installation of any type takes years, anyway.
The actual ‘elevator’ technology doesn’t exist. NASA and other groups have been trying to create rapid climbing robots, since a normal elevator tube obviously wouldn’t be practical for several reasons. These robots do not yet have the necessary speed or carrying capacity to help build a space elevator or ferry materials should we finish one.
There’s a host of other problems, but basically, the people who claim we could easily build a space elevator with existing technology either haven’t thought about the problem or over-estimate our engineering capability. They’re similar, in this respect, to the people claiming we could trivially establish a functioning, self-sustaining colony on Mars with existing technology.
There is both the physiological response (vestibular effects) and the psychomotor response (disorientation from objects behaving differently under gyroscopic motion and centrifugal radial pseudo-acceleration than under gravitational acceleration) that has to be considered. The physiological effects are easier to assess objectively, while psychomotor effects may vary dramatically between people. The effects depend on rotation rate, with <1 RPM giving no significant physiological effects, and >2 RPM considered a general threshold for continuous rotation (though some sources differ). There is relatively little experimental information on these effects in a practical space-like environment, though fairly extensive human testing has been done in a terrestrial environment. According to one source, the minimum rate off rotation and radius for normal human function is 6 RPM with a 14 meter radius, giving 0.58 g acceleration (Thompson A.B., 1965, Physiological design criteria for artificial gravity environments in manned space systems, First Symposium on the Role of the Vestibular Organs in the Exploration of Space, 20-22 January 1965, US Navy School of Aviation Medicine, Pensacola, FL, NASA SP-77, pg 233-241). Assuming a 2 RPM rate, you would need a 220 meter radius of rotation to achieve ~1 g acceleration, which would obviously be very large in comparison to existing spacecraft, though reasonable on the scale of a large permanent space habitat. This scales linearly, so you would get ~0.5 g at a 110 meter radius. If we could tolerate a rotation rate of 5 RPM, we could get 1 g at a radius of about 36 meters, or 0.5 g at 18 meters, which are somewhat more reasonable, though larger than any unitary spacecraft that might be launched from Earth’s surface. However, spacecraft could be tethered to each other or a ballast mass to generate the long moment arm sufficient to simulate gravity during a orbital transit.
We don’t have enough data to assess what kind of acceleration is necessary to maintain adequate health indefinitely, but long term habitation will require simulation of gravity, presumably by rotation.
That is almost as close to science fiction as artificial gravity or terraforming. Certainly we can envision radial genetic engineering, but the conditions of the surface of Mars are inhospitable to even the most robust archea. If there is life on Mars, it is probably very simple, buried deep within the soil, probably at the subpolar regions, and feeds on oxidation reactions rather than photochemical energy conversion. Engineering human beings to live on the surface of Mars without artificial sustainment is not possible with anything like the normal respiration processes that are part of the basic mechanics of all multicellular life on Earth.
Stranger
People are posting ideas but don’t know the real facts on terraforming Mars. What does ‘terraforming’ mean. Many are using it to denote making it Earth-like. This can never happen because Mars is lacking a magnetosphere (Earth has a molten iron-nickel core which generates ours).
The Magnetosphere protects against solar radiation and cosmic rays. Mars may have had one in the distant past but does not now and can’t ever be like Earth without remaking the whole planet using something drastic like a collision with a gigantic metal meteor or some kind of TV-magic.
Also, there’s the problem of the red dust which gets into and corrodes everything. It’s basically uninhabitable by even very advanced technology.
So, forget about going there (it’s almost impossible due to radiation and long travel times) and forget about making the atmosphere like Earth’s.
Mars’s dynamo is dead, and there doesn’t seem to be any way to get it started again. That pretty much rules it out as far as I’m concerned.