At 07:47 PM 12/16/2012, Jouni Valkonen wrote:
Actually, we will _never_ build large space or Mars colonies, because we have Venus for second home. Venus is after initial costs cheaper place to live than Earth, because solar energy at Venus is free (far cheaper than e.g. thermal cold fusion electricity could be), because outside temperatures are optimal for solar cells and solar flux is very high.
Okay, I'll provide the standard L5 Society response to this. Give me a few minutes to get that old engine running, it's a bit rusty.
The pressure problem however is really difficult and it helps greatly if orbital habitats are kept at low pressure. I could not even imagine comfortable living in vacuum. Imagine landing with airplane at worst and multiply that with figure 100. Then you should get a feeling how radically uncomfortable pressure changes are at high vacuum habitats such as in Mars, Mercury and L1 points. There is no such thing as routine when we are dealing with high vacuum.
The space colony locations proposed, for earth orbit, are L4 and L5. Get it straight! L1 has negative stability. Nobody is proposing living at low pressure, but some lower pressure, comparable to habitable places on Earth, might be okay.
There is also radiation hazard in orbital habitats.
Probably the biggest problem. Radiation shielding has been part of space colony proposals.
Of course ISS will get company and I would predict that in 2020's we are starting to build second generation space station with artificial gravity enabled into high lunar orbit. Perhaps into L1 point, what would be suitable anchor for lunar space elevator. Near Earth Asteroid material is relatively cheap to collect into high lunar orbit and it should compensate higher launch costs.
Actually, the standard Society proposal was to build a nuclear-powered railgun on the Moon and use it to launch lunar rock to a transshipment point, might have been L2, I forget.
Okay, why space before Venus? Actually, at the time, living in floating colonies at high altitude on Venus wasn't being considered, I never heard of it. The argument for space was the same reason why Earth cities were preferably built near transportation typically major rivers or ocean ports.
You want to build in a place it is easy to travel from. Easy to get to any destination from earth orbit. Hard to get to earth orbit from Earth. Hard from Venus. Once in space, you can use solar sails to move even very large mass, all you need is some patience.
The original justification for the moon project and for space colonies at L5 was to work on satellite solar power stations. The materials would come from the moon, but people would actually live at L5. Expensive to get there, but cheap to return to earth, if you want. Also cheap to move the constructed satellite solar power stations to geosynch orbit. The plan, back before 1980, was to start replacing earth-based power with satellite solar power; the solar power would be sent with phased-array antennas to receiving antenna farms on the earth, they could be anywhere the land was available. The receiving antennas would be essentially raised wires, at a certain spacing, the signal would be tuned to them (and kept in focus by a return signal, if the return signal was lost, phase lock would be lost. The energy density in the beam, even in focus, would be enough to feel warm, and I wouldn't think one would want to be in it for long times, but the density below the antenna would be fine. Basically, one could farm below the antennas, which would not obstruct sunlight.
This was seriously proposed and had some level of political support, but not enough. The budget was comparable to what was already being planned to be spent for new energy generation using non-renewable fuels; this would be clean and essentially indefinitely renewable.
I saw lots of spurious objections, the most serious real one was the number of launch missions required to establish the basic presence in space. That *would* have an environmental impact.
Hope was, eventually, to build a space elevator. (i.e., Clarke's idea.) That was optimistic, still is. The basic L5 project did not require new technology.
For humans to live in space, the biggest expense is lifting *hydrogen*. Oxygen is readily available on the moon, as oxides. Hydrogen is scarce in space.
