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Saturday, February 15, 2014

Unlimited Accessible Water in Space Means Unlimited Expansion for Humanity

   Recently I did an article for ThinkScotland  summarising the space current development field.

   After I had completed it I found this which Brian kindly allowed me to add. On my site I highlighted it.

     The reason a relatively small asteroid can hold more water than Earth is because all our water, being lighter than rock, is on the surface which, if you compare our planet to an apple would be no thicker than the skin, whereas with virtually no gravity field asteroid or cometary water can be all through it.

    The reason I think it important is that some years ago I did a Big Engineering about mass production of O'Neill space colonies. In that I said that because building such settlements are endlessly scalable so long as there is lunar soil left, and automatable or run by remote handling from earth, we could build hundreds of millions of them, enough, as I said, to make a Ringworld.

     "A recent paper in Nature says that there are enormous amounts of water in Ceres the 2nd largest asteroid in the belt beyond Mars  perhaps more than in all Earth's oceans. If so, particularly since this is just 1 asteroid, we have enough water to supply a virtually unlimited human population in space, certainly larger than Earth's population."

    But I was wrong. I assumed lack of water (back in 2008 we didn't know how much water there was on the Moon) would be a constraint, even if we brought it in from the Asteroids. This discovery, which since it is only 1 asteroid of thousands means the amount of water is only slightly short of incalculable. Being closer (much closer in terms of the energy needed to change orbits) than comets or the outer planets) it is easily available. "Easily" for a spacegoing civilisation that is - but we can have that anytime for a fraction of what we spent owning Afghanistan.

   That means we could build billions, very many billions, of such settlements. Far more than 1 for every human now living. At the time I said that at 10% annual growth there could be a Ringworld by 2195AD. That means 1 dozen Ringworlds (put them each 3 million miles further out than the last and we still fit them within the orbit of Mars) by 2022. Actually the traffic congestion would probably make it longer but you take the point.

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It would seem that the limiting factor for unrestricted human colonisation of space is not water, but the invention of an effective shield against inonising radiation and cosmic rays that does not involve large amounts of mass - invent / discover that and much is possible.
The design of O'Neill colonies involves putting a large mass at the sunward end, to stop radiation, and lighting them with mirrors. This does involve large masses but such are availbale in the asteroid belt or from lunar regolith and when construction is done in zero-G handling such is much easier than on Earth. Thus while a cheap light shield would be a major bonus I do not see its lack as limiting what can be done.
In a word ( or three ) the Van allen belts. One possible drawback to the space elevator which could bring down the cost of climbing out of earth's gravity well drastically is the time that is spent crossing through these belts of radiation needs to be as short as possible and that puts greater demands on the craft that travel on the ribbon(s )
Also whatever propulsion system you use the power and reaction mass required increases with the mass of the space craft. A lightweight radiation shield would also transform the nuclear power options.
The sun is also not the only source of radiation in space, just the nearest and brightest ( though god help us if a super nova goes of anywhere in our part of the galaxy )
Thanks for that interesting observation. The writer is correct but the mass of the car holding the passengers plus its radiation shielding is so miniscule compared to the mass of the actual elevator cords that while correct the extra shielding mass would itself make very little difference. Ideally the elevator should hang from a solar power collecting array that would provide all the power required.

Best wishes, Andy Nimmo
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