From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.policy Subject: Re: Settle the moon first using tethers References: <9186edb5.0404210736.308d9697@posting.google.com> <9186edb5.0405061618.147d85b4@posting.google.com> NNTP-Posting-Host: 207.42.133.252 Message-ID: <9186edb5.0405072323.2370bb04@posting.google.com> "Mike Combs" wrote in message news:... > The fact that the moon lies at the bottom of a gravity well is only one of > several disadvantages which O'Neill would cite. The moon is really high in Earth's gravity well. Sure the moon has a small gravity well of its own, but that one is easy for a single tether. If we can trade places with some moon rocks, we would then be in a much smaller gravity well than we are now. Tethers can let us make such a trade. Looks like a good trade to me. > OK, so there are exactly two locations on the moon that might suffer less > from one of several disadvantages of planetary surfaces. That still doesn't > make the moon as a whole competitive with all of orbital space. But until the prime real estate on the moon is all taken, it does seem the best place to go. After this, building a power network on the moon seems easier than lifting radiation shielding into space. In any case, the first problem of interest seems to be where will the first settlers go. In the long run, I agree orbital space holds more people. I am not confident I will live long enough to see the moon get full of people, so I am not so interested in the long run. > But talking long-term > (remember, O'Neill was talking about "the best site for a growing advancing > industrial society", not just where we could get the earliest modest start), > let's talk about a habitat built next door to a NEO. I don't see that > shielding mass would be any less convenient to obtain in that situation than > on the lunar surface. I agree that building on or near asteroids would be very convenient. > But you say that as though providing gravity via rotation were some > significant expense. Is it? > > O'Neill calculated the requirements to spin-up the largest of his habitat > designs, Island Three, on a time-scale of months rather than years. He > concluded that the electic motor needed to do so would be no larger than the > engine in most cars, and could be powered by no more solar energy than what > would fall on the end-cap of the habitat. One only need overcome inertia. > The same motor would also make up frictional losses. But with > sensibly-designed bearings, this would be trivial amounts of power. The expense is in making a structure that is strong enough to hold in the forces. This structure is costly enough that most (all?) of the large habitat designs have the shielding mass outside the spinning part and not spinning. This always makes me nervous because if something ever wedged in between the spinning and non-spinning parts it would be like throwing a monkey wrench in the gears of a really huge machine that many lives depended on. > > The cost > > to make a lunar settlement for a given number of people > > would be much less than for the same number in orbit. > > Are you sure? At low numbers, you're probably right, provided that the > orbital habitat, no matter how small the population, is still required to > provide spin-gravity and radiation shielding. But can you be sure that a 10 > million person lunar habitat would cost less than Island Three? Remember > that the cost of energy at the construction site would be a significant > factor. If we make solar cells from lunar materials I think they can easily cost several times less than ones in orbit. So making a power grid on the moon could cost less even if you have several times as many solar cells. The shielding is the dominant mass, which is free on the moon. So while I am not sure, I expect the moon would be cheaper even for 10 million people. But I am interested in the "low numbers" because the near term is just much more interesting to me. > And in any case, the lunar habitat could not provide one-G of > gravity, and would never be able to continuously provide a normal day/night > cycle using natural illumination. I just don't think I care about either of these. If I am not coming back to Earth, should I care if my bones/heart/etc adjust to 1/6 G? -- Vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vincent Cate Space Tether Enthusiast vince@offshore.ai http://spacetethers.com/ Anguilla, East Caribbean http://offshore.ai/vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You have to take life as it happens, but you should try to make it happen the way you want to take it. - German Proverb