From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.history,sci.space.policy Subject: Re: $5M Moon Rock Stolen From Malta Museum References: <373a0bc9.0405211458.bde154a@posting.google.com> <1ywsc.624$ZM1.488@bignews6.bellsouth.net> <9186edb5.0405250856.eeee6b9@posting.google.com> <9186edb5.0405260624.b0faebd@posting.google.com> NNTP-Posting-Host: 207.42.133.252 Message-ID: <9186edb5.0405262108.22fec503@posting.google.com> Doug... wrote in message news:... > OK -- I'll accept that he's put some time into getting his numbers. > That is certainly not obvious in his posts, where he simply tosses out > numbers like "this will cost from 100 to 1000 times less than chemical > rocket systems." Without any clue as to his assumptions and premises, > it's hard to accept those kinds of figures. All I was talking about was how much more lunar regolith you can return for the same initial launch mass. I said launch costs, not total costs. Once orbiting the moon, we can lift regolith and fling some as reaction mass (see sample 89 in spacetethers.com simulator). So we don't use rockets/fuel while we are in lunar orbit, except for an ion drive for guidance. We can also fling packages back to Earth from our tether. If we are in an elliptical orbit, we won't need much deltaV to toss something away from the moon and back to Earth (or to get into the orbit initially). So the same tether that we use to lift small amounts from the moon can toss a larger package back to Earth. It will take some time (weeks or months) to lift everything. But assuming nothing breaks, we can keep going till we run out of reentry modules. The reentry capacity is the limiting thing in this approach. Maybe we collect 5 Kg at a time from the lunar surface and toss 100 Kg at a time back to Earth. I think we can toss at least accurately enough to hit the South Pacific. I estimate a dumb Heat-Shield package at 1/3rd extra mass (so 33 Kg). This will include a tracking beacon but no rockets/guidance/computer. So for every Kg of reentry package we can send back 3 Kg of rocks. If 1/3rd of our initial mass is reentry packages then we can send back our own mass in moon rocks. A full chemical rocket approach can return a payload that is something like 1% of the mass after TLI (see earlier post in this thread by Henry). So at 100%, the tether approach is something like 100 times better. If we could make our electronics survive a slow trip through the Van Allen belts, we could get another factor of around 5 in initial mass by using our ion drive to get all the way from LEO to TLI (so like 500 times better). I would try a range of different reentry modules on the early flights. All the way from very conservative to very experimental. I like a reentry ballute that also keeps the speed down after reentry and even floats if we miss the midair catch. Clearly we will search for a reentry module design that is light weight and reliable. One of the most bleeding edge approaches would be to try to pickup polar ice and use it for water transpiration in a reentry package. (Paul Dietz metioned this idea for asteroid metals).If this worked, we might get another factor of 2, for a total of around 1,000 times better. It sounds like the Van Allen belts are too hard on electronics. There is some chance that we can shield them some with all the reentry modules. But it seems like we would be better off to avoid this problem, at least at first. You can make your own estimate for what fraction of the starting mass can be heat shield modules and what the ratio of heat shield mass to payload mass is. But whatever the real numbers are, I think it is much better than an all chemical rocket approach. -- 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 Keywords: Lunar Sample Return via Tether