From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.policy Subject: Re: China won't go to the moon References: <20040521104150.17796.00001602@mb-m18.aol.com> NNTP-Posting-Host: 207.42.133.252 Message-ID: <9186edb5.0405221026.23a41ef6@posting.google.com> henry@spsystems.net (Henry Spencer) wrote in message news:... >G EddieA95 wrote: >>Dropping rocks off the moon is still science-fiction. Using nukes is much >>cheaper and doesn't give the enemy 3 days of warning. > >Besides, you don't get to "drop" rocks off the Moon. You have to *launch* >them off, and launch them hard enough to put them in an Earth-intersecting >trajectory too. That takes rather a lot of energy, about 5% of the energy >released by the final impact. That's enough to make this distinctly less >than a magical wonder-weapon, Robert A. Heinlein notwithstanding. > >It's not merely science fiction, it's *bad* science fiction. If you had a really long tether going from the moon through L1 and on towards Earth, you could "drop" rocks off the end toward Earth. You could have a generator on the elevator going from L1 towards Earth and use that power to run the elevator lifting rocks from the moon's surface to L1. With current materials, such a tether is near the limits of buildable (with no limits on cost). Transmitting power from the "down" elevator to the "up" elevator is not trivial (maybe with lasers). You probably want 3 tethers from L1 to the moon so you could balance and stay at L1. This also would be a big easily destroyed target, so not a good weapon. So while I would not say this is currently practical, would this be bad science fiction? Basically the above is a huge hanging tether with the moon as the ballast. I am wondering if there is not some way to use a rotating tether in a funny orbit so that you loose energy when you pick rocks up off the moon but gain energy back when you toss them on down toward Earth. So far I don't see a way to do this, but am not yet sure it could not be done. It would be really cool if this could be done. -- Vince