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> <9186edb5.0405262211.1423606@posting.google.com> NNTP-Posting-Host: 207.42.133.252 Message-ID: <9186edb5.0405271134.7de58bd@posting.google.com> Doug... wrote in message news:... > Ummmm... OK, I'm not visualizing the setup very well, here. For a > tether to drop straight down from an orbiting craft, that craft would > have to be in selenosynchronous orbit, wouldn't it? And 20 km is a LOT > less than the height of a SSO, isn't it? > > From a vehicle orbiting 20 km above the surface of the Moon, how do you > propose to completely null out the orbital vehicle's velocity from the > scoop end of the tether? We are talking about a rotating space tether. It is rotating in the plane of its orbit with the part closer to the moon going backwards relative to the orbital motion. Say the orbital motion is 1.6 km/sec and the tip speed is 1.6 km/sec, so near the surface of the moon these cancle. On the high side they add together, so the tether can pickup something down low and then toss it fast up high. It does not drop exactly straight down, but for a guy sitting on the moon who only sees it when it is nearby it will mostly seem to be coming down from one side and then going up the other. This general idea is called a "momentum exchange tether". You will also hear "bolo" and "rotovator" with rotovator being the case that touches a moon/planet. I like "rotating tether" as it seems clearer. See: http://tethers.com/MXTethers.html My simulator is a Java applet, so it should be easy to run. You can just click on samples and run them to help you visualize what is going on. It is at: http://spacetethers.com/spacetethers.html -- 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