From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.policy Subject: Lunar Sample Return via Tether (was Re: China won't ... References: <20040521104150.17796.00001602@mb-m18.aol.com> <9186edb5.0405221026.23a41ef6@posting.google.com> <1085278609.833270@kyle.snap.net.nz> NNTP-Posting-Host: 207.42.133.252 Message-ID: <9186edb5.0405231020.13f98004@posting.google.com> "Pete Lynn" wrote in message news:<1085278609.833270@kyle.snap.net.nz>... >I have become increasingly enamored of the lunar rotovator that scrapes >the surface for regolith, otherwise avoiding all lunar infrastructure. I also love this idea. >No external momentum balancing required. The tip speed is just slightly >higher than the orbital speed, the necessary momentum comes from the >force of the scrape, I think? It scrapes backwards. No, I don't see that working. I don't think you could control the amount of "scrape" so well. If you hit a big rock you would break something at the kinds of speeds you would need. I think you either want to use an ion-drive or pickup some extra regolith and, after winching in some to increase tip speed, toss some regolith as reaction mass. >Mass lifting to the hub and various powering against tidal lock >systems can be used to regain rotation speed. Since you are taking mass from the end of the tether to the center, you probably have to worry more about having too much rotational speed, not gaining it back. One of the fun things about tossing some regolith after spinning up when you winch in partway is that it can fix both the orbital and rotational momentum. >With this approach you do not have to land on the lunar surface, the >advantages of which should not be underestimated. > >-No landing delta v requirement, especially during installation enabling >a much lower mass system. Agreed. >- A polar orbit might enable operation in continuous sunlight/power? >While this approach is very efficient, elevating mass requires lots of >energy. An ion-drive to ejecting 1 Kg of argon at 30 km/sec would give you the same momentum of a tether tossing 10 Kg of regolith at 3 Km/sec, but take about 10 times as much electricity. So tossing regolith is a good way to reduce power requirements. >- No infrastructure or manned presence required on the moon and the >logistics there from. - No payload guidance or catching required. I think people on Earth would pay more for lunar rocks than lunar dust. So you might want a little rover that collected rocks and put them at a special pickup spot. The other choice is that the tether picks up more than it needs but withing a few seconds releases everything less than 1 cm (or some screen size). This is probably better because you can then pickup stuff from all over the moon. >Mass can be preprocessed or repackaged into a specialized guided vessel >and tether launched to HEO. There is no real scale constraint and >technically it is relatively unchallenging. A couple of ton could see a >system up and running and it will just accrete mass in lunar orbit, >ready for shipment to whoever wants it. I rather have the probe bring the stuff back to Earth and send it down so we can sell stuff to people on Earth. A lunar rock "the size of a raisin" stolen in Malta recently was said to be worth around $5 million. So if you brought back 10,000 Kg ... >Some improvements might be >desirable, like replacing the tether wind up approach with a far more >effective continuous belt elevator, for example. If the probe lets out an empty tether as it winches in the tether with the load, things can work out well as far as energy and rotational momentum. >This is by far the quickest and cheapest step to extra terrestrial >resources I have seen, we could do this now for only a few hundred >million. Perhaps lifting a thousand times its own weight, thousands of >tons a year. I agree. And I think you could sell the returned lunar rocks for more than the cost of the mission. If you start with a Falcon-V so you have like 10,000 lbs for $12 mil, so you don't need to sqeeze every gram out of your design, so the probe does not need to be as expensive as is standard. I think even $50 mil is not out of the question. > In my mind this is the next step beyond CATS, perhaps even >warranted before CATS as it would give us something to go for, something >with which we can directly build a space civilization. This makes lunar >mass launches look just plain silly by comparison. I think this is a great first step for tethers. It avoids both the high precision rendezvous problem and the politics of operating in LEO with other sats. If someone spent $50 mil on this and made $500 mil, there would be money to setup a LEO tether. We talked about this some on sci.space.tech under the subject "Lunar Sample Return via Tether". See: http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&q=lunar+sample+return+tether&btnG=Search&meta=group%3Dsci.space.tech Also, Henry Cate (my father) gave a short talk on this idea during the last session of the 2004 Space Access conference. Stragely, it seems people there were much more excited about the idea of getting blimps up to orbital speed. In 2005 I plan to be there with pretty pictures. :-) -- Vince