From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.tech Subject: Re: Lunar Sample Return via Tether References: <20031209194336.0 6226.00001965@mb-m19.aol.com> <9186edb5.0312100949.3c86ca20@posting.google.com> NNTP-Posting-Host: 209.88.68.33 Message-ID: <9186edb5.0312142050.5a822cc4@posting.google.com> henry@spsystems.net (Henry Spencer) wrote in message news:... > >With a solar sail the only thing limiting how much you can lift is how > >long your system keeps working. > > Assuming you can make a solar-sail-based system work at all. Don't > forget that solar sails impose some troublesome constraints, like the > need for quite large surface areas and some sharp limitations on what > direction you can thrust in. My simulator can do solar sails, so I have played with them some. Tethers and solar sails can fit together well in terms of the time and direction of thrust. When you do a tether pickup it drops the far side of your orbit. To reboost you need to thrust on the same side that you picked up. A solar sail does its best thrusting on the side of its orbit where it is going away from the Sun. If you plan your pickup so that you are in the part of your orbit where you are going away from the Sun, then all works out amazingly well. The large area is not an easy fit with any real G loading. So having it be built into a rotating tether may not be practical (I have not totally given up, but it does not seem easy). One way around this is to have 2 solar sails out in front pulling (one a bit to the left and one a bit to the right) and attached to the center of mass for your rotating tether. A hanging tether could be a bit easier. So for a big tether in GEO, it could work well. It is less clear for a small probe picking up regolith from the moon. I now prefer tossing regolith for thrust to reboost the Lunar tether. Anyway, solar sails have their troubles and constraints, but I think they have a bright future with tethers. -- Vince