From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.space.policy Subject: Re: JP Aerospace Airship to Orbit References: <1083577718.392194@kyle.snap.net.nz> <9186edb5.0405231945.168c8e4a@posting.google.com> NNTP-Posting-Host: 207.42.133.252 Message-ID: <9186edb5.0405241806.35454373@posting.google.com> henry@spsystems.net (Henry Spencer) wrote in message news:... > In article <9186edb5.0405231945.168c8e4a@posting.google.com>, > Vincent Cate wrote: > >If you paint the front white and the back black, there would be a > >net forward force. This is called the "radiometric effect". > >The "radiometer" was invented by Crookes a long time ago. You > >can see a picture of this standard toy that spins in the sun at: > >http://store.yahoo.com/explo/radiometer.html > > A particularly neat variation of the Crookes radiometer is to make the > paddles *transparent* and paint one side of them flat black. Still works > just fine, which shows clearly that it's not a question of whether light > is absorbed but of *where* it is absorbed. It seems this radiometric force is enough to levitate a thin membrane: http://www.spacetransportation.com/ast/presentations/3g_know.pdf If you started at "Dark Station" (140,000 feet) you might just be able to have a really thin airship with a clear-top/black-bottom that was able to levitated to very high altitudes. I think tethers are much more practical, but this is a fun idea. -- Vince