Fred, earth to space tethers are a very promising area of research (space elevators etc.). Might be the best bet for a 50km conductive wire indeed. The technology is more speculative than balloons though :)
David, no magnetic field gradient is needed, the Lorentz force also exists in a uniform magnetic field (cf e.g. http://en.wikipedia.org/wiki/Lorentz_force ) Michel ----- Original Message ----- From: "David Jonsson" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Saturday, December 23, 2006 3:16 PM Subject: Re: [Vo]: Re: Going Van de Graaff > It does not seem like a good article.on Wikipedia. > > When direct current <http://en.wikipedia.org/wiki/Direct_current> is pumped > through the tether, it exerts a force against the magnetic field, and the > tether accelerates the spacecraft. > > Should read as > > When direct current <http://en.wikipedia.org/wiki/Direct_current> is pumped > through the tether, it exerts a force against the magnetic field gradient, > and the tether accelerates the spacecraft. > > The field is very weak and the gradient even weaker. *F*=[image: [del]](*m*· > *B*) or *F*=(*m*·[image: [del]])*B* > apparently there is some ambiguity on this subject: > http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=AJPIAS000056000008000688000001&idtype=cvips&gifs=yes > > David > > On 12/23/06, Frederick Sparber <[EMAIL PROTECTED]> wrote: >> >> Would this work, Michel? :-) >> >> Fred >> >> http://en.wikipedia.org/wiki/Electrodynamic_tether >> >> >> >> >
