Bob et al, Agreed that the forces are tiny, but what about the "differential" forces that apply when one magnetic system is between two other magnetic systems. Still tiny, but larger than either by themselves. Possibily insufficient to supply the delta v required to make useful changes to the orbit, and as Greg pointed out very difficult to do. The differential effect was the point of my original post, probably not well expressed though. When this interesting topic first arose I dismissed it out of hand, but it kept coming back, and required further pondering hence the original post. I have tried to find out more about the "tether" project but there doesn't seem to be a lot of info available. Maybe someone can point me in the right direction.(no pun intended!) If any one doubts the forces available using magnetic fields, It could be instructive to watch the cables from a high power arc welding set when the arc is struck..... I've seen them literally jump several inches!

On a totally different subject is there any "promotional" material somewhere on the net suitable for a simple club presentation about APRS?

Thanks to everyone for the interesting comments.

Don McNeil ZL1THO