Has anyone else noticed how remarkably constant the drag term is for TiPS? I can fit an orbit to 24 observations made between 1996 October 31 and 1997 January 20 with time residuals between -0.45 and +0.34 secs, and also fit the 9 observations made between 1996 December 6 and 1997 January 20 with time residuals between -0.17 and +0.08 secs. The first orbit has ndot/2 = 0.00000346 +/- 1, and the second 0.00000349 +/- 4, which is substantially the same. I deduce that the drag is electromagnetic rather than atmospheric - can anyone confirm this? Also has anyone decided if we should take positions on the geometrical centre of the tether, or the centre of gravity which is fifth of the way up the tether? David Brierley, Colorado Springs, CO.