> > >They're not perfectly still over one spot, but instead move in a figure-8 (analemma) over the course of a day. > > This is frequently stated but still it is wrong! > > Only a satellite in an orbit with an inclination of several degrees and a very small eccentricity would theoretically do that. I would be very surprised if there was any such orbit in real life! > > > > Rainer _______________________________________________ Geosats can make many fairly amazing tracks as viewed from the ground, ranging from circles to lines to sine-waves to analemmas, depending on the satellite's Mean Motion, Eccentricity, Inclination and Argument of Perigee. A satellite with a Mean Motion (revs per day) of 1.0027 is most likely "station-keeping", staying truly geosynchronus and coming back to the same Longitude on Earth once each day. If it's inclination is small as well, then it's GEOSTATIONARY as well. Most "defunct" geosats begin taking on higher inclination orbits (due to Lunar perturbations) and these have Figure-8 shaped orbits when viewed from a fixed location if they also have a small Eccentricity. The cross-over point of the Figure-8 will vary with the Argument of Perigee orbital parameter. Several examples of the different orbits geosats can attain are posted at: http://albums.photopoint.com/j/View?u=940828&a=7279996&p=42982880&Sequence=0 &res=high GEOS 9 (circle) and DBS-1 http://albums.photopoint.com/j/View?u=940828&a=7279996&p=42982883&Sequence=0 &res=high High Inclination Analemma! http://albums.photopoint.com/j/View?u=940828&a=7279996&p=42982886&Sequence=0 &res=high 3-degree Inclin./ Low Ecc. http://albums.photopoint.com/j/View?u=940828&a=7279996&p=42982888&Sequence=0 &res=high Typical High Inclination (defunct) Geosynchronus Satellite (not geo-STATIONARY). Plots are courtesy Rob Matson's SKYMAP (v6.4) Program and show several geosat "orbits" from a fixed location on the Earth for a 24-hour period. There are many other shapes possible! Enjoy. RICK BALDRIDGE Campbell, CA USA ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Wed Mar 07 2001 - 22:57:36 PST