--- On Mon, 16 Feb 1998 10:57:58 EST BahlsD@aol.com wrote: >Sounds like the 225 minute period "boundary" for LEO cited by Jeff may >come from the SGP4/SDP4 utilization boundary. IIRC, when using the >NORAD orbit propagators SGP4/SDP4 for satellites with periods greater >than 225 minutes the SDP4 analytical method should be used for orbit >determination and propagation. >For periods less than 225 minutes SGP4 is okay. I don't have the >Spacetrack #3 report handy, but I'll bet the demarcation is mentioned in >there. Yup, it sure is. See Alex A. Sergejew's http://ecco.bsee.swin.edu.au/chronos/metsat/spacetrk.html Thanks for clearing the cobwebs. Jeff Hunt <jeff@satellite.eu.org>