At 16:27 23/04/98 EDT, Jim Cook wrote: >As an amateur astronomer, I volunteer at our local park system's public >stargazing programs. Unfortunately, being a governmental body, they need to >schedule their programs months in advance. So when I'm asked by the park >staff if I know of anything interesting going on in the sky, say, next August >or September, as I was this morning, I don't usually check any of the >satellite prediction tools I have simply because I know they may not be >accurate that far down the road. But it finally dawned on me that I really >had little understanding of just what that error margin might be. Jim, Just to test a concrete example , I recovered from my collection of old elements provided by Muke McCant, a TLE for MIR epoch 97299 and compared its predictions with most current one off Alan Pickup's select ( epoch 98115) using both Mike McCant's quicksat and TS Kelso's TRAKSTAR for a pass on May 2, 1998 here in adelaide,sa(-34.97,138.7317E) With Trakstar the two predictions only differed by 5 minutes! This of course probably shows MIR hasnt had an orbital adjustment in Six months! Quicksat's output differed by 30 minutes, but still good enough to decide if a pass was going to occur that night. Mike McCants has stated to me that quicksat is not as accurate as trakstar when using old elements Tony Beresford