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Re: Wisp and ao-40???

At 08:05 PM 2000-11-26 -0500, you wrote:
>Just got back from the weekend and setting up for the pass tomorrow, but
>noticed a problem... Wisp is showing only a 10 degree max elevation pass
>???.  Nova is show a 50... What's up with that, a bug in nova or wisp?  BTW,
>ao-10 is showing correctly in both.

It all has to do with how you calculate max. elevation!  50 is much closer 
to correct.  The problem is that highly eccentric orbits sometimes show a 
progressive rise in elevation, followed by a slight drop, and then a rise 
to even higher elevation.  If the software "keys" on the first drop as 
indicating the point of maximum elevation, then the value will be low, 
sometimes very low as in the case you mention.  Not all passes exhibit this 
behavior, so sometimes the software will be correct.

I just went through this "quirk" with my own software.   The best way to 
find max. elevation is to increment time through a pass keeping track of 
the maximum elevation until the pass is over.  Even better, iterate through 
first in fairly large steps to find a value close to maximum elevation, 
then go back and "zero in" on the time of max. elevation incrementing in 
much smaller steps to get the true maximum.

I suspect WISP is probably using the technique of checking the "slope" of 
the elevation, as mentioned above, when the elevation first starts to 
decrease it assumes maximum has been reached.  Works for LEOS and most of 
the time for other orbits, but not always..... AO-40 is a good example of 
an exception.

  Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
   Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key

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