[amsat-bb] Max Range Sat Contacts - Question

Thomas Doyle tomdoyle1948 at gmail.com
Mon Jul 16 11:38:56 PDT 2012


The recent record contact between OM3BD and AC0RA peaked my interest
in the subject. Congratulations and thanks to both of them. Stuff like this
gets even old geezers like me excited.

This is slightly technical and there is a question.
 I was testing my pass prediction program and found that my program indicated
that a contact between my location and JO41KW was not possible. I use
JO41KW since it is sort of on the edge and DK1TB lives there. I checked
and found that SatPC32 indicated that a contact was possible using FO-29.
I knew that nothing could be wrong with SatPC32 so I dug a little deeper.
You may know this but FO-29 is a little different than most of the other LEO
satellites. It has a very high eccentricity compared to the rest of the fleet.
To try and speed up my calculations I was calculating the diameter of
the coverage circle and comparing it to the distance between the two locations.
If the distance between the stations was longer than the coverage circle
diameter I dumped it. This worked fine for everything but FO-29. With the
current LEO sats it is easy to forget about eccentricity. There is a difference
between the minimum and maximum coverage circle diameter of 910 miles
for FO-29. By comparison AO-27 has only a 67 mile variation.

QUESTION:
This eccentricity might result in a longer delay between good passes for
max range contacts. You need the satellite to be in the right spot and
at the max altitude to get a max range contact. The unknown at this point
is the effect of inclination. It seems as if a satellite with a very
low inclination
and stations are located at high latitudes could result in a condition where a
contact would not be possible even though the distance between them
is within the coverage circle diameter. With the speed of our present computers
and the simplicity of the calculations it is easy to just brute force
it and check
to see if contacts are possible but I wonder if anyone has looked at the effect
of inclination and station latitude on max range.

--------------------------------------------------------------------------------------------------------
AO-27  Min Elev: 0  Coverage Circle Diameter (Miles): 3756.9 To 3823.1
Location1  Lat: 43.104167  Long: -89.458333  Grid: EN53GC
Location2  Lat: 51.937500  Long: 8.875000  Grid: JO41KW
Distance between locations (Miles): 4270.3

Contact theoretically not possible using AO-27

Theoretically possible using:
AO-07  Coverage Circle Diameter (Miles): 4896.0 To 4932.4
FO-29  Coverage Circle Diameter (Miles): 3814.7 To 4724.8
---------------------------------------------------------------------------------------------------------

73 W9KE Tom Doyle


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