[amsat-bb] Re: ARISS antennae
bruninga at usna.edu
Tue Dec 30 09:14:02 PST 2008
>> Still haven't found what beam width
>> and direction the antennas view
>> from the ISS WRT its direction of flight.
> ...In either case, they are considered
> to be on the earth-facing surface...
Actually, an "earth facing" antenna can be confusing to some. Because only about 5% or less of the earth bound users that are in view are "under" the ISS. Whereas 95% of them are to the side in all directinos most of the time.
In fact, almost 70% of them are within just 20 degrees of horizontal in all directions from the ISS. So, a "down" antenna with any gain, is not the ideal spacecraft antenna.
See the plot of elevation angle versus distance and time in view on this web page: www.aprs.org/rotator1.html
That sketch is shown from the perspective of the ground station, but just turn it upside down, and you see that almost all communications to the ISS are "from the side"...
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