[amsat-bb] Re: Satellite in eclipse
bruninga at usna.edu
Wed Jan 16 14:10:56 PST 2008
> I'm going to ask this newbie sort of question...
> since most of the LEO satellites are in orbits of
> 100 minutes +/-, how can they be in eclipse for
> more than ~50 minutes.
They cant, but it is never 50% because the satellite is high, so
it sees over the horizon. Thus for a 100m orbit, we get about
65 minutes in the sun and about 35 minutes in the dark.
Here is our LESSON LEARNED on PCSAT1. Its not the "eclilpse"
that kills us, but our inability to charge enough during the 65
minutes to make it through the next 35 min eclipse. That is why
PCSAT works on every orbit after it has entered the sun. After
about 20 minutes it has charged up enough to work. But in the
remaining 45 minutes it cannot accumulate enough charge to then
fully make it through the next 35 minute eclipse.
Thus, it dies 14 times a day, and resets back to the defaults,
which enables back up receiveers and transmitters to assure
recover from the ground. It is that extra load that prevents
enough charge to make it. Only 3 times a year when the sun is
right, it can stay up long enough for us to send the command to
turn off the extra receivers and transmitters, then let it
charge up fully, and then it runs fine for a month or so until
something happens and it resets.
Just a lesson learned. *** Make sure you can charge up enough in
ONE pass in the sun, to survive the next eclipse.
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