[amsat-bb] Re: Satellite in eclipse

Mark Lockwood mark at kk7cu.net
Sat Jan 19 04:03:58 PST 2008

I operate Geo-stationary satellites for a living, and I agree with Bob on
this.  Geo-stationary birds have even shorter eclipses due to their
increased altitude (approx 22,300 miles) Those eclipses are at most 72
minutes at the peak of eclipse season (equinox). Towards end of life the
solar arrays can degrade and the problem becomes recharging the batteries
enough to make it through the next eclipse 24 hrs later.  We have in the
past reduced the transponder load on spacecraft when the arrays couldn't
support charging the battery enough to handle the full load through the

Mark KK7CU

On 1/16/08, Robert Bruninga <bruninga at usna.edu> wrote:
> > 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.
> Bob, Wb4APR
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Mark Lockwood
Former Prefect, Metropolitan Rocketry Association 2006-2007
TRA # 9863
NAR #86042

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