[amsat-bb] AO-51 orbital questions

Greg D. ko6th_greg at hotmail.com
Fri Jan 25 20:59:29 PST 2008

Hi folks,

I'm writing my monthly newsletter article for our ham club, and thought I'd talk a little about AO-51's recent challenges, experiments, and results.  You think you understand this stuff, until you try to explain it to someone else...

AO-51, I thought, is in a sun-synchronous polar orbit, right?  I thought that sort of orbit is characterized by having the satellite fly over the same point on Earth at about the same time every day.  If so, then why do we have periods of eclipse and periods of no eclipse?  If it's not sun-synchronous, is it in some other special form of a polar orbit, or just in a polar orbit?

And, about the battery temperature.  I get the idea of turning on all the transmitters, so that we "radiate" some of that excess power into space in a more useful way - in the form of RF.  But, it would seem that the difference is maybe a watt or so, at the most, which doesn't seem all that significant.  And since the power amps are never all that efficient, aren't we mostly just moving the point of dissipation from the batteries to the transmitter modules?  I can see how this would help the batteries, but how does it help the spacecraft overall?  Is this because of how the thermal design was done?

And, more to the point of all this power stuff, does the power really need to be dissipated?  I mean, you can put a solar cell in the sun, with no load, and it's not going to explode from not having some place to dump it's charge.  Is there a need to take a certain amount of power from the solar cells, in order to maintain their own health?  Or, is this really due to the design and function of the battery charging circuitry?

Finally, I seem to recall that the spacecraft entered the no-eclipse period before the last crash.  Is that the right sequence?  Any connection between the two events?

Thanks for your help, and also to the command team for the latest configuration.  Next good pass is tomorrow; time to fire up the old S-and receive system.

Greg  KO6TH

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