[amsat-bb] Re: AO-51 orbital questions

Gould Smith gouldsmi at bellsouth.net
Fri Jan 25 21:53:41 PST 2008

Hi Greg,

All good questions.

AO-51 is not in a true sun synchronous orbit, that orbit was achieved by the 
main payload.  We are close, but not text book.

We had the option of turning the transmitters off and thus no useful 
satellite or turn the TXs on high to use as much power as possible, we chose 
the latter so we could keep the satellite operational.  The entrance into no 
eclipse did precede the software crash by a week, but I have been unable to 
establish any link.

If the power is not dissapated from the solar cells they heat as well as the 
BCR (battery charge regulator board),quite a bit actually, which heats the 

I will be doing a paper on this event for the 2008 Symposium in Atlanta.

Gould, WA4SXM
----- Original Message ----- 
From: "Greg D." <ko6th_greg at hotmail.com>
To: <amsat-bb at amsat.org>
Sent: Friday, January 25, 2008 11:59 PM
Subject: [amsat-bb] AO-51 orbital questions

> 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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