[amsat-bb] Re: AO-73 Question (mode efficiency?)

[Graham Shirville]

Hi Bob,

Yes the mission requirements are exactly as your last paragraph. We have a 
dual mission and needed a simple, autonomous, on board system to make the 
change between the two modes. The  sunlight/eclipse transition is fairly 
easy to detect and forms a valid decision criteria.

The system current in daylight is around 220mA and when in eclipse it is 
"only" 140mA. If the transponder is in use then this can rise momentarily up 
to 250mA but the average eclipse consumption is probably only around 160mA 
as many of the eclipse periods are over the sea or unpopulated land areas.

Presently the power budget seems pretty good and we are hopeful that the 
solar cells and battery will maintain their present performance for some 
time to come. The bus voltage is usually around 8.3V at the end of the 
sunlight period and drops only to around 8.1V at the end of eclipse. 
Apparently this equates to less than 5% discharge.

cheers

Graham
G3VZV


-----Original Message----- 
From: Robert Bruninga
Sent: Friday, December 27, 2013 6:01 PM
To: David Johnson ; Peter Budnik
Cc: AMSAT-BB at amsat.org
Subject: [amsat-bb] Re: AO-73 Question (mode efficiency?)

> The satellite is only in transponder mode when it is in eclipse..
> In full sunlight it is in beacon mode only.

Just curious about the overall design goals of this operating mode?
Putting solar energy into and then taking it out of batteries suffers
about a 30% loss in efficiency.  All else being equal it is usually better
to use solar power directly if possible.

Maybe the value of this mode is for hams to use the satellite in the
evenings during play time instead of during the day when schools and
students could benefit.

Just curious.
Thanks

Bob, WB4aPR
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