[amsat-bb] Re: Future radical satellite designs

[G0MRF@aol.com]

In a message dated 08/07/2007 17:06:50 GMT Standard Time, N2OEQ at aceweb.com  
writes:

I did  read the whole thing.

The challenges to amateur secondary payloads on  commercial or
military spacecraft have been discussed here at length in the  past.
*My* comment was that a standalone bird *designed*  without
battery-powered transmitters might be an interesting  approach.



Hello Patrick / Maggie / John
 
As you all know battery failure has been the most common failure mode for  
AMSAT spacecraft for a very long time.
Patrick's idea of solar power only will be put into practice with this  falls 
launch of a triple cubesat Delfi3C.  It has a 40kHz linear UV  transponder 
and no batteries. - Should be very interesting.
 
However, solar power alone has its own problems. With changing angles  
between the panel and the sun the voltage or perhaps more accuratly, power, will  
change with change in attitude. Consequently the supply could drop out  
frequently unless there is some form of short term storage. Certainly there  would 
need to be some form of sequencing so that vital control electronics are  given 
priority over heavy curent parts of the payload. Super capacitors would be  a 
really neat experiment but I wonder how they would react if a large energetic  
particle pentrates the capacitor when it's holding a large charge?
Perhaps OK for LEO, maybe a bit risky for HEO through the radiation  belts.
 
There could be another approach.
The batteries usually go short circuit pulling all power from the solar  
panels to ground. Ocassionally they go open circuit....as per AO-7. but this  must 
be a rare event.
Imagine a satellite PSU which uses a battery but has a solid state relay  
between the battery and the satellite buss.  Solid state relays have very  low on 
resistance and only need a couple of milliamps to keep them in the on  
position. For 5 to 10 years the battery could supply the few milliamps required  to 
maintain the relay in the on position. When the battery eventually fails, if  
it goes short circuit it pulls all the power to ground and the satellite stops 
 working. However, at that point the relay loses its couple of milliamps 
'holding  current'. At this point the relay open circuits and the faulty battery 
is  isolated from the still functioning solar panels and the satellite is 
restored  to life.....but only in sunlight.
There may be a down side to this, but if there is I cant see it.  I  suppose 
every now and again the satellite CPU could supply a few milliamps  to the 
relay just to see if the battery has recovered.  If it has it will  be charged 
and normal operation will be restored. If not, then the supply line  will get 
shorted to ground via the battery and then the relay will open again  restoring 
the satellite to solar only power.
 
Have I missed the obvious or is this a neat idea?
 
regards
 
David  G0MRF