[amsat-bb] Re: Future radical satellite designs
G0MRF at aol.com
Sun Jul 8 13:46:53 PDT 2007
In a message dated 08/07/2007 17:06:50 GMT Standard Time, N2OEQ at aceweb.com
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?
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