[aprssig] PCSAT batteries!

Robert Bruninga bruninga at usna.edu
Sat Feb 2 10:14:30 CST 2013


>,what kind of battery is install on this kind of  satellite?
> how does it react in the cold space where it is?

We placed the batteries in the middle of the satellite.  It is quite
immune to the +90C and -100C possible fluctuations on (unattached) solar
panels (if they were not attached to the sides of the satellite).  Since
the solar panels are attached to the aluminum frame and the satellite
rotates at about 1 RPM, we don't see any temperature variations even on
the panels of more than about 10C (per orbit).

And then these 10C fluctuations on the sides only penetrate to about a +/-
1 degree variation at the batteries per orbit and per day.  Though there
is a long term variation with the Sun/Orbit beta angle.

The average temperature of PCsat is around 10C, getting as low as 0C
during full eclipse seasons (High Beta angles) and as high as 40C for a
weak or so when it is in full sun.  This cycle moves over a 2 month or so
cycle.

Right now, PCsat inside is a nice comfortable 25C.

Our problems with PCSAT (now 12 years old) is our own fatal flaw of
designing it with a reboot-after-fault-detection mode of turning on backup
transmitters and backup receivers to regain contact with the command
station. Now with 20/20 hindsight, that was dumb... especially if the
reason it faulted is due to low power!

We can get in and turn off the extra XMTRS and RCVRS any time we want
during high beta angles (maximum peak solar power available), but then
there is only 15 minutes left before it goes back into eclipse and dies
(not enough ttime to charge each orbit).

But then 2 or 3 times a year, it enters full sun periods when, if we can
get the command in, then we can send those commands to turn off all the
spares and they will hold... BUT this time of full sun, is also the time
of the worst sun angle (least average power), and so it is iffy if we can
get the command in.

See http://pcsat.aprs.org (raw packets at the bottom) and you will see
that today's attempt resulted in achieving 9 minutes of operation before
it died.  See the telemetery serial numbers starting at 001 each time it
resets.
That occurred at 2013-02-02-14:29:24z

Hope that helps
Bob, Wb4aPR


-----Original Message-----
From: APRS at yahoogroups.com [mailto:APRS at yahoogroups.com] On Behalf Of
Gervais Fillion
Sent: Saturday, February 02, 2013 9:53 AM
To: aprs at yahoogroups.com
Subject: RE: [APRS] QRT all PCSAT transmissions!


Hi Bob,what kind of battery is install on this kind of  satellite?i wonder
how it react in the cold space where it is?Do you have any data that gave
the temperature upthere?i am just curious,here in the Eastern part of
Quebec we are used to have in the -20 celcius,,,,and battery are built for
that,,how it is in space??
73 Bob
Thanks for all the info you are tellng us.
Gervaisve2cknLe Bic,Quebec








www.michelebard.com4823.73N/06839.65W

To: APRS at yahoogroups.com
From: wb4apr at amsat.org
Date: Sat, 2 Feb 2013 08:20:00 -0500
Subject: RE: [APRS] QRT all PCSAT transmissions!


























      > Question: PCSAT,does it transmit at 144.390 like other APRS
hardware ?



No and yes.  It operates up and down on 145.825 like all other APRS

satellites.



But it also has a backup transmitter on 144.39 which we can use as a

national broadcast downlink.



Problem is, most people cannot hear it due to local QRM on 144.39... but
it

is there.



If you live in the boonies and there is no other local traffic, sometimes

you can pick it up.

But there is no UPLINK there for obvious reasons.



Even in congested areas, sometimes you can receive it on 144.39 if there
is

a moment of silence when it transmits.



In fact, it was that clever idea that kills PCSAT on every orbit.  The old

batteries do not have enough power to power both XMTRS at the same time

which is what it is trying to do.



We can send the command to turn off the other XMTR, but then on the next

eclipse, it resets back to BOTH ON.  Darn...



Bob, WB4APR














   		 	   		

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