[amsat-bb:74733] AO-40 Update, 2004-01-28

["Stacey E. Mills" <w4sm@xxxxxxxxx>]

At the moment we have nothing really new to report regarding AO-40, other 
than that we are trying to see if observers in Europe can hear the K-Tx on 
today's orbit.  This is a bit of a long shot given the less than perfect 
squint angles and some really horrible snow/ice at the receiver stations, 
but we are trying.  If we have 10 - 14 volts available, the IHU-1, MUX 
hardware control unit, and receivers may be functional, but the S2 Tx may 
not wish to start up in "cold" mode from that voltage.  It was never 
designed to run below 20 volts.  We are seeing if the K-Tx will respond at 
these voltages.  As mentioned before, we are sending simple machine code 
commands to try to activate this hardware and switch to the auxiliary 
battery.  If we have close to 10 volts available, these commands should 
work.  As a safety measure, each command session ends with commands to shut 
off all of the transmitters, since we would not want to leave them on line 
at these low voltages.

If the main battery has us clamped at a voltage where the above will not 
work, we will have to wait to see if solar angle improvements help, or if 
one of the bad cells eventually goes "open".

Although we have not had time to read the bulletin board much, and we can't 
claim to fully understand what has happened, it is clear that operator 
practices, though not always perfect, had absolutely nothing to do with 
this event.  The fact that the passbands cut off on Sunday was an example 
of the kinds of safety features that we have in place to protect the 
electronics on board.  There are also input AGC's and output 
limiters.  AO-40 was designed to withstand all that you can throw at 
it.  Although there was a lot of passband activity on Sunday, and under 
really marginal conditions heavy usage could put us in transiently a 
negative power budget, it is now clear that it was the failing of another 
cell on the main battery that caused the passband shutdown at that time.

The main batteries consist of 20 40 amp-hour cells arranged on three of the 
radial support arms inside the spacecraft. There are two packs of 7 cells 
and one pack of 6 cells.  It is entirely possible or even probable that the 
main batteries suffered some damage during the 400N motor event.  One clue 
to this is the fact that we lost two of the three temperature sensors 
attached to these packs, and since that time we have been able to measure 
the temperature of only one of the three packs.  It may well be that this 
was the only "normal" main battery pack.

One mystery in the telemetry is where the "energy" is going from this 
battery failure.  With the exception of the "heat pipe" spike, which we 
believe is not real as discussed before, there are really no changes in 
temperatures anywhere over the next 15 minutes.  The answer MAY be that the 
bad cells in fact had deteriorated to the point that they had very little 
storage capacity left and so had little energy to dissipate.  The aux. bat. 
was probably only a few percent charged at the pre-event voltage and had 
little energy to contribute to the event.  The temperature on either of its 
two packs does not change during this time, supporting this conclusion.

The above (except the operator practices part), is our best understanding 
of things at the moment and is always subject to change.  We'll keep you 
posted.

--W4SM for the AO-40 Command Team


PERSONAL NOTE:
Like my colleagues on the command team, I have lived and breathed AO-40 for 
over four years.  All of us can almost mentally decode 400 bps PSK.  We 
hear it in our sleep. I was watching the battery voltage telemetry at the 
exact moment that the voltage dropped precipitously.  In my "day job" I 
have frequently watched catastrophic events unfold in human beings, and the 
feeling was EXACTLY the same.  Part of my day job is to have to make quick 
decisions during times such times, decisions that can have serious 
consequences.  I was instantly aware that we had a serious power event, and 
I considered cutting the main battery loose and trying to run on the nearly 
completely discharged and untested under load aux. battery.  However, 
because I did not have a clear understanding of where the primary fault 
was, I elected to watch things and try to figure out what was 
happening.  The general rule of, "when in doubt wait to understand" works 
most of the time...  In this case it didn't, and I'd sure like to live 
those minutes over again and cut the main battery loose.  Hindsight is 
always 20-20.  Of course, if it had crashed anyway, then I'd really be 
beating myself up.

If it's at all possible to bring AO-40 back, we will.  If the voltage is 
clamped low and there is no other damage, we may end up waiting a long time 
for a cell to "open", hopefully not as long as for AO-07.  ..or it may 
happen today.  No success for even weeks or months does not mean that we 
won't eventually be successful.  We will sure keep trying.

Several of you have written very nice notes of support.
Thank you.



-- 
  ________________________________________________________________________
  Stacey E. Mills, W4SM    WWW:  http://www.keplerian.com
    Charlottesville, VA     PGP key: http://www.keplerian.com/key
  ________________________________________________________________________  

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