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Re: PCsat's Last Hurrah!



Bob and all your helpers,

It's been great and I've had a heap of fun! Pre-dawn pass here showed 14.4 
volts and still charging ok. (around 2000Z). It'll be a shame to lose it, 
but I understand the sustained intensive effort needed to keep it alive.

Following the telemtry as I have has taught me lots too, as has the problem 
of keeping the bird alive. I wonder if you'd do anything different next 
time? Perhaps a different "fallback mode", a hardware "watchdog" on the 
supply bus, fewer "bulletins"? Operating without an OBC to do the 
housekeeping was always going to be a challenge!

It may be a little voyeuristic, but it will be interesting to watch it 
"die". There's much to be learned there too!! I wonder how long the 
commercial nicads will last, and what will be the failure mode?

Hope you've got another class of Midshipmen to do it again and impliment 
the lessons learned.

Good luck!

Norm VK2XCI.

At 09:02 22/03/2002 -0500, you wrote:
>PCsat returns for a last Hurrah!
>
>If you have been waiting to try PCsat and just not gotten around to it,
>now is your last chance.  DIGI will be on on all passes as long as it
>lives.  It will only work while in sunshine for a few more days so if you
>have had your fun, back off and let others play.  Lets see some live
>operators, not just timed beacons... Share...  Celebrate the Wake...
>
>If you can operate an IGate/Satgate, bring it up. Lets capture the moment.
>
>After a few more tries through Friday, we are throwing in the towel on our
>12 day round-the-clock PCsat recovery attempts.  In that time we have
>documented over 98 passes of command attempts.  Most have been successful
>in commanding PCsat to low power mode, but none in the last 7 days have
>resulted in PCsat making it through the next eclipse (eclipse happens
>every 100 minutes and lasts 35 minutes).  We had turned off all users
>starting on the 18th.
>
>PCsat will continue to work while in the sun for a few more days but the
>eclipse percentage even gets about 3% worse over the next week before it
>begins to improve slightly for about a week from the worst case 35% up to
>25% in 3 weeks from now.  We won't see full sun till June!  Even if we
>nursed it on every one of the 300 orbits between now and the minimum in
>early April, there is no way the batteries will make it through each
>eclipse.  That is still 300 deep discharges to go and 1100 to June!
>
>Since we cannot get it to stay in low power mode through eclipse, it is
>just going to die anyway.  Since PCsat was intended as a COMM relay and we
>have learned all we are going to learn from it (lots!), we are going to
>turn it back on for users this weekend as a last hurrah!
>
>Command stations will continue to command low power mode, but will not be
>exercising the extrordinary pre-sunrise efforts, but take the more
>convenient command passes to issue the commands.
>
>Unlike other microsats who can keep their low power transmitters on all
>the time in Sun, PCsat's packet transmitter even under full load, is only
>on say 20% of the time due to the low dutycycle of Packet.  So although
>there is enough average power to power PCsat for years while it is in Sun,
>if the batteries are completely gone, then there is not enough PEAK power
>to let PCsat even transmit a single packet even though there is plenty of
>average power.  PCsat draws 1200 ma when it transmits.  The solar panels
>in full sun only produce about 350 ma.
>
>Once the batteries can no longer provide 1200 ma for a few seconds, each
>time it tries to transmnit, the batteries will go down, and the TNC will
>reset.  This will be the end.. Actually we may be able to get packets out
>of it occassionally for weeks to come, but it all depends on when the
>first battery cells short or reverse.  Thats it...
>
>Enjoy
>
>Bob, WB4APR
>US Naval Academy Satellite Command Station
>
>----
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>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

Norm, VK2XCI
Voice of The Edge of The Outback
njmcmillan@bigpond.com

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