22 March 2002
From:  WB4APR
to:    AMSAT/APRS

SUBJECT:   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