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AO-40: S2 beacon may be off..

Dear All,

S2 beacon may be off for part of the orbit!

DF4PV reported that he was suddenly loosing signal from S2 beacon at
0.46 UTC on 12.04.2001. (Thanks for listening Günter!)

He was indeed right:

He lost the signal at 00:46 UTC on 2001-04-12, which was during eclipse
at MA=8. 

The IHU is running a software task to watch for critical situations.
One such task is to keep an eye on the battery voltage. 

Currently the IHU turns the S beacon off, if the battery voltage drops
down to 26 Volts. This was in fact the case due to bad sunangle and
solar eclipse.  While 26V is not critical, we prefer to be as safe
as possible during the current bad sunangle period.

The IHU turned the beacon back on at MA=128, about 09:36 UTC.

If you look at Event #5 in the telemetry from orbit# 205, you'll see
that this happened on the previous orbit, as well. Event #5 shows that on
2001-04-11 at 06:09:38, MA=12, the S-WATCH turned off the S2 beacon....
it came back on at MA=128. 

This may continue for the next few orbits as well.

As predicted, we lost solar lock at the end of Orbit #201 and are
officially in "hibernation" again. The magnetorquers are off and can't
be used until we are in solar lock again. 

Though the SEU (Sensor Electronic Unit) is not phase locked on the Sun,
nevertheless the Earth sensor continues to scan the Earth. Whilst its
values are meaningless, when the Earth's edge is reached, the ES upper
and ES lower counts freeze at their final values, and enable ALON to be
estimated, as well as a Sun angle, assuming the ALAT ~0. 


   Orbit   ALON     SA 
   202     143     -49
   203     139     -51
   204     136     -53
   205     134     -56
The spin rate, provided by Helmut DL1IN from beacon signal strength
fluctuation vs time is 2.2 rpm.

Due to the attitude, signal quality is improving over the next weeks..

73s Peter DB2OS
for the AO-40 command team

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