[aprssig] PCSAT normal(?) operations resume

Robert Bruninga bruninga at usna.edu
Tue Feb 5 10:31:30 CST 2013


PCSAT (NO44) is again returned to  users (but not usable until a few weeks
when sun angles get better). The Transponder on ISS is also operational now.



The variation of power available to PCSAT is inversely proportional to the
“sun-to-orbitplane-angle” (viewable in Instantrack with the “E” and “D”
keys.  It is currently above 78 degrees.  Once it went above about 65
degrees was our last successful commanding.



Recovery did not work this period.  But we learned enough to be more
successful in the Fall.



A “sun-to-orbitplane-angle”  means PCsat’s orbit is now over the day/night
terminator meaning it is in full sun (no eclipses) with solar power coming
in on the (weaker) side panels and little if any on the +Z face(best
panel).  Attitude is maintained by alignment with the Earth’s magnetic
field.   It’s the best time for a recovery (no eclipses to cause a reset),
but the worst time for commanding.  It is too weak to respond to the needed
logon and 3 additional commands.  Though it will be strong again as the sun
angle improves (lower).



Then it will have better sun on the +Z face for commanding, but then it
will be doing Eclipses.  And even though we can then command it to turn off
unnecessary loads, it does not have enough time before the next eclipse to
charge up enough to survive the next eclipse.



What we did (re)learn is a condensed command method where we can put all 3
PCSAT low-power commands in a single packet (using the TNC’s ^V pass
character).  That way, we only need a successful logon to complete the
Restoration.  1) The CONNECT ACK. 2) The password challenge, 3) Then the
command prompt.  Then we can hit it with the full low-power command set and
disconnect all in one packet which cancels the need for PCSAT to respond to
each command separately.



On the FIRST day available in full sun(our best shot), I not only got
logged on, but completed all 3 requried functions.  Then signals sounded so
good, I got greedy and put in the another three (which also improves power
budget, but not as much as the first three).  Yep, I gambled and lost.  It
died on the last one!  The next day I got all 3 in, and it died on the
3rdcommand due to a user packet I think.  Days since, I have been
unable to
logon.  Hence, end of this attempt period.



In most attempts in the past (after successful logon) we would send one
command at a time to give it a few seconds rest between each one.  But
these 3 commands then required 3 ACKS and 3 RESPONSES in addition to the 3
required to get logged.  Those extra 6 packets kill it, especially if there
was a user packet in there.  Next time all we need are the 3 loggon
responses.



Also, next time, we will give users advance warning to QRT all
transmissions when we are trying to command.  Each one of their packets
robs us of power we need to complete the command.  I failed to warn
everyone this time, and so we had some interference.



As sun angle improves, You may continue to experiment with  PCSAT during
MIDDAY passes.  That is when it is strongest (in the Northern Hemisphere),
but do limit yourself to only attended operations so humans can actually
contact humans, or if you are doing an unattended test, keep your
transmissions to once every 2 minutes.  That should let you get one good
successful packet per pass.  Which is the mission of PCSAT.



See the downlink on http://pcsat.aprs.org



There you can see the telemetry packets (list at the bottom of page) right
now are rarely getting above 001 meaning typically a  minute or so of life
before it gets overloaded and resets back to 000.



It is easy to visualize the relationship of the sun angle to the orbit
plane and to see how that affects power budget given that our best panel
(out of 5) is on the +Z face and that is magnetically aligned to point
towards magnetic South.  There is NO panel on the –Z which is why PCsat is
rarely  usable in the Southern Hemisphere (not planned, but just a result
of it crashing in every eclipse).



Just thought you would like to know what is going on with one of the oldest
student projects in space that is still “semi-operational” for users.



Bob, Wb4APR

US Naval Academy Satellite Lab





*From:* Robert Bruninga [mailto:bruninga at usna.edu]
*Sent:* Thursday, January 31, 2013 10:53 AM
*To:* amsat-bb at amsat.org
*Cc:* aprssig at tapr.org; aprs at yahoogroups.com; bruninga at usna.edu
*Subject:* QRT all PCSAT transmissions!



Please QRT all transmissions to PCsat to save power for COMMANDing.



PCSAT (W3ADO-1) is entering its 3 day RECOVERY window this year starting 31
Jan.



Today we got logged on for commanding twice, but both times user packets
killed the bird.



At best PCSAT can usually only save up enough power for 2 or 3 solid
packets per pass  and we need 3  successfully for command and recover.  One
user packet in the middle of that and we lose it for the pass.



MY fault for not making this announcement earlier.  Not their fault.  But
if you see this email and you are transmitting to PCsat, please QRT for the
next several days.



Commanding is being done from the East and West coast of the USA and over
Germany.



WB4APR, Bob

USNA Command Station
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