PCSAT(NO-44) batteries
Subject: [amsat-bb] PCSAT batteries!
From: Robert Bruninga
Date: Sat, 2 Feb 2013 11:14:30 -0500
We placed the batteries in the middle of the satellite. It is quite
immune to the +90C and -100C possible fluctuations on (unattached) solar
panels (if they were not attached to the sides of the satellite). Since
the solar panels are attached to the aluminum frame and the satellite
rotates at about 1 RPM, we don't see any temperature variations even on
the panels of more than about 10C (per orbit).
And then these 10C fluctuations on the sides only penetrate to about a +/-
1 degree variation at the batteries per orbit and per day. Though there
is a long term variation with the Sun^Orbit beta angle.
The average temperature of PCsat is around 10C, getting as low as 0C
during full eclipse seasons (High Beta angles) and as high as 40C for a
weak or so when it is in full sun. This cycle moves over a 2 month or so
cycle.
Right now, PCsat inside is a nice comfortable 25C.
Our problems with PCSAT (now 12 years old) is our own fatal flaw of
designing it with a reboot-after-fault-detection mode of turning on backup
transmitters and backup receivers to regain contact with the command
station. Now with 20/20 hindsight, that was dumb... especially if the
reason it faulted is due to low power!
We can get in and turn off the extra XMTRS and RCVRS any time we want
during high beta angles (maximum peak solar power available), but then
there is only 15 minutes left before it goes back into eclipse and dies
(not enough time to charge each orbit).
But then 2 or 3 times a year, it enters full sun periods when, if we can
get the command in, then we can send those commands to turn off all the
spares and they will hold... BUT this time of full sun, is also the time
of the worst sun angle (least average power), and so it is iffy if we can
get the command in.
See http://www.findu.com/cgi-bin/pcsat.cgi?absolute=1
(raw packets at the bottom) and you will see that today's attempt resulted
in achieving 9 minutes of operation before it died. See the telemetery
serial numbers starting at 001 each time it resets.
That occurred at 2013-02-02-14:29:24z
Hope that helps
Bob, WB4APR
[Supplement]
Subject: [amsat-bb] PCSAT normal(?) operations resume
From: Robert Bruninga
Date: Tue, 5 Feb 2013 11:31:30 -0500
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 PCsatfs 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 Earthfs magnetic field.
Itfs 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 TNCfs ^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
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