PCSAT normal (?) operations resume

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

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