PCSAT SUMMARY and SOLICITATION: Our PCSAT recovery attempt this week was unsuccessful this time, but she will be back to normal (intermittent, weak) operation in a few weeks.
BACKGROUND: PCSAT is functional a few times a day in the northern hemisphere year round. You can see its telemetry and user activity on http://pcsat.aprs.org . But it dies every orbit in eclipse because it defaults with backup systems turned ON. We can turn them off, but it can only really get enough charge to survive and keep them off during periodic full-sun periods that only happen once or twice a year in winter.
PCSAT has a permanent +/-Z magnet for alignment with the Earth's field and a 0.6 RPM spin (solar pressure about Z). The best solar panel is on the -Z (south seeking axis). On the 4 sides are our cheap plastic covered cells and there are no panels on +Z.
With a 63 degree inclined orbit, PCSAT enters a full sun period about once every 3 months. PCSAT can be fully operational during those periods and beyond if we can get command and turn off unnecessary redundant loads.
The problem is that the times when we get peak sun (peak power) on the BEST panel is when we are also experiencing maximum eclipses. SO we can command easily (peak power available for a packet), but with only 45 minutes charge time, cannot then last through the following 35 min eclipse (minimum average power available).
On the other hand, when we have full sun and there are no eclipses (plenty of average power), there is no sun on the -Z face to give us the peak power we need for the few seconds to complete the packet command sequence.
What this means is that we really only have one or two days out of the 1 or 2 week full sun windows to get command, and only in winter. Because each orbit as we approach the terminator is getting less and less peak power, but recovering it before full-sun cannot be sustained due to low average power.
VOLUNTEER STUDENT PROJECT?
Anyway, the offset between the earth's magnetic and geometric poles, suggests there are several degrees of variation in the -Z sun power depending on WHERE the commanding ground station is relative to the time of day and orbit plane with respect to magnetic North. Using simple geometry, I have estimated our best command opportunity from Maryland is when the satellite crosses about 35 deg N latitude and to our east in the morning as the orbit approaches full sun. But I have no comprehensive math model to then predict other optimum times for other potential command locations.
DK3WN's ground station in Germany I think, sees a little bit better angle differentiation due to his being perpendicular to the line between the magnetic and geographic poles, but I would like to have a good formal analysis of this geometry to better be able to coordinate our commanding.
When commanding, one only gets one attempt per orbit per day. If it fails due to lack of peak power, then the load of the satellites attempted response and RETRIES kills the batteries for that orbit.
Anyway, working all of this out with a math model and plots so we can predict these optimum times would be a great benefit to our decade old satellite (the longest operational student project satellite).
Bob, WB4APR USNA Sat Lab