[amsat-bb] Re: RS-15 heard again

Auke de Jong sparkycivic at shaw.ca
Mon Jun 30 18:36:36 PDT 2008

I have thought of another possible cause, which is still purely speculation, yet it's fun to talk about! ...

Perhaps, some of the battery cells have failed and shunted-keeping the voltage very low accross the power system.  Then as the voltage builds from charging via the solar panels, the remaining battery cells become charged, lowering their resistance, and thus the total resistance of the battery system.  A threshold is reached where the voltage gets just high enough so the transmitter is keyed.  Then the transmitter further draws the voltage down from the system, and out of the remaining battery capacity, untill another low-voltage threshold is reached, de-activating the transmitter, and starting another cycle.
This could explain why the timing periods vary from one moment to the next, as the sun-angle changes along the orbit, and maybe some solar panels are better than others on the different faces of the craft with spacecraft rotation, creating different combinations of charging currents, and transmitter keying.  Higher charging currents would cause a shorter off-period, and longer transmitting period.  unfavorable sun-angles, such as facing the antenna-side of the craft, would cause very long off-periods, and very short transmissions.  

If only we could know what the actual electronics inside the spacecraft entailed, a lot of good analysis and education could come from this gradual failure.  At this point, I dont' even know what the design capacity of the solar array was, much less be able to determine if they could power the transponder system or beacon encoder successfully without a battery!

I really hope that someday, satellite builders will be more forthcoming with technical data about the flight electronics, just as they were with AO-7 and a few others.  The benefit of this data to the larger community of Amateurs, and to spacefraft science itself, can't be overstated!  Heck!  I might as well say the obvious logical extension of this line-of-thought: It might help us to understand our past mistakes as well as the eventual failure-modes for satellites, so that we might prevent the mistakes from being repeated, and create even longer-lasting satellites!  

I would think that the ultimate goal should be that they CAN create satellites that operate forever, should they want to.  Not all of them need to, but for Communications birds in particular, the design lifespans advertised in the literature, always strike me as very short...

enough typing, time for more operating: 

  ----- Original Message ----- 
  From: w7lrd at comcast.net 
  To: Auke de Jong, VE6PWN ; AMSAT-BB 
  Sent: Sunday, June 29, 2008 7:23 PM
  Subject: Re: [amsat-bb] RS-15 heard again

  I have tried at times to give it a shot of RF uplink, "just in case".  I mean after all AO-7 came back to us!  Maybe it just needs enough up RF to jump start it.  Does anyone know what it's final demise was from?
  73 Bob W7LRD

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