[amsat-bb] Question about SEEDS telemetry...

Mark VandeWettering kf6kyi at gmail.com
Thu Jun 5 13:46:12 PDT 2008

So, I've been having a mild amount of fun using my Python code to track 
the various
recently launched cubesats, and especially SEEDS II, which I find to be 
really easy
to receive.  My script drives the frequency control on my FT-817, and 
allows me to
get easy recordings that by just aiming my Arrow at the spot it tells me 
to.  I record
these onto my laptop, and then process them into spectrograms for fun.  
For instance,
a couple of days ago, I got the following:


Each horizontal pixel is 1/50th of a second, making the width of each 
row 20 seconds,
and the full set of SEEDS II housekeeping telemetry is about 100 
seconds.  If you work
through the picture, you can confirm that I didn't make any mistakes 
when I copied the
telemetry as:

JQ1YGU SEEDS G4 01DF37DF CF1 FFE 007 00A 000 000 009 007 ABE AAC A94 AEA 
11 0000 0001 0001 0001 55DD B1 40 30

Using the documentation for SEEDS that is available online, I decoded 
this as:

Satellite Callsign: JQ1YGU
Satellite ID: SEEDS
Satellite Mode: G4
Satellite Time: 15703023 sec
Li-ion Battery Voltage: 4.04 v
Bus Voltage: 5.00 v
Solar Cell 1 current: 0.78 ma
Solar Cell 2 current: 1.11 ma
Solar Cell 3 current: 0.00 ma
Solar Cell 4 current: 0.00 ma
Solar Cell 5 current: 1.00 ma
Solar Cell 6 current: 0.78 ma
Temperature Li-ion Battery 1: -1.41 degC
Temperature Li-ion Battery 2: -0.53 degC
Temperature Transmitter: -2.27 degC
Temperature Receiver: -4.48 degC

So, here's the question.  This was a nighttime pass over CM87, and we 
see that the satellite must have
been in eclipse, as its solar panels are generating almost now power, 
and the temperatures are pretty
low.  Is this common for the cubesat during eclipse passes.  It dawns on 
me that my inability to get
it transmitting in SSTV or digitalker mode might be that I have been 
catching almost exclusively
night time passes (curse my day job).  Looking back through the list, 
I've seen housekeeping telemetry
where the temperatures are 40 degC or even higher.  Is the variation in 
temperature really that great?
Is it just that the thermal mass being low causes relatively deep cycling?

Just thinking...

    Mark KF6KYI

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