[amsat-bb] FW: NO084 PSAT Spin Rate over 10 RPM (BRICSAT listening?)

Robert Bruninga bruninga at usna.edu
Sat Jan 14 16:38:39 UTC 2017


Thanks everyone!

Here is the question.  Did anyone ever happen to hear anything on 435.350
during the last week that did *not* correlate with PSAT?  It may have been
BRICSAT in full sun!  Its PSK31 trasnponder is on the same downlink...  and
since its only problem was poor power budget, it may have been alive and no
one was listening?

It all started Friday afternoon, when I happened to tune to PSAT and heard
only about 10 seconds at the tail end of a pass and saw about a 5 second
swoosh before the transponder dropped out.  Giving me a complete guess at
maybe 12 RPM.

KO6TZ reported: a screen capture from Spectran of the "swoosh" fade lines
from the 23:30utc pass of NO-84. The tick marks … are 1 second spacing…
[with] just slightly over 5 secs between the fades. That puts the spin at
~11.7 RPM.

And of course DK3WN nailed it with this high res plot:
http://www.dk3wn.info/p/?p=76608
Showing 5 rotations in 32 seconds or about 9.4 RPM

We had to use this signal strength method since the the telemetry spin data
is of no practical use since it is undersampled.  IE, we are only sampling
at once every 5 seconds and so this is HALF the Nyquist rate.  To capture a
spin of 12 RPM we would need to sample over 24 times a minute.  So that is
why we needed people to simply listen for it and determine the spin that
way.

And it looks like today is the last day of full sun.

We had gotten excited when we noticed this full sun late Friday afternoon
and realized it would be a good time to listen for BRICSAT which also has an
HF PSK31 downlink on 435.350.  But we noticed that after 20 months in space,
that BRICSAT has separated enough that it ended its full sun period the day
before.

Then we went and looked and noticed this full sun period for both satellites
was only 5 days long anyway.  We are embarrassed that we have not been
watching the orbit and looking for these full sun periods.  They may be rare
indeed.

Bob


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