ARLA/CLUSTER: Actualização dos dados do Satélite de 50 Dolares lançado a 21 de Fevereiro

[João Costa > CT1FBF]

$50SAT update

The amateur radio PocketQube $50SAT/MO-76 - in orbit for 15 months, 15
orbits per day, and some unexpected behavior

Saturday, February 21, 2015 marked the 15 month anniversary of the
launch of $50SAT/MO-76, and you guessed it – it is still operating.

Thursday, February 12, 2015 marked a different milestone – its orbit
has decayed to the point where its mean motion crossed the 15 orbits
per day threshold. The TLEs from Saturday, February 21, 2015 indicate
it is now at 15.00521293 orbits per day.

Some of you noticed that something odd started happening on Monday,
February 23, and Tuesday, February 24. We also noticed the same thing
– during daytime passes in the northern hemisphere, $50SAT was
transmitting once per minute, always sending telemetry in RTTY format,
but never sending GFSK telemetry packets. Moreover, the total reset
count kept going up by one each time.

What seems to be happening on the decending (daytime) passes is the
CPU is reset just after sending a full RTTY telemetry message, as here
are no GFSK packets sent, but within a half minute the FM Morse beacon
is heard with Stuart’s callsign (GW7HPW, the first one in the
rotation). My guess is the battery voltage is decaying during the
operational cycle, and goes below the 2.9V reset threshold just after
sending the RTTY or just as it is about to send the GFSK packets. Once
the satellite is able to enable solar power (PCB temperature >= 0
degrees C), it starts behaving normally; it is now able to send GFSK
packets. During ascending (nighttime) passes, it behaves normally, at
least here in EN82 land.

There was a brief time where this behavior stopped (2015-02-25, 17:05
UTC through 2015-02-26, 3:47 UTC). It did, however, start back up
sometime before 2015-02-26, 05:21 UTC, and has continued since.

Why is this happening now? We are still investigating, but it is
apparent when looking at the chart of battery voltage over the
lifetime of $50SAT/MO-76 that the battery has suffered a sizeable drop
in capacity. If the battery voltage under load is dropping below 2.9V,
how is it able to recover back above 3.3 V (the minimum required to
enable transmission) and nearly complete another operational cycle?
Moreover, why does it always seem to be able to finish sending an
entire RTTY packet before resetting?

In the hopes of better understanding what is happening, I am in the
process of re-assembling my “BoxSat” test setup in an effort to
reproduce on the ground what is happening in space. In the meantime,
the once-per-minute transmission is actually convenient from telemetry
monitoring standpoint, as one no longer has to wait 3 minutes for
$50SAT/MO-76 to start transmitting. So, for any of you who have not
heard $50SAT/MO-76, now is the time. Who knows how long it will
continue to operate in this manner? Who knows how long it will
continue to operated at all? Every time an anomaly has occurred and
thought, “this is it – well, it was great while it lasted”,
$50SAT/MO-76 has proven me wrong. I hope that is the case here as
well.

The Dropbox has been updated with all the telemetry observations
through today (Wednesday, March 4 2015), and can be accessed via the
following URL:

https://www.dropbox.com/sh/l3919wtfiywk2gf/
AABRl4iM5BFqVAcLQGSmdsVga/Telemetry-analysis/Current-Telemetry

I have also uploaded an MP3 file from the daytime pass over EN82 land
on Friday, February 27, 2015 starting at 16:59 UTC (11:59 AM local
time); it can be accessed via the following URL:
https://www.dropbox.com/s/2vfbtu51qn63aoa/50USDSat-LSB-FM-2015-02-27T1659Z.mp3

During the recording, I switch back and forth between FM and LSB modes
so I can hear the FM Morse beacon as well as the RTTY telemetry.

Please keep the telemetry observations coming, especially now!

73 Michael Kirkhart KD8QBA
$50SAT/MO-76 team

$50SAT was a collaborative education project between Professor Bob
Twiggs, KE6QMD, Morehead State University and three other radio
amateurs, Howie DeFelice, AB2S, Michael Kirkhart, KD8QBA, and Stuart
Robinson, GW7HPW. The transmitter power is just 100 mW on 437.505 MHz
(+/-9 kHz Doppler shift) FM CW/RTTY. $50SAT uses the low cost Hope
RFM22B single chip radio and PICAXE 40X2 processor.

There is a discussion group for $50SAT
http://groups.yahoo.com/groups/50dollarsat/

50DollarSat http://www.50dollarsat.info/