[sarex] Re: STS-116 - RAFT - PCSAT2
bruninga at usna.edu
Fri Nov 10 09:12:27 PST 2006
> With the successful roll out of STS-116 yesterday to
> launch pad 39B for a early December launch, I
> understand that two Naval Academy PicoSats (RAFT and
> MARScom) were to be on board.
> RAFT is basically a 2 meter packet APRS digipeater
> but also carries 10 meter PSK transponder, just like
> PCSAT2 had. But sometime after a few weeks on orbit
> attached to the ISS, the PCSAT2 10 meter receiver
> seemed to become deaf.
We have the system on the ground and indications are that the
problem was not due to the excellent receiver built by students
at Brno University, under Mirek Kasal, but probably due to a
failure in the antenna. The antenna broke off into the glove of
the EVA astronaut when they were packing up PCSAT-2 for return
to earth, and we suspect that the only thing holding the antenna
on for most of the mission was the Kapton tape covering. Prior
to launch, mechanical engineers (not the RF designers at the
Academy) made two sharp right-angle bends in the tape measure
antenna, to make sure that it would not scrape up against the
primary mission solar cells. These right angle sharp bends in
the berillium copper tape-measure antenna caused it to loose all
regidity and hence very vulnerable to fatigue cracking...
> PCSAT2 was to be returned to earth after the last mission
> and I wonder if a failure analysis had been done on the
> 10 meter receiver and or PSK system?
It is in the clean room and being disassembled at this time.
Since the MISSE5 spaceframe will be reused, the disassembly
process is being done with the utmost care. So we still do not
have access to the receiver.
> Is the new RAFT Picosat using the same design that failed on
No, but we anticipate a different problem. RAFT uses a PSK-10
transciever kit from Small Wonder Labs. To stuff it and a TNC
and an RX and TX and radar transponder all in the 5" cube
satellite, we could not afford to separately shield each circuit
board in its own RFI box. Duh... Having a 10m HF receiver
within 1.2 inch of the CPU of the TNC without any shielding
yields about 20 dB of RFI. So we anticipate RX problems
again... Remember this is a secondary mission and a student
project, so we just did not have the resources to fix it before
flight. NEXT time we will do it right!
> Having been lucky enough to have had one 10 Meter CW QSO
> through PCSAT2 before it failed, no luck with PSK31, I
> wonder if RAFT is subject to the same fate?
Different fate! And a new problem has arrisen, and that is that
NASA is getting more uncomfortable with deploying us even at 170
nM for fear of us hitting the ISS. SO now they are talking
about deploying our 3 Amateur Radio Satellites even lower, at
160 nm. At that low altitude, these things we have worked on
for 3 years won't last more than a month or so.
Talk about depressing! The debate about how low to deploy us is
still going on. You can see how short the life will be by
looking at this web page:
Originally we expected 6 Months from a 185 nm orbit, but then
they wanted us to accpet a minnimum of 175 nm. Now they are
considering limiting us to 165 nm?
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