[aprssig] PCSAT-3 opportunity?

'Scott Miller' scott at opentrac.org
Tue Jun 26 17:28:58 EDT 2007

Including batteries?  .35" thick would be rather tight!  I guess you could
do it with a cell phone style prismatic Li-Poly or Li-Ion battery, if you
could get either of those approved for flight.  A AAA cell is .41" in
diameter, so that's out.

I checked with Freescale and the processors I'm using are made with a 0.25
μm process.  That should make it a lot less vulnerable to single event
effects than older 0.5 μm or 0.35 μm parts.  I suppose it's still big
compared to top-of-the-line desktop processors, but I don't know how much
smaller microcontrollers get.

Any idea what process was used in the SRAM on PCSAT-1?  I think you
mentioned once that there was a little chunk of lead over the chip.  Any
idea if that did any good?  From what I've read, depending on the thickness
of the shielding and the energy level of the radiation, using heavy elements
for shielding can potentially make things worse if you're not careful.  A
high-energy cosmic ray that might normally zip right through without
interacting with the semiconductor might instead hit the lead nuclei and
create a shower of secondary radiation that's more likely to interact with
the part.  Polyethylene might be a better choice, but I really don't know
how much you'd have to have to do any good.  It's probably better to just
build in as much tolerance of SEEs in the form of watchdog timers and such
as possible and accept that you're going to get some.

Fun stuff!  Wish I had a cyclotron to try some things out.  =]  (Hmm, maybe
it's time to check eBay...)


> -----Original Message-----
> From: Robert Bruninga [mailto:bruninga at usna.edu] 
> Sent: Tuesday, June 26, 2007 12:35 PM
> To: 'Scott Miller'; 'TAPR APRS Mailing List'
> Subject: RE: [aprssig] PCSAT-3 opportunity?
> > How far do you want to take the smaller-is-better? 
> Well, one option was to make the whole thing only .35" thick
> including housing, and then it is guaranteed a ride.  They just
> stick it on the available space.  It would have two solar cells
> on the top and be only 7cm by 10 cm.  But then where is the
> antenna?
> So I prefer to not try to squeze the elex that much, and put
> them elsewhere and only have the solar cells there.  (two cells
> at 2.5v each and about 350 mA.  We may need a voltage DC/DC
> converter to get all operating voltages.
> > Do you need KISS support?
> Whatever you need to implement:
> 1) APRS digipeater (simple)
> 2) some kind of loggon for SYSOP control
> 3) Ability to turn maybe 2 or 3 things on or off
>    (one thing might be a PSK-31 10m RX)
> > The T2... can beacon PSK31.
> That is perfect.  Because one thing we might want to "turn on",
> is an SSB PSK-31 RX and then key the FM TX for the downlink.  In
> that mode, it would be ideal to merge the Telemetry from your
> module into the PSK-31 downlink...  Using packet obliterates
> everyone.  But PSK would be seamless.
> Bob

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