Standard meteorological balloons carrying temp/humidity sonde as well
as 400 MHz feedback transmitter and GPS receiver! (and battery, hi)
go as high as 10 milibars! It's around 60000 feet. One PCB containing
the whole circuit, is shielded with a tiny metallic box, it's not too
heavy, several times less than it's huge 9V battery (~250 grams).
So, it is shielded, indeed and the only thing "exposed to the radiation"
is it's 1/4 lambda TX antenna for ~400MHz feedback transmission.
As I mentioned, the box collects the position information (GPS)
and sends it back to the ground station, along with other measurements.

 Radiation is not an issue here. Balloon itself is much more important.
Up there, the balloon will be exposed to freezing air and as long as the
atmospheric pressure makes it constantly "growing", many of them will get
blown before they reach 100 milibars. Meteo balloons are made with
quite a thick rubber but it still doesn't guarantee, they'll reach the
required distance. Usually, the monitoring process takes around 2 hours,
until the balloon will finally blow, at around 10 milibar, up there.

I saw them "in action", early this August. On Sable Island, 44N 60W.

Those are filled with Hydrogen gas since Helium is more expensive.
Hydrogen can be easily extracted from water with an electrolytic machine.
Right on site. That's what they do there.

Jarek,

VA3NCD (sp8ncd, cy0ncd)


>> If you can spare the extra pound in weight, it would probably be
>> good to encase the circuitboard in a nice metal box. You could also
>> fill the box with epoxy or RTV silicon. I believe that is what is done
>> with the "Black Box recorders" used in airplanes.
>
>Shielding the PIC may make things worse.  There are some high
>energy cosmic rays (primaries) that will go right through the PIC
>without despositing energy (because the PIC isn't substantial enough
>to slow them down).  But high energy cosmic rays impacting a layer
>of metal can create a shower of secondary cosmic rays (like it does
>for our atmosphere).  These secondaries have less energy and may be
>stopped or slowed down by the PIC.  That could cause a radiation
>problem.  Its a matter of a lot of sheilding is great (but heavy),
>while a little bit is more harmful.
>
>But my experience with the BSII on high altitude balloons is that
>cosmic rays won't cause a glitch (so far!).  We see an increase of
>cosmic rays detected with a GM tube to about 62,000 feet and then a
>decrease with altitude.
>
>>
>> >         Our team has been thinking about using a PIC16C84 as the core
of
>> > an amateur radio Balloon payload experiment. These Balloons reach over
>> > 20km (about 60,000 feet). At those altitudes, radiation is quite high.
>> > Does anybody know about the effects of this radiation on the micro,
>> > or its chances of causing latch-up.
>> >
>