A number of interesting developments have taken place in terms of design:-
1. It turns out that the HSC series of sensors do in fact go down to 0-psi. The resolution may not be great but this could work. If so, I should get rid of the SCP1000 and BMP085 for two of these to cover the required range.
2. I'm seriously considering using the V8 module instead of the 1W one, for the communications link. This would eliminate the need for the 9V supply.
3. Atmel makes a series of high-capacity serial storage - DataFlash. I can get sizes up to 4MB compared to our current 128kB. The question is if we should then replace the SD card with this instead?
Obviously the above would entail a change in layout.
Project to send a balloon into lower space with payload