I would assume that there might be some padding there. I’ll bet it would be able to go to 90K, since I think the coldest it would ever get would be -65, or 10 degrees lower than it is rated for.
Funny thing about -55C, it’s what the ‘Spirit’ Mars Exploration Rover is currently running at on mars. A pretty extreme environment for electronics even on a good day.
Also, an idea for ‘passive’ heating of the primary electronics box would be chemical hand warmers. you break the vial starting the exothermic reaction in the hand warmer and put them in the box with the electronics. It’s used by the Experimental Rocketry guys in the frozen part of northern Canada to stop their rocket flight computers freezing on the ground. [url]http://www.nakka-rocketry.net/ep_lr7.html[/url]
About -60 is as cold as it’s going to get. K Type thermocouples will work to -70c for cheap ones, other types will go several hundred degrees below.
Heffo: wow, i thought Mars would have been colder than that…
As far as chemical heaters go, all the ones i’ve seen (admittedly i’ve only looked at hand/foot warmers for snow) react with oxygen to generate heat. WIth about 0.5% atmospheric density out there i’m worried they wouldnt work very well up there. The snow ones i’ve seen you “turn them off” at the end of the day by putting them in a ziplock back so once they’ve consumed the air in there they stop heating.
If you know of any that work by themselves without the presence of oxygen that could be an excellent method of heating as long as the chemicals are not likely to go off on a chain reaction and give us a high altitude hot air balloon rather than helium haha.
http://www.amsat.org/amsat/balloons/balloon.htm
Have you looked at this site? There are many sources available on packaging for high
altitudes.
I have two latex, high altitude balloons available, if you are interested.
Thanks.
Bernard
Agreed on the chemical heaters. They tend to be charcoal plus additional accelerators, as as you say, right where you’d want the heat, you’d have no oxygen.
A more complex calculation would be whether it would be worthwhile to scavenge the heat emitted by the batteries, and maybe plan the package so the electronics are mounted to receive what little convection you’re going to get, or mount them on thermally conductive pads strapped to the batteries.
I have to wonder just how extreme an environment of -55C is to individual components; if you eliminated the water vapor. I’d have expected that the low atmospheric pressure would be more hazardous to components like electrolytic capacitors.
Solder though, is a potential problem. Pure tin crystallizes at low temperature and becomes very brittle, but lead and tin alloys have wildly varying mechanical properties, so it might be possible to source something that’s not as likely to be subject to harm, but of course, the payload is always going to have some normal consumer electronics in there, unless someone’s feeling like desoldering an entire camera and resoldering it with something different.
On the other hand, this project is hardly going where man, and CU undergraduates, have never gone before - I guess there’s an active community out there who would be able to dispel a lot of these concerns via a few phone calls.
that Amsat site looks a little outdated (last updated 2003 
). This is a project i really want to complete before the end of next year.
I think since we’ll have a range of transmitters onboard that dump a lot of heat out we could probably design the area they are in with the other PCB’s to be fairly self heating.
I might have to build a little logging board, chuck a lipo, a couple of transmitters (video, data, data) and some switchmode psu’s (inductors generate a small amount of heat) and put them into an insulated package in my car fridge. The car fridge gets down to -30c in winter but it’s warming up here so i can probably only get to -28c. I could leave it running for a day or so (or until the battery is too low voltage) and see how the temperature fluctuates, considering it can take 30-40 mins to chill down to -28 it could be an interesting test.
If that works out i can go get $15 of dry ice to add to the fridge which will get it down below -55c. This should be worse than ultra low temps at altitude i’m guessing, as the parts would have a lot more pressure/atmosphere around them to help take the heat away.
What you say about conductive plates is a really good point Mog. I never really thought about the fact that with the very little atmosphere, how well will heat transfer to components just with the air that’s left?
Ok so for altitude it turns out you can use GPS. I emailed SkyTraq to see if i could get custom firmware to go over 18km… however they responded back
If we exceed 500m/second, then something has gone DRASTICALLY wrong, as we’re exceeding the speed of sound (at sea level anyway).
I’ve been working on the controller board for the balloon, i’ve spent about 6hrs on it so far including research into parts.
There are RF shields around the Venus 638 chip (the LQBGA69 chip) and the LPC2388 (USBizi 144) and their supporting circuitry. There is a 3A 5v and 3A 3.3v switchmode psu onboard which will only be about 78% efficient (using spare parts i have already) but only have 4.4mv of voltage ripple. The MCU and GPS have their own supply circuits separated by small low resistance inductors and low ESR tantalum caps. Power should be excessively stable 
Logging will be done to a USB stick (ruggedised one, like a Corsair Dominator) and to microSD as well as position, altitude and system health getting sent down wirelessly.
The board still needs a lot of work. It needs a current sensor integrated into it (i’ll most likely just use an allegro 5a hall effect SOIC-8 chip due to size constraints.)
The PCB of course needs silkscreen and routing done. The sensor board (which will be “outside” or outside facing) also needs to be designed.
I presently have 18 temperature sensors to take down to -30c and then after weeding out the ones i dont want will take the rest to -70c and then pull a vacuum on them to see how they perform. I’m guessing the final ones with be a DS18S20 simply because it’s i2c.
Looks like we will be flying soon
Maybe next year around July, Aug, Sept.
I was thinking about flying down to AU for it, but if it’s after July, I may be in college for it 
There’s a lot of testing to be done as we want this to go off without a hitch. I’ve got friends who also want to launch payloads coming in from Canada and Singapore so we need to plan ahead for that - as well as waiting for more favourable weather (read: not 40c).
I also need to write all the software, Daniel and i need to build some sort of tracking system, build and tune some 435, 900 and 2400mhz yagi antennas etc.
I also need to build or buy a new reflow oven for this project as local assemblers cost too much for doing BGA prototypes.
Don’t you also need an xray machine to do BGA prototypes?
Dumb question: Isn’t outgassing of chips a problem?. Or is vacuum not as severe as reflow with regards to moisture content in a chip?
Thanks,
Errol