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I'm planning a high-altitude weather balloon project (to around 100000 feet) some time down the line to take video and pictures of near space altitudes and I have some questions I need to ask before doing so.

I've decided to go with a Raspberry Pi B+ with a Raspberry Pi camera module to record 720p/1080p of footage from the edge of space. However, I'm not sure what to use for powering it. I'm thinking of using this 10400 mAH / 2.1A Xiaomi Power Bank to power the electronics including an Arduino, GPS transceiver and various other sensors. Will this be a safe bet to work at the edge of space? What alternative power supply options are available for this application?

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  • \$\begingroup\$ Just out of curiosity . . . What did you need to go through to get the permits to be able to launch a balloon like this? \$\endgroup\$ – Michael Karas Oct 19 '14 at 9:24
  • \$\begingroup\$ @MichaelKaras Good question. In India, IMO you will have to contact the Indian Meteorological Department or the DCGA (India's FAA equivalent). In the USA, simply notifying the FAA 24-hours prior to the flight is good enough provided your flight's payload is less than 4 lbs. \$\endgroup\$ – shortstheory Oct 19 '14 at 9:42
  • \$\begingroup\$ People have done this previously; simply keeping it in an insulated polystyrene box can retain enough heat to stay working. \$\endgroup\$ – pjc50 Oct 19 '14 at 10:27
  • \$\begingroup\$ @pjc50 I am interested to look at such examples. Could you post the links in an answer? \$\endgroup\$ – shortstheory Oct 19 '14 at 12:48
  • \$\begingroup\$ What about putting chemical (sodium acetate) heat pads in a polystyrene box with the Pi inside ? The heat pads should compensate the temperature drop without too much issues. \$\endgroup\$ – user40669 Oct 19 '14 at 16:09
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I'd be very concerned about any circuit that uses electrolytic capacitors. A lot of them will vent their electrolyte under low pressure working. This concern includes power supply and pi.

The Illinois capacitor company state: -

enter image description here

In fact it seems all the regular manufacturers warn against the electrolyte leaching out at high altitudes.

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  • \$\begingroup\$ I suppose but others have taken their RPi's to such high altitudes with not much problem... \$\endgroup\$ – shortstheory Oct 19 '14 at 9:19
  • \$\begingroup\$ @shortstheory - how confident are you that "others" haven't replaced the electrolytic caps with solid caps? \$\endgroup\$ – Andy aka Oct 19 '14 at 9:39
  • \$\begingroup\$ Sure, you can see it here: raspberrypi.org/high-altitude-ballooning-sixth-form-style \$\endgroup\$ – shortstheory Oct 19 '14 at 9:43
  • \$\begingroup\$ Several instructables have also sent a naked RPi to space. So the Pi's caps are probably good for low pressure. \$\endgroup\$ – shortstheory Oct 19 '14 at 9:44
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    \$\begingroup\$ A quick Google image search suggests that the Raspberry Pi only has one electrolytic capacitor, and it is a solid type – see e.g. upload.wikimedia.org/wikipedia/commons/3/3d/RaspberryPi.jpg \$\endgroup\$ – ntoskrnl Oct 19 '14 at 18:10
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A LiPo power bank will usually only work down to about 0°C, but at higher altitudes you have temperatures of -50°C and even lower. Unless you're planning for some very good insulation, better choose some other battery chemistry.

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Preparation is key

The best thing to do is test, test, test.

My group built a thermal/vac chamber for testing individual components, and eventually put the whole assembled instrument inside one of NASA's huge thermal/vac chambers (the kind normally used for testing rockets).

Even still, during the middle of our flight one of our batteries failed due to over-charging. It turned out we had more solar power than our charge controller could manage. Thankfully the instrument was on a rotator so we could angle the panels away from the sun.

Power is Heat

Any talk of power in a near-vacuum environment is incomplete without considering your thermal model. The RPi's CPU gets warm to the touch in my office, which means if you take away all that convection from the air it's going to get VERY HOT.

An easy generic solution, is to enclose the whole thing in a metal box, and attach the box to a radiator with a large area (the box itself may be sufficient). You want to point this radiator at black space, and shade it from the sun or earth/snow albedo. For specific trouble spots (i.e. the CPU) add a low-thermal-impedance path such as a thick copper braid between it and your radiator.

Finally, you gain thermal efficiency by coating your metal radiators (including the inside of enclosures) with a good thermal conductive white paint.

Battery alternatives

Capacitors

Depending on your ampere-hours, you might be able to get away with capacitors instead of batteries. This will save weight and possibly lessen your thermal load in general. But be aware that ultra- and super-capacitors are a niche product already, and finding space-rated ones may be ...difficult. :)

Solar Panels

Can you get away with no batteries at all? Maybe your weight and power budgets will let you use solar power exclusively. The biggest trade-off here is between providing enough power in the worst case vs. getting rid of excess power in the best case.

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  • \$\begingroup\$ Thank you for the answer. Unfortunately there are some areas in the atmosphere that are just too cold and have enough air to keep things cold like at 40000 feet. I don't think using solar panels would be too feasible as our electronics bay will be sucking a lot of current. Super caps may suffer from the same problem outlined in Andy's answer. \$\endgroup\$ – shortstheory Oct 19 '14 at 17:17
  • \$\begingroup\$ However your ideas do make sense for near space part of the trip, so I will look into it! \$\endgroup\$ – shortstheory Oct 19 '14 at 17:18
  • \$\begingroup\$ Batteries have much better energy density (per weight and per volume) than supercapacitors. \$\endgroup\$ – ntoskrnl Oct 19 '14 at 18:18
  • \$\begingroup\$ In our experiment, we could have ran on solar power alone except during the ascent. We toyed with the idea of using a supercap for this leg of the journey, but ultimately ruled it out in favor of more tried & tested battery tech. But that was around 2012; technology has progressed since then. \$\endgroup\$ – Alex Shroyer Oct 19 '14 at 21:09

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