Protecting a tethered floating device from Lightning strikes

Question

I am building a device, current as a proof of concept, but I would like to have it in place for a long period of time (over a year) with minimal maintenance.

The device is powered by an array of solar cells, contains a microprocessor and other computational devices, and radio/microwave communications. The whole shebang is suspended underneath a weather balloon (with a few of the transceiving components and solar cells connected to the top), and that is tethered to the ground via a 200 meter length of (non-conductive) cable.

My current worry about the device is its longevity. Although in a controlled environment, the device is capable of lasting forever(ish), I am worried about environmental factors, the main being lightning strikes.

So, how can I protect the device if such an event occurs, or avoid it entirely?

EDIT

In the event anyone cares and wants to replicate what I am attempting, I went for the 600g package here on ebay.

Also if anyone knows of a better device (that could hold a greater weight without going into the 100's) that a weather balloon for suspending a device, do shout out (final weight unknown, less than 5kg)

Answer 1

A wet "nonconductive" tether is still pretty conducive to lightning. I think there's a few things worth considering:

• how likely is lightning, both in absolute terms and compared to high wind events?
• how is the baloon itself going to survive a lightning strike?

Placing the solar cells on top of the baloon strikes me as both very bad for stability and also exposing them to lightning. What I'd do as lightning mitigation is put them a meter or so below the baloon, below the tether point. Unless you're very near the equator the sun will still reach the cells at an angle.

You'll need to seal the electronics very thoroughly. You can protect a bit more against ESD by putting them in an aluminium case; sprinkling some of the traditional ESD protections (TVS diodes, small choke coils) on any connections outside the box will also help.

Realistically I would build several of these devices and accept that either you take it down during a storm or it blows away or gets vaporised by a lightning strike.

Edit: depending on height, weather, positional requirements and local aviation rules, an autonomous glider could work quite well for this sort of thing; admittedly that's a much bigger project. But check your local aviation rules for tethered baloons at that alitiude anyway.

Answer 2

Assuming the device does not need to operate during thunderstorms, you could build a lightning detector circuit into the device that automatically shuts down the sensitive electronics and disconnects the exposed antennae from the circuit. An untuned AM radio circuit with a level detector and strike frequency counter would be one option. The circuit would then re-attach and re-power the sensitive electronics after a specific period and continue monitoring for lightning activity.