Electronic – Detecting atmospheric voltages on high altitude balloon


Our High school is launching a high-altitude balloon payload and the experiment we want to perform is the detection of atmospheric voltages.

My friend and I were amazed when we saw this video where someone powered a small electrostatic motor with an antenna only about 100 feet in the air. With the Edge of Space Sciences mission we signed up for coming up, we thought it would be interesting to run some voltage experiments at a high elevation. The only problem we are running into is that we don't have a reference point (ground) because we can't dangle a long wire from 100,000 feet!

The idea we formulated was to measure the voltage between two small points (say 1 meter) with a microvolt meter and data logger and measure the change in voltage as the height increases. ex. 5 volts per meter at 1000 feet but 10 volts per meter at 10,000 feet elevation. This would give us an idea of how much voltage we would pick up if we were to elevate a giant wire by integrating the data.

So now we plan for either two metal plates or a dipole-like structure to measure the potential between to small points, and use operational amplifiers to capture the minute changes in voltages.

Well… According to this question I just asked about rectification, trying to measure the voltage or the "E Field" this method will not work, and we need a field mill. The problem with a field mill, however is the weight, and power consumption. We are limited to 800 Grams on this flight, and I don't know if a field mill will fulfill that requirement.

What is a good strategy to measure what we are trying to do? This PDF has some interesting measurements with electric field, I don't know how they did it, however.

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Best Answer

Sounds like a really cool high school experiment.

Detecting the voltage with a static pickup is nearly impossible because just about any means to measure the voltage will have lower impedance than two electrodes sitting in air. Even a really high impedance voltmeter will bleed off charge without it collecting.

The trick is to keep flipping the electrodes mechanically and look at the amplitude of the AC signal. This is what a field mill does. It's usually two electrodes on a spinning cylinder, and is how electric field strength of air for purposes like lightning research is measured. I expect you'll find lots of info using "field mill lightning" as a search term.

Try that, then come back here if you have more questions.