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Comment by simonh | Hacker News Reader

That's such a tiny thrust it might be quite difficult to measure in space. Orbits are complicated, what with complex gravitational variability of the Earth (mountain ranges, continental shelves, the fact it's not a sphere), the influence of the moon and sun, interaction with the magnetic field, solar winds, and down in low earth orbit even the last vestiges of the atmosphere.

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Those forces are actually pretty well behaved and can be readily measured and accounted for. Also, light sails have a order of magnitude less power, and the Pioneer Anomaly [1] was smaller yet. Space is probably the best place to test something like this.

[1] https://en.wikipedia.org/wiki/Pioneer_anomaly

The Pioneer Anomaly was only detectable over several decades and a journey to the furthest reaches of the solar system. I'd expect a useful propulsion system to produce effects quite a bit more detectable than that.

This effect is about 1/25 the power efficiency of the lowest power ion thrusters. Output at this level over a very long period might be useful at the interplanetary level and maybe at geostationary altitudes, but the low earth orbit environment is actualy highly variable and unpredictable at this scale of effect.

Wouldn't variations in atmospheric drag negate any possibility of detecting the actual thrust component in leo? The trusts are small, as is the device, but any variation would be extremely hard to detect and measure. Please correct me if my line of thinking is wrong though, I'm not an aerospace engineer.

Couldn't many of those effects be accounted for by having a non-operating unit in the same orbit as the test unit, and looking for differences in the motion of the two?

Yes, all I'm saying is the orbital experiment would have to be well designed. It's not necessarily trivial.

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