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Comment by kerkeslager | Hacker News Reader

So, possibly dumb question: is this basically a fan without moving parts?

This is a prototype so I'm guessing the size/cost can be reduced in the future, and if it becomes small/cheap, I could see a fan without moving parts having a lot of applications.

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Absolutely, this is a passive compressor.

It kind of works like an aerodynamic diode: it is much easier for the incoming particles to go through the intake tubes (because they are oriented along the spacecraft velocity vector) than to exit the collector. This is because after a they collide with surfaces inside the collector, their velocity vector is randomized and no longer aligned with the tubes.

[Edit] Mass is not such an issue when you contrast it with the mass of propellant that you save...

[Edit2] I forgot to precise that my description only pertained to the intake part: there is of course a plasma thruster at the back (no moving part either)

Is the principle behind the Feynman sprinkler involved in any way?

[0] https://en.wikipedia.org/wiki/Feynman_sprinkler

It works by ionizing the air, so that might lead to issues with producing ozone.

Ozone in the high atmosphere is a good thing though - the ozone layer. It's only at ground level that it can act as a health hazard.

Yeah, I should have clarified: I was responding to the "having a lot of applications" remark, which to me implied other places than low earth orbit.

Definitely. Ozone is a significant irritant (although it also has an "air freshening effect", see air ionizers), to produce significant airflow I believe you'd need very large electrodes, which would produce lots of ozone. The electrodes need to be large because the voltage is limited by air's breakdown voltage, so you can't just pump up the voltage like you can (for the most part) just increase a fan's velocity.

For lack of friction/bearings a magnetic bearing fan seems like a much better option. The strength of this technology is the great exhaust velocity, which is great for space applications.

> The strength of this technology is the great exhaust velocity, which is great for space applications.

Ah, that makes sense. Given the speed that these satellites are typically travelling at, the exhaust probably needs to go faster than that to work, right?

...not at the quantities this thing would make.

I'd be more worried about random Nitrogen Oxides (NOx) emissions, but again, too small of a volume to actually matter in any significant way. A couple of VWs are probably worse.

Fair point. Although you don't run VWs in closed spaces, but one might do so with fans (same reason why I hate it when universities or offices put laserprinters in closed rooms - always gives me headaches)

it ionizes the incoming gas and then accelerates it to very high speed with an electric field. My guess is that wouldn’t work well in normal atmospheric conditions but no idea really.

The gas collecting portion of this design wouldn't work well, but it's certainly possible to generate thrust by ionizing air at atmospheric pressure and zero relative velocity. See https://en.wikipedia.org/wiki/Ionocraft#Mechanism and https://www.youtube.com/watch?v=vzZy1Aqleno

The main challenge is whether the ionization creates enough thrust to overcome drag; this seems to be true in the upper atmosphere, but not sure if that works in the lower. Then again, you could probably do it, but it'd require more energy.

there already are fans without moving parts, manufactured by Dyson.

Edit: wrong... see below. Thx, walrus!

They have moving parts. There's a normal fan at the bottom. See here:

https://en.wikipedia.org/wiki/Bladeless_fan

There is an ordinary fan in the base and the ring is hollow with slots in it.

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