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Comment by mrfusion | Hacker News Reader

AMA? How much can these thrusters be scaled up? Or does it make more sense to stick more smaller ones on a craft if we need more thrust?

Bonus question: how would you design a planet scale thruster? (Asking for a friend)

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To scale up thrusters you can simply make them bigger, but that leads to a lot of wasted space as the thrust is only produced by a ring-shaped region of the device. To improve thrust density, you can nest these inside each other (see this page on my research group's website https://pepl.engin.umich.edu/project/high-power-hall-thruste...). More recently, we have been looking at running smaller thrusters at higher power densities, which was previously impractical due to the way older thrusters shaped their magnetic fields. Nowadays we can design thrusters such that very little power is lost to the walls so high power density operation is looking more feasible.

Per the second question, you would need a very efficient thruster to limit the amount of mass needed as propellant. If you have an entire planet, you might look into using a photon rocket. Alternatively, you can try a massive solar sail or magnetic sail but I'm not an expert on these things.

Thanks! Could super conductors help increase efficiency or density? Why or why not?

Could this be a viable space to launch a start up? With launch costs coming down there could be a lot of demand for more efficient thrusters.

They could help with improving magnetic confinement on high power density thrusters.

Yes, it is. There's a lot of small thruster startups out there. See Orbion, Thrustme, and Applied Ion Systems for examples.

By density do you just mean a ton of smaller thrusters? Does it have to be a ring shape?

Basically I am just imagining a ship with a ton of the tiniest realistically produced thrusters side by side - would be some wasted space between the rings but this seems like it could be a solid design (not to mention additional redundancy in case individual thrusters go out)

I mean density in terms of amount of plasma through the device. You can cluster these together too but that gets complex from a systems design perspective. It's something that's being researched though

Is it additional redundancy or additional points of failure? Enquiring minds want to know!

Both of those, but also additional mass due to extra plumbing and such. It's definitely a thing we could do but it's not without it's problems. Also, Hall thrusters don't tile well as they're annular/ring-shaped devices. There are linear thrusters which would tile better but they tend to work fairly poorly.

Don't tell him! He wants to move us away!

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

These thrusters need fuel to move. That ends the fun on this line of inquiry. There is no free ride (unless you sail around very slowly, but this is more like sucking Earth's wake in style)

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