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Comment by perl4ever | Hacker News Reader

>Nuclear fusion is a more likely answer to spaceflight and Earth's clean energy problem.

Considering we don't even have fission rockets or airplanes in normal use, making a fusion powerplant that is light enough to get off the ground seems very far fetched.

Even if we eventually use fusion for travel beyond earth orbit, I'd bet chemical rockets would still be in use.

Don't we already have thrusters that are useful in space, but completely unable to support themselves against 1G and so they can't lift off from the ground?

I feel like I've read something that said fusion power would fall in the same category.

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For those interested:

As absurd as it sounds nuclear powered aircraft engines are a thing.[1] They have also been proposed for spacecraft, Scott Manley does a great video talking about nuclear rocket engines[2].

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

[2]https://www.youtube.com/watch?v=cvZjhWE-3zM

I flirted with the idea of using supersized nuclear powered aircraft as the terrestrial version of the Aldrin cycler[1] concept. Basically, these things would be designed to never land but instead run in circular paths between continents with a fleet of onboard craft and hangers that will exchange cargo and passengers instead. They will be designed from the ground up to be maintanable and refuelable under constant operation (not a particularly difficult goal for a nuclear powered craft).

Safety is a very valid concern for any supersized airborne vehicle but especially a nuclear powered one! However, this is one department where scale in itself brings it's own benefits. The volume increases faster than the surface area so you could have a hull far thicker than that of many naval ships while still having a truly vast interior volume. Not needing to ever land also reduces avenues for sabatoge and presumably the craft's interior itself would be heavily compartmentalized. You can also optimise your hull to deal with a narrow air pressure range which you cannot do with normal craft which need to be able to handle a wide range from ground level to the stratospheric.

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

> Don't we already have thrusters that are useful in space, but completely unable to support themselves against 1G and so they can't lift off from the ground?

Yes. For example ion thrusters have specific impulse that is like an order of magnitude or two (or three?) better than chemical rockets, but they can't lift anything out of the atmosphere.

> I feel like I've read something that said fusion power would fall in the same category.

Sorry I have no idea about that.

DFDs seem promising, but are far from producing 1G of thrust.

https://en.m.wikipedia.org/wiki/Direct_Fusion_Drive

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