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Comment by tectonic | Hacker News Reader

We covered the rotating detonation engine on Orbital Index a few months back. The main conclusion was that, while more fuel efficient, the RDE is currently way too unpredictable for real use. Here's a cool video of the circular detonations though: https://www.youtube.com/watch?v=gEYFy3qRNdo

And the actual paper: https://journals.aps.org/pre/abstract/10.1103/PhysRevE.101.0...

(If you're into this kind of nerdery, you might enjoy subscribing to our weekly newsletter. https://orbitalindex.com)

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I was thinking that a solid state hydrogen/oxygen gas generator might be a safe way to store propellant, as it could exist in the inert, uncompressed form.

https://spectrum.ieee.org/energywise/transportation/alternat...

I think using this for vehicles is the least creative application of this tech.

It looks like AlGalCo makes an aluminum-gallium alloy that produces hydrogen + aluminum oxide when mixed with water. This seems like it would be useless in space, because the oxygen is locked away until you run the waste through an aluminum smelter.

Hmm, I wasn't thinking of re-usability for the aluminum. Just that it would keep the propellants in a safe state. water+alloy might be better than nasty toxic fluid + pressurized oxidizer. I am also not a rocket scientist.

It isn’t a question of reusable type - you need to have fuel and oxidizer to burn things. A truck can use atmospheric oxygen for the oxidizer; a rocket can’t.

I also imagine that the extra weight of the aluminum pucks would tank your Isp (though I suppose you might be able to make back some tank weight).

I willfully? missed that the O in the water binds to the Al so is unavailable for combustion (it has to, otherwise what gets consumed?).

Oh, another take, it is a molecular pump that removes oxygen from the environment and turns it into water, via burning.

I’m a recent subscriber and i really enjoy your material. Have y’all through about something similar for the aero side of aerospace?

Thanks! We sometimes talk about atmospheric vehicles, but are mostly focused on space.

Is this actually more fuel efficient than a hydrolox expander cycle like a RL-10? Any sense of how much?

Honestly don't know.

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