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Comment by gorgoiler | Hacker News Reader

This is wonderful.

I’ve never really understood how solid fuel boosters work. Are they filled with something granular like sand, that empties down the rocket tube?

The video makes it seem as if the entire tube is on fire at the same time.

It’s also fantastic that an asymmetric vehicle like the Space Shuttle was ever built. What an outlier it seems, amongst the more, I suppose traditional looking rocket designs in this video.

A very poetic leap, as well, to think that the same orbiter that climbs under so much power is the same vehicle that glides into land without power, all the way back from orbit!

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Its not really like sand, its more like toothpaste that is dried up. Its essentially a rocket fuel where the fuel and the oxidizer is premixed in the same 'paste'. This makes clear why its a pretty dangerous substance. You need to be very careful manufacturing those, as they can explode pretty easily.

The way it works, is that it burns from the insight out, like a hollow candle. The trajectory of the booster is basically molded into the hole in the middle. Once you light in on fire, the booster is gone fly its trajectory whatever you do.

Here you can see all that pretty well:

https://www.youtube.com/watch?v=k_JULlA_9Mo

As I understand it, the solid propellant is hard and hollow on the entire length: https://en.wikipedia.org/wiki/Solid-propellant_rocket. Also check this wonderful Applied Science video: https://www.youtube.com/watch?v=TLPWqCMb7DE

This is my all time favorite animation of how a solid rocket works https://i.imgur.com/E7J8pxF.mp4

so yeah it is all burning at the same time

In the OP's video, it looks like the fire is magically coming out of thin air... it'd be hard to do the animation style I linked at the distance in OP's video though, so I'm not sure how they could better animate a solid fuel rocket

Aha! Very nice! So this is why solid fuel boosters are ejected before they’ve burned out - because they will eventually burn out to the edges of the tube and the whole thing will start to glow?

If you've ever used a firecracker rocket it has solid fuel in exactly the same way. It just burns from the inside out (I think) to ensure that the rocket's center of gravity doesn't change as the burn progresses.

> traditional looking rocket designs

It’s ironic how much Starship resembles a 1930’s pulp-fiction rocket.

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