Edit thanks everyone, I’m not sure why I wasn’t understanding but you’ve all clarified it for me
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Solid rocket fuel is typically used in rockets and missiles.
Missiles like the AMRAAM and Sidewinder use Solid fuel, and the Space Shuttles two outer boosters were solid fuel.
As the name implies it is a solid at room temperature as opposed to a compressed liquid like Hydrogen.
The chemicals include both fuel and oxidizer and are pre-mixed and harden into a solid at room temperature. This makes it safe to handle and relatively stable. The solid is molded into the rocket tube leaving a gap in the center for the exhaust to form and escape.
When ignited the material burns from the top of the missiles down to the ~~nose cone~~ nozzle producing thrust.
A typical mix includes ammonium perchlorate (70%), aluminium (16%) and binder (14%). The aluminum being the fuel.
u/DarkAlman gave a pretty solid answer.
I’ll add that there are hybrid motors where you have a solid fuel and liquid oxidizer.
Solid rocket motors once started can’t be “turned off”. The entirety of the propellant will burn. It’s great if what you want to do is shoot an explosive warhead at a moving object, not having to worry about fueling the missile and being able to leave it on shelves for years. Just fire the missile and it’ll either hit the target or miss and drop once it runs out of fuel. No need to worry about leaks, etc. Great for Hydra missiles and the like.
They’re not as great if you want to be able to turn off your motor or slow down combustion. Hybrid motors let you do that with some amount of solid fuel. You can just cut throttle the supply of oxidizer. Some universities have rocket competitions and usually use hybrid motors for that.
ETA: A solid motor usually burns from the inner diameter to the outer diameter radially rather than axially like a firework fuse would. To get meaningful thrust, you need lots of gas from the combustion. For that you need surface area. End burners (burns like a fuse) can be a thing, but gases get generated a lot slower.
A rocket is just burning something fast and with a nozzle to direct the exhaust gases. Just like you can burn gasoline, and you can burn wood, the fuel you put in a rocket can be either liquid or solid. The other comments have gone in depth about the chemical compositions of exactly what you put in there and the advantages and disadvantages, but solid vs liquid fuel is like a propane grill vs a charcoal grill. You’re just changing what you burn.
Presumably you know what gunpowder is right? It’s a powder then, when ignited, rapidly combusts and produces a large amount of hot gas. Solid rocket fuel is just like gunpowder but compressed into a solid shape. You just take a mixture of powders that do roughly the same thing as gunpowder, compress them into a solid, and you’ve got solid rocket fuel. In some cases, like with fireworks and model rockets, the solid rocket fuel is just straight up gunpowder.
Added question: what does it feel like? Dry like compressed powder or waxy like a stiff gummi bear? Something else?
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