I'm a bit confused about how the fuel manages to get from wherever its being stored in a spacecraft into the engines, seeing as it is supposedly solid and so seems like it wouldn't be easy to move. could anyone explain how the solid propellant works for this?

  • $\begingroup$ See also: Why is there a hole in solid rocket engines? $\endgroup$
    – DarkDust
    Jan 24, 2018 at 10:18
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    $\begingroup$ Have you checked out model rockets? They have great solid propellant systems that you can buy in a store. en.wikipedia.org/wiki/Model_rocket#Model_rocket_motors $\endgroup$
    – JAB
    Jan 24, 2018 at 16:04
  • $\begingroup$ @JAB ... or even bottle rockets! $\endgroup$ Jan 24, 2018 at 19:14
  • $\begingroup$ @MikeHarris I haven't seen many bottle rockets with solid propellant, unfortunately. Though I suppose you could use a model rocket motor in a bottle rocket... $\endgroup$
    – JAB
    Jan 24, 2018 at 19:16
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    $\begingroup$ @JAB What kind of propellant are you used to seeing in a bottle rocket? AFAIK a bottle rocket is a tiny model rocket motor on a stick. Maybe with some chemicals added to the propellant to give it some color. $\endgroup$ Jan 24, 2018 at 19:49

1 Answer 1


The solid propellant is stored in the engine, so it doesn't have to be moved.

The engine consists of a large cylinder that contains the propellant (indicated as 'grain' in the image, but it's a solid block with a grainy structure), with the nozzle at one end of the cylinder.

enter image description here

Here's one segment of a Space Shuttle solid booster, with the void down the middle clearly visible: Shuttle SRB segment

The propellant is shaped as a hollow cylinder: the void down the middle is exposed to the elements. When the engine starts, this surface is ignited. The hot gases escape down the central void and out the nozzle.

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    $\begingroup$ grain may be confusing a bit, making one think of granules. Solid propellant usually resembles hardened resin; there's a lengthwise channel through the middle of the booster, and the propellant's whole exposed surface (length of that channel) burns. Shaping the walls of that channel changes the amount of surface (and burn profile) changing thrust as result; the cross-section of the channel - that shape profile - is usually referred to as grain. $\endgroup$
    – SF.
    Jan 24, 2018 at 12:01
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    $\begingroup$ stupid question. if you took a flame thrower to the end of that thing as pictured, would it explode? $\endgroup$
    – n00b
    Jan 24, 2018 at 14:56
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    $\begingroup$ No. It'd start burning on all exposed sides, so you wouldn't want to be anywhere near it. A flame thrower is pretty close to the normal ignition mechanism for a solid rocket. $\endgroup$
    – Hobbes
    Jan 24, 2018 at 15:04
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    $\begingroup$ @Hobbes: I believe a flamethrower would merely smoulder the insides. You'd need a blowtorch; these materials need to be very stable not to explode from rocket vibrations, pressure, compression from combustion etc, so igniting them takes some serious temperature. $\endgroup$
    – SF.
    Jan 24, 2018 at 15:58
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    $\begingroup$ @DavidRicherby: You underestimate the risk and conditions of a burning solid fuel. Many solid fuels in rocketry are literally the exact same substances as high explosives used in munitions and blasting charges, the only difference being an addition of binder that prevents breaking them up and the fact the combustion chamber has an opening (the nozzle) which prevents the combustion from turning into detonation. Without external supply of oxygen, gasoline will not explode, no matter what. These fuels contain own oxidizer, and CAN explode if subjected to too violent treatment. $\endgroup$
    – SF.
    Jan 24, 2018 at 16:21

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