Mmmm… Rocket Candy

As any schoolkid who’s into pyrotechnics will tell you, mixing an oxidising agent with any form of carbohydrate will usually get you a dramatic reaction. Trust me. I used to be one of those schoolkids. Several of the so-called “explosives” in the infamous Jolly Roger’s Cookbook, like glycerine with potassium permanganate, were based on this same idea. Reactions of this type are surprisingly potent. So potent, you can use them to power model rockets!*

This classic YouTube video shows much the same kind of reaction. A gummi bear, made primarily of sucrose sugar is dropped into molten potassium chlorate. Fwoosh! Violent oxidation reaction! Sucrose, in this case, is a partially oxidised hydrocarbon. Stable under normal conditions, but an oxidiser can easily oxidise that sugar fully into water and carbon dioxide, which is what’s happening in this video.** The byproduct from the oxidiser itself is potassium chloride, commonly found in low-sodium table salt.

This same trick can be used to make the deliciously named rocket candy!

Rocket candy is a really simple type of solid rocket propellant. The oxidiser used is potassium nitrate (KNO3), which is a rather milder oxidiser than potassium chlorate! It’s also often found in fertillisers, making it another old Jolly Roger favourite. To make it into rocket candy, you need to first melt a quantity of sugar. This needs to be done using an oil bath or similar, to prevent any hotspots which could cause the stuff to prematurely ignite. Once the sugar’s all melted, you can simply mix in the KNO3, pour it into the rocket casing and leave to solidify. Voila! A bit like Brighton rock, only a lot more flammable!

I’d imagine professionally made ones are probably made with powders which are sintered together at low temperatures, though trying to do that at home is a lot more hazardous. It’s perhaps not the best of ideas to go putting rocket fuel in an oven…

Rocket candy works so well, it’s the propellant of choice for most amateur rocketeers. As such, a recently announced project called Sugar Shot to Space aims to get the first amateur rocket into space using only an amateur propellant — as opposed to the more high end propellants such as ammonium perchlorate used professionally. I certainly plan to keep an eye on their developments. It’ll be intriguing to see how well they do!

*Yes, yes. I used to play with model rockets too. What can I say? Rockets are fun!

**Incidentally, don’t try this with any old hydrocarbon. With things like fuels which aren’t partially oxidised, the results genuinely can be explosive — which is why MSDS sheets always say to keep fuels away from oxidisers!

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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4 Responses to Mmmm… Rocket Candy

  1. invaderxan says:

    It is very cool. :)
    And a good way of showing kids exactly how much energy is in all those sweets! Setting a dollar bill on fire? Hmmm… Ethanol?
    And lol! Real-time FTIR? I tip my hat to one, geekier than I! :P

  2. invaderxan says:

    Wow. Seriously? That’s astonishing.
    So logically, it’s all about the speed of reaction and thus the power generated rather than the energy released that determines destructive potential of these things. Fascinating…
    Thanks for sharing. :)

  3. I love the gummy bear experiment. :D
    Not to mention, it’s a great demo I used to do back in undergrad when our department would do high school outreach programs to get kids interested in science. They liked that and setting a $20 USD bill on fire! :)
    BTW, the video makes me want to hook that all up to my static FTIR system and take real-time spectra as the reaction proceeds. OMG, data love!

  4. 6_bleen_7 says:

    I once calculated that, based on the technical definition of “a kiloton of TNT”, that the energy released by the detonation of TNT amounts to only 1 kcal/g TNT, versus nearly 4 kcal/g for the complete oxidation of carbohydrates.

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