Fail Of The Week: 3D Printed Parts That Burn Like NASA’s Rocket Fuel

[Integza] is on a mission to find as many ways as possible to build rockets and other engines using 3D printing and other accessible manufacturing techniques. He had an a great idea – is it possible to 3D print a solid fuelled rocket, (video, embedded below) specifically can you 3D print the rocket grain itself? By using the resin as a fuel and mixing in a potent oxidiser (ammonium perchlorate specifically – thanks for the tip NASA!) he has some, erm, mixed success.

Effective thrust vs grain cross-sectional profile

As many of us (ahem, I mean you) can attest to, when in the throes of amateur solid-propellant rocket engine experimentation (just speaking theoretically, you understand) it’s not an easy task to balance the thrust over time and keep the combustion pressure within bounds of the enclosure’s capability. Once you’ve cracked making and securing a nozzle within the combustion chamber, the easiest task is to get control of the fuel/oxidiser/binder (called the fuel grain) ratio, particle size and cast the mixture into a solid, dry mass inside. The hard part is designing and controlling the shape of the grain, such that as the surface of the grain burns, the actively burning surface area remains pretty constant over time. A simple cylindrical hole would obviously increase in diameter over time, increasing the burning surface area, and causing the burn rate and resulting pressure to constantly increase. This is bad news. Various internal profiles have been tested, but most common these days is a multi-pointed star shape, which when used with inhibitor compounds mixed in the grain, allows the thrust to be accurately controlled.

[Integza] tried a few experiments to determine the most appropriate fuel/binder/oxidiser ratio, then 3D printed a few fuel grain pellets, rammed them into an acrylic tube combustion chamber (obviously) and attached a 3D printed nozzle. You can see for yourself the mach diamonds in the exhaust plume (which is nice) due to the supersonic flow being marginally over-expanded. Ideally the nozzle wouldn’t be made from plastic, but it only needs to survive a couple of seconds, so that’s not really an issue here.

The question of whether 3D printed fuel grains are viable was posed on space stack exchange a few years ago, which was an interesting read.

We’ve seen some more sophisticated 3D printed rocket engines lately, such as this vortex-cooled, liquid-fuel engine, and over on Hackaday,IO, here’s a 3D printed engine attempting to use PLA as the fuel source.


21 thoughts on “Fail Of The Week: 3D Printed Parts That Burn Like NASA’s Rocket Fuel

  1. I wonder if you could make a “real” (you know, shoot something into orbit) with this? Just solid fuel, a graphite nozzle and a very cheap carbon fiber body, only strong enough to hold itself and cargo up on the ground. This could be as cheap or cheaper than reusable rockets or at least blow up real good.

    1. The propellant is the (relatively) easy part—I wrote a book about it (2nd ed came out in July). A liquid polyurethane binder and a solid oxidizer, plus other additives, are mixed and poured into a casing, with a mandrel to shape the core. The binder cures and the mandrel is removed. Much faster than 3D printing and probably less hazardous, depending on the oxidizer.

      And it isn’t hard to make a motor with a neutral (flat) burn, either. The most common configuration among amateurs is the BATES (ballistic test and evaluation system) grain. Each grain or chunk of propellant is about 1.5 times as long as its diameter, has a cylindrical core, and it burns on the ends as well as the core. The core increases in diameter but the grain gets shorter as it burns, and the two balance each other pretty well. The grains can be stacked for larger motors.

      Designing and building a rocket that will survive even Mach 3 is the hard part. I’ve watched hundreds of large hobby rockets at Black Rock and other launch sites. Failure isn’t uncommon…and amateurs have been doing this for some time.

      And putting a rocket into orbit is much, much harder than an up-and-down suborbital flight. The smallest rocket to orbit successfully was about 10 meters tall, half a meter in diameter, and weighed three tons.

      Incidentally, anyone planning to make rocket motors should first get a lot of experience with commercial hobby motors and high-power rocketry. Some relevant sites:

      1. Thanks for the links. Could you please tell what that book of yours is? I’d be interested. You may not be allowed to toot your own horn, but since I’m specifically asking, you’d be only answering my questions, so… please?

    2. Shoot something into orbit? No. Into space (suborbital)? Maybe.

      Why? The tyranny of the rocket equation.

      There are lots of rockery groups that do some impressive stuff, so, it is feasible for amateurs to do crazy stuff, but, once you start shooting things into the air, then the government tends to get involved.

      I think anything larger than the hobby store rocket motors requires a license, and the larger the motor, the harder it is to get a license.

      Anything even close to orbital grade would have a mountain of paperwork to legally launch.

      1. Well Musk and Bezos have done it, so the legality of it isn’t insurmountable. What really bugs me about rockets is that there is so much additional weight in them that adds nothing to the thrust. Tanks, pumps, pipes. You have to lift them into space and then just dump them, total waste. That’s why I want a “rocket” that is, as close as possible to that, all fuel zero filler, just an Estes engine the size of a Saturn V.

      2. Incorrect.

        BATFE used to require a low-explosives user permit for anything containing more than 62.5 g of propellant. That was challenged by Tripoli Rocketry Association and National Association of Rocketry. After a ten-year battle that cost almost 3/4 of a million dollars, the court ruled that BATFE had not demonstrated that ammonium perchlorate rocket propellant (APCP) was an explosive (because they had no quantitative guidelines, it was more a matter of “we wanna regulate this so we say it’s an explosive”). Now one can purchase motors up to O-impulse (about four feet long and 6″ in diameter) without a permit…but TRA, NAR, and the vendors police purchases over 160 N-s impulse.

        I was on the Tripoli BoD during eight of the ten years.

        Now, to fly a high-power rocket does require a waiver from the FAA. Rocketry organizations have regular launches, and paperwork is done to obtain blanket FAA approval for up to Class 2 rockets for a given date/time. Our local club has FAA approval for a launch one Saturday per month from October thru March or April (landowner plants crops in spring) for flights up to 10K feet. TRA/NAR members can bring a rocket and fly it, no other permits needed.

        Every fall BALLS is held in the Black Rock Desert with a virtually-unlimited ceiling (100 km or higher).

        That being said, an orbital flight is indeed a different animal and would require a mountain of paperwork.

    1. Calcium hypochlorite (pool chlorine) works, and won’t get you on a government watch list.
      Prone to clog nozzles though, leading to burst engines.
      And the hydrogen chloride exhaust might be offensive to some. :-/

      1. Calcium hypochlorite is a poor and potentially dangerous propellant oxidizer. All oxidizers are unstable to some extent, but Ca(ClO)2 has a low activation energy of decomposition. It breaks down readily in moisture to form chlorine and other nasty stuff—that’s why it smells of chlorine. Not something that you want to happen in a propellant until it’s ignited…

        It also provides poor specific impulse. Potassium nitrate, potassium perchlorate, and ammonium perchlorate are far better…and one of those can be bought in most farm stores if you know what to look for. The others are easily obtained from pyrotechnic chemical vendors such as Skylighter. Or they can be purchased by the drum for cash, no permit needed and no questions asked, by joining an appropriate organization.

  2. If you want the surface area to remain fairly constant throughout the burn, don’t make the hole go all the way through, but be an inverted cone. As it burns the upper surface should remain that inverted cone, and have fairly constant surface area.
    There would be a hiccough as it transitioned from one grain to the next, so printing one long grain might be the way to get around that.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.