Eco Friendly Space-Fuel

If you’d like to risk blowing your fingers off for a good cause this week, look no further than [M. Bindhammer]’s search for an eco-friendly rocket fuel. [M. Bindhammer] predicts the increasing use of solid rocket boosters in the future. We’re into that. For now, rocket launches are so few and far between that the pollution doesn’t add up, but when we’re shipping consumer electronics to the moon and back twice a day, we might have a problem.

The most common solid rocket fuel emits chlorine gas into the atmosphere when burned. [Bindhammer] is exploring safe ways to manufacture a eutectically balanced and stabilized fuel compromised of sugar or sugar-alcohol, and potassium nitrate. If you watch home chemistry videos for fun on the weekend like us, [Bindhammer] goes through all his thinking, and even spells out the process for duplicating his fuel safely in a lab.

He’s done a lot of work. The resulting fuel is stable, can be liquid or solid. It has a high ignition temperature, but as you can see in the video after the break. Once ignited. It goes off like rocket fuel.

64 thoughts on “Eco Friendly Space-Fuel

    1. Yep. We used to make sorbitol rockets when we were kids (30 years ago). We played with quite a few different fuel / oxidizer mixtures. Some of the mixtures were from a book called “Henley’s Formulas”.

    2. This isn’t a reply to Hirudinea actually….But rather I couldn’t actually figure out who needed this post the most. But if I recall recently, HaD had a plan to cut the racist, sexist, and in general intolerant ignorant bullshit that gets posted on here. The conclusions that were jumped, and then further attached and escalated to is absolutely unreal, and I seriously can’t believe it was allowed to continue. HaD I’m seriously disappointed.

    3. Editor’s Note: I just trashed a long thread of hateful comments. I value free speech and go to great lengths not to delete comments. In this case the content of the comments forced my hand. Please keep conversations positive and contribute to the conversation. Thanks.

      1. This censorship is a natural consequence of the politically oriented comments which are themselves a consequence of the more and more US centric and almost ideologic content of HaD. My bet: it will be much much worse in the next months.

      1. It makes perfect sense. A eutectic mixture melts and solidifies uniformly at a very narrow temperature range that is typically lower than the melting point of any pure component.

        This is relevant because 1) The lowered melting point the chosen fuel to be mixed into the molten oxidizer without decomposing. 2) it facilitates producing a uniform solid with uniform melting behavior during the burn 3) the solidified propellant will be uniformly mixed at a ~molecular level, rather than being composed of tiny particles of the different components.

        1. I know what eutectic means, although “eutectically balanced” is a meaningless phrase, and yes I can see that lower melting point. can be a property that one would want to have in this end product, however the term is still being used in that article in an awkward way.

          1. Only if one likes picking nits. Balanced as in having the proportions of ingredients balanced so to make it an eutectic.

            Now I’d not use the phrase but there’s really nothing to complain about, normal speech contains much worse terminological failures without anyone reacting.

        2. Most of the time sugar propellants are actually created slightly more lean than stoichiometically balanced, this promotes complete combustion internal to the motor, instead of wasting fuel outside the nozzle.

          Fuel burning past the nozzle is just wasted mass, even if it is a more chemically complete reaction. Hence a leaner mixture can be more powerful (higher Isp) than a perfectly chemical balanced mixture.

        1. I’ve burned literal tons of liquid oxygen in rocket (and even jet turbine) engines, it’s not terribly difficult or expensive. LIQUID hydrogen is a totally different beast. It leaks through any joint, weld and even grain boundaries in bulk metals. Air will solidify on the outside of your plumbing. Hydrogen is explosive in pretty much any ratio with oxygen and it causes hydrogen stress cracking. All liquid hydrogen plumbing needs to be through double wall vacuum jacketed stainless steel plumbing for starters. It is also fairly difficult to obtain because it is only made in a few locations and it cannot be stored for any significant duration due to heat leakage into the dewar and subsequent boil-off. It is definitely not an amateur friendly propellant. Yes, the cooled exhaust is non-toxic except in large quantities.

      1. Any idea how much? That is pressure dependent IIRC.

        As for the caramel candy fuel, when I was a kid it started to be used because laws were passed to stop paint manufacturers from selling powdered metals to kids. The fuels of choice before that were powdered zinc and sulfur and powdered aluminum or magnesium and potassium or sodium nitrate. The zinc and sulfur was safer because above a certain pressure that reaction starts spitting out chunks instead of gases. All the Al and Magnesium experiments I saw blowed up real good. Scientific American and science books in the school libraries had plenty of material on making your own rocket and they were like the one in October Skies. Chrome-molly steel tubing and steel nozzles. None of this sissy paper and balsa stuff. How do you learn anything from that?

          1. That is really my point. We actually built real bunkers or “block houses” to fire from and still had some close calls – just because you have a countdown does not mean your buddy won’t showing off to a cute girl the switches he will be throwing, while you are checking the firing wire attachments at the rocket – that is 1960’s talk for some kind of gender neutral statement today, and factual in this case. This was 5th and 6th graders. Some of the parents came to watch the launches. Nobody freaked when the rocket motors inverted themselves into high velocity ninja stars. They just joined in searching the field for parts.

  1. Sometimes the choice of fuel / oxidizer is driven by the available volume and allowed mass of the engine. I’m sure if the sorbitol / nitrate salt mixture could provide adequate specific impulse it would be used for launch vehicles already.

    1. Nonsense.

      Previous propellants were developed with different design parameters. Environmental impact was clearly not one of them. I doubt being suitable for experimentation by hobbyists was one of them either.

      Design is about tradeoffs. The fact that higher impulse fuels exist that involve different tradeoffs doesn’t say much at all about what is possible under a different set of tradeoffs. There are hard constraints about what will be possible with this propellant mix, and those constraints will likely result in less payload capacity, but while I haven’t worked through it myself, it seems that reasonable people have concluded that a “sugar shot to space” using KNO3 + sugar or sugar alcohols is theoretically possible.

      1. The SSTS project has demonstrated that it is exceedingly difficult to obtain acceptable mechanical properties of sugar-based propellant grains even at moderate sizes.

        It is also worth noting that the payload for the SSTS project is nothing more than it’s avionics bay and recovery system. Even the theoretical maximum specific impulse for sugar propellants makes them unusable for any real-world applications.

        Sugar propellants *do* have quite a number of benefits for amateurs, but unfortunately the BATF regulations on potassium nitrate compositions make it quite difficult to do this legally in the US.

        1. Unless they’ve changed the rules again so long as your propellant charge is less than 70 grams you don’t need any special licensing.

          Though private launch fields may require it

          1. No.
            The FAA doesn’t care about rocket motors less than 125g and even then they only require formal request to use the airspace, which they can deny if your plans aren’t well thought out and safe.

            As for what the ATF cares about I direct you to 27 CFR 555.141(a)(10) wherein:
            (10) Model rocket motors that meet all of the following criteria—
            (i) Consist of ammonium perchlorate composite propellant, black powder, or other similar low explosives;
            (ii) Contain no more than 62.5 grams of total propellant weight; and
            (iii) Are designed as single-use motors or as reload kits capable of reloading no more than 62.5 grams of propellant into a reusable motor casing.

            As well as the ammended definition of propellant actuated device, this link also contains information about other definitions and the changing of classification of some composite fuels.

            Lastly, to summarize those and more rulings, you only need a Federal permit if you’re crossing state lines in your rocket endeavors. And remember store safely!

    1. Yes and no. The basic approach of KNO3 + Sugar or sugar alcohol is time honored. This particular approach to mixing and forming the propellant grain is much newer. If you click through, you’ll see that M. Bindhammer, the experimenter is aware of the history.

  2. Look up M315E. Supposed to be a replacement for hydrazine, producing more thrust in monopropellant use and “less toxic than caffeine”. Be aware that some articles on it overstate the toxicity of hydrazine. has an article saying M315E requires more heat to ignite than hydrazine. Ummmm. No. Hydrazine is either decomposed with a solid catalyst (as a monopropellant) or it can be used as a hypergolic fuel with various acid based oxidizers – which are some quite nasty formulations. In either use, there’s no ignition system – which is why it’s used for maneuvering and station keeping thrusters. Just needs a single pipe to each thruster or thruster cluster and a valve for each nozzle, with the solid catalyst in each to flow through.

    Valves getting stuck closed or open has been a problem that has affected spaceflight as far back as Gemini 8 in March 1966.

      1. A 0.4 teaspoon, but who’s counting?

        Something over 10g/day is roughly considered a lethal dose – It scares me that you can (could?) get the stuff by the kilogram online. The FDA warned that you can’t measure it accurately with home measuring equipment (a zillion druggie gram scales notwithstanding).

      2. Lol. The LD50 for caffeine is 127 mg/Kg, based on rat studies.

        The average human weighs 67 kg, which shows the LD50 for that human is 7.87g of caffeine. 2g would most certainly cause palpitations and other bad effects, but probably not death.

        I’m 127 kg, and my calculated LD50 is 16.1 g (!). And speaking of that, I went on and bought caffeine. Was cheap and reagent grade. Really bitter but damn did it wake me up. I was doing about 2-3g a day of it. I’d mix it up in things like: Orange juice, coffee, water, black tea, and stuff.

        Now? I just drink 3 pots of coffee. I derive great joy in the flavor of coffee as well as the caffeine.

  3. What happened to all the hype about ALICE (aluminium and ice)? Al2O3 is fairly harmless, so is water, yet the initial small scale tests by NASA were fairly promising, the ISP was very good…

  4. The reason this fuel is different when compared to standard rocket candy mixtures is that the oxidizer actually gets fully melted and the fuel dissolved at a molecular level versus traditional rocket candy where the sugar acts as a binder around potassium nitrate.

    The fuel itself (potassium nitrate or sodium nitrate and a sugar) is nothing that special, but blending the potassium nitrate and sodium nitrate into the eutectic mixture which allows the oxidizer to have an achievable liquid state and dissolving the fuel into the oxidizer is the unique aspect of this propellant.

  5. I know I am going to be accused of pedantry here, but there is a bit of a grammar issue over the way the word ‘eutectic’ is being used here, and it made it a bit difficult for me (as English is not my first language) to understand at first what what was being written. The term ‘eutectic’ is like the term ‘alloy’ and one would not write ‘alloy mixture’ when referring to a material which was made with two metals blended into a single compound but rather simply as an alloy. It is the same with the term eutectic: the term itself implies a specific mixture, albeit with a certain specific property. In the same way, while it is clear to me now that using a potassium nitrate, sodium nitrate eutectic is an important aspect of this fuel’s fabrication process, it really isn’t a proper simple modifier to describe the final product.

    1. In my experience, the word “eutectic” is actually predominantly used as an adjective, as in “eutectic system”, “eutectic point”, etc. So “eutectic propellant” sounds perfectly legitimate to me.

      1. Well is it once the sugar has been added? That isn’t really clear, and even if it is just what aspect of that property, once the fuel has been fabricated, relates to its performance as a propellant? Look as I wrote below, it may be because I’m not an Anglophone that I’m a bit confused with the usage, but I have used the term for decades, and never have I seen it used this way.

  6. Here in Europe i really dont recommand to play with KNO3 or similar things, except you want your name on some “this-could-be-a-terrorist”-list… :-/ I suppose in US it’s almost the same thing.

      1. When I was a teen you could buy Dynamite at local hardware stores (and from grade school on, the fire department held assemblies and showed what different kinds of blasting caps looked like and to leave them alone and contact an adult if found. Every year.) and powdered metals at the local paint company. The drug store had 1 pound jars of “Flowers of sulfur” and Salt Peter. The Dynamite went first, then the metals, then the sulfur and potassium nitrate plus hardware store customers signing for ammunition, which was transient. Now good fertilizer is not available because of the sodium nitrate content. The unintended consequence is that, aside from the Dynamite, the bad guys go to ever more energetic explosives while the experimenters would have stayed with what was available back then since they didn’t want explosions – for the most part. I should add that my Jr High science teacher had a pipe bomb making contest when some of us bragged that we could blow things up. The school Principle was not happy about it but it didn’t end till a heavy steel drum used to prevent shrapnel flew over the power lines and nearly landed on the shop teacher’s classic Porsche.

        Times have changed a lot. But to what end? Younger people – dare I say Millenials? – seem to be terrified of what to me is commonplace.

  7. Ugh – HaD, please do a bit of research before you formulate your post. Either that or just post a link and say NOTHING. Let your readers bring the facts to the fore in the Comments.

    1. What was the reasoning for using red iron oxide? I know it’s a burn rate modifier, and have played a bit with it myself, however as you know it doesn’t increase you’re specific impulse, just your burn rate. I’ve always just changed my grain geometry and nozzle to change my burn time and KN values. I’ve always felt that BATES grains and or uninhibited cored grains gave me plenty of options to change my thrust curve around without having to resort to burn rate modifiers.

      1. Yeah, I used a bates grain calculator to get my design more or less in the ballpark. The red iron oxide just adds more oxygen to the party as far as I understand (plus, it looks pretty) Earlier tests with nozzle sizes showed me that I didn’t want to restrict the size too much to get the pressure I wanted. Plus a slightly larger nozzle *might* help reduce Cato from a blockage if my grain cracked. It’s all half science, half suck it and see with a large splash in of paranoid caution. That steel engine was deliberately over-thick on the body wall with a sacrificial rear bulkhead that should blow out if things go south. Fun, and as a bonus I still have my eyebrows and all my fingers. :) remember kids, don’t do this at home!

        1. Iron oxides and other catalysts work as burn rate modifiers, they don’t really add more impulse (or notable oxygen really) to a motor, just allow it to use it faster. Since it increases burn rate it means that the same grains in a motor with the catalyst (vs no catalyst) will operate at a higher pressure as well.

          From Nakka we get that catalysts work as the following:

          o Enhancing fuel decomposition
          o Enhancing oxidizer decomposition
          o Accelerating vapourized fuel reactions in the gas phase in the combustion zone
          o Increasing heat transfer at the propellant surface layer

          All of this allows the combustion process to occur at a faster rate, but doesn’t change total impulse, just the rate of use (by modifying burn rates)

          That being said, steel motors will give you significant safety margins with reasonable geometries, and if you are just looking for more thrust off the bat I can understand.

          Most of my designs I’m actually including burn rate suppressants to a degree to spread the thrust out longer in order to not destroy rockets under huge accelerations.

          Anywho, keep safe!

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