Green eutectic rocket propellant

Environment friendly chemical rocket propellant, useable in liquid or solid state

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Solid-fuel rockets using perchlorate oxidizers release chlorine gas directly into the stratosphere, where the chlorine reacts with oxygen to form ozone-destroying chlorine oxides. The Increase of international space launches and the upcoming commercial space travel boom will soon have a huge impact on ozone depletion.

Rocket propellants for experimental rockets are mostly made with sucrose or sugar alcohol as a fuel and containing an oxidizer like potassium nitrate and additives like Red iron oxide. Potassium nitrate is widely used as fertilizer and a food preservative, it is low cost and available in large quantities. Sugar/alkali metal nitrate based propellants are environment friendly but they have a significant lower specific impulse compared to solid rocket propellants usually used for space flights like APCP (Ammonium perchlorate composite propellant).
The combustion behavior of sugar/alkali metal nitrate based propellants can be improved by mixing the reagents on a molecular level to lower the activation energy, using an eutectic mixture of the oxidizers KNO₃ and NaNO₃ in which sorbitol will be dissolved.

But there are also drawbacks. The preparation of the propellant is very dangerous. Even an electrostatic discharge can ignite the propellant in liquid state. NaNO₃ is more hygroscopic than KNO₃. And irregular re-crystallization can lead to separation of the reagents.

Phase diagram of KNO₃ and NaNO₃:


An eutectic salt mixture of for example 60% w NaNO₃ and 40% w KNO₃ has a melting point of 221°C and water-free sorbitol 110-112°C. Sorbitol has furthermore the advantage that it doesn't decompose at the melting point like sucrose.

The eutectic rocket propellant can be used in solid and in liquid state. In liquid state it has nearly a viscosity like water, so the propellant is highly cast-able in according molds and can be feed through fuel pumps.

The combustion of potassium/sodium nitrate and Sorbitol forms carbon dioxide, water, nitrogen and potassium/sodium carbonate.

I started to work on eutectic rocket propellants back in 2011 while contributing on the Sugar-Shot-To-Space program. The Russian chemist Serge77 had a similar idea by 'dissolving' Alkali metal nitrates in molten sorbitol much earlier and independent of me. According to his statement 'between 2002 and 2003 several members of the Russian Rocketry Forum lunched many rockets, using propellants with sorbitol, xylitol, mannitol and some other sugar alcohols as fuel and a dissolved alkali metal nitrates as an oxidizer, but decided then to use not fully melted propellants anymore due to safety reasons'. However, the ideas are still quite different. You can't consider a solution of sugar alcohol and an alkali metal nitrate as an eutectic system until it's proven and the solubility of an alkali metal nitrate in a sugar alcohol might be as slightly as it is for ethanol, so stoichiometric correct mixtures can't be prepared in this way and are therefore useless!

My plan to build a liquid eutectic propellant rocket engine was never realized. In 2013 an amateur rocketry group from Dubai used an eutectic composite propellant containing dissolved Lithium perchlorate in prepolymers.


  • Follow chem lab safety rules
  • Put 5.4g KNO₃ and 4.6g NaNO₃ into a beaker (Borosilicate glass!)
  • Mix the two substances
  • Put the beaker with mixture on laboratory heating plate with temperature sensor and thermostat, insert temperature sensor into salt mixture
  • Pre-set the temperature to 220ºC
  • Heat till 220ºC are reached and salt mixture is liquefied (the theoretical melting point of the eutectic mixture is 218ºC)
  • Add slowly 5.4g Sorbitol, stir with glass rod till the Sorbitol is molten and 'dissolved' completely in the salt bath.
  • Pour the solution on a coated baking paper. Be careful, it has a viscosity nearly like water!
  • Let it cool down for 10 minutes
  • Ignite the mixture with a butane torch. The mixture is very difficult to ignite due to its high heat of fusion (nearly like thermite)

Combustion behavior of solid eutectic KNO₃-NaNO₃-Sorbitol propellant

Combustion behavior of liquid eutectic KNO₃-NaNO₃-Mannitol propellant

Propellant is prepared as explained above, just using Mannitol instead of Sorbitol. Mannitol has the lowest solubility in water from all sugar alcohols, therefore it is very...

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  • Hexamine

    M. Bindhammer05/26/2015 at 06:44 0 comments

    During my search for cheap and easily accessible rocket fuels I stumbled over Hexamethylenetetramine, also called Hexamine. Hexamine is a white crystalline compound, which is highly soluble in water and polar organic solvents. It sublimes in a vacuum at 280 °C. Together with 1,3,5-trioxane, hexamine is a component of hexamine fuel tablets used by campers, hobbyists, the military and relief organizations for heating camping food or military rations. It burns smokeless, has a high energy density (30.0 MJ/kg), does not liquefy while burning and leaves no ashes. Hexamine has been used in colored fireworks compositions as a low-reactivity, accessory fuel.

    But unfortunately I discovered that hexamine is not oxidizable by KNO₃, NaNO₃, LiNO₃, RbNO₃, Ba(NO₃)₂ and probably all other alkali or alkaline earth metal nitrates:

    Hexamine reacts though violently with AgNO₃ but silver nitrate is not an option. A hexamine/KNO₃ mixture form cyanide's, highly basic compounds among others when enough energy in form of heat is applied, but does not burn. There are many color reactions used in cyanide determination. I have used the classical Prussian blue method:

  • The death of Dr. Wahmke

    M. Bindhammer05/25/2015 at 08:59 0 comments

    On July 16, 1934 Dr. Kurt Wahmke and three technicians were mixing 90% H2O2 and Ethanol in a steel tank at Kummersdorf, Germany. The tank was connected to the combustion chamber of a rocket engine with a single valve between, no flame non-return finger was used. Dr. Wahmke was obsessed of the question if the use of a fuel/oxidizer mixture prior ignition would be dangerous.

    The resulting explosion after ignition killed Dr. Wahmke and two of the technicians. They were the first and only deaths of technicians of German rocket development during the Second World War.

    So I should be reminded how dangerous it is to mix fuel and oxidizer prior ignition in a single tank. I will use one tank for the liquefied fuel and a second one for the oxidizer.

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J. M. Hopkins wrote 02/01/2016 at 15:37 point

Is there an actual gain in specific impulse by using the eutectic KNO3/NaNO3 vs just KNO3? Or is this just an attempt to ease casting of solid grains by changing viscosity?

My limited testing shows comparable burn rates from standard 65/35 mixtures.

I'm still in process of a BATES grain testing rig to further my own research. I've focused more on physical properties (casting viscosity and grain brittleness) in my propellants to increase safety (which was my primary concern), but will be starting to increase grain sizes for larger motor testing here in the next year or so.

My current motors utilize 5 x 1.25" grains with .652" bore and 1 x 4" grain with .652" bore utilizing a KNO3/corn syrup/sorbitol/sucrose/CMC gum/potassium bitartrate mixture known as PNCP#6. 

Total designation around an I-530, and the very cool thing is the non brittle nature of the grain with Isp near 110 to 120. With larger grain testing I'm worried about slumping but will have to do more testing.


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M. Bindhammer wrote 02/01/2016 at 18:30 point

Yes, there is a gain, because the reagents are mixed on a molecular level, so the activation energy should be on its minimum. But I do not recommend to use it. The eutectic mixture is quite dangerous in liquid state. Even one electrostatic discharge will lead to a violent explosion.

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J. M. Hopkins wrote 02/01/2016 at 19:01 point

I'm not planning on utilizing, I was more curious on a theoretical level of how much gain in Isp there was in such a mixture, but if there are no in depth testing due to hazards I understand.

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Marc Turner wrote 02/01/2016 at 12:40 point

I'm not sure you're right that Dr. Wahmke and the two technicians were the only deaths of German rocket technicians during that period.  I had a note about another fatal accident that occurred Oct 10, 1933 in Germany.  Reinhold Tiling, his assistant Angela Buddenboehmer, and his mechanic Friedrich Kuhr suffered heavy burns from an explosion in his workshop caused by overheating of powder needed for solid-fueled rockets.  All three died from their injuries the following day. 

Also, not sure if you would count this one as they weren't technicians that died, but in 1944 in German-occupied Poland a V2 rocket crashed in a trench during a test launch, and killed 7 soldiers that were in the trench. 

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M. Bindhammer wrote 02/01/2016 at 18:43 point

Thanks. I had the information from the book "Peenemünde. Die Geschichte der V-Waffen", written by Walter Dornberger.

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Don R-Crenshaw wrote 06/04/2015 at 18:47 point

Be green, go boom! What's not to like?

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