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Could the principal of hypergolic fuels be applied to hybrid rockets? And if so, are there any known hypergolic solid/liquid combinations?

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Yes it is possible to construct a hypergolic solid-liquid rocket propellants. Case in point a metal organic framework of imidazole derivatives with Zinc, Cadmium or Cobalt metals as the solid phase and concentrated nitric acid as the liquid oxidizer.

Paper https://chemrxiv.org/articles/Hypergolic_Zeolitic_Imidazolate_Frameworks_ZIFs_as_Next-Generation_Solid_Fuels_Unlocking_the_Latent_Energetic_Behavior_of_ZIFs/7235555

Online discussion https://forum.nasaspaceflight.com/index.php?topic=47436.0

There are many other highly reactive solids and liquids which would be hypergolic on contact, but many would not be suitable for propellant use due to toxicity, cost, physical properties or the unsuitability of reaction products. For example liquid concentrated nitric acid would react explosively with solid potassium metal, but potassium would be far from ideal as a propellant and would melt as the temperature increased causing the disintegration of the rocket motor.

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  • $\begingroup$ In the tests shown (Figure 1) they use both red and white fuming nitric acid. Do you know if the solid component in the ChemrXiv article will work in a practical way with other oxidizers? $\endgroup$ – uhoh Feb 21 at 12:04
  • $\begingroup$ Perfect, thank you for the paper reference as well! $\endgroup$ – EdwardJ Feb 22 at 9:41

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