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  •  Metastable fuels and oxidizers (1+ / 0-)
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    alizard

    It's an interesting category of research.  Basically, there are some chemicals that have a tremendous amount of energy of decomposition available, but the activation energy barrier to begin the reaction is high enough that they don't just start breaking down on their own.  Xenon difluoride is an example (although not a suitable propellant in its own right).  Metastable fuels range from the already-created-but-not-on-large-enough scale (such as alane -- stabilized aluminum hydride) to the already-created-but-not-yet-suitably-controlled (such as ozone, which has a nasty problem of being explosive), to created-in-the-lab-but-lots-more-research-needed (such as cubane compounds and various nitrogen rings), to the purely theoretical (such as triplet helium).  These propellants have the potential a significant, and in the more extreme cases tremendous, increase in ISP, and even a small increase in ISP can have order-of-magnitude performance rammifications.  Alane, for example, when burned with LOX, has performance similar to H2+LOX, except that it has higher density than kerosene (a "best of both worlds" fuel).  Ozone is nearly a drop-in replacement for LOX, except is significantly higher energy.  And so on.  Cryogenic solids and hybrids are only fairly recently studied; they allow you to use some of the higher performance liquid fuels in a more dense form.  Also, there's the interesting potential for it turning liquids that are unstable into stable solids.  For example, ozone when kept in big tanks likes to explode on you, as previously mentioned.  However, tiny crystal grains of ozone aren't nearly as dangerous.

    When you say pulse combustion, do you mean pulse detonation (PDE)?  The PDE engine research I've seen done is mainly for aircraft, although it could be used for a flyback first stage.  While I'd like to see the research continue, I don't think the results have been very encouraging so far.  Last I checked, only a couple designs have shown any DDT reliability at all, most had valves (which were big problems on pulsejets), and in any case, you're dealing with detonations -- loud and destructive.  I especially worry about the vibration loads it would induce.  But again, I'm curious as to where the research will take us, so I'd like to see it continue.

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