Forum | Booster fuel thoughts

Here's a nice poster showing the delightfully simple construction of Spaceship One's hybrid rocket engine.

Here's a more detailed write up of NASA's experiments with paraffin fuelled hybrid rockets.  They literally bought their fuel from an online candle wax distributor.  It may take us some R&D time to replicate the particular spray effect they are utilising, but I suspect that this fuel will be so much cheaper than anything else we could use that the time will quickly pay for itself.

Regarding the possibility of using N2O as an oxidiser in liquid fuel rockets: I don't know anywhere near enough chemistry to know what makes particular oxidisers suitable or unsuitable for use with particular fuels.  However, Wikipedia has an excellent, large table of liquid fuel-oxidiser combos and various measurements of how well they work.  N2O doesn't appear in the oxidiser list at all.  Various other nitrogen-based molecules do, but they all seem rather nasty.  I could find any pairs on that table where at least one of them wasn't an effort or danger to handle, but I wasn't too thorough about it so I could have overlooked one.

The absence of N2O from that list doesn't necessarily mean it cannot work, of ourse.  It may just be uncommon for some reason.  We'll need to either find ourselves a combustion chemist or do some research of our own to find out.

As you've probably seen, though, N2O oxidisers are really common in the hybrid realm.  I agree that N2O seems like a really obvious choice for so many reasons, the fact that it seems to be the de facto standard for hybrids makes them seem all that more attractive to me.

The idea of adding high energy additives to the paraffin is an excellent one.  With the (currently more common) rubber and plastic based solid hybrid fuels, it seems a common process to put certain metals, like magnesium or aluminium, in for this purpose.  I don't know if they would work as well in a paraffin solution or if we should look at options.  Once again, a combustion chemist would be an awesome asset about now.

Youtube seems to abound with videos of people testing very small, very crude home built hyrbid rockets in vices.  The standard thing to do seems to be to use gaseous oxygen as the oxidiser because you can buy ready-to-go cylinders of it from medical suppliers.  I've seen people use paraffin and various plastics as fuels.  They certainly seem to burn well enough, the failures (and most videos are of failures) inevitable are due to amateur construction – steel nozzles melting through or poor gas plumbing causing leaks or blowback.  At any rate, it seems likely we can start out relatively small and slowly gain experience with hybrid techniques (although of course we should read, read, read as we do so rather than relying on trial and error).

I am pretty sold on hybrids at this stage but since it is such a huge decision I'd love to have somebody play devil's adcovate and give me a good case for why the material handling complexities of the liquid option aren't as bad as I've made them out to be and point of potential shortcomings of the hybrid route.