Hypergolicity and Liquid Rocket Propellants


tags: Books

A friend recently pointed out that archive.org has made John D. Clark's Ignition!: An informal history of liquid rocket propellants available in multiple downloadable formats here. He then characterized the book by saying "If Jerome K. Jerome had been born a half-century later and had been a rocket scientist he might have written this." Quite the sales pitch, so I've been trying it out. It didn't hurt to hear from another friend that Elon Musk is also a fan of the book.

To preface my favourite quote so far (I'm not very far into the book), I need to explain a bit. In the 1930s most rockets were made with a fuel and an oxidizer (such as methanol and nitrogen tetroxide, or - in the simplest instance - gasoline and oxygen). But you had to ignite this mix. Around the same time, someone figured out that if the two compounds reacted on contact without the need for an ignition process, you greatly simplified the rocket construction. Mixtures like this that ignite on contact are called "hypergolic," and he describes their advantages and dangers:

The discovery of hypergolicity was of major importance.  Running a rocket
motor is relatively easy.  Shutting it down without blowing something up is
harder.  But starting it up without disaster is a real problem.  Sometimes
electrical igniters are used — sometimes pyrotechnic devices.  But neither
can always be trusted, and either is a nuisance, an added complication,
when you already have more complications than you want.  Obviously, if your
combination is hypergolic, you can throw out all the ignition schemes and
devices, and let the chemistry do the work.  The whole business is much
simpler and more reliable.

But as usual, there’s a catch.  If your propellants flow into the chamber
and ignite immediately, you’re in business.  But if they flow in, collect
in a puddle, and then ignite, you have an explosion which generally
demolishes the engine and its immediate surroundings.  The accepted
euphemism for this sequence of events is a 'hard start.'

I was reading this on the TTC, where I doubled over in my seat in a futile attempt to keep the other commuters from realizing I was laughing hysterically. I wish more technical and/or history books were written so very well - I'm reminded of The Ghost Map and Bill Bryson's brilliant A Short History of Nearly Everything.