The Hybrid Myth Continues

Michael Belfiore updates his previous post, to indicate that Rocketplane (as I was quite confident was the case) has in fact been in discussions with the FAA. But he persists in his misguided (in my opinion) fear of liquid propulsion:

I say a good healthy dose of skepticism never hurt anyone about to climb into a commercial spaceship fueled with explosive liquids.

While not denying that skepticism is always appropriate to some degree, he still seems to think that hybrids cannot explode. That would come as a shock to many (including me) who watched an Amroc 250,000-lb-thrust motor launch itself down the mountain up at the rocket lab in the early 90s, as a chunk of rubber got caught in the throat, blocking the flow and causing the internal pressure to build up to the point that it blew the bolts on the aft bulkhead, with spectacular results. Hell, even steam boilers can explode (this killed many people in the early days of river transportation).

It’s true that a hybrid can’t achieve total combustion in the same way that mixing liquids can, but it’s a big mistake to think of them as intrinsically “safe” (a term that is always relative, and never absolute). I would personally feel just as comfortable on a vehicle powered by one of (for example) XCOR’s rocket engines as by any hybrid, because I’d be confident that they would build adequate margins and safeguards into it to make it as safe as reasonably possible.