[AR] Re: some interesting developments
- From: John Schilling <John.Schilling@xxxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 2 Jan 2016 14:23:13 -0800
On 1/2/2016 1:54 PM, David Weinshenker wrote:
On 01/02/2016 10:47 AM, John Schilling wrote:
With both nitrous/acetylene and oxygen/hydrogen, we're talking about a
~30% increase over other chemical propellants in the same niche. If it
works, it closes out so many of your other design challenges that an
otherwise bleeding-edge system becomes just the ordinary sort of rocket
science.
I guess the way this would make a crazy sort of sense would be if the
acetylene became stabilized by being diluted in the nitrous, similar
to the way it can be mixed in acetone for ordinary industrial storage.
At which point you now "merely" have the problem of safely handling and
firing a nitrous/hydrocarbon solution as a monopropellant - and if you
solve -that-, you've enabled acetylene as a fuel... (How do you keep the
fuel from exploding? Dissolve it in the oxidizer...?!)
But what exactly are (and aren't) the other chemical propellants
"in the same niche" here? (Seems to be an oddly-defined niche, if
"unusual hazards" -isn't- a deal-breaker, but some extant high-
performance storable biprop combinations are excluded.) For example,
seems like ClF5 with hydrazine would have higher Isp and density: yeah,
the oxidizer is violently ultra-hypergolic with -almost- everything
(except itself), but at least it isn't a bulk explosive just sitting
there...
The relevant niche is safe, storable monopropellants. For a vehicle
that is supposed to operate like a munition rather than a launch
vehicle, and that has to cost no more than $1E6 per launch (total
mission cost, not just vehicle manufacturing), the complexity of a
bipropellant system is not quite a dealbreaker but certainly something
to be avoided if possible.
Which leaves us with "safe" and "storable"; remember that the USAF
considers hydrazine to be a perfectly fine propellant to carry around in
a tactical aircraft, so the bar isn't being set impossibly high here.
And delivering bulk high explosives is pretty much their core business
model. Nitrous oxide has a long history of safe storage and use
elsewhere, and some quirks that the rocketry industry hasn't quite
gotten a handle on yet. Acetylene, likewise safe in other industries,
contingent on your dissolving it into a proper buffer (traditionally
acetone). Neither one of them, nor both together, will form a toxic
death cloud, and the vapor pressure means that any leak that doesn't
find an immediate ignition source should dissipate harmlessly.
As you note, it's counterintuitive to dissolve the fuel in the oxidizer,
but nitrous oxide is traditionally reluctant to start acting like an
oxidizer and acetylene really likes to be dissolved in *something*. As
Mitchell noted more than once, "Acetylene's worst enemy is more
acetylene"; the stuff almost catalyzes its own decomposition. So it's
not totally insane to try 7:1 nitrous oxide as your buffer. If you can
make it work, you get a potentially quite useful new propellant. If
not, you get some spectacular explosions to watch and big craters as a
monument to your efforts.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(6161) 718-0955
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