[AR] mixed monoprops (was Re: DARPA responsive launch challenge)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sun, 22 Apr 2018 15:19:27 -0400 (EDT)
On Sun, 22 Apr 2018, Henry Vanderbilt wrote:
... Low flow velocities and plumbing carefully designed and operated to
never cavitate or hammer or phase-change may be (with considerable
effort) doable on a test stand, but at high-performance flight weight
and volume constraints, not so much.
Thinking of this, it occurs to me that if you *must* experiment with mixed
monoprops, the way to do preliminary tests would be to store the fuel and
oxidizer separately on the test stand, and mix them in the plumbing just
before they reach the chamber. (Such "premixing injectors" saw some use
in the early days of rocketry, although injector explosions were common
enough that the technique went out of fashion.)
This doesn't *eliminate* the possibility of explosions, but at least it
limits the amount that can go up at once. It may not do that entirely
effectively if one of the components is itself a monoprop, like nitrous,
but it should reduce the hazards some.
If your favorite mix gives reliable, repeatable engine startup and
operation without injector explosions -- probably it won't -- *then* you
can think about adding a tank in the middle, where you do the mixing
(still by remote control, please) before engine start.
Still later would come more-flight-weight systems where the mixing happens
at fill time.
If all this seems too cautious and roundabout for you, you probably
shouldn't be trying mixed monoprops at all. This is one type of rocket
propellant where it's almost impossible to be too cautious. People doing
mixed monoprops keep finding new ways to kill themselves.
Henry
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