Thanks Ken.
Also, John Schilling was apparently consulting on ALASA for DARPA (presumably
via The Aerospace Corp where he works now). He said that publicly so I assume
repeating it here is safe.
George William Herbert
Sent from my iPhone
On Dec 1, 2015, at 10:21 AM, Ken Doyle <rocketken@xxxxxxxxx> wrote:
That was me on Facebook mentioning that some success with Nitrous/Fuel mix
was had in the gaseous phase.
I worked at Firestar in Mojave for 3 years, leaving in very early 2012. I'm
pretty sure my NDA obligations have expired, and that Firestar is defunct now.
The fundamental problem with use of a pre-mixed oxidizer/fuel in a rocket
motor is of course the issue of flashback, or a detonation wave traveling
upstream from the burning rocket motor to the tank holding the mix. We did
have success in developing Flashback Arrestors for the gaseous phase. Those
detonations usually didn't explode the SS tubing on the way to the Arrestor,
and diverting the detonation wave and bursting relief parts kept away the big
kabooms.
I setup and ran the tests of the arrestors, and the rocket motor tests.
For actual practical use in a flight motor, the higher density and smaller
plumbing sizes that come with liquid-phase operation were going to be
necessary. The ever-optomistic CEO/Chief Scientist/Pitchman believed that
the liquid phase of the mixes would be more stable and easier to arrest
flashback than the gaseous phase. That hope proved to not be the case at all.
Although they may have made some progress after I left the company; while I
was there, we were never able to arrest flashback in the liquid phase.
We did most of the work with Nitrous Oxide mixed with Ethylene or Acetylene.
We did a series of 14 meter Drop Tests of the mixes, with the
Nitrous/Ethylene being much less prone to kerbleweys than the
Nitrous/Acetylene mixes. Although some attempt at subterfuge was made to
make it appear that we had a secret ingredient to help with stability, no
ingredients other than Nitrous Oxide and the Fuel were actually used.
With the Nitrous/Acetylene stoichiometric ratio mix tested, the first Drop
Test passed, but the second failed violently. The evil mix had a tendency to
explode at unexpected times; that is, in conditions less severe than it had
previously passed through. For instance, I did a couple of slow heating
tests which failed to explode at up to about 80C. Then, a test where it
exploded at only 50C. The difference in the tests was that the 50C explosion
happened on a windy day, with some slight agitation due to the wind moving
the test apparatus.
Although the Nitrous/Ethylene mixes could pass some of the basic handling
safety tests, the arresting of flashback detonation waves in the liquid phase
was never solved while I was there.
In spite of highly negative handling safety experience with the
Nitrous/Acetylene mixes, a push persisted to make the stuff work, due to the
higher Isp number possible.
I was also chided about appearing to be afraid of the stuff, that my cautious
handling demeanor went against the company PR that it was safe to handle...
To sum up my opinion after working with Nitrous / Fuel monopropellant blends
for 3 years;
1. They are too dangerous to be anywhere near humans or valuable hardware.
2. The single tube/tank plumbing potential benefit is overcome by the
impracticality and weight of feasible flashback arresting notions.
Use of Nitrous and a reasonable fuel such as Ethylene, as a bi-prop, is worth
exploring.
It is conceivable that progress was made after I left Firestar, but none of
my sources ever indicated such.
It is also conceivable that the ALASA / Boeing work with Nitrous / Acetylene
had no influence from the Firestar work, but I doubt that.
Ken Doyle