(It's been some time since I've responded to an arocket post, so please
excuse me if I have the reply addressing wrong.)
I also have some experience with Nitrous/Acetylene as a monoprop, from time
with Firestar in Mojave, prior to the ALASA effort.
John Schilling is quite right in his cautions against pursing the
technology/(deadly-foolishness) without a significant budget. John
mentioned an eight-figure budget, although I would see that as a great way
to "make a small fortune from a large fortune" effort
I was doing significant work on the stuff with a "use prior programs scrap
plumbing" budget, and I'm lucky to have survived. For instance, I had no
money for propellant bottle burst discs, or generator fuel at times. I
blew up large quantities of salvaged tubing and Swagelok fittings from my
work on prior programs on the former Rotary Rocket, RASCAL, RPE, and
Protoflight/QuickReach/FALCON sites we were using.
I did work on several mixtures of Nitrous/Fuel blends at Firestar. The
Nitrous/Acetylene blends were the worst; and mixtures with other fuels were
"relatively" less deadly. My conclusion is that none of the blends will
ever be made relatively "safe", with the hardware flight-weight. Although
the potential for system simplicity is appealing in monopropellants, I saw
no path to acceptable user or vehicle safety levels with the technology.
Some success was achieved with gas-phase rocket motors and Flashback
Arrestors. By the time I left for less dangerous work, no success in
liquid-phase rocket motors had been achieved. Liquid-phase "Flashback
arrestors" which were effective and not massive were not achieved. The
Nitrous/Acetylene blends which I made and tested were quite shock
sensitive, and prone to going kerblewy with any motion at temps as low as
50C/130F.
(Meanwhile, I was chastised by the ignoble leadership for acting afraid of
the stuff; as not showing casual handling was not in line with the
mantra/lie that we had a safe product.)
I recall writing to Mitch Clapp with my concerns about using a manned
aircraft with the ALASA program. He replied, expressing knowledge of the
challenges. I was relieved to see the project cancelled.
I am now a firm believer that Oxidizers and Fuels should be kept apart
until they meet in a rocket chamber.
The Wiki article on NOFB is an absolute lie on the safe handling aspects,
and could lead others to attempt to continue with the technology. I should
take the time to go put my edits into the piece.
Now happily working with far more conventional propellants, somewhere in WA,
Ken Doyle
From: John Schilling <john.schilling@xxxxxxxxxxxxxx>
Subject: [AR] Re: DARPA responsive launch challenge
Date: Sat, 21 Apr 2018 20:49:47 -0700
On 4/21/2018 11:04 AM, Henry Spencer wrote:
On Sat, 21 Apr 2018, Keith Henson wrote:Yes, 7:1 Nitrous/Acetylene. And for those of you who don't know, I was
I believe John is referring to ALASA, not RASCAL et al. ALASA was
using a
stock F-15 and a mixed-monoprop nitrous/acetylene rocket...
Given that acetylene can't be liquefied or compressed beyond 2
atmospheres without becoming shock sensitive, it amazes me that
anyone would try to make such a devil's brew.
Bear in mind that it was a DARPA project, and DARPA is in the business
of trying things that look speculative and iffy.
Given the very skewed mixture ratio -- 7:1 if I recall correctly --
the acetylene was pretty thinly dispersed in the other component,
which is the way acetylene is routinely stored and handled in industry
(although in acetone rather than nitrous). So the acetylene itself
wasn't that big a concern. But nitrous with fuel in it, even a little
bit of fuel, is notoriously much more sensitive than clean nitrous --
that was the more worrisome bit.
Set against that, (a) the mix was made and stored chilled well below
room temperature, and (b) there was at least one proprietary trick
also helping. So, as Mitch Burnside Clapp (then ALASA project
manager) put it three years ago, "there are reasons why this is not
entirely insane". And indeed, mixing, handling, storage, and cold-flow
tests were free of loud surprises. (This was all being done very
gingerly by remote control, of course.) But when it came to hot-fire
tests, as John Schilling said, "it is still excessively enthusiastic
about ignition".
in charge of mission assurance for the propulsion system on ALASA, with
a key emphasis on the part of the mission that involved not causing an
F-15 to suffer what the USAF euphemistically calls a "Class A mishap".
Between dilution of the acetylene, chilling and pressurization of the
propellant, and what Henry describes as proprietary tricks, there were
reasons to believe it could be made to work and to work safely enough
for a manned system. And there were the resources to do it right, e.g.
by remote control behind reinforced concrete in the middle of nowhere
until safety had been more than adequately demonstrated. When instead we
demonstrated excessive kaboomishness in spite of all precautions, we
shut it down, but it was worth a try.
If there's a serious effort to push forth a similar technology, I'll
offer what advice I can. Starting with the word, "ethylene". But also
with the recommendation that you don't touch anything like this without
an eight-figure budget, because building custom remote-control
semi-cryogenic propellant mixing facilities and engine test stands in
bunkers in the desert is not cheap.
It would have been an honest 320-second monoprop, though. And it blew
up REAL good.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(661) 718-0955
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End of arocket Digest V6 #100
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