I agree with Ben. I personally experimented with nitrous/propane premixed, and
it was quite benign – and high performance. But I also had an on-camera
detonation of my propellant tanks before a Japanese news crew. It was due to
contamination by some volatile hydrocarbons, but still… I could tell something
was wrong while I was filling the tanks, and am lucky to still be here. As an
aside, a little bit of CO2 mixed in helps tame the mixture. All three
components have the same molecular weight.
I shut the ALASA program down not long after becoming its manager, because
there was no way in hell it would ever get anywhere. It did provide quite a
bit of value in terms of rapid mission planning software and other operational
advancements. But when you can’t get your propellant to ignite without a
detonation propagating into the propellant tank, your vehicle has limited
utility.
Sent from Mail for Windows 10
From: Ben Brockert
Sent: Saturday, January 25, 2020 8:05 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: More MAX delays.
It was tried with ethylene, the propellant tank would just disappear
about once a quarter. Building a system where valves require and
impart zero energy is impossible.
The only good use of nitrous mixed monopropellants is convincing your
enemies that they're a good idea. ALASA should have launched a
conventional solid a few times at the end of the program, claimed it
was incredible performance, and then shut down the program for
"political reasons" and later sold the secrets to unfriendlies.
FLOX is a safer propellant than nitrous mixed monoprop.
Pressurizing a LOX tank with hydrogen gas is safer than nitrous mixed monoprop.
Nitrous ethylene (not premixed) biprop would be a fairly good choice
for a pulse detonation rocket engine if you required it to be
self-presurized and room temp. Otherwise it still gets beaten by
peroxide or LOX.
On Sat, Jan 25, 2020 at 4:29 PM John Schilling
<john.schilling@xxxxxxxxxxxxxx> wrote:
I bet against it and I was in charge of mission assurance for the
program. But it was worth a try, so long as it could be done safely,
and we figured out how to do that much at least. Then I kept getting
surprised by how well it worked at every step of the process, all the
way through cold-flow testing on a real engine. You just couldn't keep
the reaction confined to the combustion chamber; it would propagate
upstream through the injector and manifold, and by the time it reached
the run tank it had transitioned to a high-order detonation. The
high-speed camera footage was truly spectacular.
It's possible that using ethylene rather than acetylene would have tamed
it enough to make it workable, but the Isp wouldn't have been much over
300 seconds and ALASA needed 320, so there was no funding for it. If
someone ever does give it try, with the resources to do it right, I'll
give them whatever pointers I can.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(661) 718-0955
On 1/23/2020 12:56 PM, Henry Spencer wrote:
On Thu, 23 Jan 2020, Peter Fairbrother wrote:
"However, DARPA ended plans to perform a flight demonstration with
ALASA in November 2015 after discovering that NA-7 was too volatile
to be safely handled."
While I guess up to half of what I buy is not really used much or
well, I think 'most everyone here could have told them that...
In fairness, DARPA exists to try things that are too speculative for
normal military funding channels. It's quite predictable that many of
the ideas they try are flops.
Nitrous/acetylene, alarming though it sounds, actually managed to pass
safety tests for things like handling, which I would definitely have
bet against. (And remember that F-15s are in the *business* of
carrying objects stuffed full of high explosive...) It just didn't
turn out to be quite tolerant enough for full-scale hot firings.
Henry
