A clever monopropellant you will want to avoid

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Winston

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Among other reasons, because even DARPA gave up on it. I discovered its story because I somehow stumbled onto the ALASA program and found one of the statements made about the reason for program cancellation to be one of the funnier understatements I've read in a while. Acetylene dissolved in nitrous oxide. Wonderful idea to simplify a liquid propellant rocket engine without using an extremely toxic monopropellant like hydrazine... if you can keep it from blowing up.

Airborne Launch Assist Space Access

https://en.wikipedia.org/wiki/Airborne_Launch_Assist_Space_Access

Airborne Launch Assist Space Access, or DARPA ALASA is a canceled program of the US defense technology agency DARPA "designed to produce a rocket capable of launching a 100-pound satellite into low Earth orbit for less than $1 million." The program was conceived, then announced in 2011, and funded development work began in 2012. The project was terminated in late 2015.

...The rocket will also feature new design technologies to lower complexity and costs. It will be powered by a monopropellant, a combination of nitrous oxide and acetylene, and mixed together in one propellant tank slightly below room temperature; the propellant choice is a dramatic simplification of the complexity of the rocket vehicle.


DARPA Scraps Plan To Launch Small Sats from F-15 Fighter Jet
November 30, 2015

https://spacenews.com/darpa-airborne-launcher-effort-falters/

“The magic” in Boeing’s design, as DARPA officials described it, was the powerful nitrous oxide-acetylene propellant, also known as NA-7. The propellant would be “pre-mixed” to reduce the plumbing needed on the rocket, enabling it to carry more payload.

Boeing led two subsystem tests in Promontory, Utah – one in August and one in April – aimed at learning how the pre-mixed propellant reacted to different temperatures, pressures and atmospheric conditions. In both tests, the propellant exploded.

“It did not go as predicted,” Brad Tousley, director of DARPA’s tactical technology office, said in a Nov. 23 interview. The “finicky” nature of the propellant led DARPA officials to believe it is too risky to store on piloted aircraft, Tousley said.


Acetylene

https://en.wikipedia.org/wiki/Acetylene

"Its most singular hazard is associated with its intrinsic instability, especially when it is pressurized: under certain conditions acetylene can react in an exothermic addition-type reaction to form a number of products, typically benzene and/or vinylacetylene, possibly in addition to carbon and hydrogen[citation needed]. Consequently, acetylene, if initiated by intense heat or a shockwave, can decompose explosively if the absolute pressure of the gas exceeds about 200 kilopascals (29 psi). Most regulators and pressure gauges on equipment report gauge pressure and the safe limit for acetylene therefore is 15 psig. It is therefore supplied and stored dissolved in acetone or dimethylformamide (DMF) contained in a gas cylinder with a porous filling (Agamassan), which renders it safe to transport and use, given proper handling. Acetylene cylinders should be used in the upright position to avoid withdrawing acetone during use."

Nitrous oxide fuel blend

https://en.wikipedia.org/wiki/Nitrous_oxide_fuel_blend

Patent application:

NITROUS OXIDE FUEL BLEND MONOPROPELLANTS

https://patentimages.storage.googleapis.com/pdfs/8996a6ac5ab6cfbdf990/US20090133788A1.pdf

NOFBX Monopropulsion Overview

https://web.archive.org/web/2011072...rg/pdf/industry/presentations/Greg_Mungas.pdf
 

boatgeek

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"The “finicky” nature of the propellant led DARPA officials to believe it is too risky to store on piloted aircraft"
Acetylene dissolved in nitrous, what could possibly go wrong?! The fact that you have to dissolve acetylene in acetone to make it stable enough to use safely says a lot about how excited it is to blow apart in a flames and bang sort of way.
 

DavidMcCann

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Acetylene dissolved in nitrous, what could possibly go wrong?! The fact that you have to dissolve acetylene in acetone to make it stable enough to use safely says a lot about how excited it is to blow apart in a flames and bang sort of way.

and yet somehow...it sounds interesting...
 

r66astro

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you can make some nasty primary explosives with acetylene. do not get it mixed with nitrates, bad stuff happens. if I remember correctly from welding class there was a lesson about it. But then I am old enough to remember the old tanks that used calcium carbide and water.
 

Winston

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Acetylene dissolved in nitrous, what could possibly go wrong?! The fact that you have to dissolve acetylene in acetone to make it stable enough to use safely says a lot about how excited it is to blow apart in a flames and bang sort of way.
That's what I thought was so funny. What could go wrong with this "finicky" propellant made from a pressure sensitive fuel that can detonate on its own which is then dissolved in a liquid oxidizer...? What happens when acetylene gas bubbles that might form in it, from cavitation for instance, are compressed beyond 15psig by some perturbation of the incompressible liquid surrounding them? Temperatures in compressed bubbles in a liquid can reach temperatures so high from their implosion that they cause the trapped gas to emit visible light.

[video=youtube;2yHDeKFW8j8]https://www.youtube.com/watch?v=2yHDeKFW8j8[/video]
 

emckee

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“It did not go as predicted,” Brad Tousley, director of DARPA’s tactical technology office, said in a Nov. 23 interview. The “finicky” nature of the propellant led DARPA officials to believe it is too risky to store on piloted aircraft, Tousley said.
Energetic materials are frequently classified by their stability. My favorite classification/description, and one in which this mixture sounds like it would fit nicely, was "capricious".
 

boatgeek

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aerostadt

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I always thought that Nitronium perchlorate NO2ClO4 that use to be listed in Rocket Propulsion Elements as an oxidizer looked like a crazy compound.

Monopropellants, especially compounds that have fuel and oxidizer together, by nature are dangerous. Nitromethane is a good example. It has been used in race cars, but in pure form can be detonated by shock. I remember some of the old rocket propulsion books reported that ethylene oxide (C2H4O) could be a monopropellant (50 years ago). The Isp was even listed as 160 seconds, but I have never seen any definite or concrete results for C2H4O. A search on Google gives ambiguous results.

A long time ago I saw a description in a rocket book of a compressed gas rocket based on carbon dioxide dissolved in acetone under pressure. I thought this sounded like a bad idea, because acetone is highly flammable and so such a device is spraying a mist of acetone everywhere. There are a lot of bad ideas out there for chemical rockets and after so many years the reasonably good chemical rocket propellants are the ones that are in widespread use.
 

rocket_troy

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That's what I thought was so funny. What could go wrong with this "finicky" propellant made from a pressure sensitive fuel that can detonate on its own which is then dissolved in a liquid oxidizer...? What happens when acetylene gas bubbles that might form in it, from cavitation for instance, are compressed beyond 15psig by some perturbation of the incompressible liquid surrounding them? Temperatures in compressed bubbles in a liquid can reach temperatures so high from their implosion that they cause the trapped gas to emit visible light.
I think the primary theory was (and there were a few very smart and extremely experienced propulsion engineers working on this), that acetylene can be significantly tamed by dissolving it in something to buffer it ie. to significantly reduce its concentration. To quote Mitch Burnside Clapp - "Acetylene's worst enemy is more acetylene"; the stuff almost catalyses its own decomposition.
The primary problem (which I don't think was properly considered in the concept phase) is N2O and its tendency to be extremely sensitised with even trace amounts of organic contaminates. Anyone who has read the N2O safety guideline report closely that came out of the Scaled composites tragedy back in 2007 would have a strong appreciation with keeping N2O well away from both organic substances and materials (even epoxy composite).

Troy
 
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