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High Energy Laminated Rocket Propellants

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Chris

Sun Oct 28 2007, 11:18AM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

This is not really meant to be a practical thing, but I find the idea of pushing rocket propellant chemistry to the limits fascinating. Though the method I describe is tedious, and many of these propellants are very hazardous materials that require special handling and demand the utmost respect, I hope to push the limits of solid rocket specific impulse to the max. Since many of these propellants are difficult and expensive to synthesize or obtain, this mainly applies to rather small engines.

I have considered the possibility of some very energetic and reactive solid fuels and oxidizers for rocket engines. Examples of some of these fuels are lithium hydride and other light metal hydrides or borohydrides or light metals themselves such as lithium, sodium, or beryllium, or other things like cubane (actually quite safe/stable), decaborane or mixtures thereof, or mixtures containing hydroxylamine. Some of the possible oxidizers are N2O5 (very volatile) or other nitronium salts, perfluorate or fluorate salts, mixtures containing hydroxylammonium salts, or alkali metal peroxides and superoxides. I have been considering combinations of many of these with each other or with other less exotic propellants.

Clearly many of these propellants are so sensitive and reactive that they could not even come in contact with each other, much less be mixed into a composite propellant. They would simply explode, many as soon as they came into contact. Some of them are quite volatile, subliming solids, and some of them are very pyrophoric and cannot even be handled outside of an inert atmosphere. As a method to allow them to be used anyway, I have proposed laminate propellants.

For core burning or ring burning designs the fuel or oxidizer constituents would be individually cast or grown into solid plates of appropriate thickness with strochiometric mass and a hole in the center for the burn chamber. They could be combined with a suitable fibrous material such as fiberglass or steel wool (where compatible) for strength, or cast or grown as a single crystal plate. The plates of fuel and oxidizer material would then be stacked alternately in the rocket tube throughout its length and glued or mounted in with a thin dividing layer between each. A protective lining would then be applied to the inside of the burn chamber, and a line or layer of flash powder or similar would be applied down its length, bridging all the plates. This would be connected to an electric ignition, and the burn chamber would be sealed with argon gas inside by a cover film over the nozzle. Some of the more volatile propellants would require that the rocket be kept refrigerated until ignition.

The basic equipment needed for building such rockets would include an isolation glove box, possibly refrigerated, casting trays, and most importantly thorough knowledge of the properties and compatibilities of each of the propellant constituents, as well as testing with small samples.

A thickness for the plates would have to be chosen, probably through experimentation, so that the burn rate would be controlled, and yet the burn is even and complete. There could be issues regarding differing melting points of thermal conductivity of the different constituents, and there may be other unexpected issues with the burn rates of the plates.

Suggestions? Criticism? Comments? All are welcome.

ragnar

Sun Oct 28 2007, 11:34AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Sounds very adventurous, very scientific, and very complex!

Never having handled explosives or propellants, I have little idea of the risks involved -- I'm sure you'll take the best of precautions... it will be great to know what the 'best'" concoctions are.

If you do work towards optimizing a particular mix, will this lead to another rocketry project?

Hmmm, does one test the propellant by strapping the rocket stationary to a sprung/deflecting fixture with a datalogger gauging the displacement... how?

Do take care... do you already have the glove box, will you be able to get your hands out quickly enough, and do I guess this is strictly an outdoor activity?

Oh, and have you got a video camera? Hehe

Bored Chemist

Sun Oct 28 2007, 12:01PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

A couple of thoughts,
if the stuff goes off in a glove box your hands won't stay in there for long- of course, they might not be a lot of use afterwards. This will be a pity since even in the ragged state they might be they would still serve to protect your eyes if you could get them to cover your face in time; trouble is it will be a bit late for that.
The only "safe" way to make these would be remotely ie you drive a robot and the robot gets blown to bits when it goes wrong.

Aside form that there's a bigger problem as I see it. Once you light these things the stresses involved are likely to shgatter the glue that's keeping the fuel and oxidant apart. At that point the aparatus converts from a rocket into a bomb.
Of course, you could avoid this by using a thick spacer layer but this would negate any advantage to these high energy density materials.
Call me a cynic but I think this isn't worth the risk.
Oh BTW, just before they died, every person killed by amateur explosives/ rocketry would have said something like "it's OK, I know what I'm doing".

MOT_man

Tue Dec 04 2007, 07:53AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

Well, this sounds like an novel idea - however, when the propellant begins to burn it will put extra pressure on any unburnt fuel/oxidizer mix causing fracture line to appear cross grain. You'll get a monstrous explosion inside the fuel housing which will destroy the rocket anything close to it....trust me I've done this. The safest and most powerful kind of unique rocket motor to date is the gas-solid fuel hybrid. Ive used NOx or straight Oxy with road tar as a fuel. VERY VERY powerful motor .

...

Tue Dec 04 2007, 03:36PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Um, all of the hyrid motors burning a fuel only solid propellent (tar, paper, PVC, etc) I have seen only come in at about 1/2 what a ammoniumperchlorate/rubber motor does... I think that for the larger motors you can get slightly higher energy densities by combining the 2 and injecting an ammoniumperchlorate/rubber motor with N2O from behind during the burn, although IIRC the improvement wasn't all that great.

I would stick with that if I were you, but whatever floats your boat...

cheers

MOT_man

Wed Dec 05 2007, 02:59AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

Well, if you lace the rocket propellant with a premix oxidizer you can get pretty darn close to Ammonium Perchlorate rocket fuel. Yes, this material is the hottest oxidizer known - but gaseous oxygen mixing with hydrocarbon fuel can burn very violently too...
Ammonium Perchlorate is HIGHLY restricted material! Good luck buying it at all!!

...

Wed Dec 05 2007, 05:11AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Um, ammonium perchlorate isn't regulated at all except for the fact that you need to ship it hazmat since it is a strong oxidiser... Heck, firefox-fx will sell you a kit of everything you need to make composite motors (instructions included!) with just a copy of your drivers license on file.

You can even buy complete cast ready to fly grains up to 62.5g with no permits at all (just wonder into your hobby shop).

Chris

Wed Dec 05 2007, 05:12AM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

Are you kidding? Ammonium perchlorate is not that hard to synthesize from scratch, and can even be purchased easily by regular folks through plenty of suppliers. While the most common, it is far from the hottest known oxidizer, and it is definitely not a hard-to-get one. Pretty much any liquid oxidizer, whether it be LOX, N2O4, H2O2, or fluorine based ones, are far more powerful than ammonium perchlorate too.

Anyways let us try to keep this thread to high impulse propellants. Ammonium perchlorate or N2O and tar doesn't cut it; pretty much any liquid propellant has higher specific impulse than these, as do some solid propellants like Mg/NH4NO3 or Al/NH4ClO3. Methods that allow even hotter combinations are of most interest to me, such as the laminated propellant or similar large-grain approaches. Really, liquid rockets are the best. Hybrid rockets seem to share all the disadvantages of both liquid and solid rockets and few of the advantages, for example they have the complexity and cost of a liquid rocket and the large pressurized area and thus great bulk of a solid rocket, as well as requiring even more careful solid grain design and liquid feed rate to keep it stochiometric.

MOT_man

Wed Dec 05 2007, 07:16AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

ammonium Perchlorate is under lock and key in Canada. All perchlorate materials for that matter.... need an explosives license, period.

I'd love to get some... but its too damn hard to get.

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