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Are Gel Propellants The Future?


Spacescifi
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Are Gel Propellants The Future?

Imagine if you will, a gel propellant that had a greater density of chemical propellant than liquid?

Would it be competitive with liquid propellants?

Or would it only have niche applications?

By competitive, I mean using gel propellants for 2 stage to orbit launch systems... and maybe even SSTO's.

One crazy idea I had was what if it was possible (is it?) to make a propellant gel that ALREADY has the oxidizer 'baked' into it, and only needs some heat applied to combust it?

Like a methalox gel? Just heat it and you are good, no need for separate oxidizer and propellant tanks, just a single tank, heating elements in the combustion chamber, and fuel injectors.

 

Edited by Spacescifi
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9 minutes ago, Spacescifi said:

Imagine if you will, a gel propellant that had a greater density of chemical propellant than liquid?

Would it be competitive with liquid propellants?

What would be your guess, why is hydrogen used so much?

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20 minutes ago, Spacescifi said:

 

Like a methalox gel? Just heat it and you are good, no need for separate oxidizer and propellant tanks, just a single tank, heating elements in the combustion chamber, and fuel injectors.

 

Read ignition, it goes into the development of most liquid rocket fuels, they tried a metholox gel at one point, it ended up needing only a slight agitation such as a bit of light for the whole thing to go off.  Also as a bit of a cautionary tale regarding the pursuit of high propellant density, at one point he was assigned to experiment with a dimethyl mercury propellant because someone thought it would be ideal based on its high density. Turns out that the danger of  handling that stuff was not worth the boost in performance, as shown by the chemical companies he called to ask hanging up on him after he asked for a decent amount of the stuff.

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Is X better than Y?

Imagine if you will, an X that is better than Y?

Would it be better than Y?

 

"One crazy idea I had was what if it was possible (is it?) to make a propellant gel that ALREADY has the oxidizer 'baked' into it, and only needs some heat applied to combust it? "

So, a solid fuel rocket?  How does this avoid the issues with solid rockets that already exist?

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27 minutes ago, razark said:

Is X better than Y?

Imagine if you will, an X that is better than Y?

Would it be better than Y?

 

"One crazy idea I had was what if it was possible (is it?) to make a propellant gel that ALREADY has the oxidizer 'baked' into it, and only needs some heat applied to combust it? "

So, a solid fuel rocket?  How does this avoid the issues with solid rockets that already exist?

He wants to be able to pump and throttle and turn off the gel like a liquid while retaining the advantages of solids. 

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59 minutes ago, insert_name said:

Read ignition, it goes into the development of most liquid rocket fuels, they tried a metholox gel at one point, it ended up needing only a slight agitation such as a bit of light for the whole thing to go off.  Also as a bit of a cautionary tale regarding the pursuit of high propellant density, at one point he was assigned to experiment with a dimethyl mercury propellant because someone thought it would be ideal based on its high density. Turns out that the danger of  handling that stuff was not worth the boost in performance, as shown by the chemical companies he called to ask hanging up on him after he asked for a decent amount of the stuff.

Was about to say, oxyliquit mixtures are often violently shock sensitive

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1 minute ago, JoeSchmuckatelli said:

He wants to be able to pump and throttle and turn off the gel like a liquid while retaining the advantages of solids. 

But if the fuel and oxidizer are combined, and only need heat to combust, how is it any different from a solid fuel?

How do you turn it off?

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Why in the world would a gel have a greater energy/power content than a solid?  Other than an even greater propensity to explode?

And then you have all the issues of a solid.  In a liquid rocket, the combustion chamber is a part of the engine.  In a sold or gel rocket, the entire "fuel tank" becomes the combustion chamber.  And since the pressure of the combustion chamber directly effects the power and efficiency of the rocket (if you want that much pressure at the throat of the combustion chamber, you need to make sure the rest of the combustion chamber can withstand that pressure), expect a heavy rocket.  Shuttle SRBs are ~100 ton steel tubes, so any SSTO based on a shuttle SRB will have 100 tons less payload (per booster) than a well designed TSTO.

I've only heard of gels being used in hybrid rockets, where the oxidizer was fed separately and the gel was entirely fuel.  Best bet is to read Ignition! to see what happened to gels and why.

 

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13 hours ago, Spacescifi said:

One crazy idea I had was what if it was possible (is it?) to make a propellant gel that ALREADY has the oxidizer 'baked' into it, and only needs some heat applied to combust it?

Quote

Then Luigi Crocco, in Italy, had another idea, and was able to talk the Ministry of Aviation into putting up a bit of money to try it out. The idea was that of a monopropellant. A monopropellant is a liquid which contains in itself both the fuel and the oxidizer, either as a single molecule such as methyl nitrate, CH3NO3 in which the oxygens can burn the carbon and the hydrogens, or as a mixture of a fuel and an oxidizer, such as a solution of benzene in N2O4. On paper, the idea looks attractive. You have only one fluid to inject into the chamber, which simplifies your plumbing, your mixture ratio is built in and stays where you want it, you don't have to worry about building an injector which will mix the fuel and the oxidizer properly, and things are simpler all around. But! Any intimate mixture of a fuel and an oxidizer is a potential explosive, and a molecule with one reducing (fuel) end and one oxidizing end, separated by a pair of firmly crossed fingers, is an invitation to disaster.

All of which Crocco knew. But with a species of courage which can be distinguished only with difficulty from certifiable lunacy, he started in 1932 on a long series of test firings with nitroglycerine (no less!) only sightly tranquilized by the addition of 30 percent of methyl alchohol. By some miracle he managed to avoid killing himself, and he extended the work to the somewhat less sensitive nitromethane, CH3NO2. His results were promising, but the money ran out in 1935, and nothing much came of the investigation.

 

12 hours ago, insert_name said:

Read ignition

 

Specifically, what you're looking for is a heterogeneous monopropellant.

Everyone quickly abandoned that idea. Instead, there were attempts to tranquilize or dope existing propellants with various additives. The record-setting hydrogen-lithium-fluorine motor would likely be operationalized as a lithium slurry in hydrogen, rather than as a separate molten metal tank. There were also several programs binding the usual UDMH-IRFNA battlefield propellant with things like carbon, or trying to dope UDMH with aluminium dust. Performance gains usually fail to realize, and engineering obstacles are many.

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55 minutes ago, wumpus said:

Why in the world would a gel have a greater energy/power content than a solid?  Other than an even greater propensity to explode?

And then you have all the issues of a solid.  In a liquid rocket, the combustion chamber is a part of the engine.  In a sold or gel rocket, the entire "fuel tank" becomes the combustion chamber.  And since the pressure of the combustion chamber directly effects the power and efficiency of the rocket (if you want that much pressure at the throat of the combustion chamber, you need to make sure the rest of the combustion chamber can withstand that pressure), expect a heavy rocket.  Shuttle SRBs are ~100 ton steel tubes, so any SSTO based on a shuttle SRB will have 100 tons less payload (per booster) than a well designed TSTO.

I've only heard of gels being used in hybrid rockets, where the oxidizer was fed separately and the gel was entirely fuel.  Best bet is to read Ignition! to see what happened to gels and why.

This, now its cases there you want trust above all else like in an launch about system or stuff like rocket propelled grenades who has to burn out inside the tube. 
Some of the early ejection seats was just an mortar, modern ones has serious trust vector control, you can eject 100 meter up flying upside down or at ground standing still, say you landed but failed but now you have leaking drop tanks and burning missiles below you. 
You also has hybrid engines who give you both with an bit of an complexity increase. 

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15 hours ago, Shpaget said:

What would be your guess, why is hydrogen used so much?

 

It's non reactive, inert with several things... barring LOX of course.

Hmmm.... would a sort of uses would abio-gel have, as we know biological processes can make methane?

Or how about an electronagnetic gel? Would that have any uses... rocketry and besides?

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On 9/11/2021 at 7:34 AM, Spacescifi said:

Are Gel Propellants The Future?

Imagine if you will, a gel propellant that had a greater density of chemical propellant than liquid?

Why do you thin that gel had greater density? Gel is made by adding some additive to liquid. If liquid is rocket propellant that additive stuff just takes room and makes it less dense.

 

On 9/11/2021 at 7:34 AM, Spacescifi said:

Would it be competitive with liquid propellants?

Why it would? Turbopumps need huge amount of power. Tens or hundreds of MW. The massive main engine of large cargo ship would struggle to run large rocket engines's fuel and oxidizer pumps. Gel would mean increased viscosity and increased power demand.

On the other hand, I do not see immediately any benefits over liquid. If I was Elon Musk and you suggested a addition to make liquids less viscose I would buy a little bottle for testing but if you suggested some stuff which makes propellants harden in tanks you would be happy that it robot dog can not bite.

 

On 9/11/2021 at 7:34 AM, Spacescifi said:

Or would it only have niche applications?

Like what?

 

On 9/11/2021 at 7:34 AM, Spacescifi said:

By competitive, I mean using gel propellants for 2 stage to orbit launch systems... and maybe even SSTO's.

One crazy idea I had was what if it was possible (is it?) to make a propellant gel that ALREADY has the oxidizer 'baked' into it, and only needs some heat applied to combust it?

You mean solid rocket fuel which would flow out of booster.

If you combined oxidiser and fuel before burn chamber you had to pump all combined volume to chamber pressure. Highly viscose stuff would need more pumping power and get heated. It would also get heat from regeneratively cooled nozzle and chamber. Plumbing should be able to handle both chemicals.

 

On 9/11/2021 at 7:34 AM, Spacescifi said:

Like a methalox gel? Just heat it and you are good, no need for separate oxidizer and propellant tanks, just a single tank, heating elements in the combustion chamber, and fuel injectors.

Only thing you would save is a dome between tanks and some parts from rocket engine. And spectacular and frequent anomalies, of course.

If I remember correctly they have estimated that few tens of percents of rockets propellants take part in "explosion". And time needed to mix them slows the reaction significantly. Actually it is not even real explosion but some kind of flash (probably it has word in English). But mixed propellants would react immediately and burn completely.

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5 hours ago, SOXBLOX said:

I *think* there was an Aviation Leak Week article a while ago that said the AIM-260 might use some sort of gelled propellant. I can't find it at the moment, though...

Oh, look at that, USAF's been reading my r/militaryworldbuilding material.

It's a reasonable inference. Northrop Grumman had developed and tested a pre-packaged IRFNA-UDMH motor (pressure-fed, @Hannu2, and most aim for gels that have a favorable rheology akin to souffle) for a TOW-equivalent missile. Before that, the US had a good run with the Bullpup, making it the most widely-produced LRPe ever.

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On 9/11/2021 at 6:46 AM, Shpaget said:

What would be your guess, why is hydrogen used so much?

Liquid hydrogen has the highest ISP of any fuels because its so light, an nerva or LV-N don't run much hotter than the shuttle engine but as its all hydrogen and you don't have to accelerate all the stupid oxygen. 
Downside is low trust as you are not throwing much mass downward. So hydrogen engines tend to be upper stage like on the Saturn 5 or you use SRB to get trust like on the shuttle and Ariane 5 

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20 hours ago, magnemoe said:

Liquid hydrogen has the highest ISP of any fuels because its so light, an nerva or LV-N don't run much hotter than the shuttle engine but as its all hydrogen and you don't have to accelerate all the stupid oxygen. 
Downside is low trust as you are not throwing much mass downward. So hydrogen engines tend to be upper stage like on the Saturn 5 or you use SRB to get trust like on the shuttle and Ariane 5 

This is also why the Shuttle  (and presumably other hydrolox engines) run fuel rich.  The extra hydrogen maintains the higher exhaust velocity and also helps cool the combustion chamber down below its melting point.

Exhaust momentum is the critical issue.  If you get exhaust velocity from heat (like chemical and nuclear rockets) you want low mass [per molecule] exhaust propellants.  If you are using electricity to directly accelerate your propellant (ions, hall effect) you want high mass per molecule (and inert as well, to keep from destroying your engine.  Inert like Xeon, Krypton, Argon).

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Milk.

Milk is the key.

***

Humans drink the milk as a fuel.
Together with oxygen as oxidizer. But LOx is the same.

A milkalox liquid fuel engine.

***

A herd of cows is herded and milked around the spaceport, producing the milk and the methane (use thin rubber balloons as scoops to collect).

The methane is used in the methalox engines, the milk - in the milkalox ones.
The oxygen is universal.

***

As the milk contains a lot of water ballast, we can either sublimate it, or make a cheese from the milk.

So, we get the cheesalox hybrid propellant,

A propely shaped piece of cheese and liquid oxygen.

***

To increase the cheesalox ISP let's dissolve the methane in the cheese (idk, how it's called before freezing) pulp.

We get a cheesemelox or mecheeselox hybrid propellant.

***

But as cheese and oxygen usually don't react very much in proper conditions (a fridge), let's also dissolve some part of oxygen in the cheese.

***

Finally we have a gelish quasi-solid slab made of cheese full of methane and oxygen bubbles, stored at low temperature.

(Depending on the gases physical state either cryogenic, or fridge temperature).

Then either the cheese slab has an axial channel to let the rest of the oxygen flow through it, or we put the cheese slab into the oxygen flow. Or both.

***

Now we have the ultimate eco-friendly biofuel one-and-a-half-component hybrid gellish cheesemelox engine.

And after every flight the milkarocket should land at any milk farm to remilk.

***

But the milk allows us to develop even a quark drive, if instead of cheese produce quark.

***

As quarmelox and cheesmelox sound too long, let's just call them quarkalox and cheesalox, because they will anyway be made of the dopped quark and cheese respectively.

Edited by kerbiloid
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