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Propulsion Systems

Posted by: Monroe - Wed Sep 24, 2008 12:11 pm
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Propulsion Systems 
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Post    Posted on: Sat Mar 14, 2009 9:31 pm
So, what are the different ways you're launching stuff? I know Prometheus are using staged SRBs with a gas gun for orbital insertion, but what about the others?

Cererean Astro (when we get started) will probably use a single disposable SRB (for most of the velocity) and a liquid fueled upper stage, possibly a monopropellent, for the actual insertion. Materials will be cardboard (if it can be made to work), plastic, foam, and as little metal as we need.

Just a thought: if only the upper stage is recovered, and the lower stage is disposable, would it still be eligible for the N-plus prize?


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Post    Posted on: Sat Mar 14, 2009 10:03 pm
There's no way a rocket made of cardboard, plastic and foam is making it orbit.


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Post    Posted on: Sat Mar 14, 2009 10:51 pm
There's no way anyone will get something to orbit on a budget of £999.99, either. Doesn't stop us trying.


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Post    Posted on: Sun Mar 15, 2009 12:40 am
Nothings impossible, just requires different thinking to the problem than what we are accustomed too. It might take you 6 months or 20yrs to do so but everything in the end is possible.
You can buy surfboards made from cardboard now, I'm sure 5-10yrs ago if you came up with that idea you would of been laughed at.


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(Sorry I just don't like people saying you cant do something when they havn't even tried, on paper it might not work but once you get started and experimenting, who knows you might find something out, but the point is your not going to know unless you try, never doubt an idea untill you see the results)


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Post Project Mockingbird   Posted on: Sun Mar 15, 2009 7:52 am
Very interesting and perfectly in line with what I'd like to do, but there is little information to be found. The rough specs are for a 4 stage 500kg rocket pump feeding H2O2 and kero at 1000psi to burn at 700psi and 333isp. The pump is piston type and powered by a second H2O2 expansion feed. Each stage is 95% fuel/oxidizer and will on paper get 5kg to orbit.

The project was at least partially run by Jordin Kare but never seems to have gotten funding so was never built. Anyone else find any more details?

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Post    Posted on: Sun Mar 15, 2009 3:01 pm
Good we are sharing information! This is how we learn! Or at least how I learn. We do want to do this right? There is so much that has already been done over the last few decades. There is not that much that hasn’t all been done before in fact I bet there are a lot of older guy's out there (if their still alive) That are saying we tried that or that’s the same idea we had. There's been way to much secrecy and fear involved over the years about rockets and experimentation. I'm sure we have lost some really good work. Besides that a lot of smart men took the information to there graves, what a loss. Share the wealth fellas it's not about you.

Monroe

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Post    Posted on: Sun Mar 15, 2009 5:08 pm
I prefer pressure fed rockets, as they are much simpler (a valve, and something to control it, and you're done). That's why Propane/Butane are such good rocket fuels. Compress it to a liquid, then let it vent into the rocket.


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Post Pressure fed vs. pumps   Posted on: Wed Mar 18, 2009 3:43 am
Pressure fed is certainly similar, but the way I see it every once of weight adds pound of fuel to the rocket. Efficiency saves weight. To get efficiency you NEED high ISPs and to get high ISPs you need high pressures. High pressure tanks are possible but they will likely be cheap OR light OR aerodynamic. Spherical tanks are the cheapest and lightest, but the least aerodynamic. Steel is probably the cheapest, but not the lightest, etc.
Pumps seem to be the possible solution by placing all the expense in one system, if that one system can be made reasonably inexpensive, then the rest of the rocket is much simpler. I read Armadillo's major expense in a launch is Helium. Can any of us afford that expense on this budget? How is anyone here even getting high pressure tanks that could pass safety within budget? Or do we drop the pressures down and add excessive fuel weight due to inefficiency?

Pumps seem to be the answer and turbo-pumps don't work in this scale, so some type of positive pressure pumps will have to be developed sooner or later.

The pump is the key to space.

MisterQED
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Post    Posted on: Wed Mar 18, 2009 6:02 am
I think you hit the nail right on the head! Tha-wack! We need a pump that runs on the exhaust gases or a venturi effect or something! I don't want to spend the time right now developing something like this. Maybe you could use combustion chamber pressure to pressurize the tanks somehow or who knows. I'm sure there's a solution but the development time without mega $$$$$$$$$$$$$$ will over run our limit for the N-Prize end date.

Monroe

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Post Re: Pressure fed vs. pumps   Posted on: Wed Mar 18, 2009 4:41 pm
How much pressure do you need to store? 2 liter bottles - IF YOU SCREEN THEM CAREFULLY - can store up to 100psi (tho not with cryo temp stuff)

My friend Ryan fills them up and if they hold shoots them with a pellet gun. It goes off like an explosive - a BIG ONE. The police thought this was teriffic and asked him how to do it :D


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Post    Posted on: Wed Mar 18, 2009 6:02 pm
Vax
I saw a video on youtube of a guy loosing his hand with one of thoes pressure bomb's from a plastic soda bottle so be Very Careful. I'm not saying don't do things by any means but learn the scientific method and keep notes and be safe! We need you! Anyway how could you figure out how much pressure one could take? And remember pressure will increase inside the bottle as the pressure reduces with altitude. Can you figure out how much the pressure would change inside the bottle at 60,000ft? If it had 20 psig (PSI Gauge) at sea level? This is important stuff here this is real rocket science. It's not for your average fellow it's just for the cool guy's. The guy's going to space.

Monroe

Are you one of those guy's? Or just an average fellow?
I bet we could push the limits of a plastic soda bottle what do you think?

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Post    Posted on: Wed Mar 18, 2009 8:01 pm
Efficiency means cost, a big low efficiency rocket is probably going to be cheaper. If you want to look at pumps have a look at reciprocating positive displacement pumps or gear pumps. I did my thesis last year on a reciprocating pump and I intend to pursue it in my own time to a working rocket motor, I probably spent ~$500AUD to make the whole system work but there was only ~$50AUD worth of metal in the pump and a few hours on my lathe. Gear pumps are good because you can buy them off the shelf, power them either with a brushless electric motor and lithium cells or a tank of compressed gas and an air turbine.


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Post    Posted on: Wed Mar 18, 2009 8:53 pm
Motors and batteries add weight and so do gas turbines. Not saying these wont work they will, but if we could eliminate these it would make the difference. We ran air off the compressor stage of our turbine engines to blow bubbles on the rim of the props to mask them from subs and we had belts of air holes in the hull that masked the ships hull too. I'm not saying this will work, but we need to think outside the box here. Like I said we aren't developing this yet. You could use pressure on the pad to start the engine and once it starts let it self pressurize. Something as stupid as a paddle wheel in the exhaust path or a pressure bleed from the combustion chamber maybe? That drives a pump. I dont know something different.

Monroe

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Post    Posted on: Thu Mar 19, 2009 2:01 am
//Efficiency means cost, a big low efficiency rocket is probably going to be cheaper.//
Why??? Is there any fuel which is soooo cheap that you can burn lots of it at low efficiency and reach orbit?
//If you want to look at pumps have a look at reciprocating positive displacement pumps or gear pumps.//
Why?? How about: external gear, screw, shuttle block, sliding vane or roots type pumps? I got the previous list off wikipedia and only deleted the flexible vane as all the others have been used as high pressure hydraulic pumps. I think we need to explore EVERY option.
//I did my thesis last year on a reciprocating pump and I intend to pursue it in my own time to a working rocket motor, I probably spent ~$500AUD to make the whole system work but there was only ~$50AUD worth of metal in the pump and a few hours on my lathe.//
Yet you don't think this can be done cheaper than thousands of $ for high pressure tanks and helium? Weirdly enough I don't think you do. If you could produce one pump for 500AUD then maybe if you made 100, they would drop to a fraction of the cost.

Then the next challenge is to power it. An electric motor makes some sense, but H2O2 motor is bound to pack more energy per gm, but maybe the controllability tips the scales back. Air motor run off of engine pressure seems like the lightest, but the heat and unbalancing may make this a bad choice.


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Post    Posted on: Thu Mar 19, 2009 5:28 am
MisterQED wrote:
//Efficiency means cost, a big low efficiency rocket is probably going to be cheaper.//
Why??? Is there any fuel which is soooo cheap that you can burn lots of it at low efficiency and reach orbit?
//If you want to look at pumps have a look at reciprocating positive displacement pumps or gear pumps.//
Why?? How about: external gear, screw, shuttle block, sliding vane or roots type pumps? I got the previous list off wikipedia and only deleted the flexible vane as all the others have been used as high pressure hydraulic pumps. I think we need to explore EVERY option.
//I did my thesis last year on a reciprocating pump and I intend to pursue it in my own time to a working rocket motor, I probably spent ~$500AUD to make the whole system work but there was only ~$50AUD worth of metal in the pump and a few hours on my lathe.//
Yet you don't think this can be done cheaper than thousands of $ for high pressure tanks and helium? Weirdly enough I don't think you do. If you could produce one pump for 500AUD then maybe if you made 100, they would drop to a fraction of the cost.

Then the next challenge is to power it. An electric motor makes some sense, but H2O2 motor is bound to pack more energy per gm, but maybe the controllability tips the scales back. Air motor run off of engine pressure seems like the lightest, but the heat and unbalancing may make this a bad choice.


Funnily enough I designed the spec of the pump I built to power an ultra-low cost module for orbital launch applications. An orbital vehicle would be a 3 to 1 cluster and stage of the modules, weigh around 1200Kg and place a 20Kg payload into LEO. It would use H2O2/kerosene both fed from low pressure composite tanks using reciprocating piston pumps, the reciprocating pistons would be driven using hot oxygen and steam from decomposed peroxide.

The modules are all essentially identical and designed for parallel and series staging/clustering allowing any range of missions to be flown from common low-cost hardware. The sheet aluminium technology used to make them would again be low cost, a complete module would have a fairly good mass ratio and could be made primarily with a sheet metal guillotine, pan brake folder, drill press and pop-rivet gun. I got as far as running initial simulations, doing some detail design work on the propulsion system and started the detailed structural design however my thesis and other work forced me to put it aside for a while.

Monroe: Interestingly enough if you look at Goddard's early work he used turbines directly in the exhaust of the rocket nozzle, linked to the propellant pumps. There are a lot of problems with this though so I don't really recommend it. My pump design could use hot gas and contained no rotating parts, making manufacturing tolerances much less critical = cheap.

MisterQED: The cheapest part of any commercial rocket has always been the propellants especially when you're getting it in ultra-bulk. All those pumps you listed are possible, what you need to look at is construction tolerances and drive methods. For small sizes I strongly discourage rotating pumps, even if they aren't fixed displacement the rotary drive source (eg motor or turbine) will still end up heavy and/or inefficient.


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