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Nuke

a very crappy rocket engine

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recently a post on hack a day about space toilets got me thinking. crap is actually rather flammable, even more so when vacuum desiccated and compressed. when formed into a hollow cylinder and combined with an oxidizer feed you have a hybrid rocket engine. further more its a way to dispose of a waste product that would need to be returned to earth at some point anyway. you could potentially use such crappy engines to re-boost the station and solve two problems at once. makes me wonder what kind of isp you could expect.

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Interesting, mabey nasa doesn't do it because public relations

any way I love that logic :sticktongue:

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You could also have them cram all their poo into a bag and use the Canadarm to fling it retrograde. Probably wouldn't move very fast but hey, that's impulse.

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It's specific impulse is pretty crappy, but yeah, maybe for a little push once in a while it'd work ok. I think the Mythbusters may have launched such a rocket once.

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16 minutes ago, cubinator said:

It's specific impulse is pretty crappy, but yeah, maybe for a little push once in a while it'd work ok. I think the Mythbusters may have launched such a rocket once.

i remember meat rocket. but not poo rocket. 

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This is something you could actually try yourself if you have access to most basic of tools. Of course, you might have trouble freeze drying it, but why do you think that would make for a better rocket? Sun dry, crush, rehydrate to paste, press into shape (directly in rocket motor tube) dry again and supply with O2.

Just make sure your family members don't realize what you're doing, or lab coat people may come for you.

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7 minutes ago, Shpaget said:

This is something you could actually try yourself if you have access to most basic of tools. Of course, you might have trouble freeze drying it, but why do you think that would make for a better rocket? Sun dry, crush, rehydrate to paste, press into shape (directly in rocket motor tube) dry again and supply with O2.

Just make sure your family members don't realize what you're doing, or lab coat people may come for you.

Dehydrating probably increases burn rate.

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Surre, but I don't see why the method of drying would be relevant.

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Posted (edited)
3 hours ago, Shpaget said:

Surre, but I don't see why the method of drying would be relevant.

more because its something thats easy to do when you are surrounded by vacuum. freeze drying is essentially putting things in a vacuum chamber, which causes the moisture to evaporate while keeping the solids. its probably more involved than that, but that's the jist of it. once its dry it can be compacted to remove the voids formerly occupied by moisture. space toilets already do these things, but the excrement is usually bagged and placed into storage for disposal on earth. instead make the compactor compact the crap into the right shape needed for a solid/hybrid engine. the "brick" can be loaded into the combustion chamber of an engine. so you need a hybrid engine design that has the ability to be reloaded during a space walk or perhaps from inside the station itself. 

21 minutes ago, kerbiloid said:

buffalo chips. 

Edited by Nuke

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You can recycle it into better fuels. Methane should be achievable. But the main weight is still oxidizer. I'm not sure you're saving enough to be worth the trouble.

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Poop -> hydroponic facility -> potatoes -> ethanol + oxygen = actually decent fuel for a rocket engine :D

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58 minutes ago, K^2 said:

You can recycle it into better fuels. Methane should be achievable. But the main weight is still oxidizer. I'm not sure you're saving enough to be worth the trouble.

I wonder about a monopropellant dung-solar engine........

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Posted (edited)
1 hour ago, sevenperforce said:

I wonder about a monopropellant dung-solar engine........

Just make a Nuclear Thermal... Sewage rocket engine.

Guy pitching the idea to SpaceX:

"Man Elon you gotta hear me out, I have a new STS  rocket engine that will save hundreds, maybe thousands of dollars!"

"Go on."

"All you need is a nuclear reactor... that's the hard part, the second is easy. We need everyone's 'number two's'."

"Yeah... I will get back with you on that."

He won't though, since even Elon would have a difficult time getting a nuclear reactor, and he is the closest thing we have to Tony Stark.

Edited by Spacescifi

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In theory, if you can generate a high enough temperature, anything can be used as propellant. Lighter elements would have better ISP, heavier elements and compounds would have better thrust...

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Using Starship as septic tank on Mars.

Wait... Oh, fuel!..

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9 hours ago, sevenperforce said:

I wonder about a monopropellant dung-solar engine........

Wait... Why aren't we doing this? No, I don't mean with dung, just in general. You can get 3,000K out of solar easy. That's plenty for NTR minus the N. (Sorry, @Nuke) I'm sure specific power will be, well, topical. But you should have the same 800s+ ISP that you get with NERVA if you feed hydrogen through it. And in principle, collectors don't have to be that much more complex than solar sails, it's just a mirror. To get 1N of thrust, you need about  0.15km² of solar sail. Or instead, you can eject 0.125g of hydrogen per second at 8km/s, which takes 40J/s. Even at 10% thermal efficiency, that's less than half a square meter of mirror, which is, well, trivial. Scaling up back to a 0.15km², that's 150MW of power, which at 10% efficiency still would be enough to give you more thrust than NERVA did. Somewhere in between, there ought to be a practical rocket.

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7 hours ago, radonek said:

Yeah, I couldn't imagine this is a new idea somehow. I'm more curious why nobody built one. Unlike NTR, this is scalable. At least, it scales down quite well. And unlike NTR, there are no regulations blocking something like this. I'm sure back in the 60s, somebody just said, "Why bother, just stick a nuclear reactor on it," as that was basically attitude towards everything, but why haven't we revisited the concept since?

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Surface coking of components would be an issue.

Potential "worlds worst/most dangerous job" episode idea - who wants to be first to sign up to do a space walk...to go inside a rocket engine... to scrub off skid marks...

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29 minutes ago, mrfox said:

Surface coking of components would be an issue.

Potential "worlds worst/most dangerous job" episode idea - who wants to be first to sign up to do a space walk...to go inside a rocket engine... to scrub off skid marks...

Laser ablation should do the job

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the good news is you are in a space suit, the bad news is you have to go inside with it on. cant leave it at the door as a farmer would do with his boots.

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6 hours ago, Nuke said:

the good news is you are in a space suit, the bad news is you have to go inside with it on. cant leave it at the door as a farmer would do with his boots.

Does he?
In every movie I can see, at home the farmers keep walking in same cowboy boots like outside. However the floor stays magically clear.

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I'm just disappointed that none of you have said, "ISPeeeeeeee" yet.

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