ISRU only from atmosphere

[kunok]

Checking a table of adiabatic flame temp of rocket fuels there is C₂N₂ in between common fuels, so I was surprised.
Researching both C₂N₂  and C₄N₂ are fuels with very high combustion temp and the better part, are made only from gases very common in the atmospheres both in Mars and Venus.

Taking C₄N₂ , looks like it will be easy to produce, expensive in energy terms but relatively simple:

With the atmospheric CO_{2 ,} O₂ can be refined with the bosch or sabatier reactions with graphite as a byproduct (needs a close circuit with hydrogen though)

According with the wiki https://en.wikipedia.org/wiki/Dicyanoacetylene C₄N₂ can be produced heating N₂ available in the atmosphere and that graphite to 3000K (yeah I know high temps).

This theoretical ISRU will give a highly energetic LO/C₄N₂ combo as rocket fuel, without the need of mining, only using atmospheric gases. It won't have good isp but the infrastructure will be simpler.

What do you think? Any other only atmosphere ISRU option out there?

[kerbiloid]

8 hours ago, kunok said:

will give a highly energetic

highly energetic hot

From ru.wiki about C4N2

Oxidizer	ISP, s	Temperature °С	Density g/cm3
H2O2	350	3257 °C	1,3
N2O4	261	4034 °C	1,24
ClF3	325	3404 °C	1,62
O2	310	5013 °C

Burns hot, but produces not much energy per mass (as no H and large ballast of N)

So, you could probably only use it to heat main fuel a little up.

Edited January 23, 2017 by kerbiloid

[KSK]

C₄N₂ might almost be too energetic. Given that it apparently burns in oxygen with the hottest flame temperature of any chemical reaction, I'm thinking it might be difficult to fire in a rocket engine, even if that engine is regeneratively cooled. Also I'm wondering how much of a problem it would have with coking?

I'm not sure what else you could make with just the Martian atmosphere though. I think it does have traces of water (thus hydrogen) but at such low partial pressures that making practical use of it might not be possible.

 

[Steel]

1 hour ago, KSK said:

C₄N₂ might almost be too energetic. Given that it apparently burns in oxygen with the hottest flame temperature of any chemical reaction, I'm thinking it might be difficult to fire in a rocket engine, even if that engine is regeneratively cooled. Also I'm wondering how much of a problem it would have with coking?

 

Yeah I think coking might be a big issue considering one of the main combustion products is carbon powder.

[KSK]

I thought it decomposed (explosively) into nitrogen gas and carbon powder? Presumably burning it in oxygen wouldn't be quite the same but whether you'd get anything near complete combustion I don't know.

[kerbiloid]

http://pubs.acs.org/doi/abs/10.1021/ja01590a075

[FleshJeb]

https://en.wikipedia.org/wiki/In_situ_resource_utilization#Mars

It requires the mining of water, but that's relatively simple, compared to mineral mining.

[ment18]

1 minute ago, FleshJeb said:

https://en.wikipedia.org/wiki/In_situ_resource_utilization#Mars

It requires the mining of water, but that's relatively simple, compared to mineral mining.

The OP is specifically talking about not having to mine water because it is much harder than sucking up the atmosphere.

There are also several other ways of using only the atmosphere to make fuel:

-CO2 NTR, the simplest possible way to do ISRU.  Pump the martian atmosphere into a fuel tank. Zubrin has some stuff on this

-Take your own hydrogen.  Either use a Methane NTR (pretty good ISP) or hydrolox, since hydrogen masses very little 

[kunok]

@kerbiloid in my book that's good enough for a mars surface to orbit rocket. To solve the too high temp and too little isp, just add more O₂ or even N₂ , it will improve a little.

29 minutes ago, FleshJeb said:

It requires the mining of water, but that's relatively simple, compared to mineral mining.

I really think that most people oversimplifies the ice mining problem.

18 minutes ago, ment18 said:

-CO2 NTR, the simplest possible way to do ISRU.  Pump the martian atmosphere into a fuel tank. Zubrin has some stuff on this

Probably in that case better to filter out the co₂ and use only the N₂ , I already proposed that, in some thread. But lets put the nuclear out for a while. The idea for this is KISS and nuclear is problematic if you want for example a disposable stage.

[FleshJeb]

1 hour ago, ment18 said:

The OP is specifically talking about not having to mine water because it is much harder than sucking up the atmosphere.

Yeah, sorry, I oversimplified. I've read The Case For Mars a few times. The original plan (second paragraph of my link) was to bring the hydrogen and not mine it.

41 minutes ago, kunok said:

I really think that most people oversimplifies the ice mining problem.

I probably did. Without doing the math, I would venture to guess that water is still easier to purify than mineral ores. However, it could very well be more energy-intensive. I agree, mining, even if it's just scraping away the regolith to get to the permafrost is MUCH more difficult than just pumping atmosphere.

However, I take the view that ice-mining is something we're going to want to do a LOT of in the future, so we might as well get the practice now. It may be less efficient for a specific mission, but building the tools and techniques has an extremely high value. I wonder if you could just throw a clear tent/greenhouse over an area, and capture the water vapor that sublimates out.

In regards to the chemical process in the OP: I was under the impression that nitrogen is extremely rare on Mars. However, after doing some research, it seems like the N/O fraction is higher than on earth.

[magnemoe]

1 hour ago, kunok said:

@kerbiloid in my book that's good enough for a mars surface to orbit rocket. To solve the too high temp and too little isp, just add more O₂ or even N₂ , it will improve a little.

I really think that most people oversimplifies the ice mining problem.

Probably however its far more like mining salt than mining iron or coal. If permafrost as it look likely on Mars the easiest is probably to drill down and use steam to melt the ice and extract water. 
on Moon poles they belive the ice is mixed with dirt and rock so you need to scrape this up and heat the mixture to get out the water. 

[DerekL1963]

39 minutes ago, magnemoe said:

If permafrost as it look likely on Mars the easiest is probably to drill down and use steam to melt the ice and extract water. 
on Moon poles they belive the ice is mixed with dirt and rock so you need to scrape this up and heat the mixture to get out the water. 

o.0  Do you not know that permafrost is ice mixed with dirt and rocks?