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Topic: Replace hydrazine propellants  (Read 4092 times)

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Offline Enthalpy

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Replace hydrazine propellants
« on: September 15, 2014, 09:39:39 PM »
Hello dear friends!

Some rocket launchers still use hundreds of tons of hydrazine, mmh and udmh as a fuel, but toxicity lets phase them out. A replacement, if keeping the rocket design, should be (1) safe (2) liquid (3) efficent. Hydrazines are more efficient than kerosene for instance, and equalling them - of possible - needs highly strained fuels, amines rather than hydrocarbons. Multiple bonds are excluded for stability in the cooling jacket, and any detonation risk is prohibitive.

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I imagine we could make diaza-diasterane and -stellane this way. 1,2,4,5-tetrahalo-cyclohexane is common. E- positions on neighbour carbons could result from dihalo addition to cyclohexa-1,4-diene. Diluted reaction with amines, like cyclopropylamine or methylamine, would produce strained cage molecules. Your opinion please?

A first arrangement of haloatoms would give the long desired diasterane, or better, a diaza homologue, substituted for the liquid range. Image joined.

The other arrangement of haloatoms would give aza-stellane, less good but not bad, so if the best tetrahalo-cyclohexane contains some of the isomer, it can be kept - the produced mix may stay liquid at a colder temperature. Image joined.

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All-trans-1,2,3,4,5,6-hexachloro-cyclohexane was a Lindane byproduct, and its reaction with ammonia might yield diaza-cubane, but I doubt it much... The favourable conformation would have the 1,3,5 chlorine at one pole and the 2,4,6 at the other, but known conformations have some equatorial chlorine. Anyway, the reactants must find a way to produce HCl, N2 and C6H6 instead.

Marc Schaefer, aka Enthalpy
« Last Edit: September 15, 2014, 09:54:39 PM by Enthalpy »

Offline Enthalpy

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Re: Replace hydrazine propellants
« Reply #1 on: September 16, 2014, 07:57:02 AM »
In their brochure "Ethyleneamines, A Global Profile of Products and Services", page 32 (Pdf p40 of 76), Huntsman suggest the stressed cage C6H8N4 (image below) as a product of ethylene diamine in excess formaldehyde.

Seducing, but how can this result from EDA and formaldehyde? The number of hydrogens doesn't fit a simple water elimination. What do you mean? An error? A different reaction? Thanks!

Offline curiouscat

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Re: Replace hydrazine propellants
« Reply #2 on: September 16, 2014, 08:08:52 AM »
In this context how do you define efficient?

Offline Enthalpy

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Re: Replace hydrazine propellants
« Reply #3 on: September 16, 2014, 06:31:45 PM »
O yes... Here I just compare the ejection speed, independently of cost, invested energy or the like.

Ejection speed (or the specific impulse, which divides the speed by g) is the means to compare propellants, knowing that other factors like safety are at least as important and considered separately.

Because each kg in orbit is much more expensive than the burned oxygen and "kerosene", it's perfectly reasonable to expend money and energy to improve the fuel a bit. (So-called "kerosene" or RP-1 resembles more Diesel oil, and is freed of aromatics, multiple bonds, volatiles, and so on).

The exponential of the ratio of the final speed (plus losses, say 9500m/s for low Earth orbit) to the ejection speed (depends on the expansion in the nozzle, 3300m/s is already good for oxygen and kerosene) give the mass ratio (except that empty stages are thrown away) between the lift-off mass and the orbital mass. As launchers start with 500t to deliver 5t in geosynchronous transfer orbit, every % in ejection speed means several % more payload mass.

The ejection speed relies on the combustion enthalpy per kg of propellantS, of which the nozzles converts 60-85% into kinetic energy. This means that hydrogen is the best atom to burn, while carbon and nitrogen (to form N2) are good, aluminium has drawbacks, everything else is inefficient or unusable.

To improve over a ramified alkane, a fuel can contain nitrogen, or bring heat of formation - but not as multiple bonds, because the fuel cools the combustion chamber hence gets and but shall not polymerize into gum there (wall hot, hole, boom). This leaves strained molecules: highly strained, because any additional bond loses two useful hydrogen atoms whose loss must first be compensated.

So unstrained cycles are not wanted (norbornane...), cyclopropanes are welcome, spiro as well, cages if evenly strained - but all this stable please!

Offline orgopete

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Re: Replace hydrazine propellants
« Reply #4 on: September 16, 2014, 11:15:54 PM »
Given that the impetus for using fuels with higher energy content is to improve the net payload per dollar, couldn't you achieve the same result by launching at a higher elevation. Rather than launching from Cape Canaveral, shouldn't you launch from Denver or Mexico City? I understand that one could still always still get an improved thrust from a higher energy fuel, but since kerosene is still being used, just launching from a higher elevation seems like a logical and simple improvement.
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Offline Borek

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Re: Replace hydrazine propellants
« Reply #5 on: September 17, 2014, 02:53:51 AM »
When you launch from Cape Canaveral you don't have to worry about collateral damage if something goes wrong - everything falls to the ocean.

Best place would be high and on the equator - not only close to the target but also with the highest initial linear speed.
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Offline curiouscat

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Re: Replace hydrazine propellants
« Reply #6 on: September 17, 2014, 03:01:20 AM »
Given that the impetus for using fuels with higher energy content is to improve the net payload per dollar, couldn't you achieve the same result by launching at a higher elevation. Rather than launching from Cape Canaveral, shouldn't you launch from Denver or Mexico City? I understand that one could still always still get an improved thrust from a higher energy fuel, but since kerosene is still being used, just launching from a higher elevation seems like a logical and simple improvement.

True in  theory. But how big are the savings? Perhaps the  difference is too small?

Offline Enthalpy

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Re: Replace hydrazine propellants
« Reply #7 on: September 17, 2014, 05:13:41 PM »
Launch altitude brings some gain, but not a huge one. Most launcher performance serves to obtain the orbital speed (like 7.3km/s), the altitude isn't very costly (falling from 300km means 2.4km/s which combine with the horizontal speed like a hypotenuse). 3000m only mean 0.2km/s or even less; falling from 297km instead of 300km makes 12m/s difference.

Some launcher start from a carrier earoplane, but the reasons are (1) save the spaceport cost (2) start from the equator (3) have initial speed (4) permit a stronger acceleration with moderate air drag (5) and finally, start from altitude. The altitude brings as a main benefit that the nozzle can expand the gas to a lower pressure hence convert more enthalpy to kinetic energy.

So in the choice of a launch location, the proximity to equator is very much favoured over the altitude. The same launcher permits 30% more mass on a geosynchronous orbit from Kourou than from Baikonur. Not because of the start's eastward speed, but because the orbit is already equatorial. For polar launches, all locations are about as good.

And, yes, the unpopulated area downrange is essential. Some launchers carry 200t hydrazine and 400t tetroxide, others 650t of solid propellant that sometimes goes bang. Accidents on YouTube explain very clearly why designers want safer propellants.

Offline Enthalpy

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Re: Replace hydrazine propellants
« Reply #8 on: September 17, 2014, 05:29:45 PM »
I've searched the Web about hexachlorocyclohexane - you know, the one wishfuly leading to diazacubane. Bad news... the beta-HCH is the all-trans configuration, but its chlorines are all equatorial on a chair ring, nearly in the same plane. I've run Pm3 on the hexaiodine and, if believing a software, all haloatoms are still nearly in the plane. So I've given up the hope of one ammonia molecule reacting with the even haloatoms and an other with the odd ones.

What do you think of the diaza-diasterane production from tetrahalocyclohexane, in the first post? Does it make any sense to you? What would be the more abundent conformation of the tetrahalo-cyclohexane, if it can be predicted?

And the cage C6H8N4 from Huntsman's documentation, on reply #1? Do you believe it can result from ethylene diamine and formaldehyde?

Offline orgopete

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Re: Replace hydrazine propellants
« Reply #9 on: September 17, 2014, 08:49:12 PM »
Given that the impetus for using fuels with higher energy content is to improve the net payload per dollar, couldn't you achieve the same result by launching at a higher elevation. Rather than launching from Cape Canaveral, shouldn't you launch from Denver or Mexico City? I understand that one could still always still get an improved thrust from a higher energy fuel, but since kerosene is still being used, just launching from a higher elevation seems like a logical and simple improvement.

I suppose I could have looked it up.
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Offline Enthalpy

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Re: Replace hydrazine propellants
« Reply #10 on: September 18, 2014, 06:23:59 AM »
While the arguments at the linked site are qualitatively correct, the numbers are not, and some other arguments are missing. For instance Denver is at 39°N, quite bad to reach geosynchronous orbit, and much worse than Cape Canaveral (28°N) whatever the altitude. Nor would one overfly half the US with a kiloton of propellants.

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