Lithium+Fluorine+Hydrogen, why not?

[Hannu2]

7 minutes ago, p1t1o said:

Its dangerous in that its a flammable rocketfuel yes, but what makes you say it is more dangerous - or more impractical - than a triple-fuelled rocket with fluorine and lithium?

 

I did not say so. Reason is obvious. I compared hydrogen to methane and kerosine with liquid oxygen. Hydrogen is extremely cold (even compared to oxygen and methane) and causes hydrogen embrittlement which gives very strict restrictions to materials. Hydrogen is light which needs large tanks. It is exceptionally flammable (compared to normal fuels, of course exotic stuff like hypergolics or fluorine are even worse). Hydrogen flows through metals and other materials which makes storage and transportation bureaucratic and expensive. Etc. I do not believe that hydrogen will ever be significant fuel in any large scale applications.

[p1t1o]

8 minutes ago, Hannu2 said:

I did not say so. Reason is obvious. I compared hydrogen to methane and kerosine with liquid oxygen. Hydrogen is extremely cold (even compared to oxygen and methane) and causes hydrogen embrittlement which gives very strict restrictions to materials. Hydrogen is light which needs large tanks. It is exceptionally flammable (compared to normal fuels, of course exotic stuff like hypergolics or fluorine are even worse). Hydrogen flows through metals and other materials which makes storage and transportation bureaucratic and expensive. Etc. I do not believe that hydrogen will ever be significant fuel in any large scale applications.

 

Yes, LH2 has its drawbacks, I shouldnt have gotten so hung up on hydrolox when I said 

 

Quote

Cheaper and [much] safer to simply build a larger hydrolox rocket - and why wouldnt you?

 

What I should have said was "cheaper and simpler to use a larger quantity of more conventional fuels than F/Li/H"

I meant to stress that I cant see any advantage with moving [from any given propellant] to F/Li/H when we have propellants which already work, for the sake of a few tens of Isps. 

Anyhoo, the OP question was "why not F/Li/H" and the given reasons ARE the actual reasons, for better or worse. It keeps blowing off bits of rocket scientist.

[farmerben]

Because 500-1000 ISP is not that interesting.  

First stage boosters can be big and cheap.  Deep space exploration can be done by high ISP non chemical energies.  

The only demand for super-exotic rockets will be for launching heavy payloads from Venus and things like that. 

Lithium and Florine are in high demand for molten salt fission reactors.  Oxygen and hydrogen are in extremely high demand in space.  An asteroid mining company will have no trouble selling those elements.  If they came out with a sodium - chlorine rocket with mediocre performance but cheap because it used an otherwise hazardous waste, that would be an attractive option for many moon and asteroid missions.

[Xd the great]

7 hours ago, farmerben said:

 If they came out with a sodium - chlorine rocket with mediocre performance but cheap because it used an otherwise hazardous waste, that would be an attractive option for many moon and asteroid missions.

Are you sure that firing table salt into orbit is a good idea?

[farmerben]

1 hour ago, Xd the great said:

Are you sure that firing table salt into orbit is a good idea?

High thrust is only required on suborbital trajectories.  Ion engines alone do not meet all the requirements for moon and asteroid miners.  

[SuperFastJellyfish]

On 3/29/2020 at 11:04 AM, RuBisCO said:

Also why not ClF3

 

Excerpt from Ignition about ClF3:

Spoiler

Chlorine trifluoride, ClF3, or "CTF" as the engineers insist on calling it, is a colorless gas, a greenish liquid, or a white solid. It boils at 12° (so that a trivial pressure will keep it liquid at room temperature) and freezes at a convenient —76°. It also has a nice fat density, about 1.81 at room temperature.

It is also quite probably the most vigorous fluorinating agent in existence—much more vigorous than fluorine itself. Gaseous fluorine, of course, is much more dilute than the liquid ClF3, and liquid fluorine is so cold that its activity is very much reduced.

All this sounds fairly academic and innocuous, but when it is translated into the problem of handling the stuff, the results are horrendous. It is, of course, extremely toxic, but that's the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water —with which it reacts explosively. It can be kept in some of the ordinary structural metals — steel, copper, aluminum, etc. —because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes. And even if you don't have a fire, the results can be devastating enough when chlorine trifluoride gets loose, as the General Chemical Co. discovered when they had a big spill. Their salesmen were awfully coy about discussing the matter, and it wasn't until I threatened to buy my RFNA from Du Pont that one of them would come across with the details.

It happened at their Shreveport, Louisiana, installation, while they were preparing to ship out, for the first time, a one-ton steel cylinder of CTF. The cylinder had been cooled with dry ice to make it easier to load the material into it, and the cold had apparently embrittled the steel. For as they were maneuvering the cylinder onto a dolly, it split and dumped one ton of chlorine trifluoride onto the floor. It chewed its way through twelve inches of concrete and dug a three-foot hole in the gravel underneath, filled the place with fumes which corroded everything in sight, and, in general, made one hell of a mess. Civil Defense turned out, and started to evacuate the neighborhood, and to put it mildly, there was quite a brouhaha before things quieted down. Miraculously, nobody was killed, but there was one casualty — the man who had been steadying the cylinder when it split. He was found some five hundred feet away, where he had reached Mach 2 and was still picking up speed when he was stopped by a heart attack.

 

[DDE]

12 hours ago, SuperFastJellyfish said:

Excerpt from Ignition about ClF3:

I think the OP, like me, read Ignition! and was not discouraged.

[mikegarrison]

2 hours ago, DDE said:

I think the OP, like me, read Ignition! and was not discouraged.

Kind of like the people who have heard all the stories but intentionally summon Cthulhu anyway, because "it can't really be as bad of an idea as everybody says it is".

 

[p1t1o]

@SuperFastJellyfish

Quote

It is also hypergolic with such things as cloth, wood, and test engineers

One of the best lines ever written - more so because of the implication that it is based on empirical observation

 

Edited April 1, 2020 by p1t1o