An extremely stupid idea

[Skye]

Just before I say anything: this is in no way whatsoever a serious proposal, and it’s purely a silly investigation 

My friend came up with a highly silly idea: what is the most awful rocket engine you could make - in terms of both handling AND performance.

I responded with a few traditionally awful propellants, as well as some less awful ones, but still icky to handle (it ended up as an quindecapropellant engine)

F2, O3, N2O4, ClF3 & 5, UDMH, H2, Li, Hg, Al, N2, B2H6, B5H9, B10H14, and - god forbid - Og. (Oganesson may be combustible, not yet proven, but you can swap this out with any extremely heavy combustible element, really)

The reason Og is there is because, not only is it radioactive, to decrease handleability, but it is also extremely heavy, which means minimal Isp.

The reason nitrogen in there is because it takes a ton of energy to break the bonds.

Most of these are fairly obvious - they’re either extremely reactive, toxic, unstable, flammable, radioactive, etc.

Hydrogen is there just because it’s flammable & super cold, but it’s not too bad aside from that. Either way, as Tesco says, “every little helps”

Literally no limit here - feel free to put any and all abominable propellant combinations!

Any you may ask “why?!” And I wouldn’t blame you, but I ask “why not?”

[Apollo22]

Hard to beat fluorine, for a start. Also the boron fuels.

[Skye]

Oh my god, how could I forget the boranes!

I’ll fix it

[laszlo]

The old Project Orion bomb chuckers. Start with a take-off that makes Musk's concrete tornado look positively amateurish, leave a trail of deadly fallout to be blown all over the planet behind you, flash and radiation burns and permanent blindness for everyone that you pass over, destructive over-pressures until you leave the atmosphere and a continuous sequence of EMPs all the way to orbit, just to to destroy the planetary tech infrastructure. Destroy every satellite in orbit, blind every orbiting observatory and kill every human in space with radiation or electronics failure or both. And that's a nominal launch.

All the fun of a nuclear exchange and a really big rocket. Somewhere there's a billionaire for that.

[Skye]

Yup, I think that mostly takes the cake. Is there anything potentially more hazardous than that?

Also, look at the stats of the biggest one, you could easily end the world with one nuclear pogo stick hopping from country to country.

I was tempted to make a thousand-yard-stare joke, but couldn’t be bothered, so [insert funny 1000-yd-stare joke here]

[edzieba]

Anything below the Nuclear Salt-Water Rocket is not worth considering on the "I don't want to be in the same solar system as that thing" scale.

[Bob Shaw]

This thread is why I come to NSF! Please keep up the bad work.

[Skye]

We absolutely will!

[Skye]

Anything below the Nuclear Salt-Water Rocket is not worth considering on the "I don't want to be in the same solar system as that thing" scale.

What about some hideous combo of Orion and NSWRs?

[Vultur]

I believe there was at one time a proposal called Helios, which was like Orion except that the nuclear explosions were meant to be contained in a "combustion chamber" - somehow...

EDIT:
The Wikipedia article actually links to an old paper
on the subject https://www.osti.gov/servlets/purl/6761138-yMEAhk/

"No fundamental fault in the concept has been found" ... "there is no reason to doubt such efforts would result in a working engine" (!!!)

Wow, they were very optimistic back then!

[Twark_Main]

Og. (Oganesson may be combustible, not yet proven, but you can swap this out with any extremely heavy combustible element, really)

The reason Og is there is because, not only is it radioactive, to decrease handleability, but it is also extremely heavy, which means minimal Isp.

The problem is you make it too radioactive and it starts contributing energy to the exhaust and starts improving efficiency, which is undesirable.

It also has worse than just "handling problems," it vanishes in milliseconds.  If we're gonna go down that route we might as well select neutronium as our propellant. 


No, you want that sweet spot of high atomic number, high radiation, but also long lifespan. In that spirit I recommend Caesium-137 + liquid Fluorine as the worst propellant combination imaginable.   

https://en.wikipedia.org/wiki/Caesium-137

Fluorine is an objectively worse oxidizer choice, but I have to admit Caesiolox (and Neutroniolox) do have a nice ring to them. I guess we have to settle for Caesioflox ("Fluorine liquid oxidizer")

[Vultur]

  If we're gonna go down that route we might as well select neutronium as our propellant. 

Now that sounds like a winner!

[Skye]

Og. (Oganesson may be combustible, not yet proven, but you can swap this out with any extremely heavy combustible element, really)

The reason Og is there is because, not only is it radioactive, to decrease handleability, but it is also extremely heavy, which means minimal Isp.

The problem is you make it too radioactive and it starts contributing energy to the exhaust and starts improving efficiency, which is undesirable.

It also has worse than just "handling problems," it vanishes in milliseconds.  If we're gonna go down that route we might as well select neutronium as our propellant. 


No, you want that sweet spot of high atomic number, high radiation, but also long lifespan. In that spirit I recommend Caesium-137 + liquid Fluorine as the worst propellant combination imaginable.   

https://en.wikipedia.org/wiki/Caesium-137

Fluorine is an objectively worse oxidizer choice, but I have to admit Caesiolox (and Neutroniolox) do have a nice ring to them. I guess we have to settle for Caesioflox ("Fluorine liquid oxidizer")

Dear. God.

[Joris]

As far as actually flown awful rockets go: About 39 years ago, RBMK reactor 4 at Chernobyl accidentally turned into a 30GWth¹ NTR that hit an apogee of several meters.

The mass of the upper biological shield with attached parts that was thrown upwards was around 2000t.²

If we assume the force was about 1.5 times the weight, so in a second it would go up a few meters, then it gives us a specific impulse of about 200s during that short flight.





1. https://www.oecd-nea.org/upload/docs/application/pdf/2020-07/neacrp-a-1987-0825.pdf
2. https://www.rri.kyoto-u.ac.jp/NSRG/reports/kr79/kr79pdf/Malko1.pdf

[Skye]

Oh, yes, I recently watched a short documentary on the disaster in physics class (we’re doing nuclear fission & fusion), where they briefly mentioned that, though whether it’s a rocket or not is debatable

[tenkendojo]

Comon, Orion pulsed nuclear drive is probably the most awesome idea. See Richard Courant's review after watching an Orion scaled model test (with chemical explosives): Zis is not nuts, zis is super-nuts!

Now speaking of a truly awful (but actually tested) awful and asinine of a rocket design, I think nothing comes close to dimethylmercury rocket. Not only (CH3)2Hg theoretically one of the heaviest chemical rocket possible, has terrible efficiency in terms of Isp, it's also an extremely potent neurotoxin that can easily penetrate skin and protective gloves. Karen Wetterhahn, a renowned chemist at Dartmouth died from spilling a few drops of dimethylmercury onto her latex gloves. If I remember correctly, the US Navy actually tested a prototype of dimethylmercury rocket motor in the 60s or 70s.

[Vultur]

Now speaking of a truly awful (but actually tested) awful and asinine of a rocket design, I think nothing comes close to dimethylmercury rocket. Not only (CH3)2Hg theoretically one of the heaviest chemical rocket possible, has terrible efficiency in terms of Isp, it's also an extremely potent neurotoxin that can easily penetrate skin and protective gloves. Karen Wetterhahn, a renowned chemist at Dartmouth died from spilling a few drops of dimethylmercury onto her latex gloves. If I remember correctly, the US Navy actually tested a prototype of dimethylmercury rocket motor in the 60s or 70s.

Yeah, that's about the worst that has been seriously proposed (at least the Orion drive would actually be dramatically more capable than conventional rockets, so you get something for the damage/risk).

 According to the book Ignition, though, it didn't actually reach the testing stage, because Kodak refused to make the quantity of dimethyl mercury required.

From Chapter 12

" Phil Pomerantz, of BuWeps, wanted me to try dimethyl mercury, Hg(CH3)2, as a fuel. I suggested that it might be somewhat toxic and a bit dangerous to synthesize and handle, but he assured me that it was (a) very easy to put together, and (b) as harmless as mother’s milk. I was dubious, but told him that I’d see what I could do. I looked the stuff up, and discovered that, indeed, the synthesis was easy, but that it was extremely toxic, and a long way from harmless. As I had suffered from mercury poisoning on two previous occasions and didn’t care to take a chance on doing it again, I thought that it would be an excellent idea to have somebody else make the compound for me. So I phoned Rochester, and asked my contact man at Eastman Kodak if they would make a hundred pounds of dimethyl mercury and ship it to NARTS. I heard a horrified gasp, and then a tightly controlled voice (I could hear the grinding of teeth beneath the words) informed me that if they were silly enough to synthesize that much dimethyl mercury, they would, in the process fog every square inch of photographic film in Rochester, and that, thank you just the same, Eastman was not interested. The receiver came down with a crash, and I sat back to consider the matter. An agonizing reappraisal seemed to be indicated."

On the other hand, mercury,-RFNA-UDMH tripropellant was tested:
"At NOTS, Dean Couch and D. G. Nyberg took over the job, and by March 1960 had completed their experiments. They used a 250-pound thrust RFNA-UDMH motor, and injected mercury through a tap in the chamber wall. And the thing did work. They used up to 31 volume percent of mercury in their runs, and found that at 20 percent they got a 40 percent increase in density impulse. (I had calculated 43.) As they were firing in the middle of the desert, they didn’t bother with the scrubber. And they didn’t poison a single rattlesnake. Technically, the system was a complete success. Practically—that was something else again."

Borane based fuels (HEF or "zip fuels", including pentaborane IIRC) are also super awful and advanced much farther. Pentaborane is both incredibly toxic and not just flammable but pyrophoric, igniting on contact with air. Apparently leaks in the piping could be spotted by jets of green flame...

(There's a whole book about that project, "The Green Flame", but a lot of that was jet fuel, not just rocket.)

[CountZ]

From a handling/stability standpoint:
How about dihydrogen trioxide (HOOOH)?  For times when hydrogen peroxide (HOOH), which is reactive with darn near everything except borosilicate glass and very pure aluminum isn't quite right.  It's been synthesized:  https://pubs.acs.org/doi/full/10.1021/ja507263f .  Does that middle oxygen molecule really know what to do with itself?

Or, really, anything flourinated to ridiculous states.  Anyone up for some tetrafluorohydrazine (F4N2)?  Most answers on the ol' google-machine claim that it was studied as a high-energy rocket propellant, but I cant find any sources for anyone daft enough to try it in a practical application.

Maybe chlorine tetra pentaflouride (ClF5) is more your taste.  Chlorine triflouride (ClF3) is bad enough.  I can't imagine that adding more flourine is the solution to increased stability.  Then again, I'm an engineer, not a chemist. 

Bromine pentaflouride (BrF5).  Apparently someone, at some point, tried it (mad lads) but it didn't catch on because of "handling problems").  http://www.astronautix.com/b/brf5hydrazine.html .

Last call:  Hydrogen cyanide - flourine.  Exhaust gas is ~43% hydrogen flouride (HF).  Yup. That's the sound of every single one of your calcium ions in your body quaking at the thought.

[side note]:  I'm completely ignoring how you would ever synthesize some of these compounds, let alone at scale.  For example, how do you get chlorine tetra pentaflouride (ClF5)?  Well, you start with chlorine triflouride (ClF3)! and add more flourine.  I'd like to buy the person that tries that a beer.

edit: correction of tetra to penta.  Whoops.  Thanks Vultur!

[Vultur]

Maybe chlorine tetraflouride (ClF5) is more your taste.  Chlorine triflouride (ClF3) is bad enough.  I can't imagine that adding more flourine is the solution to increased stability.  Then again, I'm an engineer, not a chemist. 

[...]

[side note]:  I'm completely ignoring how you would ever synthesize some of these compounds, let alone at scale.  For example, how do you get chlorine tetraflouride (ClF5)?  Well, you start with chlorine triflouride (ClF3)! and add more flourine.  I'd like to buy the person that tries that a beer.

ClF5 (chlorine pentafluoride, not tetra-) was legitimately studied as an oxidizer. Like every early crazy propellant idea, it's discussed in "Ignition!".

[Skye]

Pretty sure ClF5 was fired, not sure tho. ClF3 was definitely fired, though