All sorts of efforts were being made, during the late 50's, to increase propellant densities, and I was responsible (not purposely, but from being taken seriously when I didn't expect to be) for one of the strangest. 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.
Phil wanted density. Well, dimethyl mercury was dense, all right — d = 3.07 —but it would be burned with RFNA, and at a reasonable mixture ratio the total propellant density would be about 2.1 or 2.2. (The density of the acid-UDMH system is about 1.2.) That didn't seem too impressive, and I decided to apply the reducto ad absurdum method. Why not use the densest known substance which is liquid at room temperature — mercury itself? Just squirt it into the chamber of a motor burning, say, acid-UDMH. It would evaporate into a monatomic gas (with a low Cp, which would help performance), and would go out the nozzle with the combustion products. That technique should give Phil all the density he wanted! Charmed by the delightful nuttiness of the idea, I reached for the calculator.
...
I solemnly and formally wrote the whole thing up, complete with graphs, labeled it —dead pan —the "Ultra High Density Propellant Concept," and sent it off to the Bureau. I expected to see it bounce back in a week, with a "Who do you think you're kidding?" letter attached. It didn't.
Phil bought it.
He directed us, forthwith, to verify the calculations experimentally, and NARTS, horrified, was stuck with the job of firing a mercuryspewing motor in the middle of Morris County, New Jersey. Firing the motor wouldn't be any problem; the problem lay in the fact that all of the mercury vapor in the atmosphere would not be good for the health of the (presumably) innocent inhabitants of the county —nor for our own. So a scrubber had to be built, a long pipelike affair down which the motor would be fired, and fitted with water sprays, filters, and assorted devices to condense and collect the mercury in the exhaust before it could get out into the atmosphere. We had it built and were about ready to go, when the Navy decided to shut down —"disestablish" —NARTS, and ordered us to ship the whole mercury setup to NOTS. With a sigh of relief, we complied, and handed them the wet baby. Saved by the bell!
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
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