Great catch! That's a typo! It was meant to be DMH — dimethyl hydrazine. I fixed it to say UDMH for even greater clarity. One of the things that early Aerojet did was investigate DMH's isomers — symmetrical DMH and the unsymmetrical variant to see which one was a good fuel. That process was dangerous.
One of the things they tried was using it as a refrigerant to cool the engine nozzle. That didn't go so well. From Ignition!,
'So UDMH, for several years, was the fuel to be burned with nitric acid or N2O4. But, as designers have been trying to wring the last possible second of performance out of their motors, MMH has been growing in popularity. (It, too, has a Mil. Spec, now!) And, in applications which do not require a low freezing point, hydrazine itself is fused, either straight or mixed with one of its derivatives. The fuel of the Titan II ICBM doesn't have to have a low freezing point, since Titan II lives in a steam-heated hole in the ground, but it does need the highest possible performance, and hydrazine was the first candidate for the job. But, as hydrazine has an unfortunate tendency to detonate if you try to use it as a regenerative coolant, the fuel finally chosen was a 50-50 mixture of hydrazine and UDMH, called "Aerozine 50" by Aerojet who came up with it first, and "50-50" by everybody else.'
I give up. What is MDH? Some sort of mystery hydrazine?
Great catch! That's a typo! It was meant to be DMH — dimethyl hydrazine. I fixed it to say UDMH for even greater clarity. One of the things that early Aerojet did was investigate DMH's isomers — symmetrical DMH and the unsymmetrical variant to see which one was a good fuel. That process was dangerous.
One of the things they tried was using it as a refrigerant to cool the engine nozzle. That didn't go so well. From Ignition!,
'So UDMH, for several years, was the fuel to be burned with nitric acid or N2O4. But, as designers have been trying to wring the last possible second of performance out of their motors, MMH has been growing in popularity. (It, too, has a Mil. Spec, now!) And, in applications which do not require a low freezing point, hydrazine itself is fused, either straight or mixed with one of its derivatives. The fuel of the Titan II ICBM doesn't have to have a low freezing point, since Titan II lives in a steam-heated hole in the ground, but it does need the highest possible performance, and hydrazine was the first candidate for the job. But, as hydrazine has an unfortunate tendency to detonate if you try to use it as a regenerative coolant, the fuel finally chosen was a 50-50 mixture of hydrazine and UDMH, called "Aerozine 50" by Aerojet who came up with it first, and "50-50" by everybody else.'
Great read, fascinating topic!
By the way, have you seen the picture of the rocket pad where the reinforced concrete is totally burnt? before/after pics are really impressive : https://twitter.com/mooroobee/status/1649075280630226945