Metallic hydrogen

A quick post on this as a rocket fuel.  It is said to be capable of ISP's of close to 1700.

A little thought on this gives an impression of exaggeration.

From the Nuclear Rocket book, velocity is proportional to the square root of  temperature divided by molecular weight of the reaction mass.  Okay, so even if you are able to obtain metallic hydrogen, how do you get the molecular weight of water any lower?  You can't.  The combustion temperatures are said to be higher, but how does that do you any good if you can't get it any higher than the melting point of the toughest stuff known?  Nope, not possible.  Isp of 1700 ain't gonna happen with hydrogen oxygen combustion.

Now if you can get metallic hydrogen for a nuclear rocket, you may have something.  That's assuming that you can keep it in atomic form, for the molecular weight of the atomic hydrogen is 1.  That would simplify to velocity is proportional to the square root of the temperature.  The highest temps you'll get is about 4000 K.