What RDX?

Matthew Yglesias is asking why RDX is so important. Why not use TNT to build a nuclear device?

1. You would need to use more TNT because it has a lower yield. That means even if other concerns don't come into play your device is heavier and less transportable. Thats important for a weapons system because war at some level comes down to logistics like how much can you move and where can you move it.


2. TNT is essentially the first "stable" high explosive. Nitro-glycerin came before it, but transporting nitro was extremely hazardous. Instead people like the railroads manufactured it on site. TNT was much safer in comparison. However TNT typically has an expiration date. As the compound ages it tends to separate, "sweat" out its nitroglycerin, and become less stable and predictable. It gets covered in crystalized nitro and suddenly you can set it off by dropping it. Thats bad news for a weapons system that might sit on the shelf for a while and contains nuclear material. You really don't want that nuclear tipped SCUD going off poorly on your launch pad and spraying plutonium everywhere when the main motor starts.


3. TNT is actually quite controllable and some explosives folks still like to use it for that reason. The catch is that TNT isn't shapeable like modern explosives are. The explosives used in a modern warhead are machined (no I'm not kidding) to tight tolerances like every other part in the system. You don't get a nuke that works if they aren't.

NOTE: While I work for the Army, none of this is official anything. I don't work with any of these sorts of things. I'm an engineer who likes shooting guns and watching the history channel.