Comment Re: gosh (Score 5, Informative) 164
There are two problems with this idea. The first is that EMPs, like other EM phenomena, disperse via an inverse square law. Anything high enough to be line-of-site to the ground in most of the USA would need to have an enormous explosive yield (even by nuclear weapon standards). There are some designs that try to channel more energy into the EMP than normal, but they're very complex to build (a good 10-20 years more R&D beyond the Fat Man / Little Boy style bombs).
The second problem is the delivery. Iran does not have a significant ballistic missile capability. Getting something into space above the USA would require launching something in a suborbital trajectory. A very high suborbital trajectory if it were intended to explode that high up. The size of such a rocket would be such that it would be pretty hard to miss on satellite observation. The time in the air would give the US a very long time to formulate a response and destroying it would be relatively easy (remember, the problem with strategic defence shields in the cold war was not shooting down a missile, it was shooting down the large number of real and decoy rockets that the Soviet Union was capable of launching).