They're the same thing.
No they aren't.
The more stages you have, the worse the instabilities become. 3 stages is doable, but any more than that? Seriously questionable.
Three is more than sufficient to undermine your proof of concept "not enough fissiles" declaration.
Is that seriously an objection? Why on earth does it have to be accelerated across the Earth's surface? You're being really lazy here in not even thinking of any alternatives.
What the? Don't be absurd. "Bomb on the planet's surface." was exactly the problem specifi...
http://neo.jpl.nasa.gov/risk/2012da14.html
http://rt.com/news/paint-asteroid-earth-nasa-767/
Seems like a good opportunity to bring up existential risks. And A friendly reminder that NASA is in fact pretty damned important.
Thoughts?