When you are talking about hardened miltary targets, mass is essential for doing damage on anything but a direct hit. In an atmosphere the intense radiation heats up the stuff around it and causes the explosion. Thus the damage. Outside a certain radius even a nuclear warhead isn't going to do much damage in space. This would depend on the heat resistance of the skin of your ship, of course.
The Orion project actually included the 'propellant' -- stuff for the nuclear explosion to heat up -- with the bomb. It wasn't just a bald nuke dropped out of the craft. You can see the details as I said, by going to a search engine. So, it was not relying on just the energy.
I would really like to know where you get the information about any nuclear tests larger than 50 megatons. According to every official 'Nuclear Arms Testing' site I've ever visited the largest test ever was a Soviet nuke of 50 Mgtn which it was believed could be souped up to 100. Where on earth could anyone have tested anything larger?
Edit: The 'Tsar Bomb' was the largest nuclear weapon ever constructed or detonated. While only tested at 50 Megatons, it was intended to be a 100 megaton device. It was 'useless militarily' and was created purely for political purposes.
NB: Sakharov was the designer! (1961)
http://nuketesting.enviroweb.org/hew...ovwarhead.html
[ July 14, 2002, 03:40: Message edited by: Baron Munchausen ]