You wouldn't build one huge bomb, but instead use lots and lots of tiny bombs in an Orion-type spacecraft. That way you get a better utilisation of your energy.
Doesn't that make it even easier? But then again I think 400 megaton isn't enough. Last time I calculated it ( I probably made a ton of mistakes ;p) it was in the the 10s of thousands or something like that.
Accelerating the space shuttle to 0.10c :
(2,030 t * (0.10c)(0.10*c))/210 PJ = 8700 (wolfram alpha)
2,030 mass of space shuttle in metric tons
210PJ the energy from tsar bomba.
But then you have to add in the weight of the bombs too.
since they are each 27,000kg and then you have to sum it up to get to something that can approach 0.10c (and I don't remmember how I had figured that one out)
And what says once you get to the other planet you can't fill the tank with nuclear materials over there for the return trip?
