On the prospect of nuclear-propelled interstellar travel at 10% the speed of light?

“Lets, for the sake of argument, assume we wake up tomorrow and find that astronomers have spotted a spacecraft of unknown origin coming at us at 10% of the speed of light. It seems to be driven by a continuous series of explosions of some type of nuclear bomb. It arrives in our solar system and homes in on earth. Then, by design or mishap, it flies toward and ultimately into our planet at roughly 10% of the speed of light scattering several thousand nuclear bombs across the globe.
Do we request the phone number of the local agency in charge of interstellar environmental cleanup? Do we send a spacecraft full of lawyers back at them to sue for reparations? Would that be considered an act of war? Do we declare war?

A spacecraft full of bombs showing up unannounced seems like a rather poor way of starting a relationship. Unless your a Vogon. In which case it is pretty much expected and something of a relief that they don’t arrive and start reciting Vogon poetry.”

In case you don’t know what a Vogon is: http://en.wikipedia.org/wiki/Vogon