How do you destroy the Death Star in Trench Run?

I play and the trench just seems to go on forever. How do you actually destroy the death star?

I get up to where Han takes out Vader and says let's blow this thing and go home, but then it just goes on and on?

 

Thanks!!!

Actually, I can destroy it in Mission mode, but not on arcade mode??

Anyway, runs like crap on my 3G...