Ok how about this ?
I don't know if this has been already stated but, if the Americans already sent in the Destiny in the first place, wouldn't they already know how dense the core is ?? And so - calculate the necessary nuclear power needed ?
Anyway I just saw this movie now for the 2nd time ( first time when it came out ) and DAMN I even thought it was a pile of **** back then. The special FX are worse than what Lucas was doing in the 70s and these guys had $60M budget - JESUS !!! This is pretty much almost as much as Independence Day ( $75M ) 7 years earlier. Absolutely fantastic!