The invention of an Interstellar Empire is a needed for the safety and security of the entire planet. That being said it has recently come to my attention that although several people have advocated on behalf of a Death Star that the construction of one was not approved. I believe that it may have been too highly hoped to have created a Death Star without constructing at least one Super Star Destroyer first.
First, a Super Star Destroyer would be much cheaper as they are smaller, but do not let that fool you they are a power to be reckoned with as well.
Second, a Super Star Destroyer would give us a more mobile form of space exploration and deployment of it's complimentary wing of TIE fighters.
Third, a Super Star Destroyer does not have the weakness of a exhaust port.