If it were me, I would recommend against trying to do this. We went straight from the ship to KSC after our cruise and got into KSC at about 10:15 or 10:30 am at the earliest (the lines are horrendous to get in because their ticket system is antiquated and confusing--it is actually worse if you buy tickets ahead of time because you have to stand in an even longer voucher line to exchange for the actual tickets). We had fun and left at about 4:00 pm having only seen about 50% or less of the core stuff. It was about $23 per person for the very basic ticket as I recall, but the line for the tour and the line to get in will eat up a lot of time. If you have a rental car and are going to the airport, you will need to leave KSC by probably 2:30 pm to make your flight and return the car. IMHO, that is just too little time to do justice to the KSC. Building in the time to get the rental car in Cocoa Beach, the timing is even worse. Sorry to be pessimistic, but I think you should have a realistic view of what is actually possible.