The only place you can do the rocket launch is at mossdeep city, go to the space center and talk to this guy looking out the window he's in a white lab coat. Talk to him and if he says "the rocket has launched succesfully" and he says a number at the end if it's 56 or higher but not 100 or higher then he will ask you if you want to go to space say yes when you get to the moon there will be the legendary pokemon Deoxys save before you battle this pokemon but don't use the master ball because if he says 100 you'll get to space but instead of Deoxys there will be an even rarer pokemon Jirachi use the master ball for him he's extremly difficult to catch.