There is no space center, that is in ruby, sapphire and emerald.
In Mossdeep City.
you can get one from a man in moss deep space center in Pokemon emerald.
In Mossdeep City, to the southeast.
Northwest of the Mossdeep Space Center.
In Pokemon Ruby/Sapphire/Emerald in Mossdeep City.
You have to be lucky enough to get the man at the space center to ask you to go.
catch a solrock or talk to the sailor on the space center
You can't fly in space in Pokemon Emerald.
You cant fly to space in Pokemon ruby,sapphire, or emerald. Though you can battle team aqua/magma in emerald at the space center hoped it helped!
first you deafeat the 7th gym then meet him at the space center