It is not possible to travel to outer space in Pok?mon Emerald. Players visit the Mossdeep Space Center over the course of the game but cannot actually board a rocket to go into space.
The rumor that it is possible to go into space likely began with the Pok?mon Deoxys, which is said to come from space. Deoxys is obtained at Birth Island in this game, however. Test launches are periodically conducted at the station, and a scientist there gives a current count of the successful tests, but the player cannot participate in them in any way. The number that the scientist gives actually corresponds to the number of weeks that have passed since the current game began.
Over the course of the game, Team Magma takes over the Space Center and the player has to take it back from them. This event occurs shortly after the player earns the Mind Badge from Mossdeep Gym. Once Team Magma has taken control of the facility, the player must clear all of the Team Magma Grunts from the first floor. Once that is done, players can progress to the second floor where they meet up with Steven Stone. Stone joins the player for a double battle against Maxie and Tabatha.