A children's room – how to make it special?

We're planning to renovate our son's room. He's 6 years old and adores space, rockets, and stars. We considered putting up wall decals, but they quickly fade, and he might get bored. We want something durable, vibrant, and at the same time useful for developing his imagination. Could anyone suggest an idea for decorating the walls in the children's room that's not boring but looks beautiful?