Sean Rafferty, the son of a scientist, thinks he will be a great scientist when he grows up and plans to lead his team on the first flight to Mars. However, he suffers from a fear of heights, claustrophobia, and a fear of becoming a space freak easily, which he tries to overcome before growing up and becoming a true astronaut.

Sean Rafferty is the practical one, always insisting on doing things the old way - even though he's suddenly hanging out with Jet in a very sci-fi reality! Sean is a big fan of following the rules of the Scientific Method, which he talks about in his own song.

Sean is initially bad at using his imagination and is afraid of going into space, but these diminish over time, as in "Sean's Year In Space" where Sean pretends to spend a day in space. He proposes going into space to prove that there is actually no sound in the treehouse and Not a Sound. He even admits it, sometimes calling himself "Mr. Adventure".

Sean can be a bit of a perfectionist sometimes. The most telling example would be Eye in the Sky, where he eventually had a chart for each event he could enter.