We use big umbrella topics for the term and then interpretate them as we wish. We're doing "Up up and away" next term and going into space and aeroplanes as it gives scope for quite a lot. As long as you've got the freedom to do what you want with that topic, I would definately go into space. The children will love it and get a lot from it and at the end of the day that's what counts. The other option is to find stories with people that aspire to be something, but they would be harder stories to track down and I cant think of any off the top of my head.