A friend is writing a screenplay about the X-Prize (home-made spaceships) and asked me a question of matters aeronautical. Ordinarily, I would (in the finest tradition of ppruners) just make up the answer and spout forth my ignorance authoritatively, but this might be interesting.
"At what altitude do you enter
controlled airspace either over the UK or USA?"
So if you were (for instance) in a home-made spaceship what was returning to Mother Earth in a controlled manner, about when would you get on the radio and ask for VFR-on-top?
(putting this here per the rubric in "Questions")