[douglas]

Doing the demolish/rebuild in one turn requires either both components on the same ship, or the planet creator moving away and back before doing its thing. You could try doing it with two ships without moving first, but then the create order might be executed first and fail because there's no asteroid field there.

Edit: Planet destruction orders require that the ship already be in orbit of the planet it's going to destroy. Planet creation orders can be issued at any time and will apply to whatever asteroid field the ship happens to be in when the order reaches the top of the queue. I don't know how it chooses which asteroid field if there happen to be multiples present (if, for example, you destroyed both a planet and its moon).