but not other times
When you colonize your first planet your settlers get off the ship and colonize the planet. Then the ship disappears. Later, if you bring more settlers with another colony ship, the settlers can get off and the colony ship can go anywhere it wants so long as you leave 1 (1,000,000) on board to pilot, I guess. If you leave no one on board the ship can't leave orbit. If you build a colony ship with 4 colony pods you can move a billion people per trip. Not sure what happens if you use that type of ship for the initial colony. I think the ship might disappear.
I don't see why these ships ever disappear. Its a little annoying and confusing. If I don't want them anymore I can always give them away, sell them or upgrade them into something else. The game doesn't let you do that.
Similar rules apply to transports.
It also would have been nice if you build a very fast freighter it moves freight faster forever or it is replaced with the usual slow freighter but you get the initial freighter back so you can use its super speed to quickly set up another route.
Am I right in thinking the following...
A freighter earns you money each week for as long as it is moving even if it never reaches its destination. If it gets blown away, you still get paid and the ship is respawns at the beginning of the trade route for free. There is no penalty for lost ships or lost cargo. This type of thing is counter-intuitive.