I couldn't find this so I don't know if it has been addressed. There are a bunch of cards that have the flip: gain +1 Explore. The last game I played each player sat and went through like 10 mission cards before finally getting scared by an event and ceasing to explore, is that the way it is intended. It seemed weird that they would wait till they had everything on the table than explore till they found something they could complete (assuming they continued getting cards that game them another explore on the flip) or until something hurt them lol.
This sounds possible, but improbable. Usually you'll encounter a starship or an event before getting 10+ missions in a row. Did you shuffle the 15 starships into the exploration deck?
I think the main reason for "Flip: +1 explore" on mission cards is to allow the exploring player to have an opportunity to attempt/complete a mission before passing the turn to the next player, since you need to use an explore action to do so.