Nice idea. I don't believe it was explicitly stated, but the "join" aspect comes from the synergy between certain crewmate combinations. Over the six rounds, I found myself playing the game like the board game "Mastermind" where I try to find the optimal combination of crew for each duty. I'm sure I still missed some story elements, but that's okay.
I believe difficulty was toned down to make sure we got through, so instead some sort of high score achievement would be your goal, or seeing how many story elements you can find.
Neat game!